003-Interference Management in Umts Femtocells High-band

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Interference management in UTMS UMTS femtocells High-band

December 2013

003.06.02

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Report title: Interference management in UTMS UMTS femtocells Issue date: 01 December 2013 Version: 003.06.02

Scope

This paper [2] provides detailed results of in-depth studies of interference between femtocells and macrocells deployed in the UMTS ‘high’ bands around 2GHz. An accompanying study is also available for the UMTS ‘low’ bands around 850/900MHz [3]. For a higher level overview of the findings from both of these studies, we recommend reading our associated ‘topic brief’ [1] Related SCF Publications [1] “Topic brief: Interference Management in UMTS Femtocells”, Small Cell Forum, www.scf.io/doc/008 [2] “Interference Management in UMTS Femtocells ("High-band")”, Small Cell Forum, www.scf.io/doc/003 [3] “Interference Management in UMTS Femtocells” ("Low-band")”, Small Cell Forum, www.scf.io/doc/009

http://www.scf.io/doc/009


Executive summary

Femtocells, by virtue of their simultaneous small size, low cost and high performance, are a potentially industry‐changing disruptive shift in technology for radio access in

cellular networks. Their small size means that the spectrum efficiency they can attain is much greater than that achievable using macrocells alone. Their low cost means they can be deployed as consumer equipment, reducing the capital load and operating expenses of the host network. And their high performance means that all this can be gained at no loss of service to the customer, and in many cases, owing to the improved link budgets, improved service.

However, for these apparent benefits to translate into real advantage for network operator and consumer alike, we must answer serious questions about the interaction between the femtocell technology and the host macrocellular radio network into which they are deployed. If femtocells can only achieve their potential by disrupting the macro network, then they will be relegated to niche deployments, of little overall relevance to next generation networks. On the other hand, if the interactions between macro and femto radio layers can be managed to the benefit of all, then their properties (in terms of lowered cost, improved spectrum efficiency and link budget and general performance) can be fully realised, and femtocells will find themselves an essential component of all future radio access network designs

So, what are these interactions, and how can they be managed, and what does that all mean for the technology, to the operator and to the consumer? These are the questions that this paper is helping to answer. In doing so, it has deliberately maintained a tight focus, according to the priorities of its authors. It is exclusively concerned with W‐CDMA as an air interface technology. (Other teams within Small Cell

Forum are looking at other air interfaces.) It is, at this edition, concerned exclusively with operation around 2GHz – this being seen as the most important frequency range for early, in‐building deployment. (We provide also an edition of this paper for

850/900MHz deployment [3].) And it is exclusively a theoretical treatment, using link level and system level simulations to draw its conclusions, though we expect to back these conclusions up in due course with trial campaign data. In view of the residential application that femtocells are addressing, this paper is also exclusively concerned with femtocells operating with closed user groups. Perhaps most importantly, this paper “stands on the shoulders of giants”, drawing on the great mass of study work that has already been undertaken by 3GPP RAN4 participants in analysing these issues, and referencing them for further reading.

The interacting components of the femto‐enabled network include femtocells

themselves, which can be interacting in their downlinks with other nearby femtocells and macro cells; macrocells, which interact with nearby femtocells; users and user equipment (UEs) which by virtue of intentional radio links to femtocells and macrocells, may be causing unintentional interactions with both.

In approach, this paper has chosen to look at extreme cases, to complement as far as possible the average, or typical scenarios that RAN4 has already studied in 3GPP. In the main, the analysis has shown up internal contradictions in those extreme cases – meaning that they will never occur. For instance: analysing the case when the UE is operating at full power in its uplink towards a femtocell is shown to occur only when the macro cell is nearby – in which case the macro downlink signal is so strong that the UE will never select the femtocell over the macrocell. This contradiction shows, for


instance, that the high noise rise that a UE could in principle cause will happily never occur. In other cases, the extreme cases are avoided by uplink power‐capping or other

techniques recommended in the paper.

With these extreme cases disarmed, then of the many potential interactions between UEs, femtocells and macrocells, the summary conclusion that we have reached, in common with other studies, is that in order to be successful, femtocell technology must manage three things,Femtocell downlink power – if femtocells transmit inappropriately loudly, then the cell may be large, but non‐members of the closed user

group will experience a loss of service close to the femtocell. On the other hand, if the femtocell transmits too softly, then non‐group members will be unaffected, but the

femtocell coverage area will be too small to give benefit to its users. Femtocell receiver gain – since UEs have a minimum transmit power below which they cannot operate, and since they can approach the femtocell far more closely than they can a normal macrocell, we must reduce the femtocell receiver gain, so that nearby UEs do not overload it. This must be done dynamically, so that distant UEs are not transmitting at high power, and contributing to macro network noise rise on a permanent basis. UE uplink power – since UEs transmitting widely at high power can generate unacceptable noise rise interference in the macro network, we signal a maximum power to the UE (a power cap) to ensure that it hands off to the macro network in good time, rather than transmit at too high a power in clinging to the femtocell.

We have also shown that, with these issues addressed, the net effect of deploying femtocells alongside a macro network is significantly to increase its capacity. In numerical terms, and in terms of the simulated scenario, the available air interface data capacity is shown to increase by over a hundredfold by the introduction of femtocells.


Contents

1. Femtocells, Femtocell Access Points and the Small Cell Forum ...............................................................................1

1.1 What are Femtocell Access Points? ........................................ 1 1.2 What do Femtocells offer? .................................................... 1 1.3 What is the Small Cell Forum?............................................... 2 2. Objectives and methods of this paper ..............................3 3. Previous Work ..................................................................5 4. Simulation Scenarios and Definitions ...............................7 5. Abbreviations and Defined Terms ................................... 10 6. Scenario A: Macrocell Downlink Interference to the

Femtocell UE Receiver .................................................... 12 6.1 Description ....................................................................... 12 6.2 Analysis ........................................................................... 12 6.3 Extended scenario: HSDPA coverage .................................... 15 6.4 Conclusions ...................................................................... 17 7. Scenario B: Macrocell UE Uplink Interference to the

Femtocell Receiver ......................................................... 18 7.1 Description ....................................................................... 18 7.2 Analysis ........................................................................... 18 7.3 Conclusions ...................................................................... 23 8. Scenario C: Femtocell Downlink Interference to the

Macrocell UE Receiver .................................................... 25 8.1 Description ....................................................................... 25 8.2 Analysis ........................................................................... 26 8.3 Scenario analysis and conclusions........................................ 28 9. Scenario D: Femtocell Uplink Interference to the

Macrocell NodeB Receiver .............................................. 30 9.1 Introduction ...................................................................... 30 9.2 Analysis of Scenario D - 12k2 Voice and HSUPA .................... 31 9.3 Conclusions ...................................................................... 34 9.4 Recommendations ............................................................. 34 10. Scenario E: Femtocell Downlink Interference to nearby

Femtocell UE Receiver. ................................................... 35 10.1 Description ....................................................................... 35 10.2 Capacity Analysis .............................................................. 36 10.3 Conclusions ...................................................................... 38


11. Scenario F: Femtocell UE Uplink Interference to Nearby Femtocell Receivers ........................................................ 39

11.1 Description ....................................................................... 39 11.2 Analysis ........................................................................... 39 11.3 Conclusions ...................................................................... 41 11.4 Recommendations ............................................................. 42 12. Scenario G: Macrocell Downlink Interference to an

adjacent-channel Femtocell UE Receiver ........................ 43 12.1 Description ....................................................................... 43 12.2 Analysis ........................................................................... 43 12.3 Conclusions ...................................................................... 45 13. Scenario H: Macrocell UE Uplink Interference to the

adjacent channel Femtocell Receiver .............................. 46 13.1 Description ....................................................................... 46 13.2 Analysis ........................................................................... 47 13.3 Conclusions ...................................................................... 53 13.4 Femto System Impact ........................................................ 54 13.5 Mitigation techniques ......................................................... 54 14. Scenario I: Femtocell Downlink Interference to the

adjacent channel macrocell UE Receiver......................... 55 14.1 Description ....................................................................... 55 14.2 Analysis ........................................................................... 56 14.3 Conclusions ...................................................................... 60 14.4 Customer (MUE) Impact ..................................................... 60 14.5 Mitigation techniques ......................................................... 60 15. Scenario J: Femtocell UE Uplink Interference to the

adjacent channel Macrocell NodeB Receiver ................... 61 15.1 Introduction ...................................................................... 61 15.2 Analysis of Scenario J - 12k2 Voice and HSUPA ..................... 61 15.3 Conclusions ...................................................................... 64 16. Downlink and Uplink Scenarios Modelling Power

Control Techniques for Interference Mitigation .............. 65 16.1 Modelling of Propagation loss .............................................. 65 16.2 HNB transmit power calibration for 850 MHz ......................... 65 16.3 Simulation results for Dense Urban Deployment .................... 66 17. Summary of Findings ...................................................... 75 18. Overall Conclusions ........................................................ 84 19. Further Reading ............................................................. 85 19.1 Scenario A ........................................................................ 85


19.2 Scenario B ........................................................................ 85 19.3 Scenario C ........................................................................ 85 19.4 Scenario D ........................................................................ 85 19.5 Scenario E ........................................................................ 86 19.6 Scenario F ........................................................................ 86 19.7 Scenario G ........................................................................ 86 19.8 Scenario H ........................................................................ 86 19.9 Scenario I ......................................................................... 86 19.10 Scenario J ........................................................................ 87 19.11 Scenarios – Section 16 ....................................................... 87 20. Simulation Parameters and Path Loss Models ................ 88 20.1 Simulation parameters ....................................................... 88 20.2 Path Loss Models ............................................................... 89 References ................................................................................ 91

Tables Table 3-1 Table Title ...................................................................................... 6 Table 4-1 Femtocell Deployments in Shared Spectrum ....................................... 7 Table 4-2 Femtocell Deployments in non-Shared Spectrum ................................ 8 Table 4-3 Table Title ...................................................................................... 8 Table 6-1 Macro Node B assumptions and transmit EIRP calculation ................... 13 Table 6-2 Link budget for the received power from macro Node B to UE ............. 13 Table 6-3 EIRP for the femtocell ..................................................................... 14 Table 6-4 Required Ec/No for voice connection ................................................ 15 Table 7-1 Assumptions for Scenario B ............................................................. 18 Table 7-2 MUE link budget at the femtocell receiver. ........................................ 19 Table 7-3 FUE transmitter power requirements in order to hold a voice call ......... 19 Table 7-4 Maximum co-channel DL deadzone created by the femtocell for MUEs,

based on [R4-070969] and assuming RSSI of -65dBm ....................... 20 Table 7-5 Link budget for HSUPA ................................................................... 21 Table 9-1 Macro Node B noise floor ................................................................ 31 Table 9-2 Femto UE TX power 1000 m from macro Node B ................................ 32 Table 9-3 Noise rise calculation for Scenario D (femto UE is transmitting at

8.39dBm and 21dBm 1000m from a macro Node B for a 12K2 service and 2Mbps HSUPA service) ............................................................. 33

Table 9-4 Macro UE Tx power 1,000m away from macro Node B receiver by window on a 12K2 voice and 2Mbps HSUPA data service. .................... 34

Table 11-1 Femtocell Sensitivity and Noise Rise at AP1 ....................................... 40 Table 12-1 Macrocell Downlink Interference to an adjacent channel Femtocell UE

in this worst-case scenario .............................................................. 45 Table 13-1 Uplink radio link-budget for AMR 12.2 kbps RAB ................................ 49


Table 14-1 Maximum Macro NB – MUE separation for a given maximum Femtocell transmit power level, when the Femtocell – MUE separation is fixed at 5 m. .............................................................................. 58

Table 14-2 UE receiver performance requirement (HSDPA), [TS25.101] ............... 59 Table 15-1 Macro Node B noise floor ................................................................ 62 Table 15-2 Femto UE TX power 1000 m from macro Node B ................................ 63 Table 15-3 Noise rise calculation for Scenario D1 (femto UE is transmitting at

8.39dBm and 21dBm 1000m from a macro Node B for a 12K2 service and 2Mbps HSUPA service) ............................................................. 64

Table 16-1 Parameters for the co-channel idle cell reselection procedure. ................ 67 Table 16-2 Coverage Statistics at 850 MHz for Calibrated HNB Transmit Power ...... 67 Table 16-3 Pilot acquisition statistics at 850 MHz for dense-urban model with 24

active HNBs and calibrated HNB transmit power ................................ 68 Table 16-4 Coverage statistics for dense-urban model with 24 active HNBs and

calibrated HNB transmit power ........................................................ 68 Table 20-1 Recommended simulation parameters .............................................. 88 Figures Figure 1-1 Typical femtocell deployment scenario. .............................................. 1 Figure 4-1 Figure Title .................................................................................... 9 Figure 6-1 Scenario A .................................................................................... 12 Figure 6-2 Received signal strengths at UE, from macrocell and femtocell. ........... 15 Figure 6-3 HSDPA throughput vs. UE to femtocell distance for various femtocell

Tx powers. .................................................................................... 17 Figure 7-1 Scenario B .................................................................................... 18 Figure 7-2 Interference Scenario B, voice call ................................................... 20 Figure 7-3 HSUPA simulation, Scenario B. E-DPDCH Ec/No compared to

throughput for RFC3....................................................................... 22 Figure 7-4 Throughput for HSUPA. 70% max bit rate for all FRCs. ...................... 23 Figure 8-1 Illustration of the interference analysis for Scenario C ........................ 25 Figure 8-2 Path loss model ............................................................................. 26 Figure 8-3 TX power needed for 12.2 kbps for MUE (1000 metres away and 100

metres away respectively). ............................................................. 27 Figure 8-4 MUE throughput with HSDPA for locations at 1,000 and 100 metres

respectively. ................................................................................. 28 Figure 9-1 Interference Scenario D .................................................................. 30 Figure 10-1 Scenario E. Adjacent femto with UEs connected to each AP. ................ 35 Figure 10-2 Apartments Plan – Flats layout ........................................................ 36 Figure 10-3 Macrocell location relative to the house where the femtos are located .. 36 Figure 10-4 Dedicated carrier: CDF of HSDPA throughput .................................... 37 Figure 10-5 Shared carrier: CDF of HSDPA throughput ........................................ 38 Figure 11-1 Illustration of the Interference Scenario F ......................................... 39 Figure 12-1 Illustration of the Interference Scenario G ........................................ 43 Figure 12-2 CPICH Ec/Io for Femto ................................................................... 44 Figure 13-1 Illustration of the interference Scenario H ......................................... 46


Figure 13-2 Minimum separation between Femtocell and MUE to avoid blocking, for a given MUE transmit power level ............................................... 50

Figure 13-3 E-DPDCH Ec/No variation as a function of MUE transmit power level .... 51 Figure 13-4 Required average FUE transmit power level to meet HSUPA

throughput requirements. ............................................................... 52 Figure 13-5 E-DPDCH Ec/No variation as a function of MUE transmit power level .... 53 Figure 14-1 Illustration of the Interference Scenario I ......................................... 55 Figure 14-2 Macro Node B signal strength relative to the interfering femtocell

signal strength measured at the MUE, required for successful decoding of AMR ............................................................................ 57

Figure 14-3 Maximum MNB - MUE separation as a function of femtocell – MUE separation, assuming AMR voice service. .......................................... 58

Figure 14-4 Maximum macrocell-MUE separation as a function of femtocell-MUE separation, for reception of HSDPA .................................................. 59

Figure 15-1 Interference Scenario J. .................................................................. 61 Figure 16-1 In variance of HNB calibrated Tx Power in the two frequencies. ........... 68 Figure 16-2 DL user throughput distribution under different minimum powers ........ 70 Figure 16-3 Magnified version of Figure 1-2 showing outage statistics ................... 70 Figure 16-4 HUE uplink throughput distribution .................................................... 71 Figure 16-5 MUE uplink throughput distribution .................................................... 72 Figure 16-6 Transmit power distribution .............................................................. 72 Figure 16-7 Transmit power distribution. ............................................................. 73 Figure 16-8 UE uplink throughput distributions in 850 MHz. There are, in total, 34

UEs per macrocell, of which 24 UEs migrate to MNB in the ‘No HNBs’ case. HNB deployment increases the system capacity significantly ....... 74

Report title: Interference management in UTMS UMTS femtocells Issue date: 01 December 2013 Version: 003.06.02 1

1. Femtocells, Femtocell Access Points and the Small Cell Forum

1.1 What are Femtocell Access Points?

Femtocell Access Points (FAPs) are low-power radio access points, providing wireless voice and broadband services to customers primarily in the home environment. The FAP provides cellular access in the home and connects this to the operator’s network through the customer’s own broadband connection to the Internet.

FAPs usually have an output power less than 0.1 Watt, similar to other wireless home network equipment, and they allow a small number (typically less than 10) of simultaneous calls and data sessions at any time. By making the access points small and low-power, they can be deployed far more densely than macrocells (for instance, one per household). The high density of deployment means that the femtocell spectrum is re-used over and over again, far more often than the re-use that the macro network (with its comparatively large cells) can achieve. Trying to reach the same levels of re-use with macrocellular technology would be prohibitively expensive in equipment and site acquisition costs. By using femtocells, the re-use, spectrum efficiency, and therefore the aggregate capacity of the network can be greatly increased at a fraction of the macrocellular cost.

A typical deployment scenario is shown in Figure 1-1.

Figure 1-1 Typical femtocell deployment scenario.

1.2 What do Femtocells offer?

• Zero-touch installation by end user: Femtocells are installed by the end user without intervention from the operator. The devices will automatically configure themselves to the network, typically using ‘Network Listen’ capabilities to select settings that minimise interference with the macro network.

• Moveability: The end user may move their femtocells – for example, to another room, or, subject to operator consent, to another location entirely.


• Backhaul via the end user’s fixed broadband connection: Femtocells will use the subscriber’s broadband connection for backhaul, which typically will be shared with other devices in the home.

• Access control – the “closed user group”: The operator and/or end user will be able to control which mobile devices can access the femtocell. For example, subscribers may be able to add guest phone numbers via a web page.

• Supports a restricted number of simultaneous users: Femtocells will support a limited number (typically, fewerthan ten) of simultaneous calls and data sessions.

• Femtozone (homezone) tariffs: Mobile services accessed through the femtocell may be offered at a cheaper rate than the same services on the macro network. End users are advised when services are accessed via the femtocell, either by an advisory tone, or a display icon or some other means, so they know when the femto-tariffs apply.

• Ownership: Various ownership models are possible – for example, end users may own their femtocells, just as they own their mobile phones, or the operator may retain ownership, with end users renting the equipment (like a cable modem).

• Small cell size/millions of cells in the network: The femtocell network can easily extend to millions of devices.

• Femto as a service platform: Novel mobile services can be made available on the femtocell. For example, a femtocell-aware application on the mobile handset could automatically upload photos to a website when the user enters the home, and download podcasts.

1.3 What is the Small Cell Forum?

The Small Cell Forum (www.smallcellforum.org), formerly known as the Femto Forum, supports the wide-scale adoption of small cells.

Small cells are low-power wireless access points that operate in licensed spectrum, are operator-managed and feature edge-based intelligence. They provide improved cellular coverage, capacity and applications for homes and enterprises as well as metropolitan and rural public spaces. They include technologies variously described as femtocells, picocells, microcells and metrocells.

The Forum has in excess of 140 members including 68 operators representing more than 2.92 billion mobile subscribers – 46 per cent of the global total – as well as telecoms hardware and software vendors, content providers and innovative start-ups.

http://www.smallcellforum.org/


2. Objectives and methods of this paper

The benefits of femtocells are not straightforward to realise. While network operators will see significant capacity gains, and end users can expect higher performance, to achieve this the radio layer must be carefully managed. The management of the radio interference between the Macro and Femto Layers is a key industry concern addressed by this paper.

Interference adversely affects the capacity of a radio system and the quality of the individual communication links on that system. Adding capacity is always based on a trade-off between interference, quality and capacity. Hence, there is a need for interference management techniques to minimise interference that might otherwise counteract the capacity gains and degrade the quality of the network.

1. The principal objectives of this study are:

• To develop an industry position on the interference risks from femtocell deployments.

• To recommend mitigation techniques and any necessary associated radio frequency (RF) parameters and performance requirements, to ensure minimal disruption to the macro network or other femtocells.

