Multi-relay Cooperation Transmission Based On Rate-compatible LDPC Codes

The technology of relay cooperation can effectively counteract the adverse effects caused by multi-path fading in the transmission process.Although using multi-relay cooperative transmission can further improve the reliability of system,it will greatly increase the overhead of system resources and decrease transmission efficiency.Two adaptive half-duplex relay cooperative schemes are proposed based on opportunistic multi-relay network,the technique of Hybrid Automatic Repeat reQuest(HARQ)and rate-compatible LDPC codes are jointly applied,and channel state information of each link is fully utilized through feedback channels to realize adaptive transmission of different code rates.The main works and contributions are summarized as follows:(1)An overview of the key techniques of cooperative relay communications: analyzing the applications of LDPC codes and HARQ technique and introducing the generalized cooperative diversity technique of cooperative communications.(2)Design and analysis of multi-relay adaptive cooperative transmission schemes: for different multi-relay networks with random distribution and specific distribution,two multi-relay cooperative models based on HARQ are proposed,and the closed-form expressions for outage probability and throughput are derived.Under the specific distribution,the system model introduces relay-relay cooperative transmission to increase the opportunities for relay cooperation.Simulation results show that,the two proposed schemes can effectively reduce the outage probability of the system.Compared with the random distribution,the specific distribution can improve the performance of system in outage probability and throughput at the higher SNR.(3)Analysis of adaptive transmission based on rate-compatible LDPC codes: the techniques of rate-compatible LDPC codes and HARQ are jointly applied to the proposed multi-relay cooperative protocols,and the analysis of simulation results are demonstrated.Under the random distribution,the bit error rate performance of the two transmission phases using different modulation orders is simulated and analyzed.Simulation results show that,the proposed protocols can dramatically improve the bit error rate performance of system under the two different distributions,and the combined modulation method can improve the throughput performance while guarantee the bit error rate performance.(4)Analysis of the following research: under the proposed algorithms,further studies of adaptive modulation combination scheme based on channel condition,non-binary LDPC codes combines with high-order modulation,etc.,to improve transmission reliability and adaptability of the system.