Low-Density Lattice Codes For Two-Path Relay Channel

Two-path relay channel(TPRC)consists of a source node,two relay nodes and a destination node.The two half-duplex relay nodes successively in turn forward messages from the source node to the destination node,which overcomes the drawback that traditional three-node-relay system can work only in a half-duplex mode.Regarded as an approximate full-duplex relay system,the TPRC can improve the spectral efficiency significantly.Moreover the TPRC can improve the ability of anti-fading and obtain diversity gain.But when decoding a message sent from the source node,the relay node receives so called ?inter-relay-interference(IRI)? from the other relay node.Therefore,how to mitigate the IRI is of great importance to the performance of the TPRC system.Low-density lattice code(LDLC),which can achieve near-capacity error performance,is a novel type of practical lattice code.LDLC has linear coding and decoding complexity,and the iterative decoding algorithm based on belief propagation is appropriate for LDLC.Moreover LDLC is naturally suitable for the continuous-valued additive white Gaussian noise(AWGN)channel,because LDLC uses the same real number when encoding and transmitting in the channel.In this thesis,we exploit practical lattice schemes for TRPC based on LDLC,which can not only realize an approximate full-duplex relay transmission and improve the spectral efficiency,but also obtain coding gain and diversity gain.The main contents and results are as follows:First,an in-depth study of LDLC is made,including the basic concepts of lattice code and LDLC,LDLC shaping algorithms,LDLC decoding algorithms and so on.Second,for the AWGN TPRC with direct link,a LDLC-based transmission protocol for TPRC using successive-interference-cancellation(LDLC-TPRC-SIC)is proposed.Then theoretical achievable rates of this protocol are derived.This transmission protocol adopts decode-and-forward(DF)strategy and successive-interference-cancellation technique at the relay nodes,which can efficiently restrain the IRI.Then a joint decoding with two successive frames is conducted at the destination node.Simulation results show that the proposed LDLC-TPRC-SIC transmission protocol can effectively suppress the IRI,and acquire both coding gain and diversity gain.Finally,for the AWGN TPRC with direct link,a LDLC-based IRI cancellation transmission protocol for TPRC using dirty-paper-coding(LDLC-TPRC-DPC)is proposed.Furthermore,the theoretical achievable rates of this protocol are given.The protocol adopts DF strategy.Since the IRI is known at the source node,the dirty-paper-coding idea is introduced to encode the source sequences.Then the relay nodes directly conduct LDLC iterative decoding on the received messages.Simulation results show that the proposed LDLC-TPRC-DPC can remove the IRI,and obtain both coding gain and diversity gain.