LMDS

© Cirta Consulting LLC 1999-2003

LMDS RF Engineering

Cirta Consulting LLC

© Cirta Consulting LLC 1999-2003 2

1. LMDS : General Topics


1. 1. Definition of LMDSLMDS = Local Multipoint Distribution Service

Local : The Coverage is restricted to a limited short range, say 8 km maximumMultipoint : The service starts from a Transmitting point to different Points (Customers). The return path is, however, Point-to-Point.Distribution : Refers to the simultaneous distribution of signals (Voice, Internet, video, etc.)Service : The Relationship between the Subscriber and theOperator is based upon Service.


1. 2. History of LMDS and FrequencyAllotments Worldwide and in EuropeCoast-to-Coast Telephony in the 1970‘s

Broadband Systems in the Ku-Band

Cost shared between customers

First European LMDS Trial in Madrid : http://www.cableaml.com/madridtrialsystem.html



1. 3. Regulatory Issues and StandardsATM ForumDAVICETSI (European Telecommunication Standards Institute)

ITU (International Telecommunication Union)

The Majority of them use ATM Cells as thePrimary Transport Mechanism


1. 4. Concept of LMDS (1)Central Office/ Head End connected with fiber backbone tomany Hub base stations.

Central Office contains : Satellite, local content, Internet and Telephone Network Links, plus the O&M Systems.


1.4. Concept of LMDS (2)

Hub to Customers(PMP)

Each Customer to Hub(PP)


1. 5. Advantages of LMDS whenCompeting with Copper

Lower Entry and Deployment CostsEase and Speed of Deployment : Minimal Disruptionto the Community and the Environment.As a Result : Fast Realization and RevenueOperators spend money only when a revenuepaying customer signsNo „Stranded“ capital when customers churnCost-effective Network Maintenance, Management, and Operating Costs.Small, Medium, and Large Business Customers canbe served…(including Residential customers)


1. 6. Major Emerging Actors : Vendors and Operators in Europe

Vendors :Nortel, Alcatel, Ericsson, etc… Operators : FirstMarkCommunications, Star One, Viag Interkom, Formus CommunicationsInc., Teligent, etc.


1.7. Business niches and Market Trends throughLMDS (Internet, Voice, Data, Video, etc.)

New communications service leads to new business opportunitiesInteractive access for wideband dataand voice, as well as videoapplications.Small, medium, or large businessaccess data are possible from 6 to 50 Mbps


1. 8. Offered Services through LMDS

DataMedium businesses, with data needs up to 6 MbpsSmall businesses, require a low-cost data access of fractional E-1 CapacityWork-at-home, a rapidly growing market, needing low-cost access to corporate LANs and data rates to 10 MbpsHigh-speed Internet, a massive market waiting for high-speed access to release powerful and creative new applications (Multimedia, games, etc.)

Telephony (voice)Business and then Residential, integrated voice communications

VideoBroadcast and narrowcast, conferencing and other interactive video services


DS-0 : Digital Service Level 0 is a 64 kbps the worldwide standard speeddigitizing one voice conversation using PCM and Sampling

DS-1 : Digital Service Level 1 is a 1.544 Mbps in North America (T-1) and 2.048 Mbps elswhere (E-1). T-1 is an old Bell System standard. E-1 is an ITU-T standard.

10 Base-T : Ethernet LAN which works on twisted pair wiring. The maximumlength of a 10 Base-T is 100 m running on unshielded twisted pairs

100 Base-T : handle 100 Mbps, B stands for baseband and T stands for Trunk. In short, 100 Base-T is a 100 Mbps LAN by the generic name of Fast Ethernet

1. 8. Offered Services through LMDS


2. LMDS : Technical Description I


2. 1. LMDS System RF MaskBTR Tx and CTR Rx Filters

Frequency (GHz)27.758527.5485

Log

Mag

nitu

de

-62.7 dB

0 dB

-1.04 dB

28.00


2. 1. Exercise on In-band and Out-of-band emissions

Given the LMDS RF Mask as used previously, what amount of power is expected @ 28 GHz if an output power of 25 dBm is used ?

What would be this power @ 27.5485 GHz ?

If we have to use two different frequencies, what is the minimum frequency spacing to ensure a C/I of respectively 15, 20 and 25 dB for example ? (we assume that the same RF Mask characteristics are used as mentioned above)


Description of FDD-based SystemsFDD means Frequency Division DuplexRequire the use of two RF carriers : One for Tx and one for RxIsolation required between Tx-Rx to prevent the Tx from de-sensitizing or damaging the RxFrequency Duplexfilter is typically employed to provide therequired isolationFDD has been used in the commercial market place at microwaveFrequencies since the Early 70‘sAiming at offering :

the flexibility to support blocks of Spectrum that are either non-contiguousor as small as 10 MHz.Ability to operate over the region of 10-40 GHz without significantmodificationSupport for both Symmetrical and Asymmetrical ServicesReduced system complexity, and enhanced frequency reuse and planning



