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BSS B11 Multilayer and Multiband GSM Network Radio OptimizationGSM
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Terms of Use and Legal Notices
Switch to notes view!1. Safety WarningBoth lethal and dangerous voltages may be present within the products used herein. The user is strongly advised not to wear conductive jewelry while working on the products. Always observe all safety precautions and do not work on the equipment alone.
The equipment used during this course may be electrostatic sensitive. Please observe correct anti-static precautions.
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BSS B11 Multilayer and Multiband GSM Network Radio OptimizationGSM
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Course Objectives
Switch to notes view!
Welcome to BSS B11 Multilayer and Multiband GSM Network Radio Optimization
Upon completion of this course, you should be able to:
During the course, the trainee will be able to describe the specific radio algorithms in multiband/multilayer networks in order to enhance the offered QoS.
By the end of the course, the participant will be able to: - Describe the concepts and strategy of multiband and hierarchical networks. - Describe the specific type of cells implemented in multiband and hierarchical networks. - Describe the specific radio algorithms used in the Alcatel BSS in a multiband and hierarchical
network. - Propose default parameter values for the cells of a multiband and hierarchical network using these
algorithms. - Propose a list of specific indicators to monitor QoS and traffic in a multiband and hierarchical
network.
Note: Radio Network Planning issues like micro site detection, site planning, frequency planning is not included.
BSS B11 Multilayer and Multiband GSM Network Radio OptimizationGSM
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About this Student Guide
Switch to notes view!Conventions used in this guide
Where you can get further information
If you want further information you can refer to the following:
Technical Practices for the specific product
Technical support page on the Alcatel website: http://www.alcatel-lucent.com
Note Provides you with additional information about the topic being discussed. Although this information is not required knowledge, you might find it useful or interesting.
Technical Reference (1) 24.348.98 – Points you to the exact section of Alcatel-Lucent Technical Practices where you can find more information on the topic being discussed.
WarningAlerts you to instances where non-compliance could result in equipment damage or personal injury.
Alcatel is providing multi-layer solutions: Since R3.1: mini & microcells Improvements in B3.1 (smart speed discrimination) Improvements in B6.2 (external Directed Retry) Improvements in B7 (indoor layer introduction)
Alcatel is providing multi-band solutions: Since B5.1: multi-band BSC From B6.2: multi-band cells Improvements in B7
B5 : in one BSC, cells with different frequency bands
B6 : within one BTS : different bands, and within one cell : different bands also !
B7 improvements:
new HW capabilities with “Cell split” support
enhancement of QoS monitoring capabilities with counters split per TRX
Early adopters of multi-band technology had to deal with a low proportion of multi-band MSs Network parameters were set to send systematically all multi-band MSs
towards new band TRXs A new band is called the “Preferred band”
Since year 2000, quite all new MSs include the multi-band feature Q4 2002: the multi-band MS penetration rate is 80% Parameters settings have to be changed to avoid new band congestion! Operators introducing newly the multi-band technology use this new set of
parameters
Default values of parameters have aggressive values : because penetration rate was low, pushing 1800 MS towards 1800 band was a priority.
One unique combination of the five parameters CELL_DIMENSION_TYPE: macro, micro CELL _LAYER_ TYPE : single, upper, lower, indoor CELL _PARTITION_ TYPE : normal, concentric CELL _RANGE: normal, extended inner, extended outer CELL_BAND_TYPE :GSM; DCS (depends on BCCH frequency band) FREQUENCY_RANGE : PGSM; DCS1800; EGSM; DCS1900; PGSM-DCS1800;
EGSM-DCS1800 and GSM850
A multi-band cell is defined by: FREQUENCY_RANGE = “PGSM-DCS1800” or “EGSM-DCS1800” CELL _PARTITION_ TYPE = Concentric
Extended cell : different than the concentric cells ! Made up of two different cells, with 2 BCCH : the inner cell can cover MS up to 35km, and the outer cell can cover MS between 35km and 70km.
Link the logical cell types (as defined in the OMC-R) with the cell profile parameters.
Indoor
Micro
Mini
Umbrella
Cell Layer TypeCell Dimension TypeCell Type
5 minutes
A cell's profile parameters define the behaviour of handovers from and toward this cell : certain handovers are available only for "UPPER" cells or "MICRO" cells.
In a mono-layer network, a new band may be introduced:
In the same layer Macro 900 (single) Macro 1800 (single) 900-1800 interworking managed by priority set by the operator
In a separate layer Macro 900 (umbrella) Macro 1800 = mini 900-1800 interworking driven by a dual layer architecture (easier to
introduce but less flexible)
900 900 1800 1800
900 900
mini1800 mini1800
All examples in this document will be using 900 as an “historical” band and 1800 as a “new” band (thus preferred band).
All other network configurations are anyway possible.
The dual layer configuration is interesting in case the dual band implementation strategy is traffic driven due to a low penetration rate of multi-band MSs.
A dual layer allows for example, for a multi-band MS located in a 900 cell, to discriminate its behavior between a Forced Directed Retry and an emergency HO. 1800 neighboring cells can be favored for a FDR whereas 900 neighboring cells will be preferred on an emergency HO.
A dual layer also allows to decide the MS transfer from 900 to 1800 band on speed criterion instead of on traffic criterion if needed (macro 1800 hot spot for instance).
In a multi-layer network, a new band may be introduced:
In the upper layer Macro 900 (umbrella) Macro 1800 (umbrella) Micro 900
In the lower layer Macro 900 (umbrella) Macro 1800 = mini Micro 900
900 900 1800 1800
900 900
mini1800
µ900 µ900
µ900 µ900
In the first configuration, the major difficulty is to manage 900-1800 interworking in the upper layer. But once it is done, it is the simplest solution to manage.
In the second configuration, the operator has to deal with priority between the preferred cells: mini or micro? For both selections in idle mode and capture from the upper layer. A lot of handovers might occur, and it requires more engineering analysis ressources
Based on the concentric cell feature New band is introduced in existing cells In the INNER zone (contains only TCH) The OUTER zone contains BCCH, SDCCH and TCH
Multi-layer architecture Hardware : All generations
Note : Any BTS can be declared with the cell type = MICRO
Software : Since R3.1, with addition of External Directed Retry in B6.2 (µ cells and umbrella cells from different BSC
possible) INDOOR layer in B7
Multi-band architecture Hardware :
B5.1 : G2 BSC can manage TRXs from different bands B6.2 : 1 Evolium BTS supports TRXs from different bands within one cell B7 : 1 cell can be split over 2 BTS's (TRX 900 and TRX 1800 in different BTS's
• Maximal number of cabinets between which a given cell is shared is 2.
• Cabinets between which a cell is shared are clock synchronised in a master / slave onfiguration
Such clock synchronisation between BTSs in master / slave mode is possible both between A9100 BTSs and between A9100 BTSs and BTSs of previous generations.
6 Main Standard Handover Algorithms 59Emergency Intercell Algorithms 60Handover Cause 2: UL Quality 61Handover Cause 3: UL Level 62Handover Cause 4: DL Quality 63Handover Cause 5: DL Level 64Handover Cause 6: Distance 65Emergency Intracell Handovers 66Handover Cause 15: UL Interference 67Handover Cause 16: DL Interference 68New Parameters for Causes 15 & 16 69Causes 15 & 16: specific case of concentric cells 70Handover Cause 12: Power Budget 71Handover Cause 12: Inter-band situation 81HO Cause 12: Tuning of Microcells Parameters 84
Cause 12: Speed Discrimination in Lower/Indoor 87Exercise 88Handover Cause 23: Traffic 89Handover Cause 28: Fast Traffic HO 91Exercise 94
7 Emergency Handover Algorithms for MBML Networks 98Emergency Handovers: Introduction 99Emergency Handovers Specific to Microcells 101Microcell Emergency Handovers 102Cause 17 & 18: Comparison to High Threshold 105
8 Better Conditions Handover Algorithms for MBML Networks 110Cause 14: Lower/Indoor Capture for Slow MS 111Cause 14: Speed Discrimination 115Cause 24: General Capture 121Exercise 124Cause 21: Preferred Band 128Capture handovers 130Exercise 133
9 Multiband Cells 136Introduction 137Cause 10: Low uplink level in inner zone 140Cause 11: Low downlink level in inner zone 141Cause 13: High UL & DL level in outer zone 142Call Setup 148Outgoing intercell HO 150HO Cause 12 151Incoming intercell HO 154Intracell Handovers 156Limitations 157Additional Features 158Exercise 159
10 Candidate Cell Evaluation 161From HO Detection to Candidate Cell Evaluation 162Raw Cell List and PREF_LAYER 163Summary 167Evaluation Process 168Pre-Ranking in Standard Networks 172PBGT Filtering 173Order Evaluation 175Grade Evaluation 176Level Filtering 177FDR: Candidate Cell Evaluation 178Summary 179Exercise 180Self-Assessment on the Objectives 188End of Module 189
Neighboring cells list is sent to the MS regularly and contains all BCCH frequencies of neighbor cells to be monitored by the MS
The MS measures them regularly in order to : Perform cell selection & reselection (in idle mode) Report 6 BCCH RxLev to the BSS for handovers (in dedicated mode)
798798 2020
4545
800800
805805
22
MS shall measure the BCCH of neighbor cells and decode their BSIC at least once every 10 seconds.
Description of all SI messages : 3GPP TS 44.018 Mobile radio interface layer 3 specification; Radio Resource Control (RRC) protocol, several chapters starting from §9.1.31
It takes up more space to broadcast 1800 frequencies, therefore 2 SI are necessary.
Reported neighbors from each band can be forced thanks to the cell parameter : MULTIBAND_REPORTING
4 possible values 0: 6 strongest cells irrespective of the frequency band 1: 1 strongest cell (non-serving cell frequency band) + 5 strongest cells
(serving cell frequency band) 2: 2 strongest cells (non-serving cell frequency band) + 4 strongest cells
(serving cell frequency band) 3: 3 strongest cells (non-serving cell frequency band) + 3 strongest cells
(serving cell frequency band)
Default value: 0 for mono-band network 3 for multi-band network
For a multi band MS, the number of cells per freq band which shall be included in the measurement report is indicated by the parameter MULTIBAND_REPORTING, broadcast on BCCH.
An MS attached to GPRS shall use the parameter broadcast on BCCH. The parameter may also be sent to the MS on SACCH.
The meaning of different values of the parameter is specified as follows:
Value Meaning
00 Normal reporting of the six strongest cells, with known and allowed NCC part of BSIC, irrespective of the band used.
01 The MS shall report the strongest cell, with known and allowed NCC part of BSIC, in each of the frequency bands in the BA list, excluding the frequency band of the serving cell. The remaining positions in the measurement report shall be used for reporting of cells in the band of the serving cell. If there are still remaining positions, these shall be used to report the next strongest identified cells in the other bands irrespective of the band used.
10 The MS shall report the two strongest cells, with known and allowed NCC part of BSIC, in each of the frequency bands in the BA list, excluding the frequency band of the serving cell. The remaining positions in the measurement report shall be used for reporting of cells in the band of the serving cell. If there are still remaining positions, these shall be used to report the next strongest identified cells in the other bands irrespective of the band used.
11 The MS shall report the three strongest cells, with known and allowed NCC part of BSIC, in each of the frequency bands in the BA list, excluding the frequency band of the serving cell. The remaining positions in the measurement report shall be used for reporting of cells in the band of the serving cell. If there are still remaining positions, these shall be used to report the next strongest identified cells in the other bands irrespective of the band used.
MULTIBAND_REPORTING has to be tuned carefully in multi-band network, since no handover can be done to a cell which is not reported
The parameter value is depending on network strategy and may be tuned differently in each band
Example: give priority to 1800 cells In 900 layer cells
MULTIBAND_REPORTING = 1 is most of the time sufficient to make a handover towards the preferred band
In 1800 layer cellsMULTIBAND_REPORTING = 3 : 1800 neighboring cells have to be reported to keep the MS in the same band when possible, but 900 cells should be reliably reported as they are rescue cells.