2. To achieve these objectives, this paper develops detailed interference scenarios for evaluation and inclusion in the interference management assessment. The scenarios will cover worst-case deployment conditions and assess the respective system impact.

3. An immediate focus is to develop the assessment for W-CDMA, and in doing so devise a process that should be consistent with alternative radio technologies.

4. Two main steps were identified in order to accomplish the above goal:

• First, a baseline set of interference analysis conclusions for UMTS femtocells, based on 3GPP RAN4 interference studies, was required. This would be supplemented with specific analysis of identified micro scenarios, their likelihood, and potential impact. Interference mitigation techniques should also be considered on the understanding that vendor independence be preserved wherever possible.

• Secondly, a recommendation for a common set of behaviours (RF parameters and/or test cases) that can be derived by any UMTS femtocell was required. This is so that the femtocell can configure itself for minimal disruption to either the macrocell layer or other deployed femtocells.

5. We focus exclusively on the Closed User Group model. This is the most likely residential deployment model, and restricts the pool of allowed users to a small group authorised by the operator or the owner of the femtocell. Non-authorised subscribers may suffer coverage and service impairment in the vicinity of a closed-access femtocell (the so-called “deadzone”), which is important to assess.

6. The study will also investigate methods of controlling the impact of deploying large numbers of femtocells on the macro network. For example, different scrambling codes and adaptive power controls may be used to manage the interference in the network.

7. This paper has limited itself in scope, according to perceived priorities, as follows:


• It is exclusively concerned with W-CDMA as an air interface technology (other teams within Small Cell Forum are looking at other air interfaces).

• It is concerned primarily with the 850 MHz band in the United States, but is equally applicable to the 900 MHz band in Europe and elsewhere. It should also be broadly applicable to similar bands (eg. 700 MHz).

• It is exclusively a theoretical treatment, using link level and system level simulations to draw its conclusions, although we expect to back up these conclusions in due course with experiment.

8. The femtocells have been modelled in terms of three power classes (10dBm, 15dBm, 21dBm) or (10mW, 30mW, 125mW), although not all cases examine all three classes.

9. In approach, this paper has chosen to look at extreme cases of general industry concern, to complement as far as possible the RAN4 scenarios already studied in 3GPP. In the main, the analysis has shown up internal contradictions in those extreme cases – meaning that they will never occur in practice. Such contradictory analyses are then followed up with less extreme, more realistic scenarios, where the interference effects and their mitigation can be modelled and analysed.


3. Previous Work

Analysis in this problem space has already been carried out as part of the 3GPP Home Node B study item. 3GPP RAN4 concluded their study into the radio interface feasibility of Home Node B (aka femtocells) at RAN#39 in March 2008. Their results are presented in [TR25.820]. Part of their study included the analysis of anticipated interference scenarios covering a range of HNB deployments. A summary of their findings is presented in Table 3-1 below.

The scenarios for this paper are defined in Section 4.

Scenario (this paper)

25.820 scenario id

Summary of RAN4 conclusions

A 4 Macrocell DL interference can generally be overcome, as long as the femtocell has sufficient transmit dynamic range.

B 3 The femtocell receiver must reach a compromise between protecting itself against uncoordinated interference from the macro UEs, and controlling the interference caused by its own UEs towards the Macro Layer. Adaptive uplink attenuation can improve performance, but consideration must also be given to other system issues like the associated reduction in UE battery life.

C 2 Downlink interference from a closed-access femtocell will result in coverage holes in the macro network. In co-channel deployments the coverage holes are considerably more significant than when the femtocell is deployed on a dedicated carrier. A number of models are presented for controlling maximum femtocell transmission power, but it is acknowledged that no single mechanism alone provides a definitive solution. Open access deployment should also be considered as a mitigating option.

D 1 Noise rise on the Macro Layer will significantly reduce macro performance; consequently, the transmit power of the femto UE should be controlled. A number of mechanisms to achieve this are presented, generally providing a compromise between macro and femtocell performance. Again, open access deployment should be seen as a mitigating option in the co-channel case.

E 6 This scenario has received less coverage than the macro interference cases, but it is noted that the performance of Closed Subscriber Group (CSG) femtocells is significantly degraded unless interference mitigation techniques are used. This is generally a similar problem to macro DL interference in the co-channel scenario.

F 5 It is difficult to avoid co-channel interference between CSG femtocells, and this limits the interference reductions achieved by deploying the femtocell on a separate carrier from the macro network. Again, interference management techniques are required to manage femto-to-femto interference.

G 4 Macrocell DL interference can generally be overcome, as long as the femtocell has sufficient transmit dynamic range.

H 3 The femtocell receiver must reach a compromise between protecting itself against uncoordinated interference from the macro UEs, and controlling the interference caused by its own UEs towards the Macro Layer. This is generally an easier compromise to arrive at with adjacent-channel deployments than it is with co-channel.


Scenario (this paper)

25.820 scenario id

Summary of RAN4 conclusions

I 2 Downlink interference from a closed-access femtocell will result in coverage holes in the macro network. In adjacent-channel deployments the coverage holes are considerably easier to minimise and control than when the femtocell is deployed on the same carrier as the Macro Layer. A number of models are presented for controlling maximum femtocell transmission power; all except the “fixed maximum power” approach are generally acceptable.

J 1 Noise rise on the Macro Layer will significantly reduce macro performance; consequently, the transmit power of the Femto UE should be controlled. A number of mechanisms to achieve this are presented, generally providing a compromise between macro and femtocell performance. Adjacent-channel deployments can generally be accommodated.

Table 3-1 Table Title

In addition to the previous 3GPP analysis work, the Forum conducted an earlier study covering the same scenarios at 2 GHz [FF08]. For this study at 850 MHz, several changes were made to the simulation parameters used in that earlier 2 GHz study:

Wall loss was reduced from 20 to 10dB, to reflect greater building penetration at 850MHz.

Macro basestation antenna height was increased from 25 to 30 metres, to reflect the higher antenna heights (larger cell size) typical in North American deployments.

The minimum distance from a macro basestation was increased from 30 to 1,000 meters, to again reflect typical North American deployment scenarios where cells are larger and basestations are not typically located in residential areas. This also allowed us to eliminate the use of the ITU P.1411 propagation model, and to use the Okumura-Hata model, simplifying the analysis work.


4. Simulation Scenarios and Definitions

The Forum has identified 10 stretch scenarios that explore the limits of operation of femtocells and femtocell subscriber equipment.

The scenarios are summarised in the following tables and figure.

Scenario Description Macrocell Downlink Interference to the Femtocell UE Receiver (A)

A femtocell UE receiver, located on a table next to the apartment window, is in the direct bore sight of a macrocell (1 km distance). The macrocell becomes fully loaded, while a femtocell UE is connected to the femtocell at the edge of its range.

Macrocell Uplink Interference to the Femtocell Receiver (B)

A femtocell is located on a table within the apartment. Weak coverage of the macro network is obtained throughout the apartment. A user UE1 (that does not have access to the femtocell) is located next to the femtocell and has a call established at full power from the UE1 device. Another device UE2 has an ongoing call at the edge of femtocell coverage.

Femtocell Downlink Interference to the Macrocell UE Receiver (C)

UE1 is connected to the macro network at the edge of macro coverage. It is also located in the same room as a femtocell (to which it is not allowed to access). The femtocell is fully loaded in the downlink.

Femtocell Uplink Interference to the Macrocell Node B Receiver (D)

UE1 is located next to the apartment window, in direct bore sight of a macrocell (1 km distance). UE1 is connected to the femtocell at the edge of its range, and is transmitting at full power.

Femtocell Downlink Interference to Nearby Femtocell UE Receivers (E)

Two apartments are adjacent to each other. Femtocells (AP1 and AP2) are located one within each apartment. The owner of AP2 visits their neighbour’s apartment, and is on the edge of coverage of their own femtocell (AP2) but very close (<3m) to AP1. The owner of AP1 establishes a call requiring full power from the femtocell.

Femtocell Uplink Interference to Nearby Femtocell Receivers (F)

Two apartments are adjacent to each other. Femtocells (AP1 and AP2) are located one within each apartment. The owner of AP2 visits their neighbour’s apartment, and is on the edge of coverage of their own femtocell. The owner of AP2 establishes a call that requires peak UE power to their own femtocell while they are located next to AP1 (< 3m).

Table 4-1 Femtocell Deployments in Shared Spectrum

Scenario Description Macrocell Downlink Interference to the adjacent-channel Femtocell UE Receiver (G)

A femtocell UE is located on a table next to the apartment window, in direct bore sight of a macrocell (1 km distance). The macrocell becomes fully loaded, while a femtocell UE is connected to the femtocell at the edge of its range.

Macrocell Uplink Interference to the adjacent-channel Femtocell Receiver (H)

A femtocell is located on a table within the apartment. Weak coverage of the macro network is obtained throughout the apartment. A user (that does not have access to the femtocell) is located next to the femtocell and has a call established at full power from the UE1 device. Another device UE2 has an ongoing call at the edge of femtocell coverage.


Scenario Description Femtocell Downlink Interference to the adjacent-channel Macrocell UE Receiver (I)

Two users (UE1 and UE2) are within an apartment. UE1 is connected to a femtocell at the edge of coverage. UE2 is connected to the macrocell at the edge of coverage, and located next to the femtocell transmitting at full power.

Femtocell Uplink Interference to the adjacent-channel Macrocell NodeB Receiver (J)

A femtocell is located in an apartment, in direct bore sight of a macrocell (1 km distance). UE1 is connected to the femtocell at the edge of coverage, but next to the widow – thus, in the direct bore sight of the macrocell antenna.

Table 4-2 Femtocell Deployments in non-Shared Spectrum

In addition to these extreme scenarios, we include shared-spectrum system level simulations specifically modelling the mitigation of downlink interference and uplink noise rise by power control techniques (Section 16). These simulations also model the effect of femtocells on the total throughput and capacity of the network.

The relationship between these scenarios and those already studied in RAN4 is summarised in the following table and figure.

Victim

Femto UE DL Rx

Femto AP UL Rx

Macro UE DL Rx

Macro NodeB UL Rx

Neighbour Femto UE DL Rx

Agg

ress

or

Macro NodeB DL Tx

A, G 4

Macro UE UL Tx B, H

3

Femto AP DL Tx C, I

2 E 6

Femto UE UL Tx D, J

1

Neighbour Femto UE UL Tx F

5

Table 4-3 Table Title

A…F are the interference scenarios for co-channel deployments

G…J are the interference scenarios for adjacent-channel deployments

1…6 are the equivalent interference scenario IDs used in the 3GPP HNB analyses [TR25.820]

The following diagram illustrates and summarises Small Cell Forum Scenarios A-J:


Figure 4-1 Figure Title

FUE

F FUE

MUE

A,G

D,J

B,H

C,I

E F

F

FUE

MUE

Femto AP

Femto UE

Macro UE

Apartments

Macro NodeB

Interference path

UE Association

F


5. Abbreviations and Defined Terms

Throughout this paper a number of abbreviations are used to identify various system elements and parameters. The most frequently used are presented here for quick reference. However, a more extensive list has been produced and is available under separate cover.

AP Access Point

BER Bit Error Rate (or Bit Error Ratio) – the proportion of the total number of bits received that are decoded wrongly

BS Base Station (assumed to be a wide-area BS, as defined in [TS25.104], unless otherwise stated)

EIRP Equivalent Isotropic Radiated Power – a measure of the transmitted power in a particular direction that takes account of the antenna gain in that direction

FAP Femto AP, also known as the femtocell

FUE Femto UE, also called the Home UE (HUE)

HUE Home UE, also called the femto UE (FUE)

HNB Home NodeB

MNB Macro NodeB

MUE Macro UE

QoS Quality of Service

UE User Equipment (handset, data terminal or other device)

RAN Radio Access Network

RAT Radio Access Technology

RSCP Received Signal Code Power

RTWP Received Total Wideband Power

LOS Line-Of-Sight

P-CPICH Primary Common Pilot Channel

Victim Is a radio node (macro node-B, or femto access point) whose receiver performance is compromised by interference from one or more other radio nodes (the Aggressor). Alternatively, the Victim may be a radio link, whose quality is degraded by unwanted interference from Aggressor nodes

Aggressor Is a radio node (either macro node-B, femto access point or UE) whose transmissions are compromising the performance of another radio node (the Victim), or which are contributing to the degradation of quality of a (Victim) radio link


Deadzone Is an area where the quality of service is so poor as a result of interference that it is not possible to provide the demanded service. Deadzones are also characterised by the fact that in the absence of any interference, a normal service would be possible.

Deadzones are often specified in terms of the path loss to the Aggressor transmitter. A 60dB deadzone in the femtocell is, therefore, a region around the femtocell where the path loss to the FAP is less than 60dB.


6. Scenario A: Macrocell Downlink Interference to the Femtocell UE Receiver

6.1 Description

A UE is located on a table next to the apartment window that is 1 km distance away from a macrocell. The macrocell is operating at 50% load, while the UE is connected to the femtocell (ie. FUE) at the edge of its range. In this scenario the Victim link is the downlink from the femtocell to the FUE, while the Aggressor transmitter is the downlink from the macrocell. This interpretation of Scenario A is summarised in Figure 6-1.

Figure 6-1 Scenario A

6.2 Analysis

The objective of the analysis of this scenario is to work out the services that can be delivered to a femto UE when it is on the edge of the femtocell – the femtocell itself being positioned, as required by the scenario, 1km from the macro. The analysis strategy for this scenario is broken down as follows:

The first task is to determine the range of the femtocell as defined by the pilot power. This gives us the maximum range at which the UE can detect and decode the femto beacon, and therefore camp on to it. Secondly, we work out the services that can be offered by the femtocell at the edge of its coverage, given that interference level. The first step is accomplished by the following sequence:

• Assume a given P-CPICH transmit power for both macro and femto; then • find the power due to the macro at the distance given by the scenario (1km);

then • find the distance from the femto at which the ratio of femto power to macro

power is sufficient for the UE to detect the femtocell. This distance is the range of the femtocell as defined by the pilot power – the maximum range at which a UE can detect the femtocell and camp on to it.


The second step (to work out the services that can be offered at this range) is accomplished as follows:

• For voice, work out how much dedicated channel power is required to sustain a voice call, given the interference level calculated in the first step, and reconcile that with the total amount of power available to give the number of voice calls that may be sustained.

• For data, work out the Ec/Io that can be achieved by allocating all the remaining power to the HSDPA downlink shared channel, and derive a throughput from that, given an industry standard relationship between Ec/Io and throughput.

Assumptions for the macrocell are as defined in [FF09] with variant values shown in Table 6-1, which shows the transmit EIRP of the macrocell. The link budget for the macrocell is defined in Table 6-2.

Value Units Comments

Macro Node B utilisation as percentage of total power

50 %

Macro Node B maximum Tx power 43 dBm Ptx_max

Macro Node B Tx power 40 dBm Ptx_m= Ptx_max + 10*log(0.5)

Antenna gain 17 dBi Gm

Feeders and cable losses 3 dB Lc

Tx EIRP 54 dBm EIRP_m=Ptx_m+Gm-Lc

Table 6-1 Macro Node B assumptions and transmit EIRP calculation

Value Unit Comments Distance macro nodeB to UE

1000 m d_mu

Height macro nodeB antenna

30 m hb

Height UE from ground 1.5 m hM Path loss 125.75 dB PL_m is calculated from the

Okumura-Hata Model, + 5dB window loss

UE antenna gain 0 dBi Gue UE connector and body losses

3 dBi Lc_u

Macro nodeB received power at UE

-79.75

dBm Prx_m=eirp_m-PL_m+Gue-Lc_u

Table 6-2 Link budget for the received power from macro Node B to UE

The value Prx_m in Table 6-3 is the power due to the macrocell at the scenario distance (1 km), and takes account of the propagation, plus an allowance for the window loss (5dB).


The femtocell assumptions are presented in Table 6-4. Note that three types of femtocell are assumed with the defined femto transmit power classes (10dBm, 15dBm and 21dBm).

Value Unit Comments

Femtocell max transmit power

10

dBm Ptx_f for the three power classes modelled 15

21

Femtocell antenna gain 0 dBi Gf (same as UE)

Femtocell feeders/connector losses 1 dB Lc_f

Maximum transmit EIRP

9

dBm eirp_f=Ptx_f+Gf-Lc_f, for the three power classes modelled 14

20

P-CPICH power relative to maximum power 10 % pcp_pctage

P-CPICH transmit EIRP

-1

dBm Eirp_pcp_f = eirp_f * pcp_pctage 4

10

Table 6-3 EIRP for the femtocell

In order to complete the calculation of position of the cell edge according to P-CPICH, we calculate the P-CPICH power at the UE and compare it to the power at the UE due to the macrocell. Note that in this scenario we are fixing the UE at the window and moving the femtocell location – so the macrocell power is constant at the value calculated in Table 6-4. We use the indoor propagation model ITU-R P.1238, assuming a residential building and same floor operation, the femtocell characteristics from Error! Reference source not found. as well as the same UE characteristics as in Table 6-4. Figure 6-2 shows the femtocell P-CPICH power received at the UE, and the power at the UE from the macrocell as taken from Table 6-4.

In order for the FUE to detect the femtocell and camp onto it, the P-CPICH Ec/No must be sufficient. It is assumed that a level of -18 dB will be adequate in this respect. To find the range of the femtocell we need to find the distance below which the P-CPICH power is less than 18 dB below the power from the macrocell. By observing in Table 6-4 where the P-CPICH power exceeds the bounds on the macro interference power minus 18 dB, it can be seen that even at the 10 dBm transmit power, the FAP has a range of more than 100 m. It is to be noted that this does not necessarily mean that a UE 100m away from the FAP will select the FAP in idle mode. Rather, it means that if the UE is already connected to this FAP, it can still sustain the connection at this distance


Figure 6-2 Received signal strengths at UE, from macrocell and femtocell.

Further, it can be seen that, based on Table 6-4Error! Reference source not found., voice services are readily achievable at the edge of coverage, since they require about the same Ec/No as the minimum CPICH Ec/No assumed above.

Value Unit Comments

Chiprate 3.84e6 cps W

Bitrate of AMR voice call 12.2 kbps R

Eb/No requirement for voice connection +7 dB Eb/No

Ec/No requirement for voice connection -18 dB Ec/Io=Eb/No-10*log10(W/R)

Table 6-4 Required Ec/No for voice connection

Similarly for HSDPA, assuming that 80% of the femtocell power is reserved for HSDPA services (9dB above P-CPICH), the HSDPA Ec/No will be at least -1.8 dB (@ 100m from HNB), which corresponds to > 1.5 Mbps, according to the translation equation in [R4-080149].

6.3 Extended scenario: HSDPA coverage

The HSDPA throughput at the UE as a function of the distance between the HNB and the window is analysed by employing the rate mapping equation presented in reference [R4-080149]. The HSDPA max data rate is presented as a function of average HS-DSCH SINR.


In this work, SINR is calculated using the formula in [Hol06]:

noiseotherown

DSCHHS

PPPP

SFSINR++−

= −

)1(16 α

Equation 6-1

where:

• SF16 is the spreading factor, • PHS-DSCH is the received power of the HS-DSCH, summing over all active HS-

PDSCH codes, • Pown is the received own-cell interference, • α is the downlink orthogonality factor (assumed to be 1, fully orthogonal), • Pother is the received other-cell interference, • Pnoise is the received noise power (here it is assumed that the UE Noise figure

is 7dB).

Assuming:

• The femtocell transmit powers are 10dBm, 15 dBm and 21 dBm, with 80% allocated to HS-DSCH

• And employing the path loss assumptions of the previous section • The UE is still assumed to be 1 km away from the macrocell.

The HSDPA throughput for the FUE at different distances from the femtocell is shown in Figure 6-3.


Figure 6-3 HSDPA throughput vs. UE to femtocell distance for various femtocell Tx powers.

It can be seen from Figure 6-3 that the maximum HSDPA throughput can be expected up to 25 m away from the femto, even at the 10 dBm transmit power.

6.4 Conclusions

The scenario that has been analysed in this section examines the case of the UE being located in front of a window overlooking a macrocell that is 1 km away. Assuming standard models and parameters, it is shown that, even at 10 dBm transmit power, the femtocell is able to comfortably provide voice to the UE when the femtocell is located as far as 100 m away, and maximum HSDPA throughput can be expected up to 25 m away.