TDD Air Link Frame Structure

Dynamic allocation of bandwidth between up and downlink occurson a single RF carrier with single occupied bandwidth

As a result, frequency re-use is enhanced and planningsignificantly simplified

Example with 1 physical RF channel and 4 logical channels (timeslots)


Description of TDD-based Systems

TDD means Time Division DuplexRequire the use of one RF carrier for full duplex communicationsTx-Rx Isolation occurs in the time-domain rather than in the frequency-domainas in FDD SystemsA Repeating signal frame structure is used in which the link direction alternatesbetween Tx and Rx on a single RF carrierSignificant reduction of Radio front-end complexity with a simple 2-way monolithic switch, which replaces the FDD Duplexer


Description of TDD-based Systems


FDD : Spectrum Allocation

Optimal FDD Channel Allocations have 5% or greater Tx-Rx Separation

For example : 39 GHz band consists of 14 paired, contiguous 100-MHz channels

Since no allocated Tx-Rx guardband, manufacturers have divided the 1400 MHz band into 4 sub-bands of 350 MHz each

In this scenario Tx-Rx separation is 700 MHz, or 1.8% of the carrier frequency


TDD : Spectrum Allocation

TDD Systems are more flexible in that they can be deployed with as little as onechannel of available spectrumFor example : Wavtrace‘s system uses 8.33 MHzWith TDD, the FDD problems of Tx-Rx pairing and spacing are eliminated, letting the Operator flexibility to deploy with contiguous or non-contiguousspectral blocksTDD is flexible in that the symmetric and asymmetric links are both supportedwith spectrum efficiencyFor symmetric links, the Up and Down link duration is equivalentWith TDD, only one carrier is used. There is no need to manage the realloationof bandwidth for the duplex carrier, as would be the case with an equivalentFDD linkDynamic bandwidth allocation between up and downlink occurs on a single RF carrier with fixed occupied bandwidthAs a result, frequency re-use is enhanced and planning is significantly simplified


FDD : Duplexer

Duplexer is the element that provides Tx-Rx isolation in an FDD Radio SystemDuplexer : Three Port device consisting of two bandpass (BP) and an impedancetransforming circuit to allow both filters to connect to a common antenna port

The filter in the Receive path attenuates the Transmit energy incident at the antenna port• Prevents receiver front-end overload and/or damage depending on the Transmit level

The filter in the Transmit path attenuates the energy at the receive frequencypresent on the transmit carrierBoth filters also provide suppression of out-of-band spurious signals



Frequency Re-Use and Planning

TDD enhances frequency re-use within a Hub and between Multi-Hubs

For a given spectral block and occupied Bandwidth, use of TDD provides twicethe number of channels for the re-use pool

FDD Links require two channels per link, as opposed to the TDD

A larger pool of Channels means simpler and more efficient re-use planning

With TDD, re-use can be based on Frequency Discrimination, as opposed to the LESS ROBUST method of Polarization Discrimination

Polarization Discrimination is not an effective method because rain effects aremajor cause of De-polarization.


Frequency Re-Use and Planning

For Symmetric Links, the condition of simultaneous Transmit and Receiveoperation is avoided

Eliminates the need for high co-channel Beam Isolation within a Hub

With Asymmetric TDD Links, simultaneous Transmit and Receive operation will exist within a Hub, thus reducing the re-use relative to the Symmetric case


Interference

Multiple Operator interference is often cited as an issue with TDD Systems

Multiple Operator TDD Systems successfully deployed in Japan and in EuropeJapan : PHS (Personal Handyphone System)Europe : DECT (Digital European Cordless Telecommunications)

Currently two interference-related problems associated with mm-wave bandsFrequency bands have not been allocated on a contiguous basis :

• Very likely that some LMDS Licence Holders will sub-licence to multiple operatorsout-of-band spurious reception problem is solved using filters, however significantdifference in radiated power and high dynamic range amplifier technology associatedwith mm-wave band remain

ERP is 15 dB higher for PMP mm-wave bands compared with cellular


Conclusion

TDD is a proven Technology with significant advantages for service provider :

Works in any spectral bandNo Capacity Lost to guardbandSingle radio kit simplifies deployment, inventory and repairSimplified assymetrical servicesHigh Spectral re-useSimultaneous multiple band operaton from a single Hub rooftop

FDD offers a satisfactory solution if adequate Tx-Rx separation is madeavailable

When more flexibility is required, TDD offers the service provider a complementary alternative


2. 3. Network Architecture

Frequency Translation,Power, etc... Sector 3

Tx/Rx

Sector 2Tx/Rx

Sector 4Tx/Rx

Sector 1Tx/Rx

O/E

E/O

Analogue FiberBackbone25 km Max.

