Design of Multiplexed Coding for User Cooperation
Guosen Yue, Xiaodong Wang, Mohammad Madihian · 2006
We consider the multiplexed coding design for cooperative communications. The ideal multiplexed coding, which outperforms the superposition coding in theory, is difficult to implement with practical error-correction codes. We therefore in- troduce a partially multiplexed (PMP) coding scheme to approach the performance of fully multiplexed coding scheme. We then design the PMP coding using irregular repeat accumulate (IRA) codes. We also present a practical superposition coding scheme with two decoding methods. The outage analysis shows that all these schemes perform very close to lower cooperation bound. The simulation results demonstrate that both PMP and practical superposition block Markov coding for two-user cooperation provide significant gain over the non-cooperative system. I. INTRODUCTION Employing multiple antennas in wireless communications to achieve the transmit diversity or spatial diversity, known as the MIMO technology, has become a promising solution to combat fading channel and to provide very high data rate. Recently, cooperative communication techniques have drawn increasing interests due to the user cooperation diversity (1), (2), (3), which is another form of spatial diversity created by using a collection of distributed antennas from multiple terminals in a network. With user cooperation, the terminals share their antennas to form a virtual antenna array providing the potential of realizing spatial diversity through distributed coding and signal processing. In (4), two cooperation coding schemes are introduced, namely, multiplexed coding and superposition coding. Al- though those two schemes perform very close to lower bound of the outage probability for user cooperation, practically, these schemes are difficult to implement with binary error- correction codes. In this paper, we introduce practically im- plementable coding schemes on the multiplexed coding and the superposition coding for user coorperation in a two-user MAC. In particular, we introduce a partial multiplexed (PMP) coding scheme for the operation in low-rate region, i.e., the code rate Rc < 0.5, and propose a PMP code design method using capacity-approaching irregular repeat accumulate (IRA) code (5). The designed PMP code using IRA codes can be iteratively decoded with low decoding complexity for both the multiplexed and its component codes using the same code graph. Moreover, both the multiplexed code and its component codes have capacity approaching performance. We also pro- pose a simplified practical superposition coding scheme and implement two decoding methods for such scheme. The outage analysis shows that the designed coding schemes provide significant gain over non-cooperative MAC. Simulation results demonstrate that all the implemented coding schemes perform close to the outage probabilities and a large gain over non- 12