7. Scenario B: Macrocell UE Uplink Interference to the Femtocell Receiver

7.1 Description

A femtocell is located on a table within the apartment. Weak coverage of the macro network is obtained throughout the apartment. A user that does not have access to the femtocell (MUE) is located next to the femtocell. Another user device (FUE) is connected to the femtocell and has an ongoing call at the edge of femtocell coverage. The scenario is depicted in Figure 7-1. In this case the Victim receiver belongs to the femtocell access point (FAP), and the Aggressor transmitter is that of the nearby MUE.

Figure 7-1 Scenario B

7.2 Analysis

The general assumptions for the analysis of this scenario are presented in Table 7-1. The link budget for the MUE is shown in Table 7-2; note that three separation distances between the MUE and the femtocell are taken into account (5, 10 and 15m).

Value Unit Comments

Voice call service rate 12.2 kbps R

Chip rate 3.84 Mbps W

Processing gain 24.98 dB PG=10*log10(W/R)

Required Eb/No for voice call 8.3 dB Eb/No (performance requirement in [TS25.104] for AWGN channel, no diversity)

Frequency 850 MHz Fc (Band V)

Table 7-1 Assumptions for Scenario B

Value Unit Comments

MUE uplink transmitted power 21 dBm Ptx_mue (power class 4)

UE antenna gain 0 dBi Gue

Connectors/body loss 3 dB Lue


Value Unit Comments

MUE Tx EIRP 18 dBm eirp_mue=Ptx_mue+Gue-Lue

Distance MUE-femtocell 5, 10, 15 m d_mue

MUE-femtocell path loss 50.16 (@5m) 58.59(@10m) 63.52 (@15m)

dB PL_mue, Indoor to indoor path loss model , where d=d_mue, f=fc

Femtocell antenna gain 0 dBi Gf

Femtocell feeders/connector losses 1 dB Lf

Uplink power received by the femtocell from MUE at different MUE-femtocell separation distances

-33.16(@5m) -41.59(@10m) -46.52(@15m)

dBm Prx_mue=eirp_mue-PL_mue+Gf-Lf

Table 7-2 MUE link budget at the femtocell receiver.

In Table 8-3, the FUE's minimum transmitted power requirement for holding a voice call is calculated. Note that the power is well within the FUE's capabilities, even at the largest separation distance.

Value Units Comments

Distance between FUE and femtocell

15 m d_fue

Path loss 63.51 dB PL_fue Indoor to indoor path loss model (d=d_fue, f=fc)

Eb/N0 requirements for a voice call

8.3 dB Eb/No_fue [TS25.104]

Processing Gain 24.98 dB PG_fue

Noise power -103 dBm PN from [TS25.942]

FUE received power in order to obtain required Eb/N0 for different MUE distances (d_mue)

-49.84 (@5m) -58.27(@10m) -63.20 (@15m)

dBm Prx_fue is calculated from equation [Hol06]:

( ) ( ) PNdPPPG

NoEbmuemuerx

fuerxfuefue +

⋅=

,

,/

FUE transmitted power requirements for different MUE distances (d_mue)

17.68 (@5m) 9.25 (@10m) 4.32 (@15m)

dBm Ptx_fue=Prx_fue-Gue+Lue+PL_fue-Gf+Lf

Table 7-3 FUE transmitter power requirements in order to hold a voice call

The values calculated in Table 7-3 for the transmitted power of the FUE required are the same as the one calculated for the 1900Mhz study. The reason for this is that the reduction on frequency affects both FUE and MUE in the same way. Moreover, as the MUE is near to the femtocell, the affect of Noise Power is small in the calculation of Prx_fue.

In Figure 7-2, the results are interpolated for different UE distances and power levels.


Note that the plot includes the downlink deadzones created by the femtocell, which affects the MUE. Downlink deadzone assumptions are summarised in Table 7-4.

DL Tx power Maximum co-channel DL deadzone

MUE-femtocell distance (using ITU-P.1238 indoor path loss model)

10dBm 60dB 11.3m

15dBm 65dB 17m

20dBm 70dB 25.7m

Table 7-4 Maximum co-channel DL deadzone created by the femtocell for MUEs, based on [R4-070969] and assuming RSSI of -65dBm

Within these zones, the MUE will be re-directed to another WCDMA frequency or Radio Access Technology (RAT) by the macrocells, or the call may be dropped. In both case the interference level in the femtocell reduces, and the uplink power requirements will relax.

Figure 7-2 Interference Scenario B, voice call

7.2.1 HSUPA

In this section the affects of HSUPA are analysed. The link budget is shown in Table 7-5.

Value Unit Comments

FUE uplink transmitted power 21 dBm Ptx_fue

UE antenna gain 0 dBi Gue


Value Unit Comments

Connectors/body loss 3 dB Lue

FUE Tx EIRP 18 dBm eirp_fue=Ptx_fue+Gue-Lue

Distance FUE-femtocell 5 m d_fue

FUE-femtocell path loss 50.16 dB PL_fue Indoor to indoor path loss model (d=d_fue, f=fc)

MUE distance from femtocell 21 dBm Ptx_mue

MUE-femtocell separation 10 m d_mue

MUE power at femtocell (see Table 7-2 for d_mue=10) -41.59 dBm Prx_mue

Noise level -103 dBm N0

E-DPDCH Ec/No -2.57 dB ( )0,

,/NP

PNoEc

muerx

fuerxfue +

=

Table 7-5 Link budget for HSUPA

The simulation results in Figure 7-3 show the E_DPDCH Ec/No for two cases:

• FUE is at 5m from the femtocell • FUE is at 15m from the femtocell.

In both cases, it is expected that the MUE is transmitting at maximum power (21dBm).

Figure 7-3 shows the fixed-reference channel (FRC) #3 (see [TS25.104], Pedestrian A channel model) for the following requirements for E-DPDCH to be met:

• Ec/No of 2.4dB: provides R≥30% of max information bit rate • Ec/No of 9.4dB: provides R≥70% of max information bit rate.

Note that DL deadzones are not taken into account. However, the grey area in the figure represents the maximum extent (11.3m) of the DL deadzone for a femtocell transmitting at +10dBm. This distance would reduce if the FAP was not loaded in the downlink.

Note also that the indoor to indoor path loss model, ITU-R P.1238, may underestimate the true path loss outside 15-20m range, as it is likely that other physical features (such as furniture, walls and buildings) will affect radio propagation (this is particularly true in dense urban areas.). A larger path loss reduces MUE interference, which, in turn, allows greater FUE throughput (linked to an increase in FUE-DPDCH Ec/No).


Figure 7-3 HSUPA simulation, Scenario B. E-DPDCH Ec/No compared to throughput for RFC3.

The results in Figure 7-3 are mapped to the TS 25.104 throughput model for pedestrian A – no receiver diversity. The results are shown in Figure 7-4. Here, it is noted how interference from the MUE has a strong affect on throughput; however, it should be noted that the simulation assumes an MUE transmitting at maximum power (on the edge of the macrocell).


Figure 7-4 Throughput for HSUPA. 70% max bit rate for all FRCs.

7.3 Conclusions

Based on link budget calculations, the affects of uplink interference from one UE on the macrocell and a UE on the femtocell have been analysed; in this work it is assumed that the same frequency is used by the Macro and Femto Layer.

In the analysis, it was assumed a femtocell serving an FUE on the physical edge of the cells (assumed to be 15m away) with a 12.2kbps AMR speech call; while a co-channel interference MUE is in the proximity of the femtocell. The analysis results showed that in order to be able to maintain the uplink connection between the FUE and femtocell, the transmitted power requirements are within the capability of the UE.

Additionally, the performance of HSUPA on the femto-FUE link has been analysed in the presence of uplink interference from the Macro UE. By simulation, it has been found that in order to obtain HSUPA throughput of at least 2.8Mbps with a category 6 UE, the FUE needs to be near to the femtocell (5m) and transmit at a power level greater than 15dBm if the MUE is within 15m of the femtocell.

However, such analysis must take into account the downlink deadzone created by the femtocell. High power from the femtocell, in order to maintain the downlink, will interfere with the macrocell signal at the MUE, and will force the macrocell to handover the call to another WCDMA frequency or RAT; or, if none of these are possible, the MUE call may be dropped.


7.3.1 Customer (MUE) impact

From the point of view of the MUE, the femtocell is a source of interference to the macrocell. However, the macro network can already cope with re-directing UEs to other WCDMA frequencies or RAT if a user is affected by high interference.

Those locations with no coverage from alternative WCDMA frequencies or RATs may be adversely affected by poor Eb/No levels, leading to dropped calls.

Due to femtocells, the macrocell may also be affected by an increase of uplink interference as femto-UEs increase power levels in order to achieve required quality levels. This may be limited by capping the maximum power level transmitted by FUEs, or limiting uplink throughput.

7.3.2 Customer (FUE) Impact

The minimum separation between MUE and femtocell has a strong affect on the capability to offer the required QoS to the femtocell user. However, the FUE has enough power to sustain a voice call while the MUE is in the coverage range of the femtocell. The downlink deadzone sets a minimum separation between MUE and femtocell – meaning that the FUE transmit power is always within its capability.

For HSUPA, the user is required to go closer to the femtocell in order to be provided with the best throughput. Simulation has shown that at 5m from the femtocell, good throughput can be achieved for MUEs further away than 12m.

7.3.3 Mitigation techniques

Availability of alternative resources (a second carrier, or underlay RAT) for handing off or reselecting macro-users is the best way to provide good service when macro-users are in the proximity of femtocells.


8. Scenario C: Femtocell Downlink Interference to the Macrocell UE Receiver

8.1 Description

In this scenario, MUE is connected to the macro network at the edge of coverage (RSCP<-95dBm). MUE1 is located in the same room as a femtocell (to which it is not allowed to access). The femtocell is fully loaded in the downlink; the femto UE are denoted as FUE. The Victim receiver in this case is the MUE, and the Aggressor is the femtocell downlink transmitter.

Figure 8-1 Illustration of the interference analysis for Scenario C

Due to propagation loss and shadow fading effect, the macrocell signal strength varies at different location in the macrocell network coverage area. Femtocells are deployed at different locations in the macrocell network coverage area. Therefore, the down link interference from macrocell to the femtocell users will be location dependent. In order for the Femto to maintain its designed coverage, it should be capable of adjusting its pilot and max transmission power, while not causing undue interference to macrocell users.

Two important parameters need to be calculated or estimated. These are the minimum path loss (PLmin), when the UE is closest to the antenna, and the maximum path loss (PLmax), when the UE is farthest away from the antenna. PLmin will restrict the Femto maximum transmit power to avoid saturating the UE receiver; while PLmax is the maximum acceptable loss where the femto transmit power is sufficient to keep in-house communication with the UE.

For this purpose, we have assumed a certain house layout as an example with defined structure, and we have worked the path loss across the entire area of the house.

Figure 8-1 below shows that path loss is dependent on the area within the house.


Figure 8-2 Path loss model

The maximum indoor path loss is shown to be more than 90 dB in some locations. The minimum outdoor path loss from an indoor Femto can be less than 60 dB. This will be a challenge for operators to balance good indoor coverage while not causing excessive outdoor interference.

Studied in this section is a macrocell user (MUE) at cell edge, located in an apartment where an active femtocell is operating with full capacity. Analysis is given for the following case:

For the MUE to detect the macrocell and camp on it, or to maintain a call, the P-CPICH Ec/No must be sufficient. We assume a -20 dB threshold – ie. the received P-CPICH RSCP from the macro must be no more than 20dB below the Rx P-CPICH RSCP of the femto. It is assumed that cell-edge PCPICH RSCP for the macro is -103 dBm, and so we can infer that the femto PCPICH RSCP must be lower than -83dBm for the MUE to camp on the macrocell. (Note that techniques for facilitating cell re-selection, such as the use of hysteresis, cell re-selection parameters, HCS, HPLMN, etc, are not discussed here, and are beyond the scope of this paper; the discussion in this paper is on the generic aspect of triggers for cell re-selection only.)

We have assumed two scenarios for the location of the femto relative to the macrocell: 100 metres and 1,000 metres away from the macro have been used. We have found that when the femto is deployed in an area in close proximity to the macrocell (ie. 100 metres away), the maximum output power of the femto should be increased beyond 100 mW in order to ensure operation in high coverage. Therefore, when we study the 100 metres case, we assume the femto is able to radiate up to 125 mW, while maximum output power is limited to 20 mW when the femto is deployed further away (ie. 1,000 metres).

Figure 8-3 shows the statistics of the MUE performance when located near the femto in the above mentioned two cases.

• Femto being 100 metres away from macrocell • Femto being 1,000 metres away from macrocell.

8.2 Analysis

Macrocell configuration:


• Macrocell site-to-site distance: 100 or 1,000 metres • Antenna height: 25 m • Antenna gain: 18 dBi • Frequency carrier in 850 MHz band • Output power of the macro Node B: 20 Watts • Town size: 500m radius.

Femto location configuration:

• House size: 8.3X17.5 (m2) • Houses cover 70% of the area • Wall penetration loss: 12 dB • CPICH power is 10% of max output power.

The following figures show the required power (as a proportion of the total macrocell power) needed to support a voice call at 12.2 kbps within the house in the two deployment scenarios.

Figure 8-3 TX power needed for 12.2 kbps for MUE (1000 metres away and 100 metres away respectively).


It is evident that the required power for a well-sustained call at 12.2 kbps is higher in the following two cases:

• When the MUE is at the edge of the macrocell (ie. 1,000 metres away) and is behind the building where the femto is deployed. In this case the MUE requires the macrocell to transmit the radio link at a higher power to compensate for the high path loss affecting the macro signal and the interference from the femtocell.

• When the MUE is in close proximity to the femtocell and the MUE is located inside the house. In this case the wall loss is adding additional attenuation to the macro signal.

The following figures show the macro HSDPA throughput within the house in the two deployment scenarios (based on how far the femto is from the macro).

Figure 8-4 MUE throughput with HSDPA for locations at 1,000 and 100 metres respectively.

8.3 Scenario analysis and conclusions

In the scenario presented in this section, the performance of MUE attached to the macrocell is shown to be affected by the femtocell in some locations. This can be mitigated by the use of adaptive power control on femto. Results show that in some cases the MUE might experience “deadzone” when in close proximity to the femto. One firm conclusion from this analysis is that adaptive power control is necessary for the femtocells. Femtocells will require higher output power when the femtocell is deployed in locations near the centre of the macrocell.

Adaptive power control on the femtocell mitigates interference by offering just the required transmit power on the femto, based on the level of interference from macro. However, it is shown that a macrocell UE (MUE) might not receive an adequate signal level from the macro to compensate for the femto interference. This is evident in all places in close proximity to the femto when the macro and femtocells share the same carrier.

It is also concluded that there is no apparent and fundamental performance change whether 850 MHz or 2100 MHz is used for the carrier.

In general, if a macro network is designed to provide fixed coverage in terms of cells radius, then the macrocell requires lower output power when operating at 850 MHz. Therefore, the interference level seen by a femto is the same, regardless of the carrier frequency.


It is shown that the femto is an effective vehicle for delivering a good carrier re-use. Furthermore, femtocells are an efficient technique for delivering the high-speed data offered by HSPA to femto users. This can be compared with the macrocell case, where cell radius is larger, resulting in the distribution of the potential bandwidth of the HSDPA to a larger number of users. It is also well known that HSPA throughput is affected by the location of the UE; the closer the UE to the centre of the cell, the higher the throughput. This leads us to conclude that small cells like femtocells are an optimum complementary technique for macrocells for addressing high-data usage.


9. Scenario D: Femtocell Uplink Interference to the Macrocell NodeB Receiver

9.1 Introduction

This document provides an analysis of Femtocell Uplink Interference from femtocell mobiles (FUEs) to a Macrocell NodeB Receiver.

The scenario being investigated is as follows: An FUE is located next to the apartment window that is in sight of a rooftop macrocell (approximately 1,000 m in distance), as shown in Figure 10-1. At the same time, the FUE is connected to the femtocell at the edge of its range, and is transmitting at full power.

Figure 9-1 Interference Scenario D

In this analysis the impact to the macro Node B is measured by the sensitivity degradation, also referred to as noise rise (or relative increase in uplink Received Total Wide Band Power (RTWP)), experienced by the macro Node B, due to the femto UE. The impact is considered relative to the impact a macro UE will have on a macro Node B from the same location as the femto UE. The rest of this document is structured as follows:

• In Section 9.2, analysis of Scenario D described in [Law08] is presented, including the assumptions used. The analysis shows that the femto UEs impact on the macro Node B is no worse that the impact a macro UE from the same location would cause.

• In Section 9.4, a mitigation technique is suggested that would always ensure there is minimal impact to macro Node Bs due to femtocell UEs.


9.2 Analysis of Scenario D - 12k2 Voice and HSUPA

An analysis of this scenario is presented, based on link budget calculations. The analysis looks at the noise rise at the Macro Node B antenna connector due to the femtocell UE in the described scenario.

9.2.1 Assumptions

A macro Node B with a noise floor based on the assumption that the sensitivity of the Wide macro Node B for 12k2 voice service at the time is equal to -121 dBm (i.e. the 3GPP reference sensitivity level for a 12k2 voice service on a Wide Area Node B at the antenna connector [TS25.104]). This sensitivity captures both the loading and noise figure of the macro Node B. The noise floor calculation is shown in Table 9-1.

Value Units Comment

Sensitivity @ antenna connector -121 dBm

Pue_rec

3GPP reference sensitivity level for Wide Area Node B

UE Service Rate 12.20 kbps R Chip rate 3.84 MHz W UE Processing Gain 24.98 dB PG = 10*log(W/R)

Required EbNo 8.30 dB EbNo DCH performance without rx diversity (see [FF09])

noise floor

-104.32 dB nf_ant = Pue_rec +PG -EbNo

Table 9-1 Macro Node B noise floor

Next, the factors that could lead the femto UE to transmit at a power higher than expected are considered. This will occur if the femto UE is at the femto’s cell edge, and if the femtocell experiences a noise rise, or its receiver is experiencing a blocking effect, caused by one of the following:

• A co-channel macro UE. • An adjacent channel macro UE. • Another femto UE located very close (~1m Free Space Loss) to the femtocell

– eg. a laptop with a 3G data card doing a data upload on the same desk as the femtocell.

Subsequently, for the purposes of this scenario, the following assumptions are made:

• The femto is operating under extreme conditions, experiencing a total noise rise equivalent to 70% loading in the uplink.

• A 21 dBm class femto1 is used in the scenario that can provide a coverage path loss of up to 120 dBs (path loss estimate based on minimum RSCP sensitivity of UE of -111 dBm and an 11 dBm CPICH transmit power and assumption of negligible downlink interference from surrounding Node Bs).

Based on these assumptions, the link budget in Table 9-2 estimates the likely femto UE uplink transmission power at the femtocell edge of coverage for a 12K2 voice service and a 2Mbps HSUPA service.

1Under the same RF conditions a 21 dBm class femto cell will provide larger downlink coverage than a 15dBm class or a 10dBm class femto


Value

Units Comments 12K2 Voice

2Mbps HSUPA

Frequency 850.00 850.00 MHz F Bandwidth 3.84 3.84 MHz B Thermal Noise Density -174.00 174.00 dBm/Hz tnd Receiver Noise Figure 8.00 8.00 dB NF Receiver Noise Density -166.00 -166.00 dBm/Hz rnd = tnd +NF

Receiver Noise Power -100.16 -100.16 dBm rnp =rnd +10*log(B*1e6)

Loading 70.00 70.00 % L Noise Rise due to Loading 5.23 5.23 dB IM

= -10*log(1-L/100)

Femto Receiver Noise Floor -94.93 -94.93 dBm trnp =rnp +IM Femto UE Service Rate 12.2 kbps R Chip rate 3.84 MHz W Femto UE Processing Gain 24.98 dB PG = 10*log(W/R)

Required EbNo 8.30 dB EbNo

DCH performance without rx diversity [FF09]

Required EcNo -16.68 0 dB

EbNo– PG for 12K2 Typical EcNo to achieve HSUPA rates of ~ 2Mbps [Hol06]

Minimum Required Signal Level for Femto UE -111.61 -94.93 dB Pfmin = trnp +EcNo Femto UE Path loss to Femto 120 120 dB DLcov

Femto UE Tx Power 8.39 21 dBm Pfue

= min(21, max ((Pfmin + DLcov), -50)

Table 9-2 Femto UE TX power 1000 m from macro Node B

9.2.2 Macro Node B Noise Rise

The noise rise caused to the macro by a femto UE transmitting at 8.39dBm for a 12K2 voice service and 21dBm for a 2Mbps HSUPA service was calculated, using the link budget in Table 10-3, as 1.44 dB and 9.12 dB respectively. Assuming that a macro UE is at the same location as the femto UE by the window (path loss of 130.77dB from the macro, see Ltot in Table 9-3), Table 10-4 shows that a macro UE operating from the same location as the femto UE will be transmitting at 9.94 dBm, and 21dBm if on a 12k2 voice service and 2Mbps HSUPA data service respectively and, hence, will lead to the same amount of noise rise as the femto UE.