WLL

3 Channels (40 MHz BW) per Tx Downstream

2000-2850 MHz Downstream950-1100 MHz Upstream

US FCC Band Plan27.50 - 28.35 GHz Downstream31.075 - 1100 MHz Upstream


2. 4. System Equipment SegmentsHub (or LMDS Base Station)

Medium Gain Antennas used : 15 dBi for example is used Typical 90° Beamwidth (BW) AntennasElevation approximately 5°Low PA output powers leading to 21 dBm EIRP

Customer Premise Equipment (CPE)High Gain Antennas used : 35 dBi are typical valuesNarrow beamwidth of about 3° pointing to the HubSmall Size and low costBack-to-Front Ratio high enough to avoid interferenceCPE PA > 20 dBm @ 1 dB Compression


2. 5. Architectural Options (1/2)Most common architectural type uses co-sited base station equipment

Indoor digital equipment connects to the network infrastructure

Outdoor microwave equipment mounted on the rooftops

Typical multiple sector microwave systems are used, in which Tx and Rx sector antennas provide service over 90, 45, 30, 22.5, or 15 degree beamwidth

Base Station Digital Element

Base Station Microwave Equipment

Common Point for Cable Consolidation

NetworkConnection


Alternative option is to connect the Base Station Indoor unit to remote microwave Tx/Rx systems with Analog Fiber interconnection between the indoor and outdoor unitAs a result :

Consolidation of digital equipment, increased redundancyReduced Servicing CostIncreased sharing digital resources over large areasReduced SectorizationRequirements at each remote location

2. 5. Architectural Options (2/2)

Base Station Digital Equipt.

Analog Fiber Architecture

Analog FiberNet.Connect.


2. 6. Wireless Links and Access Options (1/5)Wireless Systems Designs built around :

TDMAFDMACDMA

Most System Operators use TDMA and FDMA Approaches for the Upstream connection

Access Methods apply to the Upstream Connection (i.e. Customer Premise to Base Station)

Downstream : Most operators use TDM streams


2. 6. Wireless Links and Access Options (2/5)Illustration of the FDMA Access Option

Base Station

TDM

CPE 1 CPE 2 CPE 3 CPE 4

FDMA 1

FDMA 2

FDMA 3

FDMA 4


2. 6. Wireless Links and Access Options (3/5)Illustration of the TDMA Access Option

Base Station

TDM

CPE 1 CPE 2 CPE 3 CPE 4FDMA 1

Shared TDMA


2. 6. Wireless Links and Access Options (4/5)The choice of either TDMA or FDMA depends upon the Customer requirements :

Expected Traffic (Speed, Capacity, etc.)Expected Access Service : Continuous traffic or bursty traffic behaviors

TDMA Large Downstream Data RequirementsLow Upstream Data RequirementsBursty behavior in the UpstreamMultiple Customer share the same modem (or channel), for Internet for exampleAllows for bursty response, no request for slots unless necessary


2. 6. Wireless Links and Access Options (5/5)FDMA

Dedicated to Large Customers with Access 24 hours a dayThe Customers pays for the connection regardless the status of the link : busy or notContinuous behavior in the UpstreamEach Customer uses a different channel (and has an allocated BW)

ExampleOperator wishes to serve 6-storey buildingEach Storey contains 20 offices : 120 in totalTraffic Estimate is necessary (done by the operator)Choice depends upon the expected burstiness of the customer


2. 7. Modulation (1/2)

In LMDS, in general, PSK and AM Modulations are used

TDMA Link Modulation Methods do not include 64-QAM

FDMA Link Modulations are rated regarding the amount of required BW for a 2 Mbps constant bite rate (CBR) connection

The Modulation Options for FDMA and TDMA access methods are almost the same


Bandwidth Required Vs Modulation Scheme

2. 7. Modulation (2/2)

Name ModulationMethod

BW for 2 MbpsCBR Connection

BPSK Binary Phase ShiftKeying 2.8 MHz

DQPSK Differential QPSK 1.4 MHz

QPSK Quadrature PSK 1.4 MHz

8-PSK Octal Phase ShiftKeying 0.8 MHz

4-16-or

64-QAM

4,16, or 64 StateQuadrature AM

1.4 MHz,0.6 MHz, or 0.4

MHz


2. 8. System Capacity (1/6)Capacity in LMDS is measured in terms of :

Data RateMaximum Number of Customer Premise Sites

For Data Rate Calculations :

LMDS System Capacity = Number of Sites × Capacity per SiteSite Capacity = Number of Sectors × Capacity per SectorSpectrum Efficiency required (expressed in Bits/s/Hz) : It is a basic figure of merit for different modulation schemes (table below)


Spectral Efficiencies

2. 8. System Capacity (2/6)

Modulation Spectral Efficiency

4-QAM 1.5 bits/Hz

16-QAM 3.5 bits/Hz

64-QAM 5 bits/Hz


ExampleGiven 1000 MHz of useable Spectrum Reuse of 2 ⇒LMDS Provides 500 MHz of useable spectrum per Sector Assumption of Symmetric Upstream and Downstream links ⇒ 250 MHz in each direction per SectorEach Customer Premise Site uses 5 MHz FDMA Links at 4-QAM

