Enhanced Bidirectional Relaying Schemes for Multi-hop Communications

This paper focuses on bidirectional relaying schemes for multi-hop communications. For a two hop communication system, traditional 4-step bidirectional relaying (TBR) method allocates 4 slots, resulting in low efficiency; Coded bidirectional relaying (CBR) method, making use of network coding, needs only 3 slots, can provide throughput improvement up to 33% compared with TBR method; Two-way relaying method performs data bidirectional relaying with 2 slots, by employing interference cancellation algorithms in the relay station, can further improve spectrum efficiency. However due to different channel condition between RS to BS and RS to MS and broadcast transmission utilized from RS to BS and MS, CBR and two-way relaying methods can not fully exploit the channel capacity from RS to BS and RS to MS simultaneously. In order to solve the problem, we propose two enhanced relaying schemes: the first one is hierarchical modulation (HM) based scheme, in which HM is adopted to allocate individual MCS for each hop and a novel network coding pattern is designed to avail the introduction of HM to relaying. To further improve the performance of the first method, another method as hybrid constellation based relaying scheme is proposed, in which each end node jointly utilizes a hybrid constellation and the prior data it previously transmitted to retrieve the information from the other end node. Performance evaluation results show our algorithms solve the problem successfully and can improve system spectrum efficiency by 5-12% compared with traditional CBR method. Finally it is concluded that the enhanced bidirectional relaying schemes are promising relaying schemes candidates for multi-hop communications.