Value

Units Comments 12K2 Voice HSUPA


Value

Units Comments 12K2 Voice HSUPA

Node B Antenna Gain 17 17 dBi Gant [FF09] Feeder/Connector Loss 3 3 dB Lf Noise Floor at antenna connector -104.32 -104.32 dBm nf_ant Table 10-1 Femto UE Tx Power 8.39 21 dBm Pfue UE Antenna Gain 0 0 dBi Gmant

Femto UE Tx EIRP 8.39 21 dBm Pfue_eirp =Pue – Gmant +m

Window/Wall Loss 5 5 dB Lw

Path loss to Macro Node B 130.77 130.77

dB

Ltot

=1000m Okumura-Hata(Node B at30m and mobile at 1.5m) +Lw

Femto UE Interference @ macro antenna connector -108.38 -95.77 dB

Pfue_rec

= Pfue_eirp – Ltot + Gant –Lf

Rise above noise floor -4.06 8.55 dB R Pfue_rec- nf_ant

Noise rise 1.44 9.12 dB NR =10*log( 1+ 100.1*R))

Table 9-3 Noise rise calculation for Scenario D (femto UE is transmitting at 8.39dBm and 21dBm 1000m from a macro Node B for a 12K2 service and 2Mbps HSUPA service)

Value Value Units Comments 12K2 HSUPA Frequency 850 850 MHz Bandwidth 3.84 3.84 MHz B Thermal Noise Density

-174.00 -174.00 dBm/Hz tnd

Receiver Noise Figure

5.00 5.00 dB NF

Receiver Noise Density

-169.00 -169.00 dBm/Hz rnd = tnd + NF

Receiver Noise Power

-103.16 -103.16 dBm rnp

=rnd +10*log(B*1e6)

Loading 50.00 50.00 % L Noise Rise due to Loading

3.01 3.01 dB IM

=-10*log(1-L/100)

Macro Receiver Noise Floor

-100.15 -100.15 dBm trnp = rnp +IM

Required EcNo

-16.68

0.00 dB EcNo

= EbNo - PG for 12k2 (see EbNo in Table 10.2) Typical EcNo to achieve HSUPA rates of ~ 2Mbps [Hol06]

Fade Margin 10 10 dB m Antenna gain 17 17 dBi Gant


Feeder/Connector Loss

3 3 dB Lf

Minimum Required Signal Level

-120.83 -104.15 dB Pfmin

= Trnp –Gant +Lf +EcNo + m

Macro UE Path loss to macro

130.77

130.77 dB DLcov

=1000m Okumura-Hata(Node B at 30m and mobile at 1.5m) +Lw

Macro UE Tx Power

9.94

21 dBm Pfue


Table 9-4 Macro UE Tx power 1,000m away from macro Node B receiver by window on a 12K2 voice and 2Mbps HSUPA data service.

9.3 Conclusions

The following conclusions can be drawn:

It is unlikely that a femto UE will be transmitting at maximum power, due to the relatively smaller coverage of the femto compared to the macro.

When the femto is operating under extreme loading conditions, the analysis for a 12k2 voice service has shown that a femto UE in the described scenario will be transmitting in the region of 8.39 dBm and will cause a noise rise of approximately 1.44 dB. Further, a macro UE on a 12k2 voice service at the same location as the femto UE will transmit at 9.94 dBm and, hence, will lead to a similar amount of noise rise.

When the femto is operating under extreme loading conditions, the analysis for a femto UE with 2Mbps HSUPA data service has shown that a femto UE in the described scenario will cause a noise rise amounting to approximately 8.55 dB; however, it should also be noted that a macro UE operating at the same position and on the same service (with the same service requirement) is expected to cause the same amount of noise rise.

9.4 Recommendations

The following recommendations are made. They will help ensure harmonious coexistence of femtocells and macro Node Bs:

• It is desirable to limit the allowed maximum transmission power of a femto UE, to avoid a noise rise to the Macro Layer.

Assuming the femtocell has certain capabilities, then:

• The maximum allowed femto UE transmission power can be limited appropriately, such that the noise rise caused by a femto UE when transmitting at its maximum allowed power is limited based on the femtocells proximity to the surrounding Macro Layer Node Bs. This is important, especially when one considers the cumulative effect of multiple femto UEs spread across a network. A similar approach is suggested in [R4-071578].

• The femtocell could also handover a femto UE to a macrocell if an in-service femto UE is at the verge of the femtocell; thereafter, uplink interference to a macrocell from this UE is avoided.


10. Scenario E: Femtocell Downlink Interference to nearby Femtocell UE Receiver.

10.1 Description

In this section, performance effect on a femto user denoted UE1 is analysed when another UE (UE2), belonging to another femtocell, operates in close proximity.

Two residential housing units are considered:

• Two apartments are separated by a wall, with a femtocell being deployed within each apartment. The two femtocells being considered are denoted AP1 and AP2. Each femtocell supports a corresponding UE – namely, UE1 and UE2 respectively. The assumption is that UE2 is not located in its own apartment, but rather in the apartment where AP1 is operating. Therefore, UE2 is at the edge of coverage of his own femtocell, but very close (<3m) to AP1 (ie. a foreign femtocell). The scenario assumes UE1 to be the Victim, while UE2 has an active call supported by AP2.

• Two houses are detached with a femtocell being deployed within each house. The two femtocells being considered are denoted AP1 and AP2. Each femtocell supports a corresponding UE – namely, UE1 and UE2 respectively. The assumption is that UE2 is not located in its own house, but rather in the house where AP1 is operating. Therefore, UE2 is at the edge of coverage of its own femtocell, but very close (<3m) to AP1 (ie. a foreign femtocell). The scenario assumes UE1 to be the Victim, while UE2 has an active call supported by AP2.

Figure 10-1 Scenario E. Adjacent femto with UEs connected to each AP.

We also assume two cases for macrocells: that the femtocells are and are not deployed in the corresponding residential premises where macrocell coverage is present.

Interference and performance degradation to the home user (i.e. UE1) from the presence of UE2 and the macrocell is analysed in this section.

AP1 AP2

UE1

Apartment 1

UE2

Apartment 2


10.2 Capacity Analysis

The effect on average throughput for the femto users can be analysed through the use of a Monte-Carlo simulation.

The simulation layout for this scenario is for case 1 and case 2, as shown in Figure 10-2 and Figure 10-3.

Figure 10-2 Apartments Plan – Flats layout

In the second scenario contained in this section, the effect of neighbouring femtocell interference on the central house (located at coordinates 0,0) is investigated. In cases where a macrocell is present, it is located at coordinates -500m, -500m.

Figure 10-3 Macrocell location relative to the house where the femtos are located

Simulation Configuration for apartment case: • Max Femto power = 13dBm (but actual output power is based on auto-

configuration) • Pilot power = 10% of femto output power • External Wall Loss = 15dB • Internal Wall Loss = 10dB • Door Loss = 5dB

-15 -10 -5 0 5 10 15-15

-10

-5

0

5

10

15

-80 -60 -40 -20 0 20 40 60 80

-80

-60

-40

-20

0

20

40

60

80

Village Plan

X Coordinate in Meter

Y C

oord

inat

e in

Met

er


• Macrocell location = -500, -500 • Macrocell antenna height = 25m. • Apartment layout: • Two-story building, height = 7m. • Femto acess point is located on the ceiling • UE height = 1.5m • Penetration loss: • External wall = 15 dB • Window = 1 dB • Doors = 3 dB • Outer door = 30 dB. • Simulation assumption for case 2 – when houses are considered – is found in

the section describing Scenario C, but is not repeated here.

The first simulation result obtained when the femtos use a dedicated carrier – shown in Figure 10-4 below. The graph provides the cumulative distribution of HSDPA throughput for the UEs when located in the various locations (ie. flat or house). The results show the CDF for HSDPA throughput for UE1 in two cases:

• when the AP1 is operating in isolation (ie. AP2 is not there, and nor is UE2) • when AP2 is operating in the adjacent location, and AP2 is connected to AP1

in active call.

It is evident that the neighbouring femtocells (AP2) and the presence of UE2 do result in throughput degradation to UE1.

It is shown that the performance degradation sustained by UE1 is greater in the case of apartment. In the case of users in apartments, the statistics for UE1 getting full throughput drops from more than 90%, to just over 40%.

Figure 10-4 Dedicated carrier: CDF of HSDPA throughput

The performance is further evaluated when macro network coverage is also provided, and the macro and femtocells share the same frequency. This is shown in Figure 10-5.

0 500 1000 1500 2000 2500 3000 35000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Throughput in kbps

Cum

ulat

ive

Dis

tribu

tion

Func

tion

Flat no NeighbourFlat with NeighbourHouse no NeighbourHouse with Neighbour


Figure 10-5 Shared carrier: CDF of HSDPA throughput

10.3 Conclusions

In Scenario E, the downlink throughput of the UE connected to Femtocell is shown to be affected by the downlink of neighbouring femtocells. The case shows that driving femtocells to provide coverage for adjacent locations deemed to be covered by other femtocells yields performance degradation.

The closer the femtocells are, the higher the mutual interference and performance degradation.

It is, therefore, strongly recommended that femtocells use effective power control to confine coverage to their premises. Where the UE cannot get service from the femto, this UE should be supported by the macro network. There is a need to make sure that the pilot and transmit power of the femto is carefully adjusted to provide coverage to UEs within the intended area.

It can be concluded that the femto coverage should aim to be restricted to a single apartment/house only in order to limit any undue interference between femtos. Adaptive power control is one method to help this. This leaves the issue of supporting visiting UEs being under the control of the macrocell.

0 500 1000 1500 2000 2500 3000 35000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Throughput in kbps

Cum

ulat

ive

Dis

tribu

tion

Func

tion

Flat at (500 500)Flat at (100 0)House at (500 500)House at (100 0)


11. Scenario F: Femtocell UE Uplink Interference to Nearby Femtocell Receivers

11.1 Description

In this scenario, there are two neighbouring Femtos: a Femto UE (UE2) is camping on femto 2 (AP2) while close to femto 1 (AP1) – see Figure 11-1 below.

Figure 11-1 Illustration of the Interference Scenario F

The analysis on this scenario mainly focuses on how the uplink receiver (UL Rx) of AP1 would be interfered with or impacted by UE2, especially when service is ongoing in UE2. In this situation the interference or impact is measure by sensitivity degradation, also referred to as noise rise (or relative increase in uplink Received Total Wide Band Power (RTWP)), experienced by AP1 due to UE2.

11.2 Analysis

Analytical analysis is carried out for the above scenario based on link-budget calculations and transceiver performance requirements taken from [FF09].

11.2.1 Assumptions

For the purposes of analysis the following assumptions are also made:

• AP1 and AP2 have equal Maximum DL powers, and CPICH channel power ratio is 10%;

• both AP1 and AP2 have only one 12.2K voice service ongoing; DL load factors are at about 50%; and

• AP2 has 50% loading in the uplink.


11.2.2 Analysis of Noise Rise received at the Victim AP

value Unit comment

Femtocell Noise Figure (NF) 8 dB Performance requirements taken from [2]

UE Processing Gain (G) 25 dB =10*log(3.84MHz/12.2kbps) Required Eb/No (EbNo) 7 dB Sensitivity (S) -118 dBm =-108+EbNo-G+NF UL load factor of AP2 (LoadUL) 50 % Noise rise due to UL loading (NRload) 3 dB =-10*log(1-LoadUL) DL load factor of AP1 50 (α ) %

DL load factor of AP2 50(β ) %

21 APAP RSCPRSCP − 10.6 dB According to formula(2)

The interference at AP1 (Rx) -104.4 dBm =S+NRload+ 21 APAP RSCPRSCP − Noise floor at AP1 (PN) -100 dBm =No+NF

Noise rise due to interference (NRinterfer)

1.3 dB = PN

RxPN

−+ )1010log(*10 1010

Table 11-1 Femtocell Sensitivity and Noise Rise at AP1

The sensitivity of a femtocell is based on the assumption that the noise figure is 8dB [FF09]. The sensitivity calculation is shown in Figure 11-1.

When UE2 get near enough to AP1, UE2 will drop call from AP2. At this point, the interference received at AP1 from UE2 is at the maximum. The assumed Ec/Io (interference margin) required to maintain a voice call is assumed -18dB.

dBRSCPIoEcAPAP RSCPRSCP

AP 1810*

%10%10*

%10%

)10/(^10log*10/10/10/

2

21

−=+

=βα

(1)

)(log*10 *1.0*1.010

218.1

dBRSCPRSCP APAP ∂−=− β (2)

In order to maintain a voice call, the transmit power of UE2 connected to AP2 can be calculated as follows:

2_222 APUEloadAPUE PathLossNRSTxpower ++= (3)

The interference from UE2 to AP1 (InterfUE2_AP1) can be calculated as follows:

1_221_2 APUEUEAPUE PathLossTxpowerInterf −=

Then the interference from UE2 to AP1 can be derived as follows:

dBRSCPRSCPPPNRSRSCPPRSCPPNRS

PathLossPathLossNRSInter

APUEAPUEAPcpichAPcpichloadAP

APUEAPcpichAPUEAPcpichloadAP

APUEAPUEloadAPAPUE

)()(

)()(

2,21,21,2,2

1,21,2,22,2

1_22_221_2

−+−++=

−−−++=

−++=

(4)


The link budget in Table 11-1 estimates the maximum uplink interference to AP1 from UE2 at the cell edge of coverage of AP2 for a 12.2K voice service from formula (4).

Both radio paths, from AP1 and AP2 to UE2, with the same model (ITU P.1238), are assumed to undergo the same signal decay loss with the increasing of distance.

The maximum interference at AP1 from UE2 depends on the difference of the pilot signal strength (RSCP) received at UE2, from AP1 and from AP2.

And in this condition, the maximum interference from UE2 to AP1 will result in 1.3dB noise rise at AP1. According to ITU P.1238 Model, there is a relationship between the distance from UE2 to AP1 and to AP2, as can be seen in the figure below.

11.3 Conclusions


• The closer UE2 to AP1, the greater interference from UE2 to AP1.

Distance between AP1 and UE2 with the maximum interference

00.51

1.52

2.53

3.54

4.55

5.56

6.57

7.5

0 5 10 15 20 25 30 35

distance between AP cells(m)

distance between UE2 and AP1(m)


• The interference reaches its maximum at the point when UE2 is disconnecting from AP2 (call is dropping). However, the analysis is based on the extreme scenarios. Usually, UE2 will handover to a macrocell before call drop, which will avoid the interference to AP1.

11.4 Recommendations

The following recommendations are made; they will help ensure the harmonious coexistence of co-channel femtocells:

• It is desirable to limit the allowed maximum transmission power of UE2 to avoid a noise rise to the nearby AP1 when UE2 is at the verge of AP2.

• The AP2 could also handover a UE2 to a macrocell (macrocell on another frequency channel preferred) if in-service UE2 is in the vicinity of the AP1; thereafter, uplink interference to AP1 from this UE2 is avoided.


12. Scenario G: Macrocell Downlink Interference to an adjacent-channel Femtocell UE Receiver

12.1 Description

In this scenario, there are two NodeBs, a macro NodeB and a Femto one (AP1); UE (UE1) is camping on the femtocell – see Figure 13-1 below.

Figure 12-1 Illustration of the Interference Scenario G

The analysis on this scenario mainly focuses on how the downlink receiver (DL Rx) of UE1 would be interfered or impacted by the macro downlink transmission, especially when service is ongoing in UE1. Here, we assume that the distance between the femto UE and macro NodeB is approximately 1,000m. In this context, Ec/Io received by the UE1 at a different place within AP1 coverage is used as the metric to evaluate the impact from macro downlink.

12.2 Analysis

Analytical analysis is carried out for the above scenario based on link-budget calculations and transceiver performance requirements taken from [FF09].

12.2.1 Assumptions

• The macrocell is 50% loaded. • Okumura-Hata model + window loss and ITU P.1238 are used, respectively,

for macrocell path loss to UE1. • ITU P.1238 is used for indoor modelling (for femtocell path loss to UE1).


• The macrocell is assumed to have a maximum transmit power of 43dBm, running at 50% utilisation; femtocell 10dBm of maximum transmit power and 50% utilisation.

• AP is1,020m away from macrocell.

12.2.2 Simulation Analysis

(a) with no interference from macrocell (left) (b) with downlink interference from adjacent-channel macrocell (right)

Figure 12-2 CPICH Ec/Io for Femto

Okumura-Hata model + window loss used for macrocell path loss to UE (approximately 1km distance).

The simulation showed that an adjacent macrocell causes little downlink interference to a femtocell.

12.2.3 Theoretical Analysis

value unit

Maximum Macro Node B Transmit Power 43 dBm

Macro Node B Loading 50 %

Macro NodeB output power (TxPowerMacroNodeB) 40 dBm

Macro Node B Antenna Gain (GtMacroNodeB) 17 dBi

Distance from UE to Macro NodeB 1 km

Window loss 5 dB

Path loss from UE to Macro NodeB (PL1) 131 dB =Okumura-Hata propagation loss +window loss

Adjacent channel selectivity of the UE receiver (ACS) 33 dB


UE Antenna Gain (AntG_UE) 0 dBi

Noise level at UE receiver from Macro NodeB -110 dBm

’=TxPowerMacroNodeB + GtMacroNodeB - PL - ACS-BL-AntG_UE

Table 12-1 Macrocell Downlink Interference to an adjacent channel Femtocell UE in this worst-case scenario

From the above table, the downlink interference level from an adjacent channel macrocell at the UE receiver is -110dBm, which is less than thermal noise when the UE is located 1km away from the macrocell. Therefore, adjacent channel macrocell causes no downlink interference to Femto UE receiver.

12.3 Conclusions

Both theoretical analysis and simulation results show that Femtocell UE experiences little adjacent channel interference from an outdoor macrocell in most cases.


13. Scenario H: Macrocell UE Uplink Interference to the adjacent channel Femtocell Receiver

The aim of this interference scenario is to evaluate impact of uplink interference experienced by a femtocell supporting closed access from a UE that is connected to a macro Node B (as it is not in the femto white list), when the UE and femtocell are located in close proximity. A weak signal is received from the macro Node B within the apartment where the femtocell is located. Further, it is assumed that the macro and femto cellular layers are deployed on adjacent frequencies. The impact of interference is evaluated using two services, AMR 12.2 kbps voice, and HSUPA. 3GPP transceiver specifications will be used in the analysis. It will be determined whether any enhancement to specifications is required.

13.1 Description

A femtocell is located on a table within the apartment. Weak coverage of the macro network is obtained throughout the apartment. A user (that does not have access to the femtocell) is located next to the femtocell and has a call established at full power from the UE1 device. Another device UE2 has an ongoing call at the edge of femtocell coverage [Law08]. Figure 14-1 illustrates the interference Scenario H.

Figure 13-1 Illustration of the interference Scenario H


13.2 Analysis

Analytical evaluation is carried out for the interference scenario based on link-budget calculations and transceiver performance requirements, as specified by 3GPP. The uplink frequency is assumed to be 850 MHz (Band V), and the antenna gains of the Femtocell and UEs are equal to unity. The frequency separation between Femtocell UE (FUE) and Macrocell UE (MUE) is 5 MHz. The assumptions used in the analysis are given below.