Solution :Capacity = 5 ×1.5 = 7.5 Mbps per Customer SiteThere are 250/5 = 50 Links ⇒ 375 Mbps of Total Upstream Capacity. The Downstream Capacity is also 375 Mbps if a 4-QAM Modulation is used

2. 8. System Capacity - FDMA Access (3/6)


ExerciseGiven 1300 MHz of useable Spectrum Reuse of 2 Assumption of Symmetric Upstream and Downstream links Each Customer Premise Site uses 5 MHz FDMA Links at :

16-QAM64-QAM

What is the expected Capacity per Customer Site ?What is the total number of Links within the system ?What is the total Upstream and Downstream Capacities for each modulation scheme ? (i.e. 16 and 64-QAM)

2. 8. System Capacity - FDMA Access (4/6)


TDMA Systems have 80% reduced Data Rate Capacity compared to FDMA systems. TDMA is suitable for many low data rate customers are to be serviced.

TDMA Systems do not use 64-QAM, implying a reduced data rate especially concerning the very dense rates achievable in FDMA

64-QAM used for shorter links due to the high values for the minimum required receive power (high C/N Requirements)

64-QAM is therefore used for high bit rate requirements and for very close customers to the Base Station

2. 8. System Capacity - TDMA Access (5/6)


ExampleAs for FDMA example, 250 MHz Upstream BW is available and 5 MHz TDMA channels are used

Each 5 MHz TDMA channel can provide 80 DS0 connections simultaneously

Total number of DS0 users per Sector on TDMA system is :80 DS0s per channel ×(250/5) = 4000 !

Total Number of DS0 per Site depends on the Number of Sectors in the Site

2. 8. System Capacity - TDMA Access (6/6)

© Cirta Consulting LLC 1999-2003

2.9. Link Budgets


2. 9. Link Bugdets : Definition (1/16)

Quantitative Description of a Link : Gains, Losses, and Levels are taken into account for both Up and Downlink Directions. All sources of noises are also considered.

Link Budgets help design Networks to fulfill quality requirements

Three Key measures of a link : Range, Capacity, and Availability (given a BER performance)

Link Budgets allow determine the tradeoffs between the three


Link budgets are used to determine the following :

Maximum Path Length (or Range)Given a target link availability, the Range is computed for both Up and Downstream directions. The Downstream is the most limiting path !

Maximum AvailabilityDifferent customers are located within different ranges, it is interesting to know what figure of link availability (in percent of time) they might expect.

Power RequirementsLink Budgets help define what amount of power reduction (or increase) on a given link is necessary to keep a balanced availability.

2. 9. Link Bugdets : Purposes (2/16)


Free Space Loss is the predominant effect in LMDS :FSLdB = 32.4 + 20 Log(FMHz)+ 20 Log(Dkm )

@ 28 GHz, FSL = 121 dB for D = 1 kmFSL = 127 dB for D = 2 km and FSL = 133 dB for D = 4 km

RainBy far, the additional attenuation due to rain is the controlling factor for Frequencies > 20 GHz, even for short rangesExtensive Rain Effects investigations published by the ITU-RRain affects Polarization of Microwaves : Horizontal Polarized waves experience slightly higher losses than vertically polarized waves

2. 9. Link Bugdets : Microwave Propagation (3/16)


The ITU-R Published a Table of Regression Coefficient to calculated the Specific Rain Attenuation :

AdB/km = aRb

a and b are frequency, polarization and rain temperature dependent parameters (see Table enclosed)

R is the Rain rate (mm/h) Depending on the World Atlas RegionExample

Suppose we want to compute the Rain attenuation for a link availability of 99.9 % of the time in The Netherlands (Region E) @ 25 GHz. We assume a Vertical polarized waves option. The Specific Attenuation would be :A = 0.113 × (6)1.030 = 0.715 dB/km For 99.99 %, A = 0.113 × (22)1.030 = 2.7 dB/kmAnd for 99.997 %, A = 0.113 × (41)1.030 = 5.2 dB/km



Precise Values for a and b parameters for intermediate frequencies can be obtained by Linear Interpolation

Statistically, the rain does not affect the entire path. We introduce the following correction factor to account for a realistic path length :

r = (90)/(90+4D)If the D = 2 km, then Dreal = D×r = 2 × 90/98 = 1.836 kmThe Attenuation due to rain is : Arain = AdB/km × Dreal

Numerical Result : Arain = 0.715 × 1.836 = 1.31 dB



Polarization Scaling (ITU-R Report 338)

If we wish to compute the Rain effect Attenuation for V Polarization given the H Polarization result or vice-versa, we should apply either equations :

We can easily notice that : AH > AV

Example : Suppose we compute AH = 30 dB then AV= 24.6 dB !

