Analysis of a hybrid multicode/variable spreading factor DS-CDMA system with two-stage group detection

High-rate uplink transmission is realized by proposing a hybrid multicode (MC)/variable spreading factor (VSF) direct-sequence code-division multiple-access system that employs precoding for a constant envelope MC signal. In connection with the hybrid MC/VSF and precoding scheme, a novel two-stage M-symbol group detection is introduced to maximize the detection gain by collecting all the signal energy carried over the entire M MC channels. With fixed M, the symbol-error rate of the proposed hybrid scheme is derived for varying spreading factor per symbol, considering both identically and nonidentically distributed channel statistics. While the information rate and average transmit power per bit are kept the same, it is shown that, with manageable receiver complexity, the hybrid scheme can be a good alternative to multidimensional MC or, even better, outperforming classical MC and VSF in view of the bit-error rate.