lmds
TRANSCRIPT
© Cirta Consulting LLC 1999-2003
LMDS RF Engineering
Cirta Consulting LLC
© Cirta Consulting LLC 1999-2003 2
1. LMDS : General Topics
© Cirta Consulting LLC 1999-2003 3
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.
© Cirta Consulting LLC 1999-2003 4
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
© Cirta Consulting LLC 1999-2003 5
© Cirta Consulting LLC 1999-2003 6
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
© Cirta Consulting LLC 1999-2003 7
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.
© Cirta Consulting LLC 1999-2003 8
1.4. Concept of LMDS (2)
Hub to Customers(PMP)
Each Customer to Hub(PP)
© Cirta Consulting LLC 1999-2003 9
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)
© Cirta Consulting LLC 1999-2003 10
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.
© Cirta Consulting LLC 1999-2003 11
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
© Cirta Consulting LLC 1999-2003 12
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
© Cirta Consulting LLC 1999-2003 13
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
© Cirta Consulting LLC 1999-2003 14
2. LMDS : Technical Description I
© Cirta Consulting LLC 1999-2003 15
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
© Cirta Consulting LLC 1999-2003 16
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)
© Cirta Consulting LLC 1999-2003 17
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
© Cirta Consulting LLC 1999-2003 18
© Cirta Consulting LLC 1999-2003 19
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)
© Cirta Consulting LLC 1999-2003 20
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
© Cirta Consulting LLC 1999-2003 21
Description of TDD-based Systems
© Cirta Consulting LLC 1999-2003 22
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
© Cirta Consulting LLC 1999-2003 23
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
© Cirta Consulting LLC 1999-2003 24
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
© Cirta Consulting LLC 1999-2003 25
© Cirta Consulting LLC 1999-2003 26
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.
© Cirta Consulting LLC 1999-2003 27
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
© Cirta Consulting LLC 1999-2003 28
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
© Cirta Consulting LLC 1999-2003 29
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
© Cirta Consulting LLC 1999-2003 30
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
© Cirta Consulting LLC 1999-2003 31
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
© Cirta Consulting LLC 1999-2003 32
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
© Cirta Consulting LLC 1999-2003 33
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.
© Cirta Consulting LLC 1999-2003 34
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
© Cirta Consulting LLC 1999-2003 35
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
© Cirta Consulting LLC 1999-2003 36
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
© Cirta Consulting LLC 1999-2003 37
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
© Cirta Consulting LLC 1999-2003 38
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
© Cirta Consulting LLC 1999-2003 39
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
© Cirta Consulting LLC 1999-2003 40
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
© Cirta Consulting LLC 1999-2003 41
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)
© Cirta Consulting LLC 1999-2003 42
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
© Cirta Consulting LLC 1999-2003 43
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)
© Cirta Consulting LLC 1999-2003 44
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)
© Cirta Consulting LLC 1999-2003 45
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)
© Cirta Consulting LLC 1999-2003 46
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
© Cirta Consulting LLC 1999-2003 48
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
© Cirta Consulting LLC 1999-2003 49
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)
© Cirta Consulting LLC 1999-2003 50
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)
© Cirta Consulting LLC 1999-2003 51
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
2. 9. Link Bugdets : Microwave Propagation (4/16)
© Cirta Consulting LLC 1999-2003 52
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
2. 9. Link Bugdets : Microwave Propagation (5/16)
© Cirta Consulting LLC 1999-2003 53
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)(
© Cirta Consulting LLC 1999-2003 54
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%
© Cirta Consulting LLC 1999-2003 55
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
© Cirta Consulting LLC 1999-2003 56
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)
© Cirta Consulting LLC 1999-2003 57
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 !!!