2. 9. Link Bugdets : Microwave Propagation (5 /16)

H

HV A

AdBA+

=335300)(

V

VH A

AdBA−

=300335)(


Recommendation IU-R PN. 837-1: Percentage of Time vs Rain Zone

2. 9. Link Bugdets : Rainfall Intensity Exceeded (5 /16)

1702501801201501005583657870424232220.001

14220014095105704555455441292621140.003

11514595636042353230282219151280.01

96105654033232818201512139650.03

7265352215122010128685320.1

4934151174.213474.52.44.52.820.80.3

24125421.88231.70.62.10.70.50.11.0

QPNMLKJHGFEDCBA%


LINK BUDGET PARAMETERS :25 GHz DOWNLINK 3 CARRIERS, EACH 10 MHz BW99.99% Availability (combined Rain & Multipath)Transmit Antenna 15 dBi Gain (90° Sector)Receive Antenna 36 dBi GainVertical PolarizationReceive Noise Figure 6.0 dB at Flange, 27 dBm at Flange, Noise Floor –98.0 dBm

2. 9. Link Bugdets : 25 GHz Ranges by Rain Region (5 /16)

44 dB25.6 dB1.01.21.51.71.92.02.264-QAM

38 dB19.4 dB1.51.92.53.03.43.64.116-QAM

32 dB12.5 dB2.32.93.94.95.55.96.6 4-QAM

Modulation

CTBCNRNMKFEDB


ExerciseAssumptions

Country : The Netherlands (Region E)Required Link Availability : 99.999 %Frequency : 27.2345 GHzDesired Range : 4 kmPolarisation : Vertical

Question :Compute the FSL in dBWhat is the expected rain attenuation ?What would be the real path length ?If we assume 99.99 %, what would be the attenuation due to rain ?

2. 9. Link Bugdets : Microwave Propagation (6 /16)


2. 9. Link Budgets : Microwave Propagation (7 /16)Answer

FSL = 133.14 dB

Applying Linear Interpolation leads to values for a and b :• a(v) = 0.137• b(v) = 1.016

For Region E, R = 70 mm/h for 99.999 % link availability• A = 10.3 dB/km

The Real Path Length is :• Dreal = 4 × 90/98 = 3.673 km• ARain = 3.673 × 10.3 = 37.8 dB

If the link availability was 99.99 %, we would apply R = 22 mm/h• A = 3.18 dB/km and ARain = 3.673 × 3.18 = 11.68 dB !!!


GasesWater Vapor and Oxygen can cause severe attenuations at resonance frequencies (i.e. 22 and 60 GHz respectively).

Losses due to Gases are computed by the following equation :

GLdB = ALdB/km × Dkm with ( ρ = 7.5 )

2. 9. Link Budgets : Microwave Propagation (8 /16)

( ) +××

+−+

++= 2

22/ 001.05.157

81.4227.0

09.600719.0 GHz

GHzGHzkmdB F

FFAL

( ) ( ) ( ) 100003.264.3259.8

93.1836.10

5.82.226.30021.005.0

2

222GHz

GHzGHzGHz

FFFF

ρρ

+−+

+−+

+−++


MultipathMultipath Terrain losses can be significant at lower microwave frequencies and long path lengths

LMDS Frequencies suffer less Multipath effects, especially that typical ranges are shorter than in VHF-UHF

Annual Outage Time (Complement of Availability) is given by :


3600100001.0 103

−

×=

MFM

ctFDT


MultipathWhere the parameters are defined as follows :

T = Annual outage time (in hours)c = Climate-Terrain FactorT = Annual Average Temperature in °F (°C ×9/5 + 32)F = Frequency (in MHz)D = Path Length (in km)MFM = Minimum Fade Margin, otherwise described as the thermal (or flat) fade margin



TransmitterOutput Power :

1 dB Compression Point (P1) power is usedTypical power P1 = 30 dBm but optimal operation use 20 dBm per Digital Carrier

3rd Order Distorsion : IP3 (or 3rd order Intermodulation Products) appear when P1 is exceeded (nonlinear behavior)IP3 have a typical value of 8 dB above P1

Inter Carrier Beating :When more than 1 carrier is applied to modulate the Tx, individual carriers beat together. Distorsion Products are generated.The effect is called Carrier to Carrier Triple Beat (C/CTB)

2. 9. Link Budgets : Equipment Considerations (11 /16)


AntennasHigh Gain and Narrow Beamwidth for CPE Antennas

Typical values of 36 dBi are encountered

Low Gain relatively wide beamwidth for the Hub AntennasTypical values of between 15 and 23 dBi are commonly used

ReceiverNoise Figure

Overall RF Receiver Sensitivity is established by the Noise FigureTypical value of 6.5 dB @ 28 GHz is quite commonSince LMDS is Range-Limited, the Noise Figure is thus a critical parameter



ReceiverDemodulator Efficiency

BER• Values are typically between 10-8 and 10-6, • Higher values imply reduction in the working range due to higher C/N

RequirementsC/N

• For proper demodulation, Minimum C/N is required for each modulation scheme

• Typical values, for a BER = 10-6, are given as follows :– 13.5 dB for 4-QAM– 20.5 dB for 16-QAM– 26.4 dB for 64-QAM



Number of CarriersFor 1 carrier, generally, the Tx Upstream Power is “backed-off” from the P1 Power Level of :

