Research On Physical-layer Networkcoding And The Performance In Asymmetric Two-way Relay Communications

Network coding is known as a revolutionary technology because it changes the store and forward work mode of the routers and allows them processing the information to improve system throughput. The application of network coding in wireless communications is a hot research area. In the wireless two-way relay communication systems, physical-layer network coding, as the physical layer form of network coding, has become a hot topic this years. Physical-layer network coding has attracted so much attention since it can significantly enhance systems’ throughput. The research about physical-layer network coding has made a lot of breakthrough progress. However, there are still so many issues to be further addressed.Under this background, the dissertation conducts systematic studies about the demodulation and mapping scheme at the relay node PNC, the performance analysis and improved schemes for PNC in asymmetric two-way relay channels.Firstly, the principles of network coding and physical-layer network coding are introduced, which are the foundation of the following studies. Based on the system model of three nodes two-way relay communication system, the work procedures of traditional routing multi-hop scheme, NC scheme and PNC scheme are detailed elaborated. The bit error rate and throughput performance for each scheme are analyzed and simulated in AWGN channel.A coherent demodulation and PNC mapping scheme is proposed for2FSK modulated two-way relay communication test-bed systems. The signal processing procedure is introduced and the expression of each variable during the procedure is provided. Then the decision thresholds in this scheme are calculated based on maximum posterior probability criterion. The expressions of decision error probability at relay node, system bit error rate and throughput are deduced. As well, the performance of this PNC demodulation and mapping scheme is verified through numerical and computer simulation results.The performance of PNC in asymmetric two-way relay channels is studied. The asymmetric TWRC is classified into four cases according to possible allocation of unreliable channels and the asymmetric system models are given. The BER performances of PNC are theoretically analyzed and simulated in AWGN channels, Rayleigh fading channels and Nakagami-m fading channels, respectively. Some valuable conclusions are obtained and the main reasons for PNC performance degradation in asymmetric TWRC are found, which is the foundation for proposing improved scheme. The improved PNC scheme in asymmetric TWRC are studied and combined orthogonal physical-layer network coding is proposed. The TWRC system model with normalized channel gain is introduced. The block diagram and signal processing procedures of the uplink and downlink phase in COPNC are detailed elaborated. The BER performances of PNC, OPNC and COPNC are theoretically analyzed and simulated in AWGN channels, Rayleigh fading channels and Nakagami-m fading channels, respectively. The results show that COPNC can effectively enhance the BER performance compared with PNC in asymmetric TWRC. Also, the best asymmetric scenarios for using COPNC are found.