© Cirta Consulting LLC 1999-2003 58
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
+−+
+−+
+−++
© Cirta Consulting LLC 1999-2003 59
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 :
2. 9. Link Budgets : Microwave Propagation (9 /16)
3600100001.0 103
−
×=
MFM
ctFDT
© Cirta Consulting LLC 1999-2003 60
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
2. 9. Link Budgets : Microwave Propagation (10 /16)
© Cirta Consulting LLC 1999-2003 61
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)
© Cirta Consulting LLC 1999-2003 62
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
2. 9. Link Budgets : Equipment Considerations (12 /16)
© Cirta Consulting LLC 1999-2003 63
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
2. 9. Link Budgets : Equipment Considerations (13 /16)
© Cirta Consulting LLC 1999-2003 64
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)
© Cirta Consulting LLC 1999-2003 65
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)
© Cirta Consulting LLC 1999-2003 66
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)
© Cirta Consulting LLC 1999-2003 67
3. Frequency Planning
© Cirta Consulting LLC 1999-2003 68
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
© Cirta Consulting LLC 1999-2003 69
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
© Cirta Consulting LLC 1999-2003 70
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
© Cirta Consulting LLC 1999-2003 71
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
© Cirta Consulting LLC 1999-2003 72
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
© Cirta Consulting LLC 1999-2003 73
3. 3. Frequency Planning : Semi-AlternatingSector Polarization
H
H V
F1, F3
F1, F3F2, F4
Downlink Shown :Uplink Opposite
2≥N
?
?
GROWTH ?
© Cirta Consulting LLC 1999-2003 74
3. 3. Frequency Planning : Semi-AlternatingSector Polarization
H
H
V
V
F1, F3
F1, F3
F1, F3
F2, F4
Downlink Shown :Uplink Opposite
2≥N
F2, F4VV
F2, F4„Rule of Odds“
© Cirta Consulting LLC 1999-2003 75
3. 3. Frequency Planning : Alternating Sector Polarization
H
V
V
H
F1, F2, F3, F4
Downlink Shown :Uplink Opposite
1≥N
F1, F2, F3, F4 F1, F2, F3, F4
F1, F2, F3, F4
© Cirta Consulting LLC 1999-2003 76
3. 3. Frequency Planning : Alternating Sector Polarization
H
V
V
H
F1, F2, F3, F4
RANGE REDUCTION1≥N
F1, F2, F3, F4F1, F2, F3, F4
F1, F2, F3, F4
RANGE REDUCTION
© Cirta Consulting LLC 1999-2003 77
3. 3. Frequency Planning : Alternating Sector Polarization
H
H
H
H
H
H
H
H
V
V
V
V
V
V
V
V
Range Reduction due toHorizontal Polarization
© Cirta Consulting LLC 1999-2003 78
3. 3. Frequency Planning : Expansion of AlternateSector Polarization
H
V H
F1, F2, F3, F4 F1, F2, F3, F4
Downlink Shown :Uplink Opposite
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
© Cirta Consulting LLC 1999-2003 79
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
© Cirta Consulting LLC 1999-2003 80
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
Sector Split forGrowth or Capacity
ExpansionV
F2, F4
© Cirta Consulting LLC 1999-2003 81
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
Sector Split forGrowth or Capacity
ExpansionV
F2, F4V
F1, F3„Rule of Odds“
© Cirta Consulting LLC 1999-2003 82
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
Sector Split forGrowth or Capacity
Expansion
V
F2,F4
V F1, F3 „Rule of Odds“V
V
F2,F4F1, F3
© Cirta Consulting LLC 1999-2003 83
3. 3. Frequency Planning : Expansion of Uniform Sector Polarization
V
V V
F1, F3
F1, F3F2, F4
Downlink VUplink H
2≥N
F2
V
Sector Split forGrowth or Capacity
Expansion
VF4
+QAM
+QAM
© Cirta Consulting LLC 1999-2003 84