13.2.1 Parameter settings

The parameter settings that are used in the analysis are given below:

Services • AMR 12.2 kbps voice, • 5.76 Mbps HSUPA.

MUE parameters • MUE max transmit power, a = 21 dBm (Power Class 4) [TS25.101] • Minimum Coupling Loss (MCL) between MUE and Femtocell, b = 45 dB

[TS25.141] • Antenna gain = 1dBi.

MNB parameters • Receiver sensitivity, RxSens = -121 dBm [TS25.104] • Required Eb/N0 for 12.2 kbps voice, Eb_N0 = 8.3 dB (without Rx diversity

[TS25.104]) • Noise floor = -104.32 dBm (RxSens + 10*log10(3.84e6/12.2e3) - Eb_N0).

FUE parameters • FUE max transmit power, c = 21 dBm (Power Class 4) [TS25.101] • HSUPA terminal category = 6 (5.76 Mbps) [TS25.104].

Femtocell parameters • Adjacent Channel Selectivity (ACS) of the femtocell receiver is equal to d =

63 dB. The specification states that femtocell should be able to decode AMR speech when the received signal strength on adjacent channel is equal to -28 dBm, while wanted signal level is at -91 dBm [TS25.104].

• Maximum allowed path loss between FUE and femtocell is calculated as the difference between the maximum UE transmit power and minimum received signal level of the wanted signal, f = 112 dB (ie. 21 - -91 [dB]).

• Antenna gain = 1 (single-antenna reception) • Noise figure = 12dB [FF09] • Maximum transmit power = 20dBm [TR25.967].

Indoor-indoor path loss model ITU P.1238, N = 28 (2.8 x 10), n = 1, floor penetration loss factor = 4dB, residential deployment, shadow fading has log-normal distribution with standard deviation of 8 dB [FF09].

13.2.2 Impact of MUE interference on AMR

AMR voice service is used in the following analysis. Assuming that the MUE is transmitting at maximum power, the minimum allowed path loss between femtocell and MUE is calculated as the difference between the MUE transmit power (21 dBm)


and the received signal level of the unwanted signal (-28 dBm). It is equal to 49 dB. This corresponds to a minimum separation of around 3.2m between femtocell and MUE, based on the ITU P.1238 indoor path loss model [FF09]. Clearly, this separation cannot be guaranteed in a residential deployment. Figure 14-2 illustrates the variation in minimum separation between femtocell and MUE for a given MUE transmit power level.

One of the mechanisms available to improve robustness against adjacent channel interference is AGC. Under this technique the receiver will dynamically reduce gain of RF front end when it is subject to a blocking signal. The drawback of this technique is that it will result in a receiver sensitivity loss. The next step is to determine whether the reduction in receiver sensitivity makes a significant difference to uplink coverage of a femtocell.

The uplink link-budget of AMR 12.2 kbps voice service is given in Table 13-1. It shows that the UE is only required to transmit at -25 dBm to achieve a typical coverage range of 25 m in uplink. Thus, there is sufficient head room available for ramping-up the UE power in response to uplink interference.


Ref Description Value Units Formula

Transmitter (UE)

Transmit power 0.003 mW Input, power allocation A As above in dBm -25.00 dBm b Antenna gain 0.00 dBi Input, omni-directional antenna pattern. c Body loss -3.00 dB Input d Cable loss 0.00 dB Input e Transmitter EIRP -28.00 dBm a + b + c + d

Receiver (Femtocell)

f Thermal noise density

-174.00

dBm/Hz Input

g Receiver noise figure 12.00 dB Input

h Receiver noise density

-162.00

dBm/Hz f + g

i Receiver noise power -96.16 dBm h + 10*log(3840000)

j Interference margin -3.00 dB Input, corresponding to 50% load [FF09].

k Required Eb/N0 8.30 dB Input [TS25.104]. l Required Ec/I0 -16.68 dB Includes the SF gain.

m Receiver sensitivity

-109.84 dBm

i + l - j, minimum requirement is -107 dBm [TS25.104].

n Receiver antenna gain 0.00 dBi Input

o Cable loss 0.00 dB Input

p Slow fading margin -8.00 dB Input

q Soft handover gain 0.00 dB Input, SHO is disabled in the Femto AP.

r Fast fading margin 0.00 dB Input

s

Allowed propagation loss for cell range 73.84 dB e-m-n+o+p+q+r+s

t Cell range 25.22 m According to ITU P.1238 indoor loss model [FF09].

Table 13-1 Uplink radio link-budget for AMR 12.2 kbps RAB

Under this interference scenario, the femtocell receiver can utilise AGC and reduce the gain of RF front end. As a result, uplink fast power control will command the FUE to increase its transmit power. Thus, the femtocell receiver will be able to tolerate a higher input level of unwanted signal. Figure 13-2 illustrates performance trends with and without AGC, assuming that the front end gain is reduced by 10 dB. Now, the


minimum separation between the femtocell and MUE is equal to 1.5 m. A much smaller separation can be supported if the MUE is transmitting at lower power levels.

If the FUE transmit power is increased in response to AGC there will also be an increase in interference to neighbouring femtocells, as well as to the macro Node Bs. Next, the impact on noise rise at the Macro Node B is evaluated. The noise floor at the macro Node B is calculated to be -104.32 dBm, as shown in Section 14.2. Assuming that the HUE is transmitting at -15 dBm and the total loss of signal strength up to the macro Node B is 110 dB (cell edge scenario), the received signal level will be -125 dBm. Adding ACS rejection of 63dB the received in-band signal strength will be equal to -188 dBm. Thus, noise rise at the macro Node B due to FUE will be insignificant. However, noise rise at neighbouring femtocells could become important as they will normally operate on the same frequency and may not be separated from each other by large distances. Thus, it is important to ensure that femtocell receiver de-sensitisation occurs only when it is necessary. Further, in order to reduce the risk of a significant noise rise in the Macro Layer due to femtocells, it is recommended to limit the maximum FUE transmit power – e.g. as suggested in [R4-071578].

Figure 13-2 Minimum separation between Femtocell and MUE to avoid blocking, for a given MUE transmit power level

13.2.3 Impact of MUE interference on HSUPA

The fixed-reference channel (FRC) no. 3 is used in the following analysis, as it corresponds to the maximum uplink bit rate that is likely to be supported by femtocells in initial deployments. According to [TS25.104], the femtocell receiver should provide R ≥ 30% of max information bit rate at reference value of Ec/No of 2.4 dB and R ≥ 70% of max information bit rate at Ec/No of 9.1 dB. “R” denotes minimum

4 6 8 10 12 14 16 18 20 220

0.5

1

1.5

2

2.5

3

3.5

MUE transmit power level [dBm]

Min

imum

Hom

e N

ode

B-M

UE

sep

arat

ion

[m]

Impact of adjacent channel interference on the Home Node B

Interfering signal level = -28 dBmInterfering signal level = -18 dBm


HSUPA throughput. These values are based on the Pedestrian A channel model. The maximum information bit rate with FRC3 is equal to 4059 kbps.

Assuming that MUE to FAP separation is fixed at 2 m, and the received MUE signal level at the femto receiver being less than or equal to -28 dBm (from ACS spec.), Figure 14-3 illustrates the variation in E-DPDCH Ec/No measured at the femto receiver for a given MUE transmit power level. It is assumed that the FUE to FAP path loss is fixed at 90 dB (coverage edge scenario). Results show that in order to achieve 70% of max information rate, the average transmit power of FUE should be at least -3 dBm. Additionally, MUE transmit power should be kept to below 2.2 dBm. Maximum allowed FUE transmit power level can be signalled by the femtocell (eg. in RRC signalling), while MUE transmit power level cannot be controlled by the femtocell. As the likelihood of MUE transmitting at high power increases at the macrocell edge, HSUPA throughput at the femtocell is likely to deteriorate under this interference scenario.

Figure 13-3 E-DPDCH Ec/No variation as a function of MUE transmit power level

Figure 13-4 illustrates the increase in average transmit power level of the FUE required to meet HSUPA throughput requirements, as a function of MUE transmit power level. The curves show that there is sufficient headroom available in uplink under this interference scenario.

Figure 13-5 illustrates the variation in E-DPDCH Ec/No as a function of MUE transmit power level, when the FAP to MUE separation is fixed at 5 m. In this case, although the FUE transmit power should be at least -3 dBm, MUE transmit power can increase to 13 dBm to achieve R ≥ 30% of max information bit rate.

-10 -5 0 5 10 15-4

-2

0

2

4

6

8

10

12


FUE

E-D

PD

CH

Ec/

No

[dB

]

Femto - MUE separation = 2 m

2.8 Mbps (=70% of 4.095 Mbps)

1.2 Mbps (=30% of 4.095 Mbps)

FUE Tx. Power = 5 dBm


FUE Tx. Power = -3 dBm


Figure 13-4 Required average FUE transmit power level to meet HSUPA throughput requirements.

-10 -5 0 5 10 15-4

-2

0

2

4

6

8

10


Req

uire

d av

erag

e FU

E tr

ansm

it po

wer

leve

l [dB

m]


R = 1.2 MbpsR = 2.8 Mbps


Figure 13-5 E-DPDCH Ec/No variation as a function of MUE transmit power level

13.3 Conclusions

This section has considered a simple analysis of the interference Scenario H based on link-budget calculations and 3GPP specifications. Analysis considers impact of interference on two services – AMR 12.2 kbps voice, and 5 Mbps HSUPA.

The relationship between minimum FAP to MUE separation and MUE transmit power level has been derived. It was found that if the MUE is transmitting at the maximum power of 21 dBm it needs to be separated from the femtocell by around 3.2 m. This separation can be reduced further by employing Automatic Gain Control (AGC) at the femtocell receiver. It has been shown that the minimum MUE to FAP separation can be reduced to 1.5 m if a reduction in gain of 10 dB is applied by AGC. The resulting loss in receiver sensitivity will not deteriorate femtocell coverage of voice, as there is sufficient power headroom available at the UE.

The performance of HSUPA has been analysed in the presence of uplink interference from the macro UE, which is operating on the adjacent frequency. The femtocell – MUE separation is fixed at 2 m and 5 m. The FUE – femtocell path loss is fixed at 90 dB, representing the coverage edge scenario. It was seen that in order to obtain 70% of nominal HSUPA bit rate with a category 6 UE, the MUE transmit power should be below 7.5 dBm and 18.5 dBm, respectively. In both cases minimum transmit power required for HSUPA transmission is equal to -3 dBm. As the likelihood of MUE transmitting at high power increases at the macrocell edge, HSUPA throughput at femtocell is expected to deteriorate in this interference scenario.

-10 -5 0 5 10 15 200

2

4

6

8

10

12


FUE

E-D

PD

CH

Ec/

No

[dB

]



FUE Tx. Power = -3 dBm


1.2 Mbps (=30% of 4.095 Mbps)

2.8 Mbps (=70% of 4.095 Mbps)


13.4 Femto System Impact

If the minimum separation between the MUE and femtocell is not maintained the femtocell receiver may not be able to decode the wanted speech signal at the required QoS level. Similarly, the HSUPA performance will deteriorate gradually as the MUE transmit power is increased for a given separation between the MUE and femtocell receiver.

13.5 Mitigation techniques

The ACS specification for the Home Node B has been enhanced recently to accommodate higher levels of blocking signals [TS25.104]. Additional robustness against uplink interference can be provided with AGC. Since reduction in RF front end gain will cause receiver desensitisation, AGC should be activated only when required. It has been shown that there is sufficient power headroom available at the UE to meet typical femtocell coverage requirements for both voice and data services. Further, to maintain overall system stability in uplink, restriction of the maximum FUE transmit power level could be considered [R4-071578]. Some of the factors governing selection of maximum transmit power of FUE are femtocell coverage, service requirements, frequency deployment, distance to nearest macrocell receiver, uplink noise rise margin, etc.


14. Scenario I: Femtocell Downlink Interference to the adjacent channel macrocell UE Receiver

The aim of this interference scenario is to evaluate the impact of downlink interference experienced by a UE that is connected to the macro Node B from a femtocell, while being located in close proximity to a femtocell. The MUE is not allowed to access the femtocell (ie. closed subscriber group). A weak signal is received from the macro Node B within the apartment where the femtocell is located. Further, it is assumed that the macro- and femto-cellular layers are deployed on adjacent frequencies. Impact of interference is evaluated using two services, AMR 12.2 kbps voice, and HSDPA. 3GPP transceiver specifications will be used in the analysis. It will be determined whether any enhancement to specifications is required.

14.1 Description

Two users (UE1 and UE2) are within an apartment. UE1 (FUE) is connected to a femtocell and at the edge of coverage. UE2 (MUE) is connected to the macrocell at the edge of coverage, and located next to the femtocell transmitting at full power [Law08]. Figure 14-1 illustrates the interference Scenario I.

Figure 14-1 Illustration of the Interference Scenario I


14.2 Analysis

Analytical evaluation is carried out for the interference scenario based on link-budget calculations and transceiver performance requirements as specified by 3GPP. The downlink frequency is assumed to be 850 MHz, and the antenna gains of the Femtocell and UEs are equal to unity.

14.2.1 Parameter settings

The parameter settings that are used in the analysis are given below [FF09]:

• ServicesAMR 12.2 kbps voice • 14.4 Mbps HSDPA. • Femtocell parametersStatic maximum total transmit power, including

control and traffic channels, Pmax = 10, 15, 20 [dBm] • Downlink frequency = 850 MHz. • Macrocell parametersMax transmit power on DCH = 33 dBm • Total transmit power = 43 dBm • HSDPA power allocation = 42 dBm (80% of total power) • Antenna gain = 17 dBi • Feeder/cable loss = 3 dB.

MUE receiver parameters • Reference sensitivity level (DPCH_Ec_<REFSENS>) = -115 dBm (Band II),

[TS25.101] • REFIor = -104.7 dBm (Band II), [TS25.101] • Max transmit power = 21 dBm (Power Class 4), [TS25.101] • Maximum input power level = -25 dBm, [TS25.101] • ACS = 33 dB, [TS25.101] • HSDPA terminal category = 10 (14.4 Mbps).

The ACS specification is valid as long as the Femtocell Downlink signal is in the range [-25,-52] (dBm) [TS25.101]. Additionally, the DPCH_Ec from the Macro Node B should be in the range [-74, -101] (dBm) [TS25.101]. Figure 14-2 illustrates the region of operation, which meets conditions specified above.

Outdoor-indoor path loss model, [FF09] • Okomura Hata + Wall/Window loss • External wall loss = 10 dB.

Indoor-indoor path loss model, [FF09] • ITU P.1238, N = 28, n = 0 (MUE is in close proximity of the femtocell).


Figure 14-2 Macro Node B signal strength relative to the interfering femtocell signal strength measured at the MUE, required for successful decoding of AMR

14.2.2 Impact of Femtocell interference on AMR service

The region of operation, shown in Figure 14-2, gives the maximum strength of the downlink interfering signal versus the minimum strength of wanted signal. Each point in the region of operation translates into distance of separation between femtocell to MUE, versus distance between macro NodeB and MUE. The ITU P.1238 model will be used to calculate path loss between the femtocell and MUE, while the Okumura-Hata model will be used on the link between the macrocell and MUE.

Figure 14-3 illustrates impact of downlink interference as a function of femtocell transmit power. The curves are obtained by converting maximum allowed path loss into distance according to specified path loss models. It is assumed that femtocell is transmitting at full power. The general trend is that as the MNB to MUE separation is increased, the distance between femtocell and MUE also needs to be increased, in order to avoid blocking at the MUE. It is clear from Figure 14-3 that downlink interference will not pose any problem to the MUE when it is located close to the macrocell. However, if the MUE is located close to the macrocell edge femtocell, interference could block the downlink signal. Figure 14-3 also illustrates the merits of adaptive control of maximum femto transmit power level, as for a fixed minimum femtocell – MUE separation the appropriate femtocell transmit power level depends on the femtocell – macrocell path loss.

Table 14-1 gives the maximum MNB – MUE separation that can be supported for different femtocell transmit power levels, when the femtocell – MUE separation is fixed at 5 m. Results are obtained by converting maximum allowed path loss into distance using appropriate path loss model. A recent 3GPP contribution on the same topic

-100 -95 -90 -85 -80 -75-55

-50

-45

-40

-35

-30

-25

Min. Macro NB Downlink signal strength (Ior) [dBm]

Max

. Fem

toce

ll D

ownl

ink

inte

rfere

nce

at M

UE

(Ioa

c) [d

Bm

]

Region of normal operation, AMR speech

Region of operation


suggests that maximum transmit power of a femtocell should be limited to 10 dBm for the adjacent channel deployment scenario [R4-090940].

Figure 14-3 Maximum MNB - MUE separation as a function of femtocell – MUE separation, assuming AMR voice service.

Femtocell transmit power (dBm) Max. Macro NB - MUE separation (km) 10 1.0 15 0.7 20 0.5

Table 14-1 Maximum Macro NB – MUE separation for a given maximum Femtocell transmit power level, when the Femtocell – MUE separation is fixed at 5 m.

14.2.3 Impact of Femtocell interference on HSDPA

Next, performance of HSDPA under this interference scenario is analysed using link-budget type calculations. Fixed Reference Channel definition H-Set 6 is selected for analysis purposes [TS25.101]. A Category 10 UE is chosen, as it supports the maximum achievable HSDPA data rate (equal to 14.4 Mbps).

The nominal average information bit rate for this FRC is 3219 kbps with QPSK, and 4689 kbps with 16QAM. The UE specification states that the receiver should meet or exceed the information bit throughput R requirements given in Table 14-2.

Parameter Value Channel model PA3 (Pedestrian A) Ioc [dBm] -60

0 5 10 15 20 25 30 35

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4M

axim

um M

acro

NB

- M

UE

sep

arat

ion

[km

]

Minimum Femtocell - MUE separation [m]

Interference Scenario I.1, AMR speech

Pmax = 10 dBmPmax = 15 dBmPmax = 20 dBm


/c orE I [dB] [TS25.133] -6, -3

ˆ /or ocI I [dB] 10

R, QPSK [kbps] 1407, 2090 R, 16QAM [kbps] 887, 1664

Table 14-2 UE receiver performance requirement (HSDPA), [TS25.101]

Based on link budget calculations, the minimum femtocell to MUE separation is found to be 1.7 m, 2.6 m and 3.9 m (to maintain given Ioc), depending on whether Pmax is equal to 10 dBm, 15 dBm or 20 dBm (ITU p.1238 model). Figure 14-4 illustrates the impact of interference in terms of maximum macrocell to MUE separation for a given femtocell to MUE separation. At each point in the curve, femtocell interference is fixed at -60 dBm, while the macrocell G-factor ( ˆ /or ocI I ) is maintained at 10 dB. Further, it is assumed that macrocell has allocated 80% of total power to HSDPA, resulting in HS-PDSCH Ec/Ior of approx. -1 dB.

Figure 14-4 Maximum macrocell-MUE separation as a function of femtocell-MUE separation, for reception of HSDPA

If the femtocell – MUE separation is fixed at 5 m, the macrocell – MUE separation should not be more than 185 m - 360 m in order to decode the HS-PDSCH at the specified rate. It is well known that a macrocell allocates highest HSDPA data rates only when UEs are located close to the cell site. Thus, it is not apparent whether interference from the femtocell will significantly deteriorate HSDPA performance at the MUE.

1 2 3 4 5 6 7 8 9 10150

200

250

300

350

400

450

500

550

600

650

Femtocell-MUE separation [m]

Max

. Mac

roce

ll-M

UE

sep

arat

ion

[m]

Interference Scenario I.1, HSDPA

Pmax = 10 dBmPmax = 15 dBmPmax = 20 dBm


14.3 Conclusions

A simple analysis of the interference Scenario I has been carried out based on link-budget type calculations and 3GPP specifications. Adjacent channel deployment for the macro- and femto-layers has been assumed. The analysis considers impact of interference on two services – AMR 12.2kbps voice, and 14.4Mbps HSDPA.

In terms of AMR service, a minimum separation of 5 m between the femtocell and MUE can be achieved if the macrocell site is within 1.0 km, and the femtocell is not transmitting above 10dBm. It is recommended to implement adaptive control of maximum transmit power level at the femtocell and restrict maximum transmit power to 10 dBm, in order to achieve a good trade-off between femtocell coverage and adjacent channel deadzone.

