Research On Cooperative Relay Technology Based On Network Coding

Wireless cooperative relay communication technology is an effective way to combat fading over wireless channels without additional complexity of multiple-input multiple-output (MIMO) systems. It can achieve spatial diversity gains and increase coverage, and has recently received significant attention and research, both from academia and communication industry. International standards organization IEEE802.16j and IMT-Advanced carry out standardization process of the relay technology. Howerver, wireless cooperative relay communication technology can not effectively improve network capacity and spectrum efficiency, and face the additional relay links, scheduling complexity, interference and other issues. Network coding allows the intermediate nodes to jointly process multiple data flows. Its advantages are to increase network throughput, balance network traffic and enhance robustness. Due to the broadcast nature of wireless channel transmissions, network coding is very suitable for wireless cooperative relay network, which can save system resource overhead and further improve system capacity and spectral efficiency. Therefore, cooperative relay communications based on network coding can obtain better system performance, which is a research hotspot in current wireless communication networks.The dissertation reviws the research development of wireless cooperative relay and network coding. Wireless cooperative relay communication based on network coding is intensively investigated. Cooperative transmission schemes and design methods are proposed to solve interference between multi-hop links, relay cooperative pattern, scheduling strategyand implementation issues. The main research works and innovative results of dissertation are expressed as follows:(1) Due to the broadcast nature of wireless transmissions, multi-link and multi-hop cooperative relay transmissions will cause interference with each other. By analyzing network interference cancellation, the cooperative relay transmission scheme with interference cancelation based on network coding is proposed to sovle the interference issues of concurrent multi-hop relay links and reduces the transmission time slot, which utilizes reasonably interference between the signals instead of avoiding interference. It can effectively improve network capacity. Moreover, the system achievable rate, outage probability and throughput expressions are derived. The system performance is analyzed in the different cooperative relay modes. Simulation results show that the interference cancellation scheme of cooperative transmissions can effectively improve the system achievable rate, throughput and wireless bandwidth utilization.(2) For the AF noise amplification and DF error propagation, demodulate-and-forward (DMF) protocol with network coding is presented for multiuser cooperative transmission scheme. The relay node uses DMF, calculates and forwards soft information, which combined with network coding can further improve system performance and reduce the processing delay and power consumption. In order to mitigate the bit error probability (BEP) of destination node, the single equivalent channel gain is expressed to evaluate the ends-to-ends (the sources-relay-destinations) channel conditions. The average BEP expressions and diversity gain are derived and analyzed for the proposed scheme over Rayleigh fading channels. Simulation results show that the proposed scheme can offer improved BEP and provably collect full diversity at lower hardware cost and higher spectral efficiency.(3) In order to combine direct transmission, cooperative relay transmission and network coding cooperative transmission and improve efficiency of resource use, the cooperative transmission scheme with opportunistic network coding is presented. The proposed scheme allows the relay node to decide whether or not to help do cooperation and employ network coding based on the limited feedback from the destinations. It will not help a transmission pair unless its direct transmission fails. Theoretical analysis and simulation results show that the proposed scheme can achieve better performance gain in terms of average mutual information, outage probability, and the limited SNR diversity-multiplexing tradeoffs.(4) In order to verify that the performance gain of network coding in cooperative relay transmission, the dissertation builds a two-way relay transmission experiment platform, designs and implements a new frame structure and coded cooperative transmission protocol. Employing channel coding interleaving and ARQ mechanism ensure the reliability of data transmission, and solve packet loss/error issue of wireless transmission. The experimental results show cooperative transmission scheme based on network coding can get25%of the system throughput gain, which is compared with the traditional cooperative relay transmission scheme under different application scenarios.