Joint rate and data detection in variable-rate CDMA systems

In this paper we consider a variable bit-rate code division multiple access systems (CDMA), wherein each user may transmit at one out of a set of available data-rates. The problem of joint detection of the data-rate and of the information symbols transmitted by each user is addressed. First of all, the optimum maximum-likelihood receiver is derived. Since this receiver has a complexity exponential both in the number of users and in the length of the data packet, several suboptimum receivers are also derived. Simulation results finally show that these suboptimum receivers, while performing worse than the optimum receiver, achieve satisfactory performance with more limited computational complexity.