3 dB for a 4-QAM6 dB for a 16-QAM9 dB for a 64-QAM

Bandwidth per CarrierLMDS bandwidth, Customer data load, growth plan are considered when configuring a Link BudgetApplied data rate is a combination of Customer data and LMDS System overhead

Modulation EncodingWhen more than 1 carrier modulates an LMDS Tx, individual carrier power levels are set based upon C/CTB values :

32, 38, and 44 dB values are used for 4, 16, and 64-QAM respectively

2. 9. Link Budgets : Signal Characteristics (14 /16)


For one or more than one carrier used to digitally modulate a single transmitter, the following power back-offs (dB) are used :

- 21.2- 18.2- 15.26 carriers- 20.1- 17.1- 14.15 carriers- 18.5- 15.5- 12.54 carriers- 16- 13- 103 carriers- 16 - 11 - 8 2 carriers- 9 - 6 - 3 1 carrier

64-QAM16-QAM4-QAM@ 24 GHz

2. 9. Link Budgets : Signal Characteristics (15 /16)


The Link Budget is done in two steps :

Determine the optimum Output Power per carrier based on C/CTB Objectives

Calculate either the Range or Link Availability using the followingparameters :

Rain Zone, Number and Bandwidth per carrier, Modulation Encoding(4, 16, or 64-QAM), Antenna Gains, Sectorization, Terrain Type, Carrier, etc.

We usually achieve Link Budget Calculations by either :Setting the Availability to a given value and compute the range orvice-versa.

2. 9. Link Budgets : Design Procedure (16/16)


3. Frequency Planning


3. 1. Frequency Reuse

1

2 3

4

56

7

Traditional re-use PlanN=7

* Uses Highly Directional Antennasto minimize Multipathing and Cross-Polarization

* Maximize the Directivity of theCell antennas by Sectorizing theDistribution system

* Maximize the Isolation amongstthe Adjacent Sector by Polarization

1

1 1

1

11

1

Re-use PlanN=1


3. 2. Reuse and Frequency PlanningIn Theory, LMDS system can achieve a Frequency reuse of N=1

Allocated Spectrum to the LMDS Operator, Technical and Operational considerations are the main Parameters for a Practical Frequency Plan

45° Regular Sectorization Mixed Irregular Sectorization

45°

45°90°

No Coverage45°

15°No Coverage


3. 3. Polarization Deployment in Sectorized CellsH

H

HHHH

HHHH

H

H

H

HHH

HHHH

H

H

H

H

H

H

H

H

H

H

H

H

VVV

VVV

V V

V

V

V

V

V

VVV

VV

V

V

V VV

VV V

VV

V

VVV

• Vertical and HorizontalPolarization

• Isolation Against theAdjacent Sector

• Improved FrequencyRe-use Plan


Example :Spectrum Licence : 80 MHzDownlink : 40 MHz, Uplink : 40 MHz

3. 3. Frequency Planning

10 MHz 10 MHz 10 MHz 10 MHz

F1 F2 F3 F4


3. 3. Frequency Planning : Semi-AlternatingSector Polarization

H

H

V

V

F1, F3

F1, F3

F2, F4

F2, F4

Downlink Shown :Uplink Opposite

2≥N



H

H V

F1, F3

F1, F3F2, F4


2≥N

?

?

GROWTH ?



H

H

V

V

F1, F3

F1, F3

F1, F3

F2, F4


2≥N

F2, F4VV

F2, F4„Rule of Odds“


3. 3. Frequency Planning : Alternating Sector Polarization

H

V

V

H

F1, F2, F3, F4


1≥N

F1, F2, F3, F4 F1, F2, F3, F4

F1, F2, F3, F4



H

V

V

H

F1, F2, F3, F4

RANGE REDUCTION1≥N

F1, F2, F3, F4F1, F2, F3, F4

F1, F2, F3, F4

RANGE REDUCTION



H

H

H

H

H

H

H

H

V

V

V

V

V

V

V

V

Range Reduction due toHorizontal Polarization


3. 3. Frequency Planning : Expansion of AlternateSector Polarization

H

V H

F1, F2, F3, F4 F1, F2, F3, F4


1≥N

V or H ?

Sector Split forGrowth or Capacity

Expansion

F1, F2, F3, F4F1, F2, F3, F4

V or H ?