We have also analysed HSDPA performance under this interference scenario using link-budget type calculations and UE specifications. At the minimum supported femtocell – MUE separation of 5 m, it was found that the macrocell – MUE separation should not be more than 185 m - 360 m in order to decode the HS-PDSCH at the specified rate. Analysis was performed for a fully loaded femtocell transmitting at 10 dBm, 15 dBm and 20 dBm. It is well known that a macrocell allocates highest HSDPA data rates only when UEs are located close to the cell site. Thus, it is not apparent whether downlink interference from femtocell will significantly deteriorate HSDPA performance at the MUE.

14.4 Customer (MUE) Impact

In terms of AMR service, it was found that femtocell downlink interference can block macrocell signal if the MUE is located close to the macrocell edge, and the femtocell transmit power is above 10 dBm. In terms of HSDPA performance, it is not clear that femtocell interference will significantly deteriorate HSDPA performance at the MUE.

14.5 Mitigation techniques

Assuming dedicated spectrum deployment for the macro and femto cellular layers, the adjacent channel deadzone created by the femtocell can be adjusted by performing adaptive control of maximum femtocell transmit power. For example, femtocell should reduce the maximum transmit power level when it detects a weak macrocell signal, and vice versa.


15. Scenario J: Femtocell UE Uplink Interference to the adjacent channel Macrocell NodeB Receiver

15.1 Introduction

This document provides an analysis of Femtocell Uplink Interference from femtocell mobiles (FUEs) to a Macrocell NodeB Receiver on the adjacent channel.

The scenario being investigated is as follows: An FUE is located next to the apartment window that is in the sight of an adjacent channel rooftop macrocell (approx 1,000m distance), as shown in Figure 16-1. At the same time the FUE is connected to the femtocell at the edge of its range, and is transmitting at full power.

Figure 15-1 Interference Scenario J.

In this analysis the impact to the macro Node B is measured by the sensitivity degradation also referred to as noise rise (or relative increase in uplink Received Total Wide Band Power (RTWP)), experienced by the macro Node B due to the femto UE. In Section 15.2 analysis of Scenario J described in [Law08] is presented, including the assumptions used. The analysis shows that the femto UE’s impact on the macro Node B is negligible.

15.2 Analysis of Scenario J - 12k2 Voice and HSUPA

An analysis of this scenario is presented based on link budget calculations. The analysis looks at the noise rise at the Macro Node B antenna connector due to the femtocell UE in the described scenario.

15.2.1 Assumptions

A macro Node B with a noise floor based on the assumption that the sensitivity of the Wide macro Node B for 12k2 voice service at the time is equal to -121 dBm (ie. the


3GPP reference sensitivity level for a 12k2 voice service on a Wide Area Node B at the antenna connector [TS25.104]). This sensitivity captures both the loading and noise figure of the micro Node B. The noise floor calculation is shown in Table 15-1.

Value Units Comment Sensitivity @ antenna connector -121 dBm Pue_rec

3GPP reference sensitivity level for Wide Area Node B

UE Service Rate 12.20 kbps R Chip rate 3.84 MHz W UE Processing Gain 24.98 dB PG = 10*log(W/R)

Required EbNo 8.30 dB EbNo DCH performance without rx diversity (see [FF09])

Noise floor -104.32 dB nf_ant = Pue_rec +PG -EbNo

Table 15-1 Macro Node B noise floor

Next, the factors that could lead the femto UE to transmit at a power higher than expected are considered. This will occur if the femto UE is at the femto’s cell edge, and the femtocell experiences a noise rise or its receiver is experiencing a blocking effect, caused by one of the following:

• An adjacent channel macro UE. • Another femto UE located very close (~1m Free Space Loss) to the femtocell

– eg. a laptop with a 3G data card doing a data upload on the same desk as the femtocell.

Subsequently, for the purposes of this scenario, the following assumptions are made:

• The femto is operating under extreme conditions, experiencing a total noise rise equivalent to 70% loading in the uplink.

• A 21 dBm class femto2 is used in the scenario that can provide a coverage path loss of up to 120dBs (path loss estimate based on minimum RSCP sensitivity of UE of -111 dBm and a 11 dBm CPICH transmit power and assumption of negligible downlink interference from surrounding Node Bs).

Based on these assumptions, the link budget in Table 15-2 estimates the likely femto UE uplink transmission power at the femtocell edge of coverage for a 12K2 voice service and a 2Mbps HSUPA service.

Value

Comments 12K2 Voice

2Mbps HSUPA

Units

Frequency 850.00 850.00 MHz F Bandwidth 3.84 3.84 MHz B

Thermal Noise Density -174.00 174.00

dBm/Hz tnd

Receiver Noise Figure 8.00 8.00 dB NF

Receiver Noise Density -166.00 -166.00

dBm/Hz rnd = tnd +NF

Receiver Noise Power -100.16 -100.16 dBm rnp =rnd +10*log(B*1e6)

2Under the same RF conditions, a 21 dBm class femtocell will provide larger downlink coverage than a 15dBm class or a 10dBm class femto.


Value

Comments 12K2 Voice

2Mbps HSUPA

Units

Loading 70.00 70.00 % L Noise Rise due to Loading 5.23 5.23 dB IM = -10*log(1-L/100)

Femto Receiver Noise Floor -94.93 -94.93 dBm trnp =rnp +IM

Femto UE Service Rate 12.2 kbps R Chip rate 3.84 MHz W Femto UE Processing Gain 24.98 dB PG = 10*log(W/R)

Required EbNo 8.30 dB EbNo

DCH performance without rx diversity [FF09]

Required EcNo -16.68 0 dB

EbNo– PG for 12K2 Typical EcNo to achieve HSUPA rates of ~ 2Mbps [Hol06]

Minimum Required Signal Level for Femto UE

-111.61 -94.93 dB

Pfmin = trnp +EcNo

Femto UE Path loss to femto 120 120 dB DLcov



Table 15-2 Femto UE TX power 1000 m from macro Node B

15.2.2 Macro Node B Noise Rise

The noise rise caused to the adjacent channel macro by a femto UE transmitting at 8.39dBm for a 12K2 voice service and 21dBm for a 2Mbps HSUPA service was calculated, using the link budget in Table 15-3 as 8.6×10-4 dB and .02 dB, respectively.

Value

Comments 12K2 Voice

2Mbps HSUPA

Units

Node B Antenna Gain 17 17 dBi Gant [FF09]

Feeder/Connector Loss 3 3 dB Lf Noise Floor at antenna connector

-104.32 -104.32 dBm

nf_ant Table 16-1


UE Antenna Gain 0 0 dBi Gmant

Femto UE Tx EIRP 8.39 21 dBm

Pfue_eirp =Pue – Gmant +m

Window/Wall Loss 5 5 dB Lw

Path loss to Macro Node B 130.77 130.77 dB

Ltot

=1000m Okumura-Hata(Node B at30m and mobile at 1.5m) +Lw

Adjacent Channel Selectivity 33 33 dB ACS

Adjacent Channel selectivity (+/-5MHz)

Femto UE Interference @ macro antenna connector

-141.38 -128.77 dB

Pfue_r

= Pfue_eirp – Ltot + Gant –Lf - ACS


Value

Comments 12K2 Voice

2Mbps HSUPA

Units

ec Rise above noise floor -37.06 -24.45 dB R =Pfue_rec- nf_ant

Noise rise 8.6 × 10-4 .02 dB NR =10*log( 1+ 100.1*R))

Table 15-3 Noise rise calculation for Scenario D1 (femto UE is transmitting at 8.39dBm and 21dBm 1000m from a macro Node B for a 12K2 service and 2Mbps HSUPA service)

15.3 Conclusions


• It is unlikely that a femto UE will be transmitting at maximum power due to the relatively smaller coverage of the femto compared to the macro.

• When the femto is operating under extreme loading conditions, the analysis for a 12k2 voice service has shown that a femto UE in the described scenario will be transmitting in the region of 8.39 dBm, and will cause a negligible noise rise of approximately 8.6 × 10-4dB.

• When the femto is operating under extreme loading conditions, the analysis for a femto UE with 2Mbps HSUPA data service has shown that a femto UE in the described scenario will cause a negligible noise rise amounting to approximately .02 dB.

• The general conclusion is that a femto UE operating on the adjacent channel to a macro Node B will not cause an impact to such an adjacent channel macro Node B.


16. Downlink and Uplink Scenarios Modelling Power Control Techniques for Interference Mitigation

In [FF08], system level simulations were presented for the downlink and uplink under deployment of femtocells for 2 GHz carrier frequency. In this section, HNB deployment in 850 MHz is discussed vis a vis a deployment in the 2 GHz band carried out in Section 17 of [FF08] and system level simulations are provided. It is shown that simple modification to the parameters setting for power calibration can be used in 850MHz to achieve nearly the same performance (Coverage and Throughput statistics) as 2GHz deployment. It is also shown with simulations that the uplink interference mitigation technique of adaptive attenuation continues to work well in 850MHz as well. All results presented in this section are under the same set-up and simulation conditions as Section 17 of [FF08], except the propagation model. We restrict our attention to the femtocell deployment in the dense urban settings.

16.1 Modelling of Propagation loss

The propagation loss models specified in [FF09] (from [ITU1238]) identify the frequency dependent term for propagation in indoor environment and for small distances as 20*log10(f) , where ‘f’ is the carrier frequency and the path loss is expressed in dB. This term suggests that the typical path loss between two points will be 20*(log10(2000/850)) ~= 7.4 dB higher in 2GHz than in 850 MHz. This is the major component of difference in the propagation loss seen in the two bands.

We apply this frequency dependent path loss offset of -7.4 dB to the path losses from 2 GHz system simulations using the simulation framework described in Section 17 of [FF08]. Specifically, all the path loss values from 2 GHz modelling (outdoor to outdoor, outdoor to indoor, indoor to indoor in same or different apartment) are reduced by the path loss offset to model 850 MHz propagation. Other components, such as outdoor to indoor wall penetration loss, are observed to be not as sensitive to this frequency difference3, and are left unchanged.

16.2 HNB transmit power calibration for 850 MHz

As identified in [FF08], the coverage of a femtocell for a given transmit power differs based on its location within a macrocell, and hence it is crucial to calibrate the transmit power of the femtocell. A reference power calibration algorithm that attempts to strike a balance between increasing the femtocell coverage and reducing the interference to the macro network was specified in [FF08, Section 17.1.2.4, and TR25.820].

This power calibration algorithm uses the downlink receiver at the femtocell to obtain the RF conditions (total signal strength and pilot signal strength from other Node Bs). It selects maximum femtocell transmit power to satisfy certain criterion at a desired coverage edge of the HNB. This edge of HNB coverage is described by a target path loss. For example, the results in Section 17 of [FF08] for 2 GHz are obtained by assuming a target path loss of 80 dB. This target path loss corresponds to a geographical boundary of coverage.

3 Various studies over the years have produced inconclusive and sometimes contradictory trends in the behaviour of outdoor to indoor penetration loss with change in frequency (e.g. see [Kob92, Stav03, Dav97]).


The same geographical boundary of coverage is reached for 850 MHz at a path loss nearly 7.4 dB lower – ie. at nearly 72.6 dB. Hence, the version of HNB power calibration algorithm for 850 MHz can be specified as follows.

1. To maintain an Ecp/Io of -18dB for a MUE located 72.6 dB away from HNB (ie. to protect the macro user).

2. To ensure that HNB is not causing unnecessary interference to others by enforcing an SIR cap of -5dB for HUE at 72.6 dB away from HNB.

3. To maintain an Ecp/Io of -18dB for a MUE on the adjacent channel, located 39.6 dB away from the HNB (ie. to protect the adjacent channel macro use).

This simple change in the parameter for HNB power calibration ensures that the algorithm works well in 850 MHz as well.

16.3 Simulation results for Dense Urban Deployment

In this section we show illustrative results and compare with 2 GHz deployment to show that outage and throughput performance in 850 MHz band does not significantly differ from that in 2 GHz band, provided the power calibration of femtocells takes into account the impact of the frequency band. We show the results for dense urban model depicted in Section 17 of [FF08]. Similar to Section 17 of [FF08], we assume 2000 apartments per cell with 4.8% HNB penetration giving 96 HNBs per cell. Out of these, 24 HNBs are simultaneously active (have HUEs in connected mode). If an HNB is active it transmits at full calibrated power, else it transmits only the pilot and overhead channels.

16.3.1 Idle Cell Reselection Parameters

Similar to Section 17 of [FF08], we assume co-channel deployment where HUEs and MUEs share the same carrier. Closed subscriber group is assumed throughout. We say a UE is unable to acquire the pilot if the CPICH Ec/No is below Tacq. We use Tacq=-20dB for our analysis. For this analysis, the MNBs are assumed to transmit at 50% of the full power (ie. 40dBm). The CPICH Ec/Ior for MNBs and HNBs are set to -10dB (ie. 33dBm). In addition, we take into account idle cell reselection procedure to determine whether a HUE is camped on its HNB or on a MNB, or whether it is moved to another carrier. A HUE will be moved to another carrier if it is not able to acquire the pilots of the HNB and macro on the shared carrier, or if the HUE attempts to perform an idle cell reselection to a neighbour HNB. Similarly, a MUE will be moved to another carrier if it is not able to acquire the macro pilot or if it attempts to perform an idle cell reselection to a HNB. Table 16-1 summarises representative co-channel idle cell reselection parameters used in our analysis. These parameters are set such that priority is given to HNBs over MNBs when a UE is performing idle cell reselection. However, a minimum CPICH Ec/No of -12dB is enforced for HNBs, so that idle cell reselection to an HNB happens only when the HNB signal quality is good.


Table 16-1 Parameters for the co-channel idle cell reselection procedure.

Table 16-2 Coverage Statistics at 850 MHz for Calibrated HNB Transmit Power

In this section we analyse the coverage statistics of UEs with calibrated HNB transmit power algorithm described in previous sections. Table 16-3 and Table 16-4 show the pilot acquisition and outage statistics for dense-urban model, with calibrated HNB transmit power. We compare three cases:

1. Calibrated HNB transmit power with Pmin=-20dBm and Pmax=20dBm 2. Calibrated HNB transmit power with Pmin=-10dBm and Pmax=20dBm 3. Calibrated HNB transmit power with Pmin=0dBm and Pmax=20dBm.

The results show the expected trade off between good HNB coverage and interference to Macro UEs as a function of the HNB transmit power.

Results corresponding to Pmin=-10 dBm and Pmin=0 dBm were presented in [FF08] for 2 GHz. Additionally, this section presents results for Pmin=-20 dBm. It can be readily seen that the statistics corresponding to Pmin=-10dBm and Pmin=0 dBm in Table 16-3 and Table 16-4 closely matche those in Table 17.7 of [FF08]. Each point on the cell sees a lower path loss in 850 MHz from both macro and femtocells and, consequently, switching to 850 MHz makes the system slightly more interference limited compared to 2 GHz. As the reduced path loss is taken into account to set the target cell edge coverage for femtocells, the calibrated power for the femtocell remains nearly unchanged in 850 MHz compared to 2 GHz. This is evident in the comparison of CDFs of calibrated power in 2 GHz and 850 MHz, as shown in Figure 16-1 where the CDF corresponding to both bands coincide4.

This also suggests that HNB with a given power will have similar coverage radius in both bands, irrespective of the location.

It is also seen that in dense urban environment a significant number of HNBs reach their minimum power limit.

Pmin=-20dBm, Pmax=20dBm


Pmin=0dBm, Pmax=20dBm

HUEs unable to acquire HNB pilot 3.9% 1.9% 0.5%

HUEs unable to acquire HNB or macro 0.6% 0.2% 0.2%

4 In these simulations the possible calibrated transmit powers for HNBs are assumed to take a continuous range of values. In practice, these values will be quantised with a given granularity.

HNB cells: 3dBMacro cells: 5dB

HNB cells: -50 dBMacro cells: 3dB

Qhyst+QoffsetSIB11

Qqualmin

Sintersearch

Sintrasearch

Qqualmin -18dB-18 dB

SIB3

HNB cells: -12 dBMacro cells: not needed

NA

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Macro

Not needed

NA

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HNBSIB/Parameter

HNB cells: 3dBMacro cells: 5dB

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Qhyst+QoffsetSIB11

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Sintersearch

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NA

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Not needed

NA

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pilot MUEs unable to acquire macro pilot 2.7% 5.2% 12.0%

Table 16-3 Pilot acquisition statistics at 850 MHz for dense-urban model with 24 active HNBs and calibrated HNB transmit power



Pmin=0dBm, Pmax=20dBm

MUEs moved to another carrier 9.7% 13.5% 25.5%

HUEs unable to camp on own HNB 9.6% 4.9% 2.4%

HUEs switched to macro on shared carrier

7.7% 3.6% 1.1%

HUEs moved to another carrier 1.9% 1.3% 1.3%

Table 16-4 Coverage statistics for dense-urban model with 24 active HNBs and calibrated HNB transmit power

Figure 16-1 In variance of HNB calibrated Tx Power in the two frequencies.

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HNB Tx Power: 850 MHz ,PL Edge 72.6 dB, PMin -10 dBm


16.3.2 Downlink Throughput Simulations

In this section we study the performance of HSPA+ DL on 850 MHz under HNB deployment by system level simulations. The assumptions for the simulation are the same as those in Section 17 of [FF08]. In the dense-urban model, blocks of apartments are dropped into the three centre cells of a macrocell layout with ISD of 1 km. We drop 2,000 apartment units in each macrocell that corresponds to 6,928 households per square kilometre. This represents a dense-urban area. Taking into account various factors such as wireless penetration (80%), operator penetration (30%) and HNB penetration (20%), we assume a 4.8% HNB penetration, which means 96 of the 2,000 apartments in each cell have a HNB installed from the same operator. Out of these, 24 HNBs are simultaneously active (have a HUE in connected mode). We assume co-channel performance for all HUEs and MUEs. All UEs have one receive antenna. We assume that the power transmitted for the overhead channels, including CPICH pilot is 25% and the transmit power for the pilot, is 10%. The transmit power of HNBs is calibrated using the algorithm specified in Section 16.2. We assume a Rician channel with Rician factor K=10 and 1.5 Hz Doppler frequency. Macrocells are loaded with HNBs, HUEs and MUEs. There are 10 MUEs per cell, and 96 HNBs, of which 24 are active. Each active HNB has one HUE. We assume a full-buffer traffic model and all active cells are transmitting at full power. HNBs that are not active are only transmitting the overhead. The maximum number of HARQ transmissions is 4. The maximum modulation is 64 QAM. A proportional fair scheduler is implemented for the macro users. Only UEs that are not in outage on the shared channel are included in the simulations. However, those users in outage are included in the following CDFs as zero throughput users. If the operator has another frequency for macro operation, many of the MUEs, now considered in outage, will be switched to the other frequency and will not be in outage. Figure 16-2 shows the throughput CDF of all user throughputs.

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User Throughput Distributions, 10 MUEs, 24 HUEs

All UEs: No HNB presentAll UEs: HNB Present, Pmin = -10 dBmAll UEs: HNB Present, Pmin = -20 dBm


Figure 16-2 DL user throughput distribution under different minimum powers

Figure 16-3 Magnified version of Figure 1-2 showing outage statistics

It is seen that deployment of HNBs helps all users. The users served by HNBs see very good RF conditions and dedicated Node B and, hence, see very high throughputs. The users on macrocells see a reduced load on the network and, hence, experience better throughputs. Even when the lower limit on the transmit power to HNBs is reduced to -20 dBm, the HUEs continue to experience high user throughputs. Figure 16-3 shows a magnified version of the lower range of throughputs to identify the impact of Pmin on outage.

16.3.3 Conclusions

To summarise, HNB deployment continues to provide the benefits identified in Section 17 of [FF08] in 850 MHz. The small change in parameters of power calibration enables the same algorithm to be used in 850 MHz, and results in nearly the same transmit power distribution on HNBs as that in 2 GHz.

16.3.4 Uplink throughput simulations with adaptive attenuation

In this section we study the HNB and macro uplink throughput performance in a co-channel deployment of HNBs for 850 MHz. In [FF08] the benefits of uplink adaptive attenuation at an HNB were identified. This section carries out the uplink throughput analysis and comparison of HNB deployment with and without adaptive attenuation in 850 MHz in a dense urban scenario. The layout and deployment scenario is the same as those in [FF08] and Section 16.2.

