Near-optimal convolutionally coded synchronous CDMA with iterative multiuser detection/decoding

We consider in this paper a convolutionally coded synchronous DS-CDMA system with iterative multiuser detection and decoding. Each user´s bits are convolutionally encoded, interleaved, and differentially encoded before being transmitted over the multiuser CDMA channel. In contrast to previous work in this area, a differential encoder is inserted to effect an interleaver gain. The receiver consists of a soft-in soft-out multiuser detector followed by a bank of iterative decoders matched to the convolutional code-differential encoder combination. Dramatic gains over systems which contain no differential encoder are demonstrated. We also show that there exists an optimal code rate under a bandwidth constraint. The gains and optimal code rates are demonstrated via bit error rate simulations and density evolution analyses