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.

We previously proposed a next generation cellular system for IMT-2000 based on the Wideband DS-CDMA with TDD scheme (W-CDMA/TDD) and have evaluated its performance by computer simulation, laboratory and field experiment. With the W-CDMA/TDD, because of its correlation between the downlink and the uplink, transmission and reception space diversity (SD) at a base station and open-loop transmit power control (TPC) can be simply realized. This paper reports performance of laboratory and field experiments using a developed testbed. The results shows it has been confirmed that transmission and reception SD and open-loop TPC have sufficient performance under a field environment as well as laboratory environment.

We previously proposed a next generation cellular system for IMT-2000 based on wideband DS-CDMA with TDD scheme and have evaluated its performance by computer simulation, laboratory and field experiments. This paper presents the design concept of TDD-mode operation on wideband DS-CDMA systems. These systems employ almost the same techniques with a little difference as FDD-mode. We also present the schemes of the TDD-mode specific techniques such as fast cell search, transmission diversity and transmitter power control and show the evaluation results of them are effective. Performance can be improved by use of enhanced techniques such as interference cancellation and adaptive antenna array diversity.