17-Leading Edge--Enhanced Cdma2000 1x Technology Boosting Network Capacity

8/6/2019 17-Leading Edge--Enhanced Cdma2000 1x Technology Boosting Network Capacity

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Huawei Technologies

2005.10 8



Leading Edge

MAY 2009 . ISSUE 4949

Enhanced CDMA2000 1X technology

boosts network capacityEnhanced CDMA2000 1X technology can greatly reduce the carrier frequency capacity required by voice services, and

help to develop both CDMA2000 1X voice services and EV-DO data services based on limited spectrum resources. By fully

using the existing carrier frequency, operators can enhance their competitiveness.

By Wu Weidong, Jing Xiaoyun & Wang Yunfeng

Enhanced CDMA2000 1X technology boosts network capacity


http://slidepdf.com/reader/full/17-leading-edge-enhanced-cdma2000-1x-technology-boosting-network-capacity 3/4MAY 2009 . ISSUE 49

Huawei Communicate

5

ost global operators stillgenerate more than 50%o total revenue rom voiceservices . Amid growing

competition between similar products,revenues are dropping despite increasingtraic. Low-cost voice services are whatoperators need to keep their competitiveedge, and enhanced CDMA2000 1X technology is an ideal cost-cutting solutionor CDMA voice services.

Improved voice codingtechnology

h e e n h a n c e d C D M A 2 0 0 0 1 X technology introduces enhanced variablerate codec B (EVRC-B), or 4th generationvocoder s (4GV) , us ing condi t ion-specic rames o diferent sizes to achieveconversions between high voice quality and large system capacity.

As shown in Fig. 1, rames in 4GV-COP0 (capacity operating point 0) aredistributed in a ormat similar to thecurrent EVRC. Ten, ull-rate rames willgradually give way to low-rate rames.Emulation results show that 4GV-COP6delivers voice quality comparable to

EVRC. 4GV-COP6 provides an averageuser speed 30% lower than that providedby EVRC, with the system capacity increased by 20%.

4GV supports smooth adjustment o the voice code mode in COPs. When theload is lighter, a lower COP is used toimprove voice quality. When the network capacity needs to be increased, the COPis increased dynamically to enhance thesystem capacity, but at the cost o voicequality.

Optimized forward/reverse power

Power is a key actor that determinesthe system capacity. Optimizing andlowering power per user can certainly boost system capacity. Analysis o the userpower distribution shows that 50% o the CDMA network power is consumedby the reverse power control subchannels

and 1/8 rate rames. his leaves a lot o space or optimization. he enhancedCDMA2000 1X technology eatures threeoptimization measures to lower power peruser: eicient closed-loop power control,smart blanking o 1/8 rate rame and early termination.

Closed-loop power control

he closed-loop power control lowersthe power control requency rom 800Hzto 400Hz. Emulation results show that thesingle-user orward power is reduced by upto 17%.

Smart blanking of 1/8 rate frame

1/8 rate rames are designed to transmit

background noise and do not transmitany valid inormation but use 14% o the orward power per user. he smartblanking o 1/8 rate rame reduces thenumber o 1/8 rate rames considerably by sending “only the irst 1/8 rate ramein every our consecutive rames” or “only the changed 1/8 rate rames”. he 1/8rate rame power consumption is greatly lowered and the technology is being usedin the 3G VoIP eld.

Early terminationSpeech rames are somewhat repeated

during physical coding. he lower the

Mrame rate, the more rames are repeated.I the air interace unctions properly, thereceiver is able to decode speech ramesin advance. In the CDMA2000 1xEV-DO solution, the hybrid automaticr e t r a n s m i s s i o n r e q u e s t ( H A R Q )technology is based on this principle. Teenhanced CDMA2000 1X technology also introduces early termination to reducecode repetitions.

Speciically, the receiver will make adecoding attempt at an interval o severalpower control groups (PCGs). I decodingis successul, the receiver sends an ACK message to the sender over the powercontrol subchannel. hen, the senderstops sending rames and the PCG willbe empty. his technology can reduce

intererence per user in the sector andenhance sector capacity.

h e t e r m i n a l w i l l s e n d d a t acontinuously i the terminal used in theexisting network does not support early termination regardless o whether theBS decodes reverse rames successully.Presently, the enhanced CDMA2000 1X technology can work out later servicesymbols according to decoding-generatedreverse rames and eliminate intererencecaused by subsequent PCGs.

h e t h r e e p o w e r o p t i m i z a t i o n

technologies can be combined to reducethe orward transmit power per user by upto 40%, signiicantly boosting the system

Fig. 1 Frame distribution across coding modes

4GV—

100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

0%

COP0 COP1 COP2 COP3 COP4 COP5 COP6 COP7

4GV— 4GV— 4GV— 4GV— 4GV— 4GV— 4GV— EVRC

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Leading Edge

MAY 2009 . ISSUE 4951

capacity.

