Research Of Wireless Cooperative Relay Technology Based On Network Coding

Wireless cooperative relay technology is a new spatial diversity solution, which can overcome the limitations of MIMO in practical applications, extend the network coverage and gain larger capacity through spatial diversity effect. It has drawn growing attention in the field of broadband wireless communications. However, wireless cooperative relay technology mainly focuses on combating multi-path fading thorough diversity, and is limited to improve the transmission capacity of