F1, F2, F3, F4


3. 3. Frequency Planning : Uniform Sector Polarization

V

V V

F1, F3

F1, F3F2, F4

Downlink VUplink H

2≥N

F2, F4

V

RecommendSets 1,3 and 2,4Vs 1,2 and 3,4


3. 3. Frequency Planning : Expansion of Uniform Sector Polarization

V

V V

F1, F3

F1, F3F2, F4

Downlink VUplink H

2≥N

F2, F4

V


ExpansionV

F2, F4



V

V V

F1, F3

F1, F3F2, F4

Downlink VUplink H

2≥N

F2, F4

V


ExpansionV

F2, F4V

F1, F3„Rule of Odds“



V

V V

F1, F3

F1, F3F2, F4

Downlink VUplink H

2≥N

F2,F4

V


Expansion

V

F2,F4

V F1, F3 „Rule of Odds“V

V

F2,F4F1, F3



V

V V

F1, F3

F1, F3F2, F4

Downlink VUplink H

2≥N

F2

V


Expansion

VF4

+QAM

+QAM


3. 3. Frequency Planning : Physical vs Logical Sectors

F1, F3

F1, F3

F2, F4

F2, F4

2:90° PHYSICAL

2:45° LOGICAL* Allows DistributionOf Frequencies throughoutthe Sector for planning withObstacles

* Provides Possible Overlapbetween Adjacent AntennaPatterns


3. 3. Frequency Planning : Theoretical Minimum C/N

BER Exp 4-QAM 16-QAM 64-QAM3 10 16,1 22,56 12,3 19,5 25,68 13 20 26

10 13,9 21 2712 14,2 21,5 27,5

Most Vendors and Operators use a BER of 10-6


Co-channel interference Modeled as Broadband NoiseThis implies that N+I is modeled as a pure thermal noise

The amount of interference degrades the system performancecan be expressed as System Loss

In LMDS :Noise Level > Interference Level (Range-Limited or Noise-Limited Syst.)

(N-I)dB = Thermal Allowance

The System Loss can be derived for different Thermal Allowancevalues

3. 3. Frequency Planning : Thermal Margin and Adjustment for Interference


C/N + THERMAL = Total C/N

BER =1.00E-64-QAM 13.5 10 23.5 dB16-QAM 20.5 10 30.5 dB64-QAM 26.5 10 36.5 dB

BER =1.00E-84-QAM 15.0 10 35.0 dB16-QAM 21.8 10 31.8 dB64-QAM 28.2 10 38.2 dB

3. 3. Frequency Planning : Calculation of Required C/N


C/N (@ BER=1E-06) = 26.5 dBThermal 10.0 dB3 Interferers 05.0 dBTotal C/I Required 41.5 dB

„5R“ -14 dB or „3R“ -9.5 dB

Mitigation : Earth CurvatureBlocking of interference by natural and man-made obstructionsSignificant antenna tilt when low CPE Antenna are considered

3. 3. Frequency Planning : 64-QAM C/I Requirements

Required Additional Isolation for in-line Interference Control27.5 dB or 32.0 dB


3. 3. Frequency Planning : Intereference

3R

5R

Interfering CPE

Interfering CPE

Hub 1 Hub 2 Hub 3

Note : Interfer is same Polarisation


3R => 9.5• +4.5 dB

5R => 14• +3 dB

7R => 17• +2 dB

9R => 19• +2 dB

11R => 21• +1 dB

13R => 22

C/I Computation Method :@ 5R the I = K(5R)-2

@ R the C = K(R)-2

Hence the C/I = 10log10(25) = 13.97 dB (approaches 14 dB)

Conclusion : Distance Alone is notPractical due to Diminishing Returns and Rapidly Increasing FrequencyRe-used

3. 3. Frequency Planning : C/I Reduction by Distance


3. 3. Frequency Planning : Antenna Front-to-Back Ratio

CPE1 CPE2

HUB 1 HUB 2

Required C/I (for 64-QAM) = 36.5 dB = Minimum AntennaFront-to-Back Ratio


3. 3. Frequency Planning : N=2 Mirror

1

1

1

1

1

1 1

1

1

1

1 1

1

1

1

1 1

1

2 2 2

2

2

2

2 2

2

2

2

2

2

2

2

2

22

* Uniform Sector Polarization isassumed

* 3R Distance :Co-channel C/I = 9.5 dB

* Nearest Interferersare marked in Blue

* CPE Antennas are of Narrowbeamwidth : 1.7-2.5°

* Currently F/B = 40 dB and sidelobes better than 40 dB

(Also Applies to 8 Sectors/Hub Site)


3. 3. Frequency Planning : N=4 Mirror

1

3

3

1

1

1 1

3

1

1

3 3

1

1

3

3 3

3

2 2 2

4

4

2

4 4

4

2

2

4

2

2

4

2

44

* Uniform Sector Polarization isassumed

* 5R Distance :Co-channel C/I = 14 dB

* Nearest Interferersare marked in Blue

* CPE Antennas are of Narrowbeamwidth : 1.7-2.5°

* Currently F/B = 40 dB and sidelobes better than 40 dB

(Also Applies to 8 Sectors/Hub Site)


Based on field experience, the following are recommendationto be applied :

1. Deployment of a 64-QAM can be achieved using a minimumfrequency reuse of N=4 and no Polarization Isolation betweensectors

2. Deployment of a 64-QAM can be achieved using a minimumfrequency reuse of N=2 and no Polarization Isolation betweensectors

3. Field conditions may require additional consideration by RF engineering personnel

3. 3. Frequency Planning : Co-channel Deployment


In addition to co-channel, the Frequency Plan must also combat adjacent-channel interference

