Low-Density Graph Codes for Coded Cooperation on Slow Fading Relay Channels
The authors study Low-Density Parity-Check (LDPC) codes with iterative decoding on Block-Fading (BF) Relay Channels. They consider two users that employ coded cooperation, a variant of decode-and-forward with a smaller outage probability than the latter. An outage probability analysis for discrete constellations shows that full diversity can be achieved only when the coding rate does not exceed a maximum value that depends on the level of cooperation. They derive a new code structure by extending the previously published full-diversity root-LDPC code, designed for the BF point-to-point channel, to exhibit a rate-compatibility property which is necessary for coded cooperation. They estimate the asymptotic performance through a new density evolution analysis and the word error rate performance is determined for finite length codes.