WCDMA Air Interface

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3/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:1 of 22WCDMA Air Interface Training Part 3CDMA Capacity Considerations3/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:2 of 22Cell PlanningFDMA systems Frequency Reuse Planning SNR Link BudgetTDMA systems Frequency Reuse Planning Timeslot Allocation SNR Link BudgetCDMA systems Code Reuse Planning SNR Link Budget Interference Link Budget3/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:3 of 22F1F2F7 F3F6F5F4F1F2F7 F3F6F5F4F1F2F7F3F6F5F4F1F2F7F3F6F5F4F1F2F7 F3F6F5F4F1F2F7 F3F6F5F4Frequency ReuseBasic Reuse Pattern of 7F1F2F7 F3F6F5F43/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:4 of 22Frequency ReuseReuse Patterns of 4 , 3F1F2F3F4F1F2F3F4F1F2F3F4F1F2F3F4F1F2F3F4F1F2F3F4F1F2F3F4F1F2F3F1F2F3F1F2F3F1F2F3F1F2F3F1F2F3F1F2F3F1F2F3F1F2F3F1F2F3Reuse = 4 Reuse = 33/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:5 of 22Frequency ReuseCell Sectorization123789101112131415161718192021456123789101112131415161718192021456123789101112131415161718192021456123789101112131415161718192021456123789101112131415161718192021456123789101112131415161718192021456123789101112131415161718192021456Reuse Pattern7/213/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:6 of 22CDMA Efficiency vs. FDMA, TDMAMultiple Access Frequency Reuse Carriers per 5 MHz Users per Carrier Users per Cell [2,3] AMPSFDMA7166124 IS-136TDMA7166372 GSMTDMA7[1]25828 IS-95CDMA14 35(Theoretical) 18(Practical) 140 (Theoretical) 72(Practical) cdma2000 (1x)CDMA14WWSWWS WCDMACDMA11WWSWWS Notes:[1] GSM also uses frequency reuse of 4, frequency hopping, and other techniques to optimize cell planning efficiencies.[2] Users per cell is calculated in a 5 MHz carrier, assuming a frequency reuse of 7 for FDMA, TDMA; 1 for CDMA[3] All FDMA, TDMA, and CDMA systems can make proportional capacity gains by using cell sectorization patternssuch as 7/21, 4/12, etc.[4] Theoretical capacity of cdma2000 and WCDMA depends on Orthogonal Code allocations, and is therefore dependent on the mix of users and data rates.Practical capacity will depend on these and many other factors.3/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:7 of 22CDMA Code PlanningPN1PN2PN7PN3PN6PN5PN4PN1PN2PN7 PN3PN6PN5PN4PN1PN2PN7 PN3PN6PN5PN4PN1PN2PN7 PN3PN6PN5PN4PN1PN2PN7 PN3PN6PN5PN4PN1PN2PN7PN3PN6PN5PN4PN1PN2PN7 PN3PN6PN5PN4CDMA Frequency Reuse:1PN Code Reuse Factor:7 Sectorization: 3-Sector (7/21) ReuseCodes available for code planning:IS-95:512*cdma2000: 512*WCDMA: 512* IS-95 and cdma2000 use 512 discrete time offsets of the same PN code to facilitate cell planning.In practice, IS-95 consecutive codes are avoided in order prevent potential time overlap of transmissions from widely spaced cells.The maximum number of available codes is therefore 256.3/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:8 of 22CDMA CapacityWhat determines the capacity of an FDMA system?What determines the capacity of a TDMA system?What determines the capacity of a CDMA system?3/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:9 of 22CDMA CapacityFactors influencing CDMA capacity Eb/N0 (Energy per bit - to - Noise ratio)Limited by transmit power; All base station transmissions share a single transmit power budget Eb/I0(Energy per bit - to Interference Ratio) Uplink: SSMA interference from mobiles in same cell, mobiles in other cellsDownlink: SSMA interference from surrounding base stations, distant base stationsExcessive interference associated with imperfect power control Spread Spectrum Processing Gain is reduced at higher data rates Multipath reflections, doppler shift, near-far ratio, obstructions, etc. 3/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:10 of 22CDMA Capacity Example of Eb/N0 and Eb/Io capacity limitations Cell 1Cell 2MS1MS2MS3 Cell 1 cannot accommodate MS3 because: Cell 2 cannot accommodate MS2 because:3/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:11 of 22CDMA Capacity Digital SNR: Eb/NobbRSEEnergy per bit (Eb) equals the average signal power (S) divided by the data bit rate (Rb)pb bbG SNRRBNSN RSNE

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.|0 01Energy per bit (Eb) - to - Noise RatioThe Signal-to-Noise Ratio (SNR) times the SSMA Processing GainBNN0Noise power density (N0)The total noise power in the signal bandwidth, divided by the signal bandwidth3/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:12 of 22CDMA Capacity Eb/No vs. Probability of Error (BPSK, QPSK)0 2 4 6 8 10 12 1410-1210-1010-810-610-410-2100Eb/No (dB)Pe (Probability of bit error)For QPSK Modulation, an Eb/N0 of ~ 7.5 dB is required to achieve a Pe of 10-3

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.|021NEerfc Pbe3/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:13 of 22CDMA CapacityUplink Capacity Limit due to SSMA InterferenceInterferingSignalsDesired Signal11M ISSignal-to-Interference RatioThe signal-to-interference ratio for any single user.(Assumes perfect power control; all users received at the same power)pbb bGM RBM B IEIE