We assume a Rician channel with K factor of 10 dB and 1.5 Hz Doppler fading. The MUEs and HUEs are assumed to transmit full-buffer traffic using 2ms TTI HSUPA. The maximum number of transmissions is set to 4. Power control is enabled for both MUEs and HUEs. The maximum transmit power for the UEs is set to 24dBm and the minimum transmit power is set to -50dBm.

Single-frequency co-channel deployment is considered. For the uplink simulations, we only keep those UEs that are not in outage on the downlink.

An NF of 5dB and Noise Rise Threshold (NRT) of 5dB are assumed for MNBs. For HNBs, three cases are considered:

0 1 2 3 4 5 6

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FUser Throughput Distributions, 10 MUEs, 24 HUEs

All UEs: No HNB presentAll UEs: HNB Present, Pmin = -10 dBmAll UEs: HNB Present, Pmin = -20 dBm


1. Baseline 1: HNB NF=5dB and HNB NRT=5dB 2. Baseline 2: HNB NF=20dB and HNB NRT=10dB 3. Enhanced: Adaptive attenuation at HNB (max attenuation=40dB) and HNB

NRT=6dB.

In Baseline 1, the NF setting at HNB is similar to MNB. In Baseline 2, a fixed NF of 20dB is assumed at the HNB. This is similar to the 19dB NF used in local area basestation class specified in [TS25.104]. The Enhanced case uses adaptive attenuation (or noise figure), which means additional attenuation is added only when needed, depending on out-of-cell and in-cell signal strength.

We run uplink simulations for the scenario described in the previous section. Figure 16-4 and Figure 16-5 show the HUE and MUE uplink throughput CDFs for Baseline 1, Baseline 2 and Enhanced cases. The HUE and MUE transmit power distributions are shown in Figure 16-6 and Figure 16-7.

It is seen from Figure 16-4 that the HUE Baseline 1 uplink throughput performance is poor, due to intra-HNB, inter-HNB and Macro-to-HNB interference. Adding 15dB fixed attenuation at HNBs (ie. Baseline 2) improves the HUE performance significantly, but there are still some HUEs that have poor uplink throughput. This is because 15dB fixed attenuation does not solve inter-HNB interference problem. In addition, in some cases, more than 15dB attenuation is needed to overcome Macro-to-HNB interference. With fixed uplink attenuation (ie. Baseline 2), the HUE transmit powers are higher compared to adaptive attenuation. As seen in Figure 16-4, adaptive UL attenuation completely eliminates HUE throughput outage and achieves good throughput performance. It is also seen from Figure 16-5 that the MUE uplink performance is not impacted by adding attenuation at HNBs. In addition, Figure 16-6 and Figure 16-7 show that the transmit power in 850MHz is roughly 7 to 10dB lower than that in 2GHz. The reduced power will both reduce interference and improve battery life.

Figure 16-4 HUE uplink throughput distribution

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10 MUEs + 24 HUEs per macro cell

Baseline 1Baseline 2Enhanced


Figure 16-5 MUE uplink throughput distribution

Figure 16-6 Transmit power distribution

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Figure 16-7 Transmit power distribution.

Figure 16-8 shows the throughput CDFs for two cases. The first case is when HNBs are deployed; there are 24 active HNBs, each with one HUE per macrocell, and there are 10 MUEs per macrocell. The second case is when there are no HNBs deployed and the 24 UEs served earlier by HNBs are served by the MNB instead; thus, there are a total of 34 (10+24) MUEs. When there are HNBs, adaptive attenuation is used at the HNBs. The UEs that are in outage are included in these CDFs and are assigned zero throughputs. The results are similar to those found in the 2GHz study. As seen in the figure below, deploying HNBs continues to result in a significant improvement in the overall system throughput. Firstly, the UEs that use HNBs achieve much higher uplink throughputs compared to before. Secondly, the uplink throughputs of the MUEs also improve, since some of the users are offloaded to HNBs.

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Figure 16-8 UE uplink throughput distributions in 850 MHz. There are, in total, 34 UEs per macrocell, of which 24 UEs migrate to MNB in the ‘No HNBs’ case. HNB deployment increases the system capacity significantly

16.3.5 Conclusions

Simple adjustment of Power Calibration settings, namely changing the HNB target coverage path loss, is sufficient to make HNB deployments nearly equivalent in different frequency bands. Similar DL throughput performance is seen in Dense Urban deployment of HNBs in 850 MHz and 2 GHz. UL throughputs are higher in Dense Urban deployments of HNBs in 850 MHz, compared to 2GHz. The UE transmit powers are seen to be smaller for 850 MHz compared to 2 GHz.

In summary, HNB deployment continues to provide expected benefits in 850 MHz band as well.

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34 MUEs + 0 HUEs per macro cell10 MUEs + 24 HUEs per macro cell with adaptive uplink attenuation


17. Summary of Findings

Scenario Conclusions Impacts

A - Macrocell Downlink Interference to the Femtocell UE Receiver

When a strong macro signal is present, customers already obtain excellent service; adding a co-channel femtocell offers little additional coverage gain. Assuming standard models and parameters, it is shown that even at 10 dBm transmit power, the femtocell is able to comfortably provide voice to the UE when the femtocell is located as far as 100 m away and maximum HSDPA throughput can be expected up to 25 m away.

Low, but a way of identifying customers who are unlikely to benefit from femto because of already high macro coverage would be desirable. If the macro is dominant, the consequence for the customer is that they will be provided service by the macro carrier – so the impact of this scenario is mainly on zonal-based propositions.



B - Macrocell UE Uplink Interference to the Femtocell Receiver

The analysis results showed that in order to be able to maintain the uplink connection between the FUE and femtocell, the transmitted power requirements are within the capability of the UE. Additionally, the performance of HSUPA on the femto – FUE link has been analysed in the presence of uplink interference from the Macro UE. By simulation, it has been found that in order to obtain HSUPA throughput of at least 2.8Mbps with a category 6 UE, the FUE needs to be near to the femtocell (5m) and transmit at a power level greater than 15dBm, if the MUE is within 15m of the femtocell. However, such analysis must take into account the downlink deadzone created by the femtocell. High power from the femtocell in order to maintain the downlink will interfere with the macrocell signal at the MUE, and will force the macrocell to handover the call to another WCDMA frequency or RAT; or, if none of these are possible, the MUE call may be dropped.

From the point of view of the MUE, the femtocell is a source of interference to the macrocell. However, the macro network can already cope with re-directing UEs to other WCDMA frequencies, or RAT, if a user is affected by high interference. Those locations with no coverage from alternative WCDMA frequencies, or RATs, may be adversely affected by poor Eb/No levels, leading to dropped calls. Due to femtocells, the macrocell may also be affected by an increase of uplink interference, as femto-UEs increase power levels in order to achieve required quality levels. This may be limited by capping the maximum power level transmitted by FUEs, or by limiting uplink throughput. The minimum separation between MUE and femtocell has a strong effect on the capability to offer the required QoS to the femtocell user. However, the FUE has enough power to sustain a voice call while the MUE is in the coverage range of the femtocell. The downlink deadzone sets a minimum separation between MUE and femtocell, meaning that the FUE transmit power is always within its capability. For HSUPA, the user is required to go closer to the femtocell in order to be provided with the best throughput. Simulation has shown that at 5m from the femtocell, good throughput can be achieved for MUEs further away than 12m. Availability of alternative resources (a second carrier, or underlay RAT) for handing off or reselecting macro-users is the best way to provide good service when macro-users are in the proximity of femtocells.



C - Femtocell Downlink Interference to the Macrocell UE Receiver

In the scenario presented in this section, the performance of MUE attached to the macrocell is shown to be affected by the femtocell in some locations. This can be mitigated by the use of adaptive power control on the femto. Results show that in some cases the MUE might experience “deadzone” when in close proximity to the femto. One firm conclusion from this analysis is that adaptive power control is necessary for the femtocells; another is that femtocells will require higher output power when the femtocell is deployed in locations near the centre of the macrocell. Adaptive power control on the femtocell mitigates interference by offering just the required transmit power on the femto based on level of interference from macro. However, it is shown that a macrocell UE (MUE) might not receive adequate signal level from the macro to compensate for the femto interference. This is evident in all places in close proximity to the femto when the macro and femtocells share the same carrier. It is also concluded that there is no apparent and fundamental performance change between the case when 850 MHz or 2100 MHz is used for the carrier. In general, if a macro network is designed to provide fixed coverage in terms of cells radius, then the macrocell requires lower output power when operating at 850 MHz. Therefore, the interference level seen by a femto is the same, regardless of the carrier frequency. It is shown that the femto is an effective vehicle for delivering a good carrier re-use. Furthermore, femtocells are an efficient technique for delivering high-speed data offered by HSPA to the femto users. This should be compared to the macrocell case where cell radius is larger resulting in the effect of distributing the potential bandwidth of the HSDPA to a larger number of users. It is also a well known that HSPA throughput is affected by the location of the UE, the closer the UE to the centre of the cell the higher the throughput. This lead us to conclude that small cells like femto cells are an optimum complimentary technique to macro cells for addressing high data usage.

For operators without a dedicated carrier on which to deploy femto, adaptive power control is essential for the success of the network Even though the intrinsic coverage of the macro network is reduced by the deployment of femto, other studies have shown (eg. Section 17) that the total capacity of the network (macro + femto) may increase a hundredfold.



D - Femtocell Uplink Interference to the Macrocell NodeB Receiver

It is unlikely that a femto UE will be transmitting at maximum power, due to the relatively smaller coverage of the femto compared to the macro. The analysis for a 12k2 voice service has shown that a femto UE in the described scenario will be transmitting in the region of 8.39 dBm, and will cause a noise rise of approximately 0.07dB. Further, a macro UE at the same location as the femto UE will cause a 0.09dB noise for the same 12k2 voice service. The analysis for a femto UE with 2Mbps HSUPA data service has shown that a femto UE in the described scenario will cause a noise rise amounting to approximately 1.09dB; however, it should be noted that a macro UE operating at the same position and on the same service (with the same service requirement) is expected to cause the same amount of noise rise.

The maximum allowed femto UE transmission power can be limited appropriately, such that the noise rise caused by a femto UE when transmitting at its maximum allowed power is limited based on the femtocells proximity to the surrounding Macro Layer Node Bs. This is important, especially when one considers the cumulative affect of multiple femto UEs spread across a network. A similar approach is suggested in [R4-071578]. The femtocell could also handover a femto UE to a macrocell if an in-service femto UE is at the verge of the femtocell; thereafter, uplink interference to a macrocell from this UE is avoided.



E - Femtocell Downlink Interference to Nearby Femtocell UE Receivers

The downlink throughput of the UE connected to the femtocell is shown to be affected by downlink of neighbouring femtocells. This case shows that driving femtocells to provide coverage to adjacent location deemed to be covered by other femtocells yields performance degradation. The closer the femtocells are, the higher the mutual interference and performance degradation. It is therefore strongly recommended that femtocells use effective power control to confined coverage to their premises, and where the UE can not get service from the its femto, this UE should be supported by the macro network. There is a need to make sure that the pilot and transmit power of the femto is carefully adjusted to provide coverage to UEs within the intended area. It can be concluded that the femto coverage should aim to be restricted to a single apartment/ house only in order to limit any undue interference between femtos. Adaptive power control is one method to help this. This leaves the issue of supporting visiting UEs to be under the control of the macrocell.

If the femto coverage is controlled through mechanisms such as adaptive power control, then this scenario will generally result in the visiting UE being handled by a Macro Layer. These impacts exist when a UE femtocell experiences interference levels in the order of -50dBm. Consequently, there is a risk that for adjacent apartment deployments coverage may not be assured from the femtocell under all circumstances.



F - Femtocell UE Uplink Interference to Nearby Femtocell Receivers

The following conclusions can be drawn: The closer UE2 to AP1, the greater interference from UE2 to AP1. The interference reaches maximum at the point when UE2 is disconnecting from AP2 (call is dropping). However, the analysis is based on the extreme scenarios. Usually, UE2 will handover to a macrocell before call drop, which will avoid the interference to AP1. The following recommendations are made, which will help ensure harmonious coexistence of co-channel femtocells: It is desirable to limit the allowed maximum transmission power of UE2 to avoid a noise rise to the nearby AP1, when UE2 is at the verge of AP2. The AP2 could also handover a UE2 to a macrocell (macrocell on another frequency channel preferred) if in-service UE2 is in the vicinity of the AP1; thereafter, uplink interference to AP1 from this UE2 is avoided.

In typical cases, both wanted and Aggressor femtocells should have dynamically optimised coverage to their respective UE; hence, this co-channel scenario is unlikely to occur. If this femtocell power optimisation does not occur, the co-channel interference can indeed occur, and range reduction is the consequence. This range reduction can be mitigated to an extent by the normal dynamic power control of the wanted UE. Consequently, this is manageable as long as minimum performance requirements for adaptive power control are agreed.

G - Macrocell Downlink Interference to the adjacent channel Femtocell UE Receiver

Both theoretical analysis and simulation results show that femtocell UE experiences little adjacent channel interference from an outdoor macrocell in most cases.

There is no impact.



H - Macrocell UE Uplink Interference to the adjacent channel Femtocell Receiver

It was found that if the MUE is transmitting at the maximum power of 21 dBm, it needs to be separated from the femtocell by around 3.2 m. This separation can be reduced further by employing Automatic Gain Control (AGC) at the femtocell receiver. It has been shown that the minimum MUE to FAP separation can be reduced to 1.5 m if a reduction in gain of 10 dB is applied by AGC. The resulting loss in receiver sensitivity will not deteriorate femtocell coverage of voice, as there is sufficient power headroom available at the UE. The performance of HSUPA has been analysed in the presence of uplink interference from the macro UE, which is operating on the adjacent frequency. The femtocell – MUE separation is fixed at 2 m and 5 m. The FUE – femtocell path loss is fixed at 90 dB, representing the coverage edge scenario. It was seen that in order to obtain 70% of nominal HSUPA bit rate with a category 6 UE, the MUE transmit power should be below 7.5 dBm and 18.5 dBm, respectively. In both cases minimum transmit power required for HSUPA transmission is equal to -3 dBm. As the likelihood of MUE transmitting at high power increases at the macrocell edge, HSUPA throughput at femtocell is expected to deteriorate in this interference scenario.

If the minimum separation between the MUE and femtocell is not maintained, the femtocell receiver may not be able to decode the wanted speech signal at the required QoS level. Similarly, the HSUPA performance will deteriorate gradually as the MUE transmit power is increased for a given separation between the MUE and femtocell receiver.



I - Femtocell Downlink Interference to the adjacent channel Macrocell UE Receiver

In terms of AMR service, a minimum separation of 5 m between the femtocell and MUE can be achieved if the macrocell site is within 1.0 km, and the femtocell is not transmitting above 10dBm. It is recommended to implement adaptive control of maximum transmit power level at the femtocell and restrict maximum transmit power to 10 dBm, in order to achieve a good trade-off between femtocell coverage and adjacent channel deadzone. We have also analysed HSDPA performance under this interference scenario using link-budget type calculations and UE specifications. At the minimum supported femtocell – MUE separation of 5 m, it was found that the macrocell – MUE separation should not be more than 185 m - 360 m, in order to decode the HS-PDSCH at the specified rate. Analysis was performed for a fully loaded femtocell transmitting at 10 dBm, 15 dBm and 20 dBm. It is well known that a macrocell allocates highest HSDPA data rates only when UEs are located close to the cell site. Thus, it is not apparent whether downlink interference from femtocell will significantly deteriorate HSDPA performance at the MUE.

In terms of AMR service, it was found that femtocell downlink interference can block macrocell signal if the MUE is located close to the macrocell edge and the femtocell transmit power is above 10 dBm. In terms of HSDPA performance, it is not clear that femtocell interference will significantly deteriorate HSDPA performance at the MUE. Assuming dedicated spectrum deployment for the macro and femto cellular layers, the adjacent channel deadzone created by the femtocell can be adjusted by performing adaptive control of maximum femtocell transmit power.

J - Femtocell UE Uplink Interference to the adjacent channel Macrocell NodeB Receiver

It is unlikely that a femto UE will be transmitting at maximum power, due to the relatively smaller coverage of the femto compared to the macro. The analysis for a 12k2 voice service has shown that a femto UE in the described scenario will be transmitting in the region of 8.39 dBm and will cause a negligible noise rise of approximately 3.4 × 10-5dB. The analysis for a femto UE with 2Mbps HSUPA data service has shown that a femto UE in the described scenario will cause a negligible noise rise amounting to approximately 6.2 × 10-4dB. The general conclusion is that a Femto UE operating on the adjacent channel to a macro Node B will not cause an impact to such an adjacent channel macro Node B.

The uplink noise rise experienced by the macro nodeB from the adjacent channel femto UE is likely to be significantly less than the noise rise experienced by the macro Nodes Bs own UE transmitting from the same location. Consequently, there is negligible impact to the adjacent channel macro.



Section 16 System Simulations

A simple adjustment of Power Calibration settings – namely, changing the HNB target coverage path loss – is sufficient to make HNB deployments nearly equivalent in different frequency bands. Similar DL throughput performance is seen in Dense Urban deployment of HNBs in 850 MHz and 2 GHz. UL throughputs are higher in Dense Urban deployments of HNBs in 850 MHz compared to 2GHz. The UE transmit powers are seen to be smaller for 850 MHz compared to 2 GHz. In summary, HNB deployment continues to provide expected benefits in 850 MHz band.

The conclusions depend on the operation of important techniques, such as adaptive CPICH power setting, adaptive attenuation (AGC) in the femto receiver, and UE transmit power capping. With these techniques in play, the impact on the performance of the networks is total available data capacity gain of two orders of magnitude for the simulated conditions.


18. Overall Conclusions

By examining a series of scenarios, building on the work of 3GPP RAN4 as well as the previous Small Cell Forum work at 2 GHz, we have reached and confirmed the following conclusions:

• Femtocell performance at 850 MHz is very much similar to that at 2 GHz. • Power management of the UE is important to manage the noise rise in the

macro network.

• In normal operation, the noise rise contribution from the UE is small (a decibel or less).

• Power capping of the UE when operating in the femto environment ensures that, even in difficult radio conditions, the UE hands-off to the macro network before its transmit power increases to the point where macro noise rise is a problem.

• Dynamic receiver gain management in the femto (AGC or adaptive attenuation) ensures that femtos can offer good service to both near and far UEs, without unnecessarily increasing the UE transmit power, and, therefore, keeping the noise rise contribution to a minimum.

• An increase in the dynamic range specifications is required to accommodate femto operation in both near and far cases.

• Downlink power management is equally key in managing the tradeoff between service range (in the closed user group cases), and deadzone.

• By measuring its environment, the femto can set its transmit power appropriately for both dense urban and suburban deployment, even in shared carrier situations.

• Given a reasonable distribution of indoor and outdoor users, the link budget indoors with femto is so good in comparison with the corresponding macro link budget that the total air interface capacity can be a hundred times greater with femto than without it.

• With these power management techniques in place, femto operation in the co-channel deployment with macro is possible. A second carrier is preferred, to give macro users service even within the deadzones of the femtocells.

Some of these factors (adaptive attenuation, power capping, and downlink power management) are becoming widely available in the industry. Others (increased receiver dynamic range) are already approved in standards. All of them will deliver the performance and capacity gains required for next-generation cellular networks.


19. Further Reading

19.1 Scenario A

Title: Macrocell Downlink Co-Channel Interference to the Femtocell UE Receiver

3GPP Analysis References: [R4-071941] R4-071941, "Simulation results for Home NodeB to Home NodeB downlink co-existence considering the impact of HNB HS utilization", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #45, November 2007.

[R4-072004] [R4-080409] [R4-080149] R4-080149, Ericsson, "Simulation assumptions for the block of flats scenario”, 3GPP TSG-RAN Working Group 4 (Radio) meeting #46, February 2008.

[R4-080150]

19.2 Scenario B

Title: Macrocell Uplink Co-Channel Interference to the Femtocell Receiver

3GPP Analysis References: [R4-070825] [R4-070969] R4-070969, “Home B output power”, Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #43bis, R4-070969, June 2007.