Because the modulator has not a sharp cutoff, out-of-band radiation exists

Within the same sectors, if adjacent channels are used, a significant amountof energy spills into adjacent channel (mutual interference)

The „Over-the-air“ bandwidth is 4.224 MHz, the occupied BW is 5.28 MHz

Noticeable emissions extend out to 8 MHz from the carrier center frequency

As a result, about 10.5 MHz of carrier spacing is required to control adjacent-channel interference

3. 3. Frequency Planning : Adjacent-Channel Interference


3. 3. Frequency Planning : LMDS Modulator Performance


Bandwidth Terminology

Log

Mag

nitu

de

0 dB

FrequencyOccupied Bandwidth

Channel SpacingBandwidth

Over The Air Bandwidth

4.224 MHz

5.47 MHz

5.28 MHz



Over-the-air Bandwidth (OABW)OABW = Symbol Rate = 4.224 MHz Upstream

Occupied Bandwidth (OCBW)OCBW = Symbol Rate*(1+Rolloff)OCBW = 4.224 Mps*1.25 = 5.28 MHz Upstream

Channel Spacing Bandwidth (CSBW)CSBW = OCBW + Carrier ToleranceCSBW = 5.28 MHz + 8 ppm*24 GHz = (5.28 + 0.192) MHz CSBW = 5.47 MHz Upstream

Actual Channel Spacing BandwidthACSBW = 5 MHz Upstream



Deployment of an N >=2 Hub without considering Adjacent ChannelInterferenceC/I = 41.5 dB (for 2 interfering channels)Calculated with all carriers of equal level16 frequencies are spread over the 4 sectors


1

23

4Sectors 1 & 3 Sectors 2 & 4

F1 F2 F3 F4 F6F5 F7 F8

FrequencyCarriers are separated by 5 MHz


Deployment of an N >=4 Hub without considering Adjacent ChannelInterferenceC/I = 41.5 dB (for 2 interfering channels)Calculated with all carriers of equal level16 frequencies are spread over the 4 sectors


1

23

4Sectors 1 Sectors 2...etc

F1 F2 F3 F4 F6F5 F7 F8

FrequencyCarriers are separated by 5 MHz


f2 f4 f1 f3 f1 f3 f2 f4 f4 f2 f3 f1 f3 f1 f4 f2f6 f8 f5 f7 f5 f7 f6 f8 f8 f6 f7 f5 f7 f5 f8 f6









f10 f12f14 f16

f12 f10f14 f16

f12 f10f16 f14

f12 f10f16 f14

f10 f12f14 f16

f10 f12f14 f16

f10 f12f16 f14

f14 f16f10 f12

f14 f16f10 f12

f14 f16f10 f12

f14 f16f10 f12

f16 f14f12 f10

f16 f14f12 f10

f16 f14f12 f10

f16 f14f12 f10

f12 f10f16 f14

f7 f5f3 f1

f7 f5f3 f1

f7 f5f3 f1

f7 f5f3 f1

f5 f7f1 f3

f5 f7f1 f3

f5 f7f1 f3

f5 f7f1 f3

f1 f3f5 f7

f1 f3f5 f7

f1 f3f5 f7

f1 f3f5 f7

f3 f1f7 f5

f3 f1f7 f5

f3 f1f7 f5

f3 f1f7 f5


f9 f11 f2 f4 f2 f4 f9 f1 f11 f9 f4 f2 f4 f2 f11 f9

f13 f15 f6 f8 f6 f8 f13 f15 f15 f13 f8 f6 f8 f6 f15 f13




f6

1

2

3

4

F4F2 F6 F8

Frequency

F1 F3 F5 F7

Frequency

4 SECTOR HUB

(4/16QAM)

C/1=54 dB(2 Interfering Channels)


Symbol Rate =4,224 Ms/s

Note:Calculated with all carriers of equal level

F7

f5f3 f1

f8

F4

f2F2

f4

f6f8

F1 f3

f5f7

Sectors 1&3

Sectors 2&4

2≥N


5

3

f4f2 f6 f8

f1 f3 f f7

4 SECTOR HUB

(64 QAM)



Symbol Rate =4,224 Ms/s

Note: Calculated with all carriers of equal level

4≥N

f9 f11 f13 f15

f12f10 f14 f16

f12

14

F9

f11 f15f13

f10

F14

f16F2

f4

f6f8

F1 f3

f5f7

2

Sector4

Sector 3

Sector 2

Sector 1


Sector2

Sector1

f2

f4f8

f6

f1

f3f5

f7f1

f2Sector 1 90 degree

Antenna patternFalls into Sector 2

Sector1

Sector2

Selectivity deploy the carriers at the edge of the sector.

Set frequencies such that short hops in the overlappingregion have adjacent carriers to those of long hops in sector 1

Set receive levels at minimum for availability.

This technique ensures higher wanted to unwanted RSL.

This technique is used only when C/I for the interfering hopin the overlap region is not significantly degraded

by reducing its receive signal level. Future sector deployment must be considered.

LMDS

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