Study On The Application Of Network Coding In Relay Cooperation Communication

Because of its limited frequency-band resources and power, the research hotspots of the future wireless communication system would be on how to make full use of space resources to improve the system throughput, such as, multi-antenna technology, relay technology, etc. whereas the traditional relay technology, which reduces the resource utilization, is mainly used to forward the user's information, so it becomes the main transmission bottlenecks of networks. The overall network performance can be improved, if the relay node can increase the forwarding capacity of multi-user's information. While the network throughput, robustness, maintainability and safety can be improved with the help of Network coding technique, which not only can enable the relay node to encode and transmit the received information of different paths, but also ensure the original information can be demodulated correctly at the receiving node. In recent years, there have been a great deal of research results in both the theory and implementation of network coding, but most of the relatively mature achievement is on its application in wired networks,but not wireless networks. Therefore, Wireless network coding becomes a research hotspot as it can solve the relay transmission bottlenecks in multi-hop wireless network.In order to improve the network performance further, the thesis applies network coding technology to relay cooperative network, including:①Starting from the traditional relay cooperation mechanism, the thesis analyzes and simulates the AF, DF and CC, which are three common cooperation modes, and expound the basic principles of network coding; Then the applications of network coding in wireless network are further studied, so are the several application schemes in the relay network.②In order to overcome the problems, namely, frequency selective fading and time error, encountered in implementing PNC at actual wireless channel environment, a mixed-signal transmission scheme, in which the PNC was applied in OFDM system, is designed. Because OFDM system can fight against multi-path interference and time-domain error, PNC can be implemented under the non- ideal conditions of signal and channel, by adding / removing a CP at the node which is greater than channel impulse response time. Results show that, in the slow fading channel, the proposed scheme has a better diversity performance, and the decoding performance is not degraded, compared to single-income OFDM system.③After comparing the traditional network coding and network coding and channel decoding co-design, a rate adaptive soft network coding transmission scheme is designed, which combined the soft information to achieve end-to-end channel encode and decode. On the one hand, compared to the traditional network coding scheme, the proposed scheme do not need channel decoding and re-encoding at the relay nodes, which greatly reduce the computational complexity and power consumption; on the other hand, according the channel SNR valuation between nodes, the source node adjust adaptively transmission rate in physical layer to further improve the system throughput performance. Simulation results show that the scheme proposed in this paper reduces the complexity and power consumption in the relay node and achieves a much higher information rate, compared with the fixed rate network coding scheme. It can meet different transmission quality requirements, maximize channel capacity and optimize the system performance while maintain low BER performance.