Comparative Evaluation between Parallel Combinatory CDMA and Direct Sequence CDMA for High Speed Radio Communication

Osamu KATO
Mitsuru UESUGI
Koichi HOMMA

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E81-A    No.7    pp.1406-1414
Publication Date: 1998/07/25
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Fundamentals of Multi-dimensional Mobile Information Network)
DS-CDMA,  parallel combinatory CDMA (PC-CDMA),  2 Mbps transmission,  mobile radio,  

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Comparative performance evaluation between parallel combinatory CDMA (PC-CDMA) and Direct Sequence CDMA (DS-CDMA) has been conducted for high speed radio communication up to 2 Mbps under a multipath Rayleigh fading environment. For both DS-CDMA and PC-CDMA, user information rate per code of 128 kbps, convolutional code with 1/2 coding rate, the same bit interleaving and QPSK data modulation are applied to get transmission symbol rate of 128 ksps. The chip rate of 4. 096 Mcps is used to investigate the possibility of 2 Mbps transmission using only 5 MHz bandwidth. So the spreading factor of the spreading code is 32 for DS-CDMA. In PC-CDMA, 128 ksps data stream is divided into four 32 ksps data streams and according to the every four bits pattern, corresponding spreading code of spreading factor of 128 and its polarity are selected out of eight candidate spreading codes. In soft decision Viterbi decoding applied to PC-CDMA, branch metric is calculated for every bit by weighting the output levels of the PC-CDMA correlators for eight candidate spreading codes. By computer simulation under vehicular environment model with six multipaths, it has been shown that PC-CDMA can offer more capacity approximately by double than DS-CDMA for both downlink and uplink under the condition such as for vehicular for BER of 10-3, and 2 Mbps transmission per cell for downlink is possible not only in isolated cell condition but also in omni cell condition by PC-CDMA.