Iterative multiuser detection
In this paper, we propose a novel scheme for iterative multiuser detection and turbo decoding. Multiuser detection is based on the soft output maximum a posteriori (MAP) detector, which passes soft metrics to the single-user turbo decoders. Parallel concatenated convolutional codes (PCCC) are employed as single user turbo-codes, where each user is assigned a unique pseudorandom interleaver. Turbo decoding is done in a parallel fashion and decoders are modified to produce a posteriori probabilities of coded bits. The PCCC turbo decoder and multiuser detector are coupled such that after each single-user turbo decoding iteration, the extrinsic probabilities of the interfering users are passed to the multiuser detector and after each multiuser iteration, updated a posteriori probabilities are passed to the single-user turbo decoders as the soft input metrics. Simulation results for binary synchronous multiuser systems in additive white Gaussian noise show that the proposed iterative detection/decoding scheme approaches the multiuser capacity limit within I dB in the low signal-to-noise ratio region.
code division multiaccess multiuser channels concatenated coding iterative methods