Code rate optimization for coded packet CDMA cellular networks

Individually, CDMA multiple access for digital cellular communications, and ATM for wired multimedia communications, are receiving much attention. In anticipation of the union of these two technologies, packet based CDMA is studied. In particular, for a fixed size data packet, the effects of code rate on the decoded bit error rate is investigated. By increasing the redundancy for error correction, more errors can be corrected; however, more co-channel interference is introduced. Through the analysis of the trade-off between redundancy and co-channel interference, it will be shown that an optimum code rate exists. For a Rayleigh fading and lognormal shadowing channel with ideal power control and ideal interleaving, the channel symbol error rate for the forward and reverse link is derived. Using these expressions, an upper bound on the decoded bit error rate is determined. Performing a numerical evaluation, some results are provided