Throughput of RCPT Hybrid ARQ for DS-CDMA with Diversity Reception and Rake Combining

In this paper, we evaluate by computer simulations the throughput performance of rate compatible punctured turbo coded hybrid ARQ (RCPT HARQ) for direct sequence code division multiple access (DS-CDMA) with antenna diversity reception and rake combining in a frequency selective Rayleigh fading channel. The impact of a range of transmission system parameters and propagation parameters (viz.: the information sequence length, puncturing rate, spreading factor, number of diversity antennas, fading rate, and the power delay profile of the multipath channel) on the throughput is investigated. It is found that RCPT HARQ system has the highest throughput when minimum amount of redundancy bits is transmitted with each retransmission. In addition, the evaluations show that over a frequency selective fading channel, the throughput is almost insensitive to the information sequence length and the fading rate. It is also found that smaller spreading factor (SF) for a given chip rate gives a higher throughput in bps/Hz. Furthermore in the multi-user case, when the number of users is equal to SF, the total throughput for downlink is higher than that for uplink and is more or less independent of SF. Keywords— hybrid ARQ, rate compatible punctured turbo codes, DS-CDMA, mobile communication