[R4-070970 [R4-071619] [R4-071941] R4-071941, "Simulation results for Home NodeB to Home NodeB downlink co-existence considering the impact of HNB HS utilization", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #45, November 2007.

[R4-072004] [R4-080097] [R4-080409] [R4-080153]

19.3 Scenario C

Title: Femtocell Downlink Co-Channel Interference to the Macrocell UE Receiver

3GPP Analysis References: [R4-071231] [R4-071253] [R4-071263] [R4-071540] [R4-071554] [R4-071578] [R4-071660] [R4-071661] R4-071661, "Impact of HNB with controlled output power on macro HSDPA capacity", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #44bis, October 2007.

[R4-072004] R4-072004, Huawei, "Performance Evaluation about HNB coexistence with Macro networks", 3GPP TSG-RAN Working Group 4 (Radio) meeting #45, November 2007.

[R4-071941] R4-071941, "Simulation results for Home NodeB to Home NodeB downlink co-existence considering the impact of HNB HS utilization", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #45, November 2007.

[R4-072004] [R4-080409] [R4-080151]

19.4 Scenario D

Title: Femtocell Uplink Co-Channel Interference to the Macrocell NodeB Receiver

3GPP Analysis References: [R4-070969] R4-070969, “Home B output power”, Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #43bis, R4-070969, June 2007.


[R4-070970 [R4-071231] [R4-071578] [R4-071619] [R4-071941] R4-071941, "Simulation results for Home NodeB to Home NodeB downlink co-existence considering the impact of HNB HS utilization", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #45, November 2007.

[R4-072004] [R4-080409] [R4-080154]

19.5 Scenario E

Title: Femtocell Downlink Interference to Nearby Femtocell UE Receivers

3GPP Analysis References: [R4-071617] R4-071617, “HNB and HNB-Macro Propagation Models”, Qualcomm Europe, 3GPP TSG-RAN Working Group 4 (Radio) meeting #44bis, October 2007.

[R4-071618] [R4-080409] [R4-080151] [R4-080149] R4-080149, Ericsson, "Simulation assumptions for the block of flats scenario”, 3GPP TSG-RAN Working Group 4 (Radio) meeting #46, February 2008.

[R4-080150] R4-081344

19.6 Scenario F

Title: Femtocell Uplink Interference to Nearby Femtocell Receivers

3GPP Analysis References: [R4-070971] [R4-071185] [R4-071617] R4-071617, “HNB and HNB-Macro Propagation Models”, Qualcomm Europe, 3GPP TSG-RAN Working Group 4 (Radio) meeting #44bis, October 2007.

[R4-071618] [R4-080409] [R4-080152] [R4-080153]

19.7 Scenario G

Title: Macrocell Downlink Adjacent Channel Interference to the Femtocell UE Receiver

3GPP Analysis References: [R4-071941] R4-071941, "Simulation results for Home NodeB to Home NodeB downlink co-existence considering the impact of HNB HS utilization", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #45, November 2007.

[R4-072004] [R4-080409] [R4-080149] R4-080149, Ericsson, "Simulation assumptions for the block of flats scenario”, 3GPP TSG-RAN Working Group 4 (Radio) meeting #46, February 2008.

[R4-080150]

19.8 Scenario H

Title: Macrocell Uplink Adjacent Channel Interference to the Femtocell Receiver

3GPP Analysis References: [R4-070825] [R4-070971] [R4-071185] [R4-071941] R4-071941, "Simulation results for Home NodeB to Home NodeB downlink co-existence considering the impact of HNB HS utilization", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #45, November 2007.

[R4-072004] [R4-080097] [R4-080409]

19.9 Scenario I

Title: Femtocell Downlink Adjacent Channel Interference to the Macrocell UE Receiver


3GPP Analysis References: [R4-071211] [R4-071231] [R4-071263] [R4-071540] [R4-071554] [R4-071660] [R4-071661] R4-071661, "Impact of HNB with controlled output power on macro HSDPA capacity", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #44bis, October 2007.



[R4-072004] [R4-072025] [R4-080409] [R4-080151]

19.10 Scenario J

Title: Femtocell Uplink Adjacent Channel Interference to the Macrocell NodeB Receiver

3GPP Analysis References: [R4-070971] [R4-071185] [R4-071231] [R4-071619] [R4-071941] R4-071941, "Simulation results for Home NodeB to Home NodeB downlink co-existence considering the impact of HNB HS utilization", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #45, November 2007.

[R4-072004] [R4-080409] [R4-080152]

19.11 Scenarios – Section 16

Title: Downlink and Uplink Scenarios Modelling Power Control Techniques for Interference Mitigation

3GPP Analysis References: [R4-081344] [R4-081345] [R4-081346]


20. Simulation Parameters and Path Loss Models

This section provides a set of recommended values and path loss models for the interference studies at 850 MHz.

20.1 Simulation parameters

Table 20-1 lists the simulation parameter values that were used in this paper unless otherwise stated in the text.

Parameter Value External Wall Loss 10dB [COST231] Window Loss 5dB Maximum Macro Node B Tx Power 43dBm Maximum Micro Node B Tx Power 38dBm Macro Node B Antenna Gain 17dBi Macro Node B Feeder/Cable Losses 3dB Micro Node B Antenna Gain 2dBi Micro Antenna Feeder Loss 1dB Node B sensitivity Based on reference sensitivity in 3GPP Spec [TS25.104] Femtocell Noise Figure 8dB (and 12dB) Macro Node B Loading 50% Femto Loading 50% Downlink/Uplink Channel performance (ie. EbNos & EcNos for various services)

Minimum performance requirements based on 3GPP specs [TS25.101][TS25.104]

UE transmission power range Based on 3GPP spec [TS25.101] Femtocell Maximum DL powers Up to 21dBm. Analysis to cover 10dBm, 15dBm & 21dBm

power levels Maximum co-channel DL deadzone created by femto for non-femto UEs [R4-070969]

60dB for 10dBm Femto DL Tx Power 65dB for 15dBm Femto DL Tx Power 70dB for 21dBm Femto DL Tx Power

Maximum adjacent DL deadzone created by femto for non-femto UEs

Corresponding co channel deadzone less 33dB ACS loss

Height of mobile 1.5 m Height of femto 1m Height of macro basestation 30 m Frequency 850 MHz Building dimensions (width by length)

Apartment – 10m by 10m House – 15 by 15m

Indoor to indoor path loss modelling

ITU P.1238 [ITU1238]

Indoor to outdoor path loss modelling

Okumura-Hata [COST231] + Wall/Window loss (d > 1 km)

Outdoor to outdoor path loss modelling

Okumura-Hata [COST231] (d > 1 km)

Outdoor to indoor path loss modelling

Okumura-Hata [COST231] + Wall/Window loss (d > 1 km)

Table 20-1 Recommended simulation parameters


20.2 Path Loss Models

Several path loss models are used within the study to calculate the signal attenuation as it propagates within different environments. These have been chosen from the range of models in the public domain that are widely accepted within the industry. They are, therefore, not ‘tuned’ to a specific environment or set of measurements. The models should, however, be indicative of the realistic range of path loss values that are likely to be encountered in a realistic deployment. The path loss models are described in this section.

20.2.1 Okumura-Hata

Although the Okumura-Hata (OH) model is a fully empirical model, entirely derived from the best fit of measurement data without real physical basis, the model remains widely used and is well-accepted by the mobile cellular community. It is the most widely implemented model and is available as the main model in most radio planning tools.

The expression of OH for built-up urban areas is as follows:

)()log())log(55.69.44()log(82.13)log(16.2655.69 MBB hFdhhfL −−+−+=

−××

−×−×−×=

cities largefor 97.4))h(log(11.753.2

cities small tomedium)8.0)log(56.1()7.0)log(1.1()( 2

M

fhfhF M

M

The parameters in the above expressions stand for:

[km]n basestatio from distance :[m] ground aboveheight station mobile :

[m] level ground aboveheight station base :[MHz] frequency :

dhhf

M

B

The range of validity of OH is as follows:

kmdmhm

mhmMHzfMHz

M

B

1101

200301000150

>≤≤≤≤

<<

20.2.2 ITU-R P.1238

This model predicts path loss between two indoor terminals assuming an aggregate loss through furniture, internal walls and doors represented by a power loss exponent N that depends on the type of building (residential, office, commercial, etc.). Unlike other site-specific models (such as Keenan and Motley 0), this method does not require the knowledge of the number of walls between the two terminals, and therefore offers a simpler implementation.

The expression for the path loss is provided below:


where:

In the frequency range 900 MHz, P.1238 suggests using the following power loss coefficients N:

• Residential: --- • Office: 33 • Commercial: 20

And the following values for the floor penetration loss factor Lf:

• Residential: --- • Office: 9 (1 floor), 19 (2 floors), 24 (3 floors) • Commercial: ---

P.1238 doesn’t provide power loss coefficient or floor penetration loss for residential buildings at 900 Mhz, but does say that for the power loss coefficient it is acceptable to use the value given for office buildings. After some discussion among the members of the simulation team it was decided to use a value of 28, which is slightly less than that for office buildings but consistent with measured data. It was also decided by the members of the simulation team that a floor penetration loss factor of 4 dB per floor penetrated would be used, since that is consistent with measured data. For fading, a log-normal distribution is assumed with a standard deviation of 8 dB.

20.2.3 System Simulation (Section 16) Path Loss Models

In Section 17 the following simplified path loss models were used:

The free-space component for the micro-urban model is given by

ddBPL microfs 10, log4028)( +=

Where d is the distance in m.

Other models used in this section are similar to those in [R4-071617].


References

[FF08] Small Cell Forum, “Interference Management in UMTS Femtocells”, December 2008.

[FF09] Small Cell Forum Working Group 2, “Recommended Simulation Parameters 850 MHz”, April 2009.

[COST231] Commission of the European Communities, “Digital Mobile Radio: COST 231 View on the Evolution Towards 3rd Generation Systems”, L-2920, Luxembourg, 1989.

[ITU1238] International Telecommunication Union, “ITU-R Recommendations P.1238: Propagation data and prediction models for the planning of indoor radiocommunications systems and radio local area networks in the frequency range 900MHz to 100GHz”, Geneva, 1997.

[ITU1411] International Telecommunication Union, “ITU-R Recommendations P.1411-3: Propagation data and prediction methods for the planning of short range outdoor radiocommunication systems and radio local area networks in the frequency range 300 MHz to 100 GHz”, Geneva, 2005.

[Hol06] H. Holma and A. Toskala, “HSDPA/HSUPA for UMTS: High Speed Radio Access for Mobile Communications”, J. Wiley & Sons, Ltd, 2006.

[Kob92] H. Kobayashi, G. Patrick, Preliminary Building Attenuation Model, NTIA Technical Memorandum 92-155, 1992.

[Stav03] Stavrou, S. Saunders, S.R., Factors influencing outdoor to indoor radio wave propagation, Intl Conference on Antennas and Propagation (ICAP), 2003.

[Dav97] Davidson, A. and Hill C., Measurement of Building Penetration into Medium Buildings at 900 and 1500 MHz, IEEE Transactions on Vehicular Technology, February 1997.

[Kee90] J. M. Keenan, A. J. Motley, “Radio coverage in buildings”, British Telecom Technology Journal, vol. 8, no. 1, Jan. 1990, pp19-24.

[Lai02] J. Laiho, A. Wacker and T. Novosad, “Radio Network Planning and Optimization for UMTS”, J. Wiley & Sons, Ltd, 2002.

[Oku68] Y. Okumura, E. Ohmori, T. Kawano and K. Fukuda, “Field strength and its variability in VHF and UHF land mobile radio service”, Rev. Electr. Commun. Lab., Vol. No 16, pp825-73, 1968.

[Sha88] K. S. Shanmugan and A. M. Breipohl, “Random Signals: Detection, Estimation and Data Analysis”, J. Wiley & Sons, Ltd, 1988.

[Law08] A. Law, “Interference Management Evaluation Scenarios”, April 2008. [TR25.814] 3GPP, “Physical layer aspects for evolved Universal Terrestial Radio

Access (UTRA)”. 3rd Generation Partnership Project, Technical Specification Group Radio Access Networks, TR25.814, v7.1.0, 10-2006.

[TR25.820] “3G Home NodeB Study Item Technical Report”, 3rd Generation Partnership Project, Technical Specification Group Radio Access Networks, TR25.820 v8.0.0, 03-2008.

[TR25.848] 3GPP, “Physical layer aspects of UTRA High Speed Downlink Packet Access”, 3rd Generation Partnership Project, Technical Specification Group Radio Access Networks , TR25.848 v4.0.0, 03-2001.

[TR25.942] 3GPP, “Radio Frequency (RF) system scenarios”, 3rd Generation Partnership Project, Technical Specification Group Radio Access Networks, TR25.942, v.7.0.0, 03-2007.

[TR101.112] 3GPP, “Selection procedures for the choice of radio transmission technologies of the UMTS”, 3rd Generation Partnership Project, Technical Specification Group Radio Access Networks, TR101.112, v3.2.0, 04-1998.

http://www.3gpp.org/ftp/Specs/archive/25_series/25.814/25814-710.zip




http://www.3gpp.org/ftp/Specs/archive/30_series/30.03U/3003U-320.zip

http://www.3gpp.org/ftp/Specs/archive/30_series/30.03U/3003U-320.zip


[TS25.101] 3GPP, “User Equipment (UE) radio transmission and reception (FDD)”, 3rd Generation Partnership Project, Technical Specification Group Radio Access Networks, TS25.101, v7.12.0, 05-2008.

[TS25.104] 3GPP, “Base Station (BS) radio transmission and reception (FDD)”, 3rd Generation Partnership Project, Technical Specification Group Radio Access Networks, TR 25.104, v7.9.0, 01-2008.

[R4-070825] R4-070825, "Home BTS consideration and deployment scenarios for UMTS", Orange, 3GPP TSG-RAN Working Group 4 (Radio) meeting #43, May 2007.

[R4-070969] R4-070969, “Home B output power”, Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #43bis, R4-070969, June 2007.

[R4-070970] R4-070970, "Initial simulation results for Home Node B receiver sensitivity", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #43bis, June 2007.

[R4-070971] R4-070971, "Initial simulation results for Home Node B receiver blocking", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #43bis, June 2007.

[R4-071185] R4-071185, "The analysis for Home NodeB receiver blocking requirements", Huawei, 3GPP TSG-RAN Working Group 4 (Radio) meeting #44, August 2007.

[R4-071211] R4-071211, "Recommendations on transmit power of Home NodeB", Alcatel-Lucent, 3GPP TSG-RAN Working Group 4 (Radio) meeting #44, August 2007.

[R4-071231] R4-071231, "Open and Closed Access for Home NodeBs", "Nortel, Vodafone", , 3GPP TSG-RAN Working Group 4 (Radio) meeting #44, August 2007.

[R4-071253] R4-071253, "Minutes of Home NodeB/ ENodeB Telephone Conference #3. Aug 7, 2007", Motorola, , 3GPP TSG-RAN Working Group 4 (Radio) meeting #44, August 2007.

[R4-071263] R4-071263, "System simulation results for Home NodeB interference scenario #2", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #44, August 2007.

[R4-071540] R4-071540, "LTE Home Node B downlink simulation results with flexible Home Node B power", Nokia Siemens Networks, 3GPP TSG-RAN Working Group 4 (Radio) meeting #44bis, October 2007.

[R4-071554] R4-071554, "The analysis for low limit for Home NodeB transmit power requirement", Huawei, 3GPP TSG-RAN Working Group 4 (Radio) meeting #44bis, October 2007.

[R4-071578] R4-071578, "Simulation results of macro-cell and co-channel Home NodeB with power configuration and open access", Alcatel-Lucent, 3GPP TSG-RAN Working Group 4 (Radio) meeting #44bis, October 2007.

[R4-071617] R4-071617, “HNB and HNB-Macro Propagation Models”, Qualcomm Europe, 3GPP TSG-RAN Working Group 4 (Radio) meeting #44bis, October 2007.

[R4-071618] R4-071618, "Home Node B HSDPA Performance Analysis", Qualcomm Europe, 3GPP TSG-RAN Working Group 4 (Radio) meeting #44bis, October 2007.

[R4-071619] R4-071619, "Analysis of Uplink Performance under Co-channel Home NodeB-Macro Deployment", Qualcomm Europe, 3GPP TSG-RAN Working Group 4 (Radio) meeting #44bis, October 2007.

[R4-071660] R4-071660, "Impact of HNB with fixed output power on macro HSDPA capacity", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #44bis, October 2007.

http://www.3gpp.org/ftp/Specs/archive/25_series/25.101/25101-7c0.zip


http://www.3gpp.org/ftp/tsg_ran/WG4_Radio/TSGR4_43/Docs/R4-070825.zip

http://www.3gpp.org/ftp/tsg_ran/WG4_Radio/TSGR4_43bis/Docs/R4-070969.zip
















[R4-071661] R4-071661, "Impact of HNB with controlled output power on macro HSDPA capacity", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #44bis, October 2007.



[R4-072004] R4-072004, "Performance Evaluation about HNB coexistence with Macro networks", Huawei, 3GPP TSG-RAN Working Group 4 (Radio) meeting #45, November 2007.

[R4-072025] R4-072025, "Proposed HNB Output Power Range", Qualcomm Europe, 3GPP TSG-RAN Working Group 4 (Radio) meeting #45, November 2007.

[R4-080097] R4-080097, "Minutes of Home NodeB/ ENodeB" Telephone Conference #7, Jan 31, 2008.

[R4-080409] R4-080409, "Simple Models for Home NodeB Interference Analysis", Qualcomm Europe, 3GPP TSG-RAN Working Group 4 (Radio) meeting #46, February 2008.

[R4-080151] R4-080151, "Simulation results for Home NodeB to macro UE downlink co-existence within the block of flats scenario", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #46, February 2008.

[R4-080152] R4-080152, "Simulation results for Home NodeB uplink performance in case of adjacent channel deployment within the block of flats scenario", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #46, February 2008.

[R4-080153] R4-080153, "Simulation results for Home NodeB uplink performance in case of co-channel deployment within the block of flats scenario", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #46, February 2008.

[R4-080154] R4-080154, "Simulation results for Home NodeB to Macro NodeB uplink interference within the block of flats scenario", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #46, February 2008.

[R4-080149] R4-080149, Ericsson, "Simulation assumptions for the block of flats scenario”, 3GPP TSG-RAN Working Group 4 (Radio) meeting #46, February 2008.

[R4-080150] R4-080150, "Simulation results for the Home NodeB downlink performance within the block of flats scenario", Ericsson, 3GPP TSG-RAN Working Group 4 (Radio) meeting #46, February 2008.

[R4-080154] R4-080154, Ericsson, "Simulation results for Home NodeB to Macro NodeB uplink interference within the block of flats scenario", 3GPP TSG-RAN Working Group 4 (Radio) meeting #46, February 2008.

[R4-080939] R4-080939, Ericsson, “Downlink co-existence between macro cells and adjacent channel Home NodeBs”, 3GPP TSG-RAN Working Group 4 (Radio) meeting #47, May 2008.

[R4-080940] R4-080940, Ericsson, “Downlink co-existence between a realistic macro cell network and adjacent channel Home NodeBs”, 3GPP TSG-RAN Working Group 4 (Radio) meeting #47, May 2008.

[R4-081344] R4-081344, “HNB and Macro Downlink performance with Calibrated HNB Transmit Power”, Qualcomm Europe, 3GPP TSG-RAN Working Group 4 (Radio) meeting #47bis, June 2008.

[R4-081345] R4-081345, “HNB and Macro Uplink Performance with Adaptive Attenuation at HNB”, Qualcomm Europe, 3GPP TSG-RAN Working Group 4 (Radio) meeting #47bis, June 2008.




















[R4-081346] R4-081346, “Interference Management Methods for HNBs”, Qualcomm Europe, 3GPP TSG-RAN Working Group 4 (Radio) meeting #47bis, June 2008.

[R4-081597] R4-081597, Airvana, Vodafone, ipAccess, “Impact of uplink co-channel interference from an un-coordinated UE on the Home Node B”, 3GPP TSG-RAN Working Group 4 (Radio) meeting #47bis, June 2008.



003-Interference Management in Umts Femtocells High-band

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