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.| 1111) / (0Energy per bit (Eb) - to - Interference RatioThe Signal-to-Interference ratio times the SSMA Processing Gain3/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:14 of 22CDMA CapacityUplink Capacity Limit due to SSMA Interference( )]]]

+ 0/1I EGMbpSolving for M (The number of users that can be accommodated at a given Eb/I0):( )]]]

0/ I EGMbpAssuming that M >> 1;The number of users equals the SSMA processing Gain divided by the desired Eb/I0( )]]]]

f bpv I EGM1/0Taking into account Voice Activity Factor:Voice Activity Factor ranges from 0.35 to 0.653/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:15 of 22CDMA CapacityTheoretical Uplink Capacity Example (one MS, one cell)455 . 0162 . 5128310]]]

PeMGp = 128 Spread Spectrum Processing Gain; vf = 0.5Case I:Desired Pe = 10-3 ; Eb/I0 = 7.5 dB = 5.62Case II:Desired Pe = 10-2 ; Eb/I0 = 5.1 dB = 3.23 Approximately 45 SSMA users can co-existin a single-cell systemwith a Peof 10-3 if each has a processing gain of 128795 .123 . 3128210]]]

PeM3/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:16 of 22CDMA CapacityUplink Capacity in a multi-cell network

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.| 110MGIEpbRequired Eb/No in a single-cell network:( ) ( ) ( )]]]]

+ fpbv f MGIE1 110Required Eb/No in a multi-cell network:Interference from other cells during soft handover is given by f; ( ) ( ) ( )]]]]

+ f bMAXv f I EGp M1 /10Inter-cell interference factor increases with thestandard deviation of path loss; typical values of (f) range from 0.4 to 2.6 (V. Garg, IS-95 and cdma2000, Table 13-1)Also Taking into account other cell interference3/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:17 of 22CDMA CapacityExample 1: Uplink Capacity in a multi-cell IS-95 networkSSMA Bandwidth (B) 1.25 MHz Intercell Interference f = 0.6 (typical for 3-way soft handover, path loss deviation 8 dB)Voice Activity FactorVf =0.5Required Pe10-3 (Eb/I0 = 7.5 dB = 5.62) for 9.6 kbps10-4 (Eb/I0 = 8.5 dB = 7.62) for 14.4 kbps28) 5 . 0 )( 6 . 0 1 )( 62 . 5 (11286 . 9 ,]]]

+ kbps MAXMCase I: Data rate = 9.6 kbps; Gp = 1.2288 Mcps / 9.6 kbps = 128Case II: Data rate = 14.4 kbps; Gp = 1.2288 Mcps / 14.4 kbps = 85.3315) 5 . 0 )( 6 . 0 1 )( 1 . 7 (1854 . 14 ,]]]

+ kbps MAXM3/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:18 of 22CDMA CapacityExample 1: Uplink Capacity in WCDMASSMA Bandwidth (B) 3.84 MHz (equal to W-CDMA chip rate for this example) Intercell Interference f = 0.6 (typical for 3-way soft handover, path loss deviation 8 dB)Voice/data activity 0.5Required Pe10-3 (Eb/I0 = 5.62)28) 5 . 0 )( 6 . 0 1 )( 62 . 5 (112815 ,]]]

+ kbps MAXMCase I: Data rate = 30 ksps; Gp = 3.84 Mcps / (60 kbps/2) = 1281) 5 . 0 )( 6 . 0 1 )( 62 . 5 (1492 . 1 ,]]]

+ Mbps MAXMCase II: Data rate = 960 ksps; Gp = 3.84 Mcps / (1.92 Mbps/2) = 4Many other factors will affect actual capacity... see next page3/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:19 of 22CDMA CapacityOther factors influencing capacity Other Factors that increase capacity:Cell Sectorization Antenna GainAntenna DiversitySoft Handover Macrodiversity Gain Use of higher-strength error protection (e.g., turbo coding)Statistical multiplexing of packet data users Other Factors that decrease capacity: Imperfect Power ControlDownlink Interference from other Base Stations Absorption (body, terrain, structural, atmospheric...)Use of lower strength error protection on high-speed channels Multipath fadingFrequency-selective fading3/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:20 of 22CDMA CapacityDownlink Capacity Fundamental Capacity Limitation is available RF transmit power One RF power budget must be split between all Mobile Stations!Fixed portion of RF power Budget allocated to Pilot, Broadcast, Paging channels SSMA interference from other Base StationsGrowing problem in Microcellular and Hierarchy topologies Traffic channel power is allocated based on Mobile Station needsMore power allocated to distant MSs; less to nearby MSsIS-95B provides 20msec downlink power update for 14.4 kbps data rate WCDMA, cdma2000 use fast power control on the downlink traffic channels3/038 13 - EN/LZU 108 5306 Rev A WCDMA Air InterfacePart 3:21 of 22Soft BlockingSoft vs. Hard Blocking FDMA/TDMA:When all frequencies and/or timeslots are used, calls are blockedCDMA:When interference levels are too high, calls are blockedMaking enough money? Adjust Interference LimitYesNoYesNew User requests AccessNew User requests Access Interference within limits?GrantAccessBlock AccessNoAdmissionControlInterference within limits?Send users to other cells, frequencies, or systemsReduce non-CBR data ratesReduce packet data throughput Reduce error protectionIgnore downlink TPC from MSSelectively drop callsYesNoLoad(Congestion)Control3/038 13 - EN/LZU 10