Research On Cooperative Relaying With High Spectral Efficiency

With the explosive growth of wireless data traffic and the emergence of new business and application scenarios,how to improve the spectral efficiency to support higher data rate and massive equipment connection with limited spectrum resources becomes a key problem of future wireless communication.Cooperative relaying has shown huge advantages in expanding the coverage of wireless communication and improving the reliability of the system,but conventional cooperative communication based on half-duplex(HD)induces the loss of spectral efficiency compared with direct transmission.Therefore,a series of advanced cooperative relaying technologies with high spectral efficiency become the hot topics,including two-path relaying(TPR),full-duplex(FD)relaying and two-way relaying(TWR).Most of these cooperative relaying schemes apply coherent detection,in which instantaneous channel state information(CSI)is required.However,accurate instantaneous CSI is hard to obtain when the channel environment changes rapidly or the propagation delay is high.Based on differential modulation with non-coherent detection,this dissertation proposes a series of cooperative relaying schemes with high spectral efficiency in which instantaneous CSI is not required.The contributions in the dissertation can be summarized as follows.1.A denoise-and-forward(DNF)TPR(DNF-TPR)scheme is proposed,and the theoretical analysis is given.Two HD relays send and receive in turn to form a virtual FD relay.The superimposed signals received by the relay from the source and another relay are mapped into a denoised symbol through non-coherent maximum likelihood(ML)decoder without instantaneous CSI,and the destination utilizes the denoised symbol received in the previous timeslot to cancel the inter-relay interference in the current timeslot.The closed-form end-to-end bit error rate(BER)and the diversity gain are derived.The simulation results validate the theoretical analysis,and show that the BER and the spectral efficiency of DNF-TPR outperform that of FD relaying with residual self-interference(RSI)exceeding a certain level(almost 8dB).Compared with HD relay selection scheme,the spectral efficiency is significantly improved by DNF-TPR.2.A FD relaying scheme with distributed antenna based on decode-and-forward(FDDAR)is proposed,and the theoretical analysis is given.The non-coherent ML decoder designed for the relay with distributed antenna could obtain the source information from the received superimposed signals of the source signal and the self-interference without instantaneous CSI,which avoids the problem in classical FD relaying that the performance depends on the level of RSI.The closed-form end-to-end BER of FDDAR is derived.The simulation results validate the theoretical analysis,and show that the BER and the spectral efficiency of FDDAR outperform that of the FD relaying with RSI exceeding a certain level(almost 6dB).Compared with the HD relaying,FDDAR improves the spectral efficiency significantly.3.A FD mode TWR scheme based on DNF(FD-DNF-TWR)and a two-timeslot FD mode distributed antenna(FDDA)TWR scheme based on decode-and-forward(FDDA-TWR)are proposed,and the theoretical analysis is given.In FD-DNF-TWR,two sources send messages to the relay,and the relay generates common information according to the superimposed signals from the two sources and the RSI through a non-coherent ML decoder without instantaneous CSI.At the same time,the relay forwards the common information generated in the previous timeslot to the two sources,and the source could obtain the information from another source according to the common information and its own information.In FDDA-TWR,a source exchanges information with the relay in the odd timeslots,and another source exchanges information with the relay in the even timeslots.Two sources and the relay with distributed antenna extract the useful information from the superimposed signals of the useful information and the self-interference by the non-coherent ML decoder without instantaneous CSI,respectively.Thus,the back-propagating self-interference and the RSI in FD-DNF-TWR are avoided.The closed-form end-to-end BER of the two schemes are derived.The simulation results validate the theoretical analysis,and show that compared with the HD mode TWR scheme based on DNF(DNF-TWR),FD-DNF-TWR achieves similar BER performance and improves the spectral efficiency further.The BER and the spectral efficiency of FDDA-TWR outperform that of two-timeslot FD mode TWR scheme based on decode-and-forward(FD-TWR)with RSI exceeding a certain level(almost 6dB).