Coding Schemes for User Cooperation in Low-Power Regimes

We consider the design of cooperation coding schemes for a two-user multiaccess channel (MAC). In particular, we consider two block Markov coding schemes, namely, the multiplexed coding and the superposition coding. Although the fully multiplexed (FMP) coding outperforms the superposition coding in theory, it is difficult to implement with practical error-correction codes. We, therefore, introduce a partially multiplexed (PMP) coding scheme for code rate R < 0.5, and propose a simplified superposition coding scheme. The outage analysis shows that these cooperation schemes provide significant gains over the non- cooperative MAC in the low-power regime when the bandwidth W rarr infin. We then propose a PMP code design using irregular repeat accumulate (IRA) codes. The design method can be extended to build the low-rate PMP codes using irregular repeat zigzag Hadamard (IRZH) codes, a new class of capacity achieving low-rate codes. Simulation results demonstrate that the block Markov multiplexed coding using PMP-IRA codes outperforms the practical superposition coding by 2 dB at 10^-2 FER, and it provides a 10-dB gain over the noncooperative MAC. The multiplex coding using PMP-IRZH codes offers 1-dB gain over the superposition coding, and a 9.5-dB gain over noncooperative MAC at 10_-2 FER. Moreover, the PMP-IRZH coding performs only 0.5 dB away from the outage capacity of multiplexed coding in the low-power regime.