Adding a new band/layer is a powerful way of increasing network capacity if the MS can be sent to the preferred cell In dedicated mode: see next sections But also in idle mode, so that the call is established directly in the preferred
cell Really increase capacity Maintain high QoS level, without creating extra HO
At startup (IMSI Attach), the MS is selecting cell with
Defined priorities with CELL_BAR_QUALIFY Best C1 amongst highest priority cells (using CBQ)
Once “camped on” one cell (in idle mode)…
… The MS can decide to reselect another one if:
C1 criterion < 0 The MS cannot decode downlink signalling blocks of Paging Channel The current cell is becoming forbidden (e.g. barred) A random access attempt is still unsuccessful after "Max retrans" repetitions MS detects the network has failed authentication check There is a better cell, regarding C2 criterion
MAX_RETRANS is a cell parameter, transmitted in SI-2.
Authentication check : during SDCCH phase (call setup, location update)
Note:
Cell selection (first selection) is performed using C1 criterion only (the chosen cell is the one with the best C1)
Reselection is done using the mechanisms referenced above.
e.g., the MS cannot access the cell.
It can be linked to SDCCH congestion, filtering of CHARQD due to TA greater than RACH_TA_FILTER, radio access problem during the Radio Link Establishment phase.
If SDCCH is to be seized for LU purpose, the MS will reselect on another cell.
If SDCCH is seized for something else (e.g., MOC), the MS « may » reselect (this is up to the MS vendor choice!!!). Some MSs do nothing. Call will never be possible. Some others do reselect. In that case, the user has to reattempt his call (after the reselection, but before the MS is back to the original cell due to better C2, etc. (done after 5 s, etc.)).
WARNING: usage of CELL_BAR_QUALIFY: interacts with CELL_BAR_ACCESS
A cell with low priority (CELL_BAR_QUALIFY = 1) cannot be barred
Some MSs will be able to access it, whatever the value of CELL_BAR_ACCESS
normal (see note 1)low11
normal (see note 1)low01
barredbarred10
normalnormal00
Status for cell reselectionCell selection priorityCELL_BAR ACCESS
CELL_BAR QUALIFY
NOTE 1: Two identical semantics are used for cross phase compatibility reasons. This allows an operator to declare a cell always as a low priority one for a phase 2 MS, but keeps the opportunity for an operator to decide whether a phase 1 MS is permitted to camp on such a cell or not.
Because phase-1 MS do not support this feature, it is recommended to keep cell bar qualify = 0.
Also, some early phase-2 MS do not handle this parameter properly.
This is only useful during selection (switching the MS, before C1 computation). Afterwards, only reselection will take place.
Therefore, a 1800 cell will provide less coverage than a 900 cell Delta = 8~10dB Less traffic is carried by 1800 cells (more capacity available)
Additionally, the 1800 frequency planning is usually cleaner than the 900 one.
Even at low RxLev, a 1800 cell might provide a coverage with good quality and good capacity
For this reason, CRO is used to advantage 1800 cells over 900 cells. Within a same layer : CRO(1800) = CRO(900) + 2~8dB Among different layers : CRO(1800) = CRO(900) + 4~12dB
The risk is to have congestion in the preferred cell! Classical band / upper cells are unloaded… … as all MSs are sent to new cells in idle mode
This phenomenon is further amplified by handovers behavior
Multi-band/multi-layer algorithms are based on CAPTURE mechanisms Send the MS in the preferred cell as soon as it is OK… … Without comparing serving and preferred cells… … to reach the maximum capacity increase(See handover parts for details)
When a MS camps on a cell in Idle mode, it will perform call setup on this cell (and all other procedures : locationupdate, SMS, etc.).
EN_DR = enable (DR execution is enabled in the cell)
EN_DR = disable (DR execution is disabled in the cell)
Executed only if no TCH available in serving cell and standard intercellHO detected
Except Intracell HO causes 10, 11 and 13 (concentric cells) and causes 15 and 16 (interference HO)
Except Cause 28 (Fast Traffic HO)
The target cell is chosen by the BSC based on the HO detected
If the target cell is congested, the counter MC555 is incremented :
Definition : Number of incoming internal directed retry (forced or normal) -preparation failures due to congestion (on Air or A-bis interface). The target TCH channel can be in HR or FR usage.
Trigger condition
1) Whenever there are no free TCH in the target cell during a forced or normal internal directed retry.2) Whenever no TCH resource is available on A-bis interface for a forced or normal internal directed retry. (not valid in B7)
EN_EXT_DR : enables/disables the Outgoing External Directed Retry procedure (on a per BSC basis)
L_RXLEV_NCELL_DR(n): level required in the neighboring cell n The parameter considered is the one set in the neighboring cell The default value depends on the network architecture See the next slide
Freelevel_DR(n): number of free TCH channels required in the neighboring cell n The parameter considered is the one set in the neighboring cell Default value = 0 to 4 TCHs (linked to the nb of TRXs) (cf. Candidate Cell Evaluation)
A_PBGT_DR: average window Default value = 4 SACCHs
Normal DR Pro's: no radio problem as MS's remain within the service area of the new
serving cell Con's: poor probability of happening, as MS is already camping on the best
server cell
Forced DR Pro's: Probability of detecting a FDR depends on parameter settings. Con's: Interference problems because MS is perhaps outside the cell normal
service area
Umbrella cell
Micro cell
FDRcapture
Forced Directed Retry strategy:
Between one micro cell and its umbrella macro cell
Prevention of congestion in the “old” cells MSs are sent in idle mode to the “preferred cell” HO strategy favoring the “preferred cell” in dedicated mode
Prevention of congestion in the “preferred cell” Forced Directed Retry to the “old” cells
Intelligent MS sharing between available resources Avoid congestion of historical band (for old MS) Consider traffic conditions of all layers Use full capacity of new resources (1800 band is offering more channels) Consider MS speed for layer discrimination
Avoid too many handovers Degradation of voice quality In order to ease traffic analysis, it is recommended to avoid too many handovers
Standard HO causes cause 2 : too low quality on the uplink cause 3 : too low level on the uplink cause 4 : too low quality on the downlink cause 5 : too low level on the downlink cause 6 : too large distance between the MS and the BTS cause 15 : high interference on the uplink (intra-cell HO) cause 16 : high interference on the downlink (intra-cell HO) cause 26 : AMR channel adaptation HO (HR to FR)
cause 12 : power budget evaluation cause 23 : traffic cause 27 : AMR channel adaptation HO (FR to HR) cause 28 : Fast traffic HO cause 29 : TFO HO cause 20 : FDR
EM
BC
These causes will always work, whether the network is monoband monolayer, or multiband multilayer.
HO causes for MB-ML networks cause 10 : too low level on the uplink in the inner zone cause 11 : too low level on the downlink in the inner zone cause 7 : consecutive bad SACCH frames received in a microcell cause 17 : too low level on the uplink in a microcell compared to
a high threshold cause 18 : too low level on the downlink in a microcell compared
to a high threshold
cause 13 : too high level on the uplink and the downlink in the outer zone
cause 14 : high level in the neighboring cell of a lower or indoor layer for slow mobile
cause 21 : high level in the neighboring cell in the preferred band cause 24 : general capture
cause 7 : consecutive bad SACCH frames received in a microcell cause 17 : too low level on the uplink in a µcell compared to a high threshold cause 18 : too low level on the downlink in a µcell compared to a high threshold cause 2 : too low quality on the uplink cause 3 : too low level on the uplink cause 4 : too low quality on the downlink cause 5 : too low level on the downlink cause 6 : too large distance between the MS and the BTS cause 10 : too low level on the uplink in the inner zone cause 11 : too low level on the downlink the in inner zone cause 26 : AMR channel adaptation HO (HR to FR) cause 15 : high interference on the uplink (intra-cell HO) cause 16 : high interference on the downlink (intra-cell HO)
cause 21 : high level in the neighboring cell in the preferred bandcause 14 : high level in neighboring cell of a lower or an indoor layer cell for slow mobilecause 24 : general capturecause 12 : power budget evaluationcause 23 : traffic
cause 13 : too high level on the uplink and downlink in the outer zone cause 27 : AMR channel adaptation HO (FR to HR) cause 20 : Forced Directed Retry DR cause 28 : Fast traffic HO
EM
BC
The handover causes are checked with the priority order defined here.
The better condition causes 21, 14, 24, 12 and 23 have the same priority. For each cell in the list of possible candidate cells is associated a cause.
If a cell is in the candidate cells list because of 2 different causes, only the one with the highest priority in the ordered list (cause 21, cause 14, cause 24, cause 12 and cause 23) in which cause 21 has the highest priority is kept.
Emergency intercell handovers cause 2 : too low quality on the uplink cause 3 : too low level on the uplink cause 4 : too low quality on the downlink cause 5 : too low level on the downlink cause 6 : too large distance between the MS and the BTS
May be triggered From any serving cell (any band, any zone, any layer) Towards any neighbour, except the serving cell
Note : EM HO detected while in the inner zone of a cell the outer zone is a candidate
Quality and Level causes (2, 3, 4, 5, 15, 16)The aim of these causes is to keep the call going when the radio link is degrading otherwise the radio link failure might be detected and the call released. These causes wait generally for the power control process to increase the BTS and MS power to their maximum values, except for the causes specific to microcellular environment.Handover on "too low level" is used to avoid situations where the interference level is low, while the attenuation is quite high. These conditions may appear for example in big city streets which ENABLED a line of sight propagation from the BTS antenna. There is in this case a risk of abrupt quality degradation, if the MS moves away from the line of sight street.In case of simultaneous low-level and low-quality signals, an intercell handover is requested.
Size of window for averaging distance : A_RANGE_HO
AV_RANGE_HO > U_TIME_ADVANCE
and EN_DIST_HO = ENABLED
AV_RANGE_HO > U_TIME_ADVANCE
and EN_DIST_HO = ENABLED
This cause is used when a dominant cell provides a lot of scattered coverages inside other cells, due to propagation conditions of the operational network. These spurious coverages is the probable production of a high level of co-channel interference.
This cause is different from the others as it is more preventive. It does not make use of the propagation conditions of a call. It just does not allow an MS to talk to a BTS if it is too far away.
It may happen for example that some peculiar propagation conditions exist at one point in time that provide exceptional quality and level although the serving BTS is far and another is closer and should be the one the mobile should be connected to if the conditions were normal.
It may then happen that these exceptional conditions suddenly drop and the link is lost, which would not have happened if the mobile had been connected to the closest cell. For these reasons also, this cause does not wait for the power control to react.
CAUSE 15 and CAUSE 16: THR_RXQUAL_CAUSE_15 (or 16) and EN_CAUSE_15 (or 16) are specific to
variable computed by the BSC :
THR_RXQUAL_CAUSE_15 (or 16) = L_RXQUAL_XX_H for a non AMR call (same threshold as CAUSE 2 or CAUSE 4) L_RXQUAL_XX_H_AMR for an AMR Narrow Band call L_RXQUAL_XX_H_AMR_WB_GMSK for an AMR Wide Band call
EN_ CAUSE _15 (or 16) = EN_INTRA_XX for a non-AMR call EN_INTRA_XX_AMR for an AMR Narrow Band call EN_INTRA_XX_AMR_WB_GMSK for an AMR Wide Band call
B10
XX = UL or DL
For a non AMR call, the thresholds used are identical to the ones used for CAUSE 2 and CAUSE 4.
In this case and if EN_INTRACELL_REPEATED = DISABLED, when a HO CAUSE 15 (or 16) fails, it can be modified as UPLINK (or DOWLINK) QUALITY, HO CAUSE 2 (respectively HO CAUSE 4).
With the introduction of AMR Wide Band, in B10, specific thresholds have been defined for Cause 15 and Cause 16 of an AMR WB call.