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
© Cirta Consulting LLC 1999-2003 85
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
© Cirta Consulting LLC 1999-2003 86
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
© Cirta Consulting LLC 1999-2003 87
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
© Cirta Consulting LLC 1999-2003 88
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
© Cirta Consulting LLC 1999-2003 89
3. 3. Frequency Planning : Intereference
3R
5R
Interfering CPE
Interfering CPE
Hub 1 Hub 2 Hub 3
Note : Interfer is same Polarisation
© Cirta Consulting LLC 1999-2003 90
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
© Cirta Consulting LLC 1999-2003 91
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
© Cirta Consulting LLC 1999-2003 92
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)
© Cirta Consulting LLC 1999-2003 93
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)
© Cirta Consulting LLC 1999-2003 94
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
© Cirta Consulting LLC 1999-2003 95
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
© Cirta Consulting LLC 1999-2003 96
3. 3. Frequency Planning : LMDS Modulator Performance
© Cirta Consulting LLC 1999-2003 97
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
3. 3. Frequency Planning : Adjacent-Channel Interference
© Cirta Consulting LLC 1999-2003 98
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
3. 3. Frequency Planning : Adjacent-Channel Interference
© Cirta Consulting LLC 1999-2003 99
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
3. 3. Frequency Planning : Adjacent-Channel Interference
1
23
4Sectors 1 & 3 Sectors 2 & 4
F1 F2 F3 F4 F6F5 F7 F8
FrequencyCarriers are separated by 5 MHz
© Cirta Consulting LLC 1999-2003 100
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
3. 3. Frequency Planning : Adjacent-Channel Interference
1
23
4Sectors 1 Sectors 2...etc
F1 F2 F3 F4 F6F5 F7 F8
FrequencyCarriers are separated by 5 MHz
© Cirta Consulting LLC 1999-2003 101
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
f1 f3 f2 f4 f2 f4 f1 f3 f3 f1 f4 f2 f4 f2 f3 f1f5 f7 f6 f8 f6 f8 f5 f7 f7 f5 f8 f6 f8 f6 f7 f5
f1 f3 f2 f4 f2 f4 f1 f3 f3 f1 f4 f2 f4 f2 f3 f1f5 f7 f6 f8 f6 f8 f5 f7 f7 f5 f8 f6 f8 f6 f7 f5
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
f6 f8 f5 f7 f1 f3 f6 f8 f8 f6 f7 f5 f7 f5 f8 f6f2 f4 f1 f3 f5 f7 f2 f4 f4 f2 f3 f1 f3 f1 f4 f2
f5 f7 f6 f8 f6 f8 f5 f7 f7 f5 f8 f6 f8 f6 f7 f5f1 f3 f2 f4 f2 f4 f1 f3 f3 f1 f4 f2 f4 f2 f3 f1
f5 f7 f6 f8 f6 f8 f5 f7 f7 f5 f8 f6 f8 f6 f7 f5f1 f3 f2 f4 f2 f4 f1 f3 f3 f1 f4 f2 f4 f2 f3 f1
f6 f8 f5 f7 f5 f7 f6 f8 f8 f6 f7 f5 f7 f5 f8 f6f2 f4 f1 f3 f1 f3 f2 f4 f4 f2 f3 f1 f3 f1 f4 f2
© Cirta Consulting LLC 1999-2003 102
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 f9f13 f15 f6 f8 f6 f8 f13 f15 f15 f13 f8 f6 f8 f6 f15 f13
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
f13 f15 f6 f8 f6 f8 f13 f15 f15 f13 f8 f6 f8 f6 f15 f13f9 f11 f2 f4 f2 f4 f9 f11 f11 f9 f4 f2 f4 f2 f11 f9
f13 f15 f6 f8 f6 f8 f13 f15 f15 f13 f8 f6 f8 f6 f15 f13f9 f11 f2 f4 f2 f4 f9 f11 f11 f9 f4 f2 f4 f2 f11 f9
© Cirta Consulting LLC 1999-2003 103
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)
C/1=47 dB(10 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
© Cirta Consulting LLC 1999-2003 104
5
3
f4f2 f6 f8
f1 f3 f f7
4 SECTOR HUB
(64 QAM)
C/1=54 dB(2 Interfering Channels)
C/1=47 dB(10 Interfering Channels)
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
© Cirta Consulting LLC 1999-2003 105
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.