Interference cancellation

he CDMA system operates in a co-requency mode. Intererence betweenusers is a key actor that determines thesystem capacity and its cancellation isthe most eective and simplest approachto increase CDMA system capacity. heintererence cancellation is designed toremove decoded signals rom incomingsignals to avoid intererence on remainingsignals (not yet decoded). In this way,the signal-to-noise ratio (SNR) will beincreased or subsequent user decoding,acilitating signal demodulation.

Based on the total channel capacity,the ollowing analysis examines uplink intererence cancellation in the enhancedCDMA2000 1X system. Suppose thatthree users (A, B, and C) in the systemare using the uplink channel o enhancedCDMA2000 1X service at the same time.hey share the uplink channel throughscrambling codes. Assuming that the noiselevel is 1, the total user power received by the system is 7, and the signal power isallocated at the ratio o 4:2:1 (A:B:C). Tetheoretical capacity o this channel should

be 3bps according to the Shannon ormula. When the intererence cancellation

Dual-antenna terminalreceiving diversity

he use o multiple antennas or

receiving diversity helps increase the systemcapacity signiicantly. In the absence o additional spectrum resources in theBS, this method can linearly enhancethe incoming SNR. However, excessiveantennas may complicate terminalsconsiderably and increase their pricesgreatly. he enhanced CDMA2000 1X technology is designed on the assumptionthat a terminal supports dual-antennatechnology. he use o two antennascan generate a gain o at least 3dB, andincrease the orward link capacity by 2.5dB

and the capacity gain by 80%.In addition to the range o technologies,

including voice codecs, power adjustment,intererence cancellation, and terminalr e c e i v ing d i v e r s i t y , t he enhanc edCDMA2000 1X technology also usesthe quasi orthogonal unction (QOF)to signiicantly increase the maximumcapacity o each sector to 240 users so thata single carrier (RX) can support 120users.

Within a 10MHz bandwidth, thetechnology can support up to 840 users.his has created sharp competitivead van t age s ove r UM S and LEnetworks and enables CDMA operatorsto attract more voice and data users

without additional band resources orreconsolidation o the industry chain.

Suppose operator A currently has ivebands with our used or CDMA20001X and one used or the CDMA20001xEV-DO data services. By upgradingthe system to the enhanced CDMA20001X technology, operator A can reduce the

number o bands used or CDMA20001X voice services to two. Tereore, threebands become available or CDMA20001xEV-DO data services . When thenumber o voice users reaches its peak, theoperator can support multi-carrier DORA or DORB rapidly or data services.

When it comes to capacity, bigger isalways better and enhanced CDMA20001X, the right choice.

Enhanced CDMA2000 1X technology boosts network capacity

Editor: Xue Hua [email protected]

Fig. 2 User capacity comparisons between CDMA, UMTS, and LTE

800

600

400

200

0

Subscribers

245

Current Future Current Future

CDMA2000 1X UMTS LTE

130

380440

840

technology is used, the BS rst decodesthe incoming signals o user A. At thistime, the system cannot recognize signalsrom users B and C as these signalsinterere with those o user A. hus,the signal power or user A is 4, theintererence power 3, and the noise power1. According to the Shannon ormula, thecapacity or user A is to be 1bps.

Ater user A’s data is decoded correctly,the BS proceeds to decode the signalso user B. Now, as the data o user A isalready decoded correctly, the BS canscramble user A’s codes, that is, recoveruser A’s data, and then remove therecovered signals o user A rom incominguplink signals. Ater user A’s signals areeliminated, received uplink signals contain

only signals o user B and C, in whichuser C’s signals interere with the signalso user B. Te signal power o user B is 2,the intererence power 1, and the noisepower 1. he capacity or user B will be1bps. Similarly, the capacity or user C isalso 1bps and the system will be allocateda total capacity o 3bps.

In other words, intererence cancellationhelps to realize the maximum theoreticalcapacity or the channel. Actual emulationresults show that when the intererencecancellation technology is used or 20

users, system spectrum utilization can beimproved by an impressive 55%.

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17-Leading Edge--Enhanced Cdma2000 1x Technology Boosting Network Capacity