Low Density Parity Check Codes over Wireless Relay Channels

We exploit the capacity approaching capability of low density parity check (LDPC) codes to design coding schemes for relay channels. We consider the classical relay channel model, and the use of both full-duplex relays and half-duplex ones. In addition to the design of practical coding schemes and the development of the appropriate receiver structures, we also exploit the use of average mutual information to characterize the convergence behavior of the proposed systems. Using the convergence predictions and the simulation results, we demonstrate that the proposed LDPC coded relay systems, in particular, with irregular LDPC codes, have the capability to approach the ergodic/outage information rates very closely. This is true for both ergodic fading channels where the Shannon type (constrained, i.e., modulation specific) capacity is considered, and non-ergodic fading channels where the outage capacity provides the appropriate limits of reliable communication. For the (time-division) half-duplex relay schemes, we also discuss the optimization of the time-division parameters, and the bit allocation strategies to improve the system performance further.