Definition of PBGT HO : Possible targets depends also on the cells band type :
GSMAnyGSM
EN_MULTIBAND_PBGT_HO= Disable
EN_MULTIBAND_PBGT_HO= Enable
Any
Target Band Type
DCS
Serving Band Type(MS not in inner zone of
a MB cell)
DCS
A multiband cell is "GSM" if the outer zone is in GSM (cf. note)
The cell band type is an internal variable in the BSC, it depends on the BCCH frequency only. Therefore a multiband cell has a cell band type = GSM if the outer zone is in GSM900.
This scheme highlights well the difficulty of introducing multi-band cells if EN_MULTIBAND_PBGT_HO is disabled (this was the only configuration in the first B6.2 networks): Multi-band cells interoperate only with, etc. multi-band cells.
The value of PBGT(n) is calculated every SACCH period for each neighboring cell n whose measures are kept in the book-keeping list
A : favor cell with highest difference between RXLEV(n) and RXLEV(s)
B : compensate for effect of the power control in DL (if PC DL attenuates BS TXPWR by 4dB, the RXLEV(s) is also attenuated by 4dB)
C : favor the cell where the MS is the most limited in TX power (to limit UL interference and extend battery life)
automatic bonus of +3dB from 900-serving to 1800-neighbours.
automatic handicap of -3dB from 1800-serving to 900-neighbours.
* In the case of concentric or multiband cells, if the channel is in the inner zone (ZONE_TYPE = INNER), BS_TXPWR_MAX and MS_TXPWR_MAX in equation must be replaced by BS_TXPWR_MAX_INNER and MS_TXPWR_MAX_INNER respectively.
If the channel is in the outer zone (ZONE_TYPE = OUTER), the formulation of equation (HO-7) is not changed.
A Handover cause 12 is detected only if the following conditions are met :
Size of window for level averaging: A_PBGT_HO
if EN_TRAFFIC_HO(0,n) = DISABLED
then PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER (*)
and AV_RXLEV_PBGT_HO ≤ RXLEV_LIMIT_PBGT_HO
and EN_PBGT_HO = ENABLED
if EN_TRAFFIC_HO(0,n) = DISABLED
then PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER (*)
and AV_RXLEV_PBGT_HO ≤ RXLEV_LIMIT_PBGT_HO
and EN_PBGT_HO = ENABLED
(*) OFFSET_HO_MARGIN_INNER is applied only if the MS is currently located in the inner zone of a concentric cell (multiband or monoband). This parameter will be explained in chapter 7.
In case the feature "Traffic HO" is enabled, the previous condition is modified :
Size of window for level averaging: A_PBGT_HO
if EN_TRAFFIC_HO(0,n) = ENABLED
then PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER (*)+ max(0, DELTA_HO_MARGIN(0,n))
and AV_RXLEV_PBGT_HO ≤ RXLEV_LIMIT_PBGT_HO
and EN_PBGT_HO = ENABLED
if EN_TRAFFIC_HO(0,n) = ENABLED
then PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER (*)+ max(0, DELTA_HO_MARGIN(0,n))
and AV_RXLEV_PBGT_HO ≤ RXLEV_LIMIT_PBGT_HO
and EN_PBGT_HO = ENABLED
max(0, DELTA_HO_MARGIN(0,n)) is always positive it increases the HO_MARGIN(O,n)max(0, DELTA_HO_MARGIN(0,n)) is always positive it increases the HO_MARGIN(O,n)
Cause 12 HO is correlated with cause 23 HO. This is why there is a difference according to the activation of cause 23 HO (EN_TRAFFIC_HO).
(*) OFFSET_HO_MARGIN_INNER is applied only if the MS is currently located in the inner zone of a concentric cell (multiband or monoband). This parameter will be explained in chapter 7.
DELTA_HO_MARGIN(0,n): evaluated according to the traffic situation of the serving cell and the neighboring cell n (Traffic_load(n)) in the following way:
Philosophy:This mechanism aims at penalizing cause 12 detection when the traffic in the serving cell is low and is high in the cell n
If Traffic_load(0) = high and Traffic_load(n) = low, DELTA_HO_MARGIN(0,n) = - DELTA_DEC_HO_MARGIN
If Traffic_load(0) = low and Traffic_load(n) = high, DELTA_HO_MARGIN(0,n) = + DELTA_INC_HO_MARGIN
Else DELTA_HO_MARGIN(0,n) = 0
If Traffic_load(0) = high and Traffic_load(n) = low, DELTA_HO_MARGIN(0,n) = - DELTA_DEC_HO_MARGIN
If Traffic_load(0) = low and Traffic_load(n) = high, DELTA_HO_MARGIN(0,n) = + DELTA_INC_HO_MARGIN
What is the traffic_load() ? Computed for every cell by the BSC
Not available for neighbour cells that are external (different BSC's)
Can have three values: HIGH: cell is loaded LOW: cell is unloaded INDEFINITE: cell load is neither loaded nor unloaded, or unknown
Modified according to the long term traffic evaluation algorithm using the following parameters: A_TRAFFIC_LOAD, N_TRAFFIC_LOAD : averaging windows HIGH_TRAFFIC_LOAD, IND_TRAFFIC_LOAD, LOW_TRAFFIC_LOAD: load
thresholds TCH_INFO_PERIOD: cannot be modified (5 s)
Annex 1
TCH_INFO_PERIOD = 5 s period used by the BSC to count the number of free TCH.
Allow the flow of PBGT HO between the 2 bands EN_MULTIBAND_PBGT_HO = enable
1800 cells 900 cells
EN_MULTIBAND_PBGT_HO = enable or disable
HO_MARGIN(0,n) =5 dB HO_MARGIN(0,n) = 5 dB
HO_MARGIN(0,n) = 2 dB
EN_MULTIBAND_PBGT_HO = enable
HO_MARGIN(0,n) = 8 dB
EN_MULTIBAND_PBGT_HO = enable
Typical example: dense urban area covered in 1800, and surrounding cells, outside the city area, are in 900.
For cells which are not in the vicinity of cells from other band, the parameter " EN_MULTIBAND_PBGT_HO" has no impact on HO detection (except for multiband cells)
Note : to ease design of parameters, one can use the following syntax (i.e. for the case above) :
HO_MARGIN(900,900) = 5dB
HO_MARGIN(900,1800) = 8dB
HO_MARGIN(1800,1800) = 5dB
HO_MARGIN(1800,900) = 2dB
EN_MULTIBAND_PBGT_HO(900) = enable
EN_MULTIBAND_PBGT_HO(1800) = enable
Why 8dB ? Because there is a automatic bonus of 3dB from 900 1800 (cf p.77). In order keep a difference of 5dB of RXLEV, it is necessary to increase the HO_MARGIN by 3dB.
Solution 1 : Allow the exit from "border 1800", but use other HO causes to manage "core 1800"
macro 900
macro 1800HO_MARGIN(0,n) = 5 dB
HO_M(1800,900)= 2 dB
"Border" strategySmooth exit of the 1800 areaEN_MULTIBAND_PBGT_HO = Enable
"Core" strategyPrevent PBGT HO, to keep MS in 1800 EN_MULTIBAND_PBGT_HO = Disable
HO_MARGIN(900,1800)= 8 dB
HO_MARGIN(0,n) = 5 dB
Dual coverage of an area : full coverage in 1800 and full coverage in 900. However, to compensate for line (C) in slide 77, we must compensate by 3 dB.
This way, there is no priority given to the 1800 band nor the 900 band.
When handling different bands with power budget HO only, the recommended CRO in the 1800 cell is:
HO Cause 12: Tuning of Microcells Parameters [cont.]
HO_MARGIN(0,n) Avoid ping-pong HO in urban environment Avoid emergency HO after street corners Avoid transcient PBGT HO Default value: up to 10 dB in dense urban microcellular area, with
short A_PBGT_HO. Optimized: can be reduced to 5dB or 0dB when applying an anti ping-
pong mechanism and long A_PBGT_HO.
A_PBGT_HO To find a compromise with HO_MARGIN(0,n) Default value: 8 SACCHs for urban microcells, 6 for dense urban
The aim of this cause is to speed HO detection when The serving cell is loaded The target cell is unloaded
Counter-reaction of cause 12
Checked between :
LAYER : Cells with the same CELL_LAYER_TYPE
BAND : If EN_MULTIBAND_PBGT_HO = disable Cells with the same CELL_BAND_TYPE if MS in inner zone of a multi-band cell, it can only go to another multi-band cell
If EN_MULTIBAND_PBGT_HO = enable Any CELL_BAND_TYPE
CAUSE 23
CAUSE 12
In some multi-band networks, the radio coverage is ensured by DCS cells in one geographical area and by GSM cells in another geographical area. As these cells form a multi-band and mono-layer network, the capture handovers between cells of different bands will be inefficient to regulate the CS traffic load in the serving cell neighboringhood.
The solution consists in allowing intra-layer traffic handovers (Cause 23) based on a power budget evaluation between cells of different bands.
DELTA_HO_MARGIN(0,n) uses the same algorithm as in p.77.
DELTA_HO_MARGIN(0,n) < 0 dB
AND PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER+ DELTA_HO_MARGIN(0,n)
AND EN_TRAFFIC_HO(0,n) = ENABLED
DELTA_HO_MARGIN(0,n) < 0 dB
AND PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER+ DELTA_HO_MARGIN(0,n)
AND EN_TRAFFIC_HO(0,n) = ENABLED
The principle of this handover is to reduce the size of the serving cell when it is high loaded relatively to a low loaded cell.
When the mobile moves away from the BTS, the power budget will increase and a better cell handover will be triggered earlier.
It is recommended to inhibit Traffic handover towards 1 TRX cells. These cells do not have enough resources to receive incoming handovers due to congestion of neighboring cells. Moreover because of the great variation of traffic in the 1 TRX cells, traffic load is never considered as low.
This cause is inhibited for handover from SDCCH to SDCCH.
Cause 23 is checked over all the neighboring cells belonging to the same layer. It means that it is checked between cells whose CELL_LAYER_TYPE is single or upper, between cells whose CELL_LAYER_TYPE is lower, and between cells whose CELL_LAYER_TYPE is indoor.
In addition to the condition on the cell layer type, the cell frequency band condition for checking Cause 23 is as follows whether or not the MS is in the inner zone of a multi-band cell:
The MS is not in the inner zone of a multi-band cell
If the flag EN_MULTI-BAND_PBGT_HO is set to “disabled”, Cause 23 must not be checked between cells which use different frequency bands (i.e cells having different CELL_BAND_TYPE).
If the flag EN_MULTI-BAND_PBGT_HO is set to “enabled”, Cause 23 will be checked over all the neighboring cells without any cell frequency band restriction.
The MS is in the inner zone of a multi-band cell
If the flag EN_MULTI-BAND_PBGT_HO is set to “disabled”, Cause 23 is checked over all the neighboring cell multi-band cells (FREQUENCY_RANGE= PGSM-DCS1800 or EGSM-DCS1800) which belong to the same BSC as the serving cell.
If the flag EN_MULTI-BAND_PBGT_HO is set to “enabled”, Cause 23 will be checked over all the neighboring cells without any cell frequency band restriction.
Same thresholds and window as Cause 20 (FDR) EN_CAUSE_28 is an internal HOP process variable, ENABLED when a request
is queued
AV_RXLEV_NCELL(n) > L_RXLEV_NCELL_DR(n) + max (0, [MS_TXPWR_MAX(n) - P])
and t(n) > FREELEVEL_DR(n)
and EN_CAUSE_28 = ENABLED
and EN_FAST_TRAFFIC_HO = ENABLED
AV_RXLEV_NCELL(n) > L_RXLEV_NCELL_DR(n) + max (0, [MS_TXPWR_MAX(n) - P])
and t(n) > FREELEVEL_DR(n)
and EN_CAUSE_28 = ENABLED
and EN_FAST_TRAFFIC_HO = ENABLED
HO cause 28 process:
If EN_FAST_TRAFFIC_HO = enabled, when an assignment request (or external emergency HO request) is queued, the RAM process sends to the HOP process a Fast Traffic HO request which contains the queued request reference and its channel rate.
Then, HO cause 28 becomes checkable (EN_CAUSE_28=enabled).
Once an HO alarm for cause 28 is triggered, the flag EN_CAUSE_28 is set to “disabled” so as not to perform more than one handover. In the same time, the HOP process gets back to the RAM process a Fast Traffic HO Acknowledge which contains the queued request reference and the reference of the MS that can perform HO.
If several answers are sent to the RAM process, only the first one corresponding to the queued request is taken into account.
The RAM process checks if the request is still queued. If it is so, RAM asks HOP to start HO for this mobile; otherwise the process is stopped.
Once the HOP process receives this message, the first two conditions of Cause 28 (good enough level, enough free resources in the target cell) are checked one more time. If the conditions are fulfilled, the HOP process sends an alarm to the HOM entity and the timer T_FILTER is started; otherwise the process is stopped.
Note: the first two conditions of cause 28 are tested twice in order to be sure that the candidate cells are still valid when the « cause 28 start HO » message is received from the RAM process.
Emergency handovers specific to microcells cause 7 : consecutive bad SACCH frames received in a microcell cause 17 : too low level on the uplink in a microcell compared to a high
threshold cause 18 : too low level on the downlink in a microcell compared to a high
threshold
May be triggered From microcells only (cell_dimension_type = micro)
High threshold (U_RXLEV_XX_MCHO) the HO is triggered when the signal drops under the threshold the corresponding HO causes consist in comparing, at 2 successive SACCH
periods, the DL and UL levels in the serving microcell with a high threshold
Beginning a call under the threshold does not trigger an HO
Cause 17 & 18: Comparison to High Threshold [cont.]
High threshold (U_RXLEV_XX_MCHO)
With high value, mobiles will be sent too early to the macro layer
With low value, mobiles turning at a street corner will be maintained in the microcell layer during a longer period
Problems for MS's with a signal strength level close to the high threshold : due to fading, multiple handovers can be triggered during a call:
MS in Indoor cell : decrease in RXLEV leads to emergency HO UmbrellaMS in Umbrella : RXLEV of indoor cell becomes good again, capture HO Indoor… and so on.
Alternative strategy : U_RXLEV_XX_MCHO < L_RXLEV_XX_H
ii-1
t
AV_RXLEV_XX_MCHO
High Threshold
µHO alarm
t
Standard Threshold
High Threshold
Standard Threshold
Std HO alarm
Based on 4-SACCH sliding averagesGoal : detect corner street effects
Based on 10-SACCH sliding averagesGoal : detect MS slowly exiting the cell
AV_RXLEV_XX_HO
Alternative strategy offers a different approach :
The "high" treshold U_RXLEV_XX_MCHO is not "high" anymore. Use this threshold as "emergency" exit from a microcell, when the MS turns around a street corner.
The standard threshold should be used as a standard exit from microcell : don't forget that HO cause 12 towards another cell in the same layer might not always be possible. In this case, the only way to exit a micro cell or an indoor cell is to perform an emergency HO !
Therefore it is necessary to use one dedicated emergency HO as a "safe exit" HO, to keep a good RXLEV while performing a HO towards another layer.
Example :
U_RXLEV_DL_MCHO =-92dBm
L_RXLEV_DL_H = -83dBm
A_LEV_MCHO : 4 SACCH
A_LEV_HO : 10 SACCHEN_MCHO_H_DL = ENABLE
In Uplink, default values can be kept for the standard emergency HO, and EN_MCHO_H_UL = DISABLE (exit performed with DL is enough)
8 Better Conditions Handover Algorithms for MBML Networks
Cause 14: Lower/Indoor Capture for Slow MS [cont.]
If cell_layer_type (0) = lower
Averaging window: A_PBGT_HO Anti ping-pong: not checked if T_INHIBIT_CPT is running
mini micro
indoor
AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n)
and MS_SPEED ≠ FAST
and EN_MCHO_NCELL = ENABLED
AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n)
and MS_SPEED ≠ FAST
and EN_MCHO_NCELL = ENABLED
MS_SPEED different than fast, because at call setup, the MS SPEED is set to indefinite. It cannot be set to "SLOW". A "SLOW" MS might be a MS that came from an umbrella previously.
Therefore, in a mini cell, a MS with MS SPEED = indefinite should be able to be sent to an indoor cell.
8 Better Conditions Handover Algorithms for MBML Networks
Cause 14: Speed Discrimination
Only available for UPPER layers (umbrella cells)
Speed discrimination objectives : Maximize capacity (maximum traffic in lower/indoor cells) While optimizing quality (minimize the number of handovers)
Smart speed discrimination : 1. If the load of umbrella is too high reduce the time a MS can stay in the
umbrella2. If the load of umbrella is low increase the time a MS can stay in the
umbrella3. If the MS speed is fast in lower/indoor cells it is sent to the umbrella
cell
Benefits of the smart speed discrimination :
Case 1 : The umbrella cell is kept "less loaded" in order to accept incoming handovers and call setups (most of call setups will be done on the umbrella cells, because of the better coverage). The extra-capacity of lower/indoor cells is fully used.
Case 2 : No HO is performed in this case, because the umbrella has room to keep the calls. It is interesting to avoid handovers, because less HO during a call better voice quality.
Case 3 : a fast moving user should stay in upper layers, in order to avoid performing too many HO (increase the risk of call drops, especially in lower layers)
8 Better Conditions Handover Algorithms for MBML Networks
Cause 14: Speed Discrimination [cont.]
Initialization of C_DWELL(n) in serving umbrella cell :
if EN_SPEED_DISC = ENABLE C_DWELL(n) = 0 MSs will handover to the lower/indoor layer after MIN_DWELL_TIME seconds
if EN_SPEED_DISC = DISABLE C_DWELL(n) = 2 x (MIN_DWELL_TIME - L_MIN_DWELL_TIME) MSs will handover to the lower/indoor layer after L_MIN_DWELL_TIME seconds
MIN_DWELL_TIME is not a parameter ! It is a variable computed by BSC : it varies, depending on the umbrella traffic load.
8 Better Conditions Handover Algorithms for MBML Networks
Cause 14: Speed Discrimination [cont.]
Example with default values (EN_SPEED_DISC = disable) Initialization values
H_MIN_DWELL_TIME = 20s (= MIN_DWELL_TIME at initialization)L_MIN_DWELL_TIME = 8sC_DWELL(n) = 2 x (MIN_DWELL_TIME - L_MIN_DWELL_TIME)
= 2 x (20 - 8) = 24 SACCH (= 12 seconds)
AlgorithmMS is deemed as slow if C_DWELL(n) > 2 x MIN_DWELL_TIME C_DWELL(n) starts at 24, and is increased by 1 when RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n)
0 4 8 12 16 20 24 28 32 36 40 44
: EN_SPEED_DISC = Disable: EN_SPEED_DISC = Enable
INDEFINITE or FAST SLOW
Maximum time to reach MIN_DWELL_TIME
=L_MIN_DWELL_TIME
C_DWELL MIN_DWELL_TIMEC_DWELL
MIN_DWELL_TIME is in seconds, whereas C_DWELL is in SACCH. This is the reason why MIN_DWELL_TIME is multiplied by 2.
8 Better Conditions Handover Algorithms for MBML Networks
Capture handovers [cont.]
Tuning of MULTIBAND_TRAFFIC_CONDITION andCAPTURE_TRAFFIC_CONDITION
Recommended setting: ANY_LOAD
If HIGH or NOT_LOW: Capture to the preferred cell is limited to the loaded hours This choice is sensible: during unloaded hours, the non-preferred cells
provide a good coverage, with little interference.
The following parameters will impact the computation of traffic_load : Avg windows: TCH_INFO_PERIOD, A_TRAFFIC_LOAD, N_TRAFFIC_LOAD Thresholds: LOW_TRAFFIC_LOAD, IND_TRAFFIC_LOAD,
When changing a cell from "normal" to "concentric", 3 more handovers are available !
Those are only INTRA-CELL handovers Cause 13 : entry in inner zone, from outer zone Causes 10 & 11 : exit to outer zone, from inner zone
Cell A
inner
outer
cause 13
cause 10/11
The activation of causes 10 and 11 is automatic, as soon as a cell type is defined as "CONCENTRIC"
The activation of cause 13 is controlled by EN_BETTER_ZONE_HO.
The parameters HO_INTRACELL_ALLOWED and EN_INTRACELL_REPEATED have no impact on those handovers, they are used only for causes 15 & 16 (interference) and 25 & 26 (AMR).
Setting these 3 handover causes is simple1. Work with downlink thresholds first2. Propose an entry treshold, i.e. -75dBm MS enters in the inner zone only if the expected received level in the
inner zone is above -75dBm3. Propose an exit threshold, i.e. -83dBm MS exits the inner zone if the received level is less than -83dBm
Cause 13: High UL & DL level in outer zone [cont.]
NEIGHBOUR_RXLEV(0,n) Avoid sending a MS in the inner zone if a neighbour cell is too strong Tuning depends on frequency planning By default, NEIGHBOUR_RXLEV(0,n) = -47dBm
When inner zone frequency planning is very tight (i.e. reuse cluster = 3)
In this example, the inner zone of cell C_3 can be interfered locally by the inner zone of cell B_2C_2 by E_3…
Cause 13: High UL & DL level in outer zone [cont.]
RXLEV_UL_ZONE : Uplink level threshold for inner to outer zone handover. From -110dBm to -47dBm. [-86 dBm]
RXLEV_DL_ZONE : Downlink level threshold for inner to outer zone handover. From -110dBm to -47dBm. [-76 dBm]
ZONE_HO_HYST_UL: Hysteresis applied to RXLEV_DL_ZONE for outer to inner zone handover. From -40dB to +40dB. [13 dB]
ZONE_HO_HYS_DL: Hysteresis applied to RXLEV_UL_ZONE for outer to inner zone handover. From -40dB to +40dB. [16 dB]
MS_TXPWR_MAX_INNER: MS maximum allowed transmission power in the inner zone of a concentric or multiband cell. From 5dBm to 43dBm. [30 or 33 dB]
BS_TXPWR_MAX_INNER) : This parameter defines the power reduction relative to the maximum GMSK output power of the TRX of the inner zone in a concentric or multi-band cell. From -30dB to 0dB. [0dB]
NEIGHBOUR_RXLEV(0,n) : Threshold of maximum received level from the neighbour cells for cause 13. From -110dBm to -47dBm. [-47dBm]
RXLEV_UL_ZONE and RXLEV_DL_ZONE are usually separated by 10dB, because (if path balance = 0)
UL_RXLEV = DL_RXLEV – 10dB
ie: MS receives a DL signal at -80dBm => BTS receives an UL signal at -90dBm
1. Radio Link Establishment Phase2. SDCCH Phase3. TCH Assignment Phase
In which zone will the TCH be allocated?
The TCH is allocated in the inner zone if : UL and DL RxLev in outer zone are satisfying BSC can allocate a TCH in inner zone MS is multiband
Otherwise, TCH is allocated in the outer zone
INNEROUTER
??
The cell's RXLEV is the one being measured by the MS while performing SDCCH phase and TCH Assignment phase. Therefore, it is measuring only the outer zone RXLEV !!
And AV_RXLEV_DL_HO > RXLEV_DL_ZONE + ZONE_HO_HYS_DL+ (BS_TXPWR - BS_TXPWR_MAX_INNER)
And AV_RXLEV_NCELL_BIS(n) ≤ NEIGHBOUR_RXLEV(0,n)
And EN_CAUSE_13 = ENABLE
THEN : The TCH is allocated in the INNER zone
ELSE : The TCH is allocated in the OUTER zone
MS_TXPWR - MS_TXPWR_MAX_INNER = 33 – 30 = 3dB
To take into account the limitation of MS POWER at 30dBm in UL in the inner zone.
Averaging Windows : A_LEV_HO for AV_RXLEV_UL_HO , AV_RXLEV_DL_HO
A_PBGT_HO(n) for AV_RXLEV_NCELL_BIS(n)
If less measurements done than the averaging windows, the averaging is done on the available measurements (no filling up with "-110dBm"). It allows a fast decision (the MS is not in the queue ! The call setup shall be performed as quickly as possible)
What are the possible outgoing handovers from the inner zone ? Emergency ? Better conditions ?
Only 2 parameters have an influence EN_BI-BAND_MS(n) EN_MULTIBAND_PBGT_HO(0)
innerouter
GSM900
DCS1800
serving cell innerouter
YESYES
EN_MULTIBAND_PBGT_HO : Enable/disable the power budget handovers Cause 12 and the traffic handovers Cause 23 between cells belonging to different frequency bands
Recommended value: Enable
EN_BI-BAND_MS(n) : Enables/disables the incoming handovers of bi-band MSs from the preferred-band into a classical band cell, in cause 14 and cause 24
Recommended value: Enable
From inner zone of a multiband cell, if both parameters are set to enable, all outgoing HO's are possible
If EN_MULTIBAND_PBGT_HO = Disable, cause 12 only possible to other multiband concentric cells (very restrictive !)
If EN_BI-BAND_MS(n) = Disable, cause 14 and cause 24 only possible towards cells with same frequency band asthe inner zone (i.e. DCS1800 cells)
If the MS in inner zone of a concentric cell, the PBGT equation is modified :
PBGT(n) = AV_RXLEV_NCELL(n) - AV_RXLEV_PBGT_HO
- (BS_TXPWR_MAX_INNER – AV_BS_TXPWR_HO)
- (MS_TXPWR_MAX(n) – MS_TXPWR_MAX_INNER)
- PING_PONG_MARGIN(n, call_ref)
PBGT(n) = AV_RXLEV_NCELL(n) - AV_RXLEV_PBGT_HO
- (BS_TXPWR_MAX_INNER – AV_BS_TXPWR_HO)
- (MS_TXPWR_MAX(n) – MS_TXPWR_MAX_INNER)
- PING_PONG_MARGIN(n, call_ref)
9001800 900 1800Cell 1 Cell 2
RxLev on TCH = -79dBm RxLev of BCCH = -70dBm
The parameter HO_MARGIN(cell 1, cell 2) is set to 5 dB
If RxLev(cell 2) = -70 dBm, PBGT(cell 2) = +6 dB
Cause 12 is triggered, the MS is sent in the outer zone of cell 2, with RxLev(cell 2) = -70 dBm.Let's assume that the "outerinner" HO is triggered: the MS enters the inner zone of cell 2.
The received level of cell 1 is NOT -79 dBm (this was the level of the inner TCH).
Field results show that a 900 BCCH will be received roughly at -79+10=-69 dBm.
The received level of cell 2 is NOT -70dBm (that was the RXLEV of the outer zone). In the inner zone, the RXLEV = -70dBm – 10dBm = -80dBm.
PBGT(cell 1) = (-69+80)-3 = +8dB PBGT HO is triggered from cell 2 to cell 1!!
In fact, cause 12 HO cell 1 cell 2 should NOT have been triggered in the first place.
A solution is to be found in tuning OFFSET_HO_MARGIN_INNER used in cause 12 equation. See next slide.
What is happening in this situation ? How to fix the problem ?
HO_MARGIN(1,2) = 5dB and HO_MARGIN(2,1) = 5dB OFFSET_HO_MARGIN_INNER= 0dB Inner zone entry threshold DL = -70dBm
9001800 900 1800Cell 1Serving
Cell 2Target
RxLev on TCH = -75 dBm RxLev of BCCH = -66 dBm
10 minutes
Inner zone entry threshold DL is a combination of 2 parameters :
RXLEV_DL_ZONE + ZONE_HO_HYST_DL
(cf. § HO cause 13)
To fix the problem : find the OFFSET_HO_MARGIN_INNER that would lead to leave the inner zone only for a neighbour that is 5dB greater than the outer zone. This tends to reproduce a standard behaviour.
OFFSET_HO_MARGIN_INNER is used to compensate the difference of propagation between inner and outer zones (carrying BCCH)OFFSET_HO_MARGIN_INNER = 0dB [monoband concentric cell]OFFSET_HO_MARGIN_INNER = 7 … 12dB [multiband concentric cell, with
BS_TXPWR_MAX_INNER = 0]
Warning : The OFFSET_HO_MARGIN_INNER is used regardless of the frequency band of the target cell !
In monoband CC cells, it is most of the time compensated by MS_TXPWR_MAX_INNER
If BS_TXPWR_MAX_INNER is reduced compared to BS_TXPWR_MAX, MS_TXPWR_MAX_INNER may be reduced in the same manner. Therefore the PBGT equation is already taken the compensation into account. No need for the OFFSET_HO_MARGIN_INNER.
Is an incoming handover directly to the inner zone possible ? Emergency ? Better conditions ?
innerouter
GSM900
DCS1800
target cellinner
outer
YESYES
EN_MULTIBAND_PBGT_HO : Enable/disable the power budget handovers Cause 12 and the traffic handovers Cause 23 between cells belonging to different frequency bands
EN_BI-BAND_MS(n) : Enables/disables the incoming handovers of bi-band MSs from the preferred-band into a classical band cell, in cause 14 and cause 24
Towards inner zone of a multiband cell, if both parameters are set to enable, all incoming HO's are possible
If EN_MULTIBAND_PBGT_HO = Disable, cause 12 only possible from other multiband concentric cells or from cells with same BCCH freq band as the MB cell (i.e. GSM900)
If EN_BI-BAND_MS(n) = Disable, cause 14 and cause 24 only possible from cells with different BCCH freq band as the MB cell (i.e. DCS1800)
Interference: Causes 15 & 16 MS in the inner zone, all TRX's are candidate MS in the outer zone, only outer TRX's are candidate Note: the serving TRX can never be a candidate
For other intracell handovers, the MS will stay in the same zone as before (TFO, AMR, return to CS zone)
Multiband cell secured TCH assignment [B8 MR7] Subsequent TCH allocation in outer zone, if previous attempt in the inner
zone failed Improved CSSR (TCH assignment failure due to radio is reduced)
EN_LOAD_OUTER ENABLE [default]: all load computations (short, medium and long terms) are
based on the outer zone load only DISABLE: all load computations are based on the overall amount of timeslots
(inner + outer) Default: Enable, in order to compute the correct load for (E)GPRS PDCH
allocation
Subsequent allocation of outer TCH is failure during assignment of an inner zone TCH :
RTCH_assign_fail_radio = MC746b 1/ incremented when a failure in inner zone isfollowed by subsequent failure in outer zone2/ not incremented when failure in inner zone is followed by success in outer zone
An important parameter to be tuned in a multi-band cell is OFFSET_HO_MARGIN_INNER Takes into account the propagation difference between 900 and 1800 Proposed values between 7dB to 12dB
Using all available optimization tools (RNO, drive-tests, traces, …), propose a method for tuning accurately this parameter
As soon as an intercell HO alarm has been detected
HO Detection sends to Candidate Cell Evaluation the list of potential candidates (it depends on type of handover cause)
the HO cause value
the preferred layer for the target cell indicated by the variable PREF_LAYER (it depends on the cell network architecture and on the operator strategy)
10 Candidate Cell Evaluation
From HO Detection to Candidate Cell Evaluation
CandidateCell
Evaluation
Handover
Detection
Raw cell list
cell 1: cause C1cell 2: cause C2cell 3: cause C3…
Max 32 cells
PREF_LAYER
BSCBSC
For intracell handovers, the only target cell is the serving cell the raw cell list and the candidate cell evaluation processes are skipped.
Priority (0, n) = 0Cell 2: cause C2Cell 3: cause C2Cell 4: cause C2
Priority (0, n) = 1Cell 1: cause C2
Priority (0, n) = 2Priority (0, n) = 3
Cell 5: cause C2Cell 6: cause C2Cell 7: cause C2Cell 8: cause C2
Priority (0, n) = 4Priority (0, n) = 5
Raw cell list
Cell 1: cause C2Cell 2: cause C2Cell 3: cause C2Cell 4: cause C2Cell 5: cause C2Cell 6: cause C2Cell 7: cause C2Cell 8: cause C2... max 32 cells
The HO candidate evaluation process is run after all intercell handover alarms.
In case of intra-cell handover alarm (HO causes 10, 11, 13, 15, 16), the candidate cell evaluation process is skipped: the target cell is the serving cell.
The handover detection gives as indication the raw cell list (built from the book-keeping list) and the preferred layer for the handover.In case of emergency handover alarms or cause 20 alarm, the cell evaluation will order the cells given in the raw list, putting in the first position the cells belonging to the preferred layer, having the highest priority (if EN_PRIORITY_ORDERING=ENABLED) and/or having the same frequency band type as the serving cell. In case of an intercell handover alarm, if the serving cell belongs to the raw cell list (emergency handover from the DCS 1800 inner zone of a multi-band cell), this cell is put at the end of the candidate cell list with the MS zone indication OUTER.
In case of better condition handover alarms (except cause 20), the cell evaluation will order the cells given in the raw list, putting in the first position the cells belonging to the preferred layer and having the highest priority (if EN_PRIORITY_ORDERING=ENABLED).
PBGT filtering [B5 onwards] Enabled with EN_PBGT_FILTERING For Emergency HO and Fast Traffic HO only Filter out cells from the target list that do not fulfill:
OFFSET_HO_MARGIN_INNER is only applied when the MS is in the inner zone of a concentric or multi band cell
The average window is A_PBGT_HO
PBGT(n) > HO_MARGIN_QUAL (0,n) for causes 2, 4, 7or PBGT(n) > HO_MARGIN_LEV (0,n) for causes 3, 5, 17, 18, 28or PBGT(n) > HO_MARGIN_DIST (0,n) for cause 6
PBGT(n) > HO_MARGIN_QUAL (0,n) for causes 2, 4, 7or PBGT(n) > HO_MARGIN_LEV (0,n) for causes 3, 5, 17, 18, 28or PBGT(n) > HO_MARGIN_DIST (0,n) for cause 6
HO_MARGIN_xx, with xx = LEV, DIST or QUAL accordingly to the HO Cause.
OFFSET_HO_MARGIN_INNER is not applied to the serving cell when it is in the target cell list.
Note: the average window used for this process is A_PBGT_HO (even for emergency handovers, where handover alarm could have been raised through A_LEV_HO or A_QUAL_HO samples).
Beware: HO_MARGIN is used for handover detection (cause 12 or 23), HO_MARGIN_xx are used for candidate cell evaluation.
Let us see three examples:
If HO_MARGIN_xx = 5 dB, risk that no target cell is found !
In that case, when an emergency handover is triggered (level, quality, distance, etc.), all neighboring cells are filtered regarding their PBGT compared to 5 dB! By the way, if a cell that is not greater than the serving one + 5 dB will be filtered out: this handover, detected as an emergency case, is in fact a better cell one.
If HO_MARGIN_xx = -30 dB, risk of ping-pong emergency handovers
For example, all cells have L_RXLEV_DL_H = -97dBm. If Lev(cell1)=-98dBm, HO can be triggered to cell2 with level -99dBm (-99>-98-30), and then, as -99<-97, HO is triggered back to cell1: ping-pong of emergency HO.
HO_MARGIN_xx can be used to simulate PBGT HO (for example, usage of distance HO to simulate 900-1800 PBGT HO before it was existing).
HO_MARGIN_DIST is very small (e.g., 2 on 1800). Thus, a Distance HO alarm is raised very early. If HO_MARGIN_DIST (1800,900)= 8 dB, no HO will be in fact triggered before the level of the 900 neighboring cell is greater than the one of
1800 + 8 dB: this distance HO is in fact a PBGT HO between bands.
CELL_EV = ORDER For all HO causes, candidate "n" is ranked among others according to
the best ORDER:
If EN_LOAD_ORDER = ENABLED and cell n is internal to the BSC
LINK_FACTOR(0,n) is an operator parameter to give a bonus/penalty to a cell FREEfactor(0) and FREEfactor(n) are a bonus/penalty based on the absolute load
of the cell
If EN_LOAD_ORDER = DISABLED or cell n is external to the BSC
Two types of cell evaluation algorithms can be used: ORDER and GRADE.ORDER and GRADE are two different methods of cell ranking. They both consist in giving a mark or ’figure of merit’ to each candidate cell.The basic differences between ORDER and GRADE are that: with ORDER:
The candidate cell evaluation process interacts with the handover detection by use of cause dependent handover margins.
The candidate cell evaluation process takes into account the number of free TCH in the candidate cells. with GRADE,:
The candidate cell evaluation process does not interact with the handover detection. The candidate cell evaluation process takes into account the relative load of traffic channels in the
candidate cells.The type of cell evaluation is chosen by the operator on a (serving) cell basis and is provided to the BSC with the parameter CELL_EV
HO_MARGIN_XX = HO_MARGIN in case of better cell HO causes, otherwise HO_MARGIN_xx, with xx = LEV, DIST or QUAL accordingly to the HO Cause.
For any handover cause, the first cell in the list is taken as the target cell, i.e. the cell with the highest value of ORDER(n). The cells do not need to fulfil any other condition.If no cell fulfils the condition and the serving cell does not belong to the target cell list, the target cell list is empty and no further action is carried out.
Note: the A_PBGT_HO average window is used for this process.
LINKfactor(0,n) is a parameter set by OMC command for each cell(n).
LINKfactor(n1,n2) allows the operator to handicap or to favor the cell n1 with respect to its neighboring cell n2. In particular, it can be used to disadvantage an external cell when an internal cell is also a possible candidate.
For any handover cause the first cell in the list is taken as the target cell, i.e. the cell with the highest value of GRADE(n). If no cell fulfils the condition and the serving cell does not belong to the target cell list, the target cell list is empty and no further action is carried out.
Note: the A_PBGT_HO average window is used for this process.
Note: an example summarizing all steps of candidate cell evaluation, in case of a multi-band network, can be given here: MS on a 1800 cell, 3 possible neighboring cells (1*900 + 2*1800). P(1800,900)=1 and P(1800,1800)=0. All HO_MARGIN_xx = 0 dB. PBGT:
PBGT (900) = +5 (second cell seen in the book-keeping list)
PBGT (1800_1) = -2 (first cell seen in the book-keeping list)
PBGT (1800_2) = +2 (third cell seen in the book-keeping list)
Pre-ranking using PREF_LAYER, PRIORITY(0,n), frequency band
Filtering process AV_RXLEV_NCELL_DR(n) > RXLEVmin(n) + max(0,MS_TXPWR_MAX(n) - P)
Number of free TCHs t(n) > FREElevel_DR(n)
The remaining cells are sorted according to their PBGT_DR(n) (averaging window A_PBGT_DR) PBGT_DR(n) = AV_RXLEV_NCELL_DR(n) - AV_RXLEV_PBGT_DR
(BS_TXPWR_MAX - BS_TXPWR)
(MS_TXPWR_MAX(n) - MS_TXPWR_MAX)
For external cells, t(n) is fixed to the arbitrary value t(n) = 255. Therefore, setting FREElevel_DR(n) to 255 for an external cell inhibits outgoing external fast traffic handover towards this cell. Setting FREElevel_DR(n) to anyother value will allow outgoing external fast traffic handover towards this cell.
If the BTS has dual rate capability, t(n) = absolute number of free Dual Rate TCH
In a hierarchical network (umbrella + micro cells) EN_SPEED_DISC is ENABLED A slow moving MS starts a call in lower layer After a while, this MS becomes a fast moving MS (for
example, a car starting at traffic light)
Explain the exact process that will send the MS towards the umbrella layer
Which is the best target cell? Emergency qual ho triggered in serving cell HO_MARGIN_QUAL(0,n) = -2 dB PRORITY(0,n) = 1, LINK_FACTOR(0,n) = 0 dB EN_RESCUE_UM = Enabled
Which is the best target cell? Emergency qual ho triggered in serving cell EN_PBGT_FILTERING=Enable HO_MARGIN_QUAL(0,n)=-2dB CELL_EV=GRADE EN_LOAD_ORDER=Disable LINK_FACTOR(0,n)=0dB RXLEVmin=-100 dBm
Which is the best target cell? Emergency qual ho triggered in serving cell EN_PBGT_FILTERING=Enable HO_MARGIN_QUAL(0,n)=-2dB CELL_EV=GRADE EN_LOAD_ORDER=Disable LINK_FACTOR(0,n)=0dB RXLEVmin=-100 dBm
Which is the best target cell? Emergency qual ho triggered in serving cell EN_PBGT_FILTERING=Enable HO_MARGIN_QUAL(0,n)=-2dB CELL_EV=GRADE EN_LOAD_ORDER=Disable LINK_FACTOR(0,n)=0dB RXLEVmin=-100 dBm OFFSET_HO_MARGIN_INNER = 10 dB
1 Adding a Microcellular Layer 72 Adding Hot Spot Microcell for Traffic 263 Adding Indoor Microcells for Coverage 304 Monitoring QoS in a Multi-Layer Network 32
The principle is to implement antennas below roof level confined propagation and low Tx power interferences avoidedeasier frequency planning
Benefits : Higher network capacity per sq. km The right capacity at the right place (Airport, shoping malls, etc.) Improve the outdoor coverage and the indoor coverage (at street level) Improve the voice quality, thanks to cleaner frequencies
Avoid call drops on microcells Specific emergency HO towards umbrella rescue cells
Avoid unnecessary handovers To ensure good QoS and speech quality Force idle mode in microcells to avoid subsequent capture Fast MSs are kept in the umbrella layer
Choose a handover to push traffic from these cells to the microlayer Cause 24 if all collocated cells and micro cells are all "Single" Cause 14 if collocated cells are Umbrella and micro cells are Micro
The exercise next slide will show the best solution
This setting is highly dependent on MICRO cells density : the more MICRO per sq.km, the higher the CRO can be, without any risk of degrading quality. In very dense network, a CRO(Micro) = 40dB can be set.
On the contrary, if there are only few micro cells per sq.km, then a CRO=10dB might be too high ! Reduce it to CRO=6dB.
The Setting of PRIORITY(0,n) is very important as network behavior will not be driven by Pref_layer which is equal to "none" in this case.But setting L_RXLEV_NCELL_DR(n) to -47 dBm in the micro cells inhibits the incoming FDR to them. Therefore Priority(0,n) can be kept to the same value everywhere.
Priority(umb,micro) is set to 0 for Better Cell purpose (see the next pages).
A microcell surrounded by other microcells in a dense environment
Rule The MS is comfortably installed in the microcell area. Calls have to be
handled by a micro layer, which is a “traffic-catcher” Fast capture HO from the umbrella to micro cell If the MS is already on call in the micro-layer, it must stay on it
Only fast mobiles can perform a PBGT HO to an umbrella cell (with low load)HO_MARGIN(micro, umb) = 5dB
All other parameters not shown here are identical to inner microcells.
A capture towards a microcell is triggered after MIN_DWELL_TIME which will vary from H_MIN_DWELL_TIME down to L_MIN_DWELL_TIME if the umbrella 900 cell is loaded. MIN_DWELL_TIME is increased to prevent tangential MSs from being captured by the border microcell.
Definition An indoor area located within the micro cell area This indoor cell aims at absorbing traffic in a strategic building
Rules Absorb indoor traffic, and only indoor traffic Do not catch outdoor MS (Idle or Dedicated) An MS nearby the building door but still outside should camp on the outdoor
cell Beware of "indoor" exit strategy Beware of jamming at higher floor
Indoor Microcell
Another type of indoor microcell can be defined:
Indoor microcell for coverage, when the indoor cell is a hotspot and the indoor coverage from the macro layer is not good. This chapter does not deal with this case. See the next slides for detailed parameter settings of indoor microcell for coverage.
In high floors, the level from surrounding umbrella cells is very high More than 6 cells might be measured at -47dBm (maximum measured value) How can we ensure the indoor cell is included in the chosen 6 ?
One solution Dedicate one cell to cover these floors Set a high CRO (8dB … 12dB) : the C2 is not limited Define many incoming adjacencies but just few selected outgoing
adjacencies Use SFH with broad band to avoid interferences
A high threshold HO is used to trigger HO towards the umbrella cell for the microlayer zone exit.
Definition A microcell totally isolated from any other microcell
Rules Capture shall occur only if the MS is not moving There are no neighbour from the same layerNo better cell handover can be trigerredAn emergency HO shall be used as an exit strategy
QoS indicators in each layer Create a cell zone for each cell type : Umbrella, Mini, Micro, Indoor, Single Perform your QoS Monitoring per cell zone
Goal 1 : Traffic split RTCH_Load_BH (TCTRBHR) in lower layers above 80% RTCH_Load_BH in upper layers below congestion RTCH_duration_avg (TCTRMHT) should be long in lower layers (> 20s) …and might be shorter in umbrellas, because of cause 14 (Min Dwell Time)
Goal 2 : Quality of Service Main KPI's shall be better or identical in lower than in upper TCH Drop Rate, CSSR, SDCCH Congestion rate HO Incoming & Outgoing efficiency rates Handover causes split should reflect your parameter settings
DL Level HO (5) as exit strategy for hotspot/border cells Capture HO (14) shall be the main cause of HO for Umbrellas
RTCH Duration Average is related to the HO/Call indicator. But it gives a better physical sense of possible ping pong handovers.
Goal 3: Simplicity of parameter settings Apply the same settings within each cell type Find the best "overall" settings in order to obtain the best results (regarding
goal 1, goal 2 or both) Once this is achieved, fine tune problematic cells only
Additional investigation : Forced Directed Retry With good settings, FDR should not occur too much But if it does, ensure it is working correctly
DR_Out_success_rate (DRORSUR) in lower layers DR_Inc_internal_success_rate (DRIBSUR) in upper layers
Specific indicators : Traffic flows HO per couple of cells (PMC type 180) In case of problem, use ODMC type 26 and 27 for detailed incoming and
1 Adding a Microcellular Layer for Traffic and Coverage Increase 72 Adding Hot Spot Microcell for Traffic 263 Adding Indoor Microcells for Coverage 304 Monitoring QoS in a Multi-Layer Network 32
1 Adding a Microcellular Layer for Traffic and Coverage Increase
Strategies
Several cases should be considered in order to cover all the possibilities What is the current architecture prior to the introduction of the new band ?
1. Monolayer2. Multilayer
What is the planned architecture after the introduction of the new band ?1. Monolayer : the new band is located in the current layer2. Multilayer : the new band is located within an existing layer3. Multilayer : the new band is located within a dedicated layer
In order to save cost, the new cells will be collocated with the existing cells1. Dual-BCCH ? (two different cells)2. Single-BCCH ? (multiband concentric cells)
Colocate the new band with :1. Existing single cells (monolayer)2. Existing umbrella cells
Existing micro cells in classical band
3. Existing mini cells Existing umbrella cells in classical band
Implement the new band in a new layer1. New micro layer (for hotspot coverage)
refer to previous chapter "Adding a Microcellular Layer"
2. New mini layer (for continuous coverage) this solution is not practical: macro cells in the new band are always colocated with
existing cells
3. New umbrella layer (for extension of coverage) this solution is not realistic: umbrella cells are always deployed first in a network
In this course, we focus only on realistic solutions which are chosen by all operators : the new band is never deployed in a country without colocation with existing cells.
If the network is monolayer, there is no difference between Singles and Umbrellas.
The only difference will appear if introduction of microcells in the future :1. For Umbrellas, the cause 14 is available to push traffic to microlayer2. For Single, the cause 24 (General Capture Handover) must be enabled
In a case study, we will see the differences between the two solutions.
Futureproof solution: set all your cells as "Umbrella"
For dual-BCCH cells, use "Preferred band HO" (cause 21)
CELL_RESELECT_OFFSET(B) > CELL_RESELECT_OFFSET(A)
Cell B
Cell A
cause 21
cause 5
CRO(B)
CRO(A)
CAUSE 21: Entry HO, based on DL RxLev of cell BL_RXLEV_CPT_HO(A,B)MS_TXPWR_MAX(B)MULTIBAND_TRAFFIC_CONDITION(A)HIGH_TRAFFIC_LOAD(B)EN_PREFERRED_BAND_HO(A)T_INHIBIT_CPT(B)
CAUSE 5: Exit HO, based on DL RxLev of cell BL_RXQUAL_DL_H(B)L_RXLEV_DL_H(B)EN_RXLEV_DL(B)
3 Colocate the new cells in upper layer of a multilayer network
Single-BCCH strategy
As seen earlier, it is simpler to use single-BCCH In the OMC-R, create your collocated cells as "Concentric"
Choose a handover to push traffic from these cells to the microlayer Cause 24 if collocated cells and micro cells are all "Single" Cause 14 if collocated cells are "Umbrella" and micro cells are "Micro"
The choice has been done previously: The best solution is "cause 14" in order to take into account fast moving
mobiles.
This strategy was fully studied in "Adding a Microcellular Layer""
: top choice: second choice: third choice: last choice
Directed Retry shall always be enabled : it will act as a standard HO (better cell or emergency, depending on the trigger cause). Refer to previous slides (EM HO and BC HO). The possible DR are not represented by arrows on this slide, because it can work from any cell towards any cell.
Fast Traffic HO shall be enabled in microcells : an upper layer might not be available to each user, so the FDR might not work (esp. in case of indoor situation). In order to have a higher probability of F.T.H, it is necessary to lower the HO MARGIN LEV(micro, umbrella).
The more this value is reduced, the higher the efficiency of F.T.H.
Priority(1800, colocated 900) is one more time very useful here. Since the colocated 900 is fully overlapping the 1800, there is absolutely no degradation of quality whether the call is on the umbrella 900 or umbrella 1800.
: top choice: second choice: third choice: last choice
Priority(0,n) is used to favour emergency HO from 1800 umbrella towards its colocated 900 umbrella. This is useful also for Forced Directed Retry.
It migh be complex to define priority(1800, colocated 900) = 1 and priority(1800, other 900) = 0. However, by using NPO, it is possible to customize adjacency types to take into account this specificity. Then, by using a NPO Tuning Session, the tuning is very straight forward.
HO MARGIN LEV and HO MARGIN DIST shall be set above 0dB, in order to avoid emergency HO ping pong (which might be rare in a city anyway). Def value = 2dB.
HO MARGIN QUAL is different. If there is a quality issue in the 900 (since the 900 frequency band is more interfered, this situation is probable), the colocated 1800 must be a possible candidate. But don't forget that the colocated 1800 is 10dB lower than the 900 : the HO MARGIN QUAL should not filter out this cell.
So a HO MARGIN QUAL = -12dB is chosen.
HO MARGIN QUAL(umb 900, coloc 1800) = -12dB
HO MARGIN QUAL(umb 900, other 1800) = -2dB
HO MARGIN QUAL(umb 900, umb 900) = -2dB
HO MARGIN QUAL(umb 1800, umb *) = -2dB
HO MARGIN QUAL(umb *, μ)= -2dB
Micro :
The Umbrellas 900 & 1800 are a rescue for a micro. If there is a quality/interference problem in a micro, the RxLev(Micro) may be very high. Therefore we need to put a very low HO MARGIN QUAL, in order to accept a target cell with a lower RxLev than the micro.
The HO MARGIN LEV is set to -5dB, in order to give Fast Traffic HO a higher chance of happening (refer to previous slide)
4 Colocate the new cells in lower layer of a multilayer network
Single-BCCH vs. Dual-BCCH
Assumptions: New cells are colocated with classical Mini cells Umbrella cells are in the classical band
The easiest solution is to create Concentric Multiband Mini cells Refer to "Create a multilayer network" The new band is "transparent", it does not impact algorithms other than
intra-zone handovers (causes 10, 11, 13)
In this chapter, the dual-BCCH solution is studied
() In order to activate FDR towards MINI 900, if Umbrella are full and Mini 1800 are still congested, it is simple :
Gradually decrease the value of L_RxLev_Ncell_DR(Mini 900) from -60dBm to -80dBm, until a significant decrease of the congestion in MINI1800 occur.
HO MARGIN LEV(mini, umb)=-5dB : in order to increase the probability to perform a fast traffic HO. To increase the probability, decrease to -10dB, and so on.
Umbrella will unload with cause 14, with a dwell time of 6 seconds.
We need to favour direct HO from umbrella to mini 1800, rather than doing Umbrella Mini 900 Mini 1800.
The Mini 900 is received 10 dB greater than the Mini 1800. So by default, with" cause 14" candidate cell evaluation, the Mini 900 will have a better ORDER than the Mini 1800 (the PBGT(900) is 7dB greater than PBGT(1800))
To reverse this situation, we need to favour the Mini 1800, either with :
1) priority(umb, mini 1800) = 0 or
2) with link_factor(umb, 1800) = +12dB (so ORDER(1800) are 5dB greater than ORDER(900))
This solution is closer to what we want : the mini cells offer a good coverage. If no mini cells are available, it is not a problem : the umbrella can still be a valid target cell.
Special attention must be paid to PBGT Filtering : Mini cells can be filtered out, but Umbrellas should stay in the list.
Remark : Priority(0,n) = 1, for all adjacencies.
Regarding the possibility to use priority(umb, mini1800) = 0 (cf. "Better conditions HO" in this chapter) : it will impact the EM HO from umbrella. The end result will be :
EM HO from umbrella other umbrella > mini 1800 > mini 900.
The link factor is therefore a better choice, so far.
Quality HO in an umbrella : As the mini 1800 is seen 10dB lower than the mini 900, there is a risk the mini 1800 will be filtered out during PBGT filtering.
Quality HO in a mini 900 : If no other Mini 900 is around with less than -2dB difference, then the next choice will be a mini 1800. In order to keep the mini 1800 colocated in the list, it is necessary to reduce the HO MARGIN QUAL(mini900, coloc1800) below -10dB.
Ho_Margin_Lev(mini,umb) = -5dB For Fast Traffic HO
Link_Factor(umb, mini1800) = +12dB For better condition HO : cause 14 towards Mini 1800 rather than towards Mini 900.
Create a cell zone for each cell type & band Umbrella 900 Mini 900 Micro 900 Indoor 900
Perform your QoS Monitoring per cell zone Goal 1: Intelligent traffic split Goal 2: Balanced QoS between different layers and bands Goal 3: Globalized settings
Special attention to: HO/Call and RTCH Duration Avg in intermediate layer
Too many incoming HO from top layer (probably due to capture) Too many outgoing HO CPT (towards bottom layer) Action 1: L_RxLev_Cpt_Ho(top, intermediate) = -80dBm -70dBm Action 2: Cell_Reselect_Offset(bottom) = 8dB 12dB
capture
capture
TOP
INTERMEDIATE
BOTTOM
capture
Intermediate layer :
1. Umbrella 1800 in case of Umbrella 900 / Umbrella 1800 / Micro
2. Mini 900 in case of Umbrella 900 / Mini 900 / Mini 1800
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Table of Contents
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1 Radar Cell 72 Symmetric Microcells at a Street Corner 93 Asymmetric Microcells at a Street Corner 114 Indoor Microcell within a Monolayer Network 135 Trilayer Network: Indoor Cell within a Multi-Layer Network 156 Indoor Cell Congestion 177 Transforming a Microcell into an Indoor Cell 198 Picocells in Skyscrapers 21
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2 Symmetric Micorcells at a Street Corner
Exercise
An indoor microcell is introduced within a monolayer network, for a new coverage Define relevant parameter settings to obtain good QoS in the microcell layer
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5 Trilayer Network: Indoor Microcell withing a Multi-Layer Network
Exercise
An indoor microcell is introduced within a multi-layer network (macro + micro cells), for capacity & coverage increase So called « trilayer » network Define parameter settings for both idle and connected mode
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6 Indoor Cell Congestion
Exercise
An indoor microcell has been introduced within a multi-layer network (macro + micro), based on the previous exercise recommendations
When an indoor microcell is congested, the FDR may not be working as some MSs can be covered only by this cell Define parameter settings to find a good solution in case of indoor cell
GSMBSS B11 Multilayer and Multiband GSM Network Radio Optimization
Multiband-Multilayer Optimization · Case Studies 1 · 5 · 22
8 Picocells in Skyscrapers
Exercise
Skyscrapers may need several picocells to achieve a sufficient coverage while avoiding interference (sufficient received level from the serving cell Define parameters settings to deal with this configuration
Long term measurement of the load of a cell corresponds to function Traffic_load(cell) Traffic_load() value is determined from a number N_TRAFFIC_LOAD of
consecutive non-sliding window load averages AV_TRAFFIC_LOAD calculated from Nb free TCH samples updated every A_TRAFFIC_LOAD x TCH_INFO_PERIOD s
3 possible values for Traffic_load(): high, low, indefinite initialization: Traffic_load() = indefinite Traffic_load() becomes : corresponds to function Traffic_load(cell) high if the last N_TRAFFIC_LOAD consecutive AV_TRAFFIC_LOAD load
averages are all greater than the HIGH_TRAFFIC_LOAD threshold low if the last N_TRAFFIC_LOAD consecutive AV_TRAFFIC_LOAD load
averages are all lower than the LOW_TRAFFIC_LOAD threshold
Freq BCCH OUTER <> Freq BCCH INNER MS reports measurements on both
cells for the handover algorithms BSICINNER = BSICOUTER
INNER cell can decode the RACH received on OUTER BCCH frequency
INNER cell always BARRED MS always camps on OUTER cell OUTER cellINNER cell
At the border of the two cells, an overlapping area allows to provide a continuous coverage. When the MS moves from one cell to the other, a handover is triggered in the overlap zone. Two BCCH channels are needed (one for the inner cell, one for the outer cell), so that the MS reports measurements on both cells for the handover algorithms.
The TRXs of the inner cell and of the outer cell are synchronised, but the reception of the outer cell is delayed by 60bits period to account for the propagation delay.
In the inner cell, the MS can receive the BCCH inner frequency as wells as the outer BCCH frequency. To avoid to manage RACH reception on two different frequencies in the inner cell, the MS is forced to access the inner cell on the outer BCCH frequency. For this purpose, the RACH reception (BCCH TRX) of the inner cell is tuned to the outer BCCH frequency, and the inner cell is barred1. So on time slot 0 of the inner cell, transmission is done on the inner cell BCCH frequency, and reception is done on outer BCCH frequency.
The chosen implementation allows to make use of all timeslots2 of the TDMA frame and to use the combined configuration for the CCCH channel.
Radio Link Establishment - MS Located in the Outer Cell Area
The inner cell is always barred, so the MS cannot camp on the inner cell, even if located in the inner cell range. In the whole extended cell coverage, the MS has a good reception of the outer cell BCCH, so the MS will always be camping in the outer cell, whether in the inner cell or outer cell range.
For this reason, a special radio and link establishment procedure is used to cope with this behaviour .
It consists of receiving the CHANNEL REQUEST messages on outer BCCH frequency, and allocating the SDCCH channel according to the MS estimated position. The IMMEDIATE ASSIGNMENT COMMAND for an SDCCH is sent on the outer cell BCCH frequencies, but the SDCCH may be allocated in either inner or outer cell, depending on the MS position.
(1) The MS camping on the outer cell sends an access burst on the RACH on outer cell BCCH frequency. These bursts will be received successfully in the inner cell by the BCCH TRE. In the outer cell, the access burst arrives too early and cannot be decoded.
(2) The inner cell BCCH TRE sends a CHANNEL REQUIRED message to the BSC containing the random reference sent by the mobile, the TDMA frame number when the message was sent over the air and the measured TOA.
(3) The TCU controlling this TRE allocates an SDCCH subchannel to the transaction in the inner cell and asks the BTS to activate this subchannel.
(4) The BTS activates the requested channel and sends back and acknowledgement, once this is done.
(5) The TCU sends the IMMEDIATE ASSIGNMENT COMMAND (which provides the description of the allocated SDCCH) to the BCCH TRE of the inner cell.
The TCU controlling the inner cell BCCH sends a copy of the message to the TCU handling the BCCH of the outer cell. This is done if and only if the timing advance IE included in the CHANNEL REQUIRED is smaller than 60, thus indicating that the MS is strictly in the inner cell (in order to avoid that the MS receives two Immediate Assignment messages when located in the overlap zone).
The TCU controlling the outer cell BCCH forwards the IMMEDIATE ASSIGNMENT COMMAND to the outer cell BCCH TRE.
(6) The IMMEDIATE ASSIGNMENT message is sent over the air to the MS on the AGCH of the outer cell.
(6') The IMMEDIATE ASSIGNMENT message sent by the inner cell is lost, because the MS listens to the outer cell frequency.
(7) The mobile switches its transceiver to the SDCCH allocated in the inner cell and sends repeatedly an SABM frame to establish the layer 2 connection with the BTS.
(8) The BTS acknowledges the establishment of the LapDm link to the MS with a UA frame sent on the SDCCH allocated to the MS.
Radio Link Establishment - MS Located in the Inner Cell Area
The TCU sends the IMMEDIATE ASSIGNMENT COMMAND (which provides the description of the allocated SDCCH ) to the BCCH TRE of the inner cell.
The TCU controlling the inner cell BCCH sends a copy of the message to the TCU handling the BCCH of the outer cell. This is done if and only if the timing advance IE included in the CHANNEL REQUIRED is smaller than 60, thus indicating that the MS is strictly in the inner cell (in order to avoid that the MS receives two Immediate Assignment messages when located in the overlap zone).
The TCU controlling the outer cell BCCH forwards the IMMEDIATE ASSIGNMENT COMMAND to the outer cell BCCH TRE.
(1) The MS in the outer cell sends an access burst on the RACH of the outer cell. This burst is successfully received by the outer cell BCCH TRE. In the inner cell, the access burst arrives too late to be successfully decoded.
(2) The outer cell BCCH TRE sends a CHANNEL REQUIRED message to the BSC containing the random reference sent by the mobile, the TDMA frame number when the message was sent over the air and the measured TOA.
(3) The TCU controlling this TRE allocates an SDCCH subchannel in the outer cell to the transaction and asks the BTS to activate this subchannel.
(4) The BTS activates the requested channel and sends back an acknowledgement, once this is done.
(5) The TCU then sends the description of the channel in the IMMEDIATE ASSIGNMENT COMMAND to the outer cell BCCH TRE.
(6) The IMMEDIATE ASSIGNMENT message is sent over the air to the MS on the AGCH of the outer cell.
(7) The mobile switches its transceiver to the required channel and sends repeatedly an SABM frame to establish the layer 2 connection with the BTS.
(8) The BTS acknowledges the establishment of the LAPDm link to the MS with a UA frame sent on the SDCCH allocated to the MS.
Radio Link Establishment - MS Located in the Overlap Zone [cont.]
(1a&b) The MS camping on the outer cell sends an access burst on the RACH. This burst is correctly received by the inner cell BCCH TRE and outer cell BCCH TRE.
(2a&b) The inner cell and outer cell BCCH TRE send a CHANNEL REQUIRED message to the BSC containing the random reference sent by the mobile, the TDMA frame number when the message was sent over the air and the measured TOA.
(3a&b) Both TCUs controlling the TREs having BCCH allocate an SDCCH subchannel to the transaction and ask the BTS to activate this subchannel.
(4a&b) The BTS activates the requested channels and sends back an acknowledgement for each, once this is done.
(5b) The TCU controlling the outer cell, sends the IMMEDIATE ASSIGNMENT COMMAND with SDCCH description in the outer cell to the outer cell BCCH TRE.
(5a&c)The TCU controlling the inner cell sends in the IMMEDIATE ASSIGNMENT COMMAND with SDCCH description in the inner cell. Two cases are possible:
Access Delay IE > 59 the inner cell TCU will not send a copy of the IMMEDIATE ASSIGNMENT command to the outer cell TCU. This is the desired behaviour.
Access Delay in [58,59] range, the inner cell TCU sends a copy of the IMMEDIATE ASSIGNMENT command to the outer cell TCU. This is not the desired behaviour (corresponds to inner cell scenario). This is due to the fact that the BSC definition of the overlap zone does not match the exact BTS overlap area (negative values of TOA in the outer cell up to –2, are clipped to 0).
(6b) The IMMEDIATE ASSIGNMENT message describing the SDCCH allocation in outer cell, is sent to the MS on the outer cell BCCH frequency. In most cases this message should be received by the MS (except if 6c is received first)
(6a) The IMMEDIATE ASSIGNMENT message describing the SDCCH allocation in inner cell is lost on the inner cell air interface, because the MS does not listen to that frequency. The unused SDCCH will be released by the BSC when the supervising timer expires6.
(6c) Access Delay in [58,59] range: The IMMEDIATE ASSIGNMENT message describing the SDCCH allocation in inner cell is sent on the BCCH frequency of the outer cell. In most cases, the MS should have received message (6b) before and has already switched to the SDCCH in the outer cell, and so this message is lost. It is however possible, in case the message (6b) is delayed in the inner cell, that the message (6c) is received earlier by the MS. In this case establishment will occur on the SDCCH allocated in the inner cell (not drawn).
(7b) The mobile receives the IMMEDIATE ASSIGNEMENT describing the SDCCH allocation in outer cell on the BCCH outer cell frequency. It then switches to the designated channel and sends repeatedly an SABM frame to establish the layer 2 connection with the BTS in the outer cell. If the message (6c) is received before (6b), then the establishment will occur in the inner cell.
(8b) The BTS acknowledges the establishment of the LapDm link to the MS with a UA frame sent on the SDCCH allocated to the MS.
(9) The unused SDCCH is released in the inner cell (double SDCCH allocation). If message 6c arrives first, then the unused SDCCH release will occur in the outer cell.
In the extended cell , the handover procedure is purely controlled by settings of the handover detection parameters. Two special causes allow handover from the inner cell to the outer cell and handover from the outer cell to the inner cell. There is no change in the BSC handover algorithm either for handover preparation or execution.
From the inner cell to the outer cell , the handover alarm is only triggered by the handover cause “too long MS-BS distance”. When this cause is triggered the extended outer cell is always a candidate cell.
However the operator setting of the handover parameters must insure that this cause is only triggered when the distance from the serving inner cell BTS is greater than the limit of the overlap zone (TA > 62) by setting U_TIME_ADVANCE to 62.
In order to avoid the extended outer cell to be filtered by the filtering process the flag EN_PBGT_FILTERINGmust be set to DISABLE.
The candidate cell evaluation process is recommended to be the GRADE mode.
Cause 22 is only checked if Cell_range(serving) = extended_outer
In the same way, from the outer cell to the inner cell , the handover alarm is only triggered by the handover cause “too short MS-BS distance”. When this cause is triggered the extended inner cell is always a candidate cell.
However the operator setting of the handover parameters must insure that this cause is only triggered when the timing advance applied by the mobile reaches 0, this is achieved by setting L_TIME_ADVANCE to 0.
In order to avoid the extended inner cell to be filtered by the filtering process the flag EN_PBGT_FILTERINGmust be set to DISABLE.
The candidate cell evaluation process is recommended to be the GRADE mode.
Handover - From the INNER Cell to the OUTER Cell toward Another Cell
All the standard HO causes can be used Emergency HO causes 2, 3, 4, 5 Better condition HO causes 12, 23, 24
The OUTER or INNER cell is always present in the Candidate CellEvaluation
The setting of the handover parameter does not prevent any handover cause to trigger an alarm for a handover towards a third cell.
It is possible to use exactly the same rules and parameters for handover towards a third cell as in the macro cellular normal cases.
The synchronous handover does not work between the inner and the outer cell.
In order to avoid call terminations due to directed retry into the inner or outer cell with an incorrect distance range it is recommended to disable the forced directed retry towards the inner and the outer cell. For this purpose, the parameter FREELEVEL_DR(n) is set to the maximum value (255) for the inner and the outer cell.
Activation of the PS service in an Extended cell No specific parameter is foreseen Same procedure as the one used for standard cell is applied
TRX_PREF_MARK = 0
If used, PS must be activated in both INNER and OUTER cell
Reselection Because the INNER cell is barred
this cell should must not be declared in the neighbor cells reselection adjacencies NC2 is not allowed NACC and (P)SI STATUS are not allowed The INNER cell and OUTER cell must belong
to the same location area
The Master channel is not allowed in both INNER and OUTER cell
Packet access procedure Same principle as in CS, since it’s performed on CCCH only The MS always performs its access on the RACH of the outer BCCH frequency The BTS provides the BSC with the initial TA Depending on the TA value, the BSC chooses the suitable cell (INNER or
OUTER) In UL, whatever the multislot class of the MS, only one PDCH is allocated
Its right or left TS can not be allocated neither for PS nor for CS (see comment) This TS is considered as a restricted TS by the MSF The same constraint is applied in DL for the TS carrying the PACCH
UL
Restricted
Allocated
Restricted
Allocated
INNEROUTER
When a MS passes from inner/outer cell to outer/inner cell, the TA estimated by the BTS stalls progressively. So the MS is not able to apply the suitable correction of its TA for its uplink transfer (data and/or signaling). This leads progressively to the impossibility for the BTS to decode the uplink radio blocks because they shift out of their allocated RTS.
For a given MS, its uplink radio blocks progressively come out of its allocated RTS and jams the neighbor RTS.
It jams the right RTS when the MS moves from inner to outer cell. This right RTS can also be the RTS0 of the next TDMA frame if the RTS7 is allocated to a TBF.
It jams the left RTS when the MS moves from outer to inner cell. This left RTS can also be the TS7 of the previous TDMA frame if the RTS0 is allocated to a TBF.
If the neighboring RTS is dedicated to other MS for PS or CS call, this jam causes interferences on these RTS and the BTS can not decode the radio blocks of those MS leading to the drop of these calls.
This drawback only occurs for the uplink direction. The downlink direction does not raise any problem.
To overcome this drawback, some radio resource allocation constraints are to be applied:
An UL TBF is only allocated on one RTS.
On BCCH or non BCCH inner TRX,
A RTS is allocable to a UL TBF if its right RTS is allocated for PS traffic to the MFS, and is not used by a UL TBF.
When a RTS is allocated, its right RTS cannot be allocated to PS call.
On BCCH or non BCCH outer TRX,
A RTS is allocable to a UL TBF if its left RTS is allocated for PS traffic to the MFS, and is not used by a UL TBF.
When a RTS is allocated, its left RTS cannot be allocated to PS call.
NETWORK_CONTROL_ORDER = NC0 EN_NACC = Disable EN_PSI_STATUS = Disable NB_TS_MPDCH= Disable MAX_PDCH, MAX_PDCH_HIGH_LOAD and MIN_PDCH must be set to
even values (see comments) EN_STREAMING = Disable
As in UL TBF allocation, the MFS uses at least 2 TS (a “restricted” one and the one allocated in UL) the number of PDCH allocable in the extended cells (MAX_PDCH, MIN_PDCH, MAX_PDCH_HIGH_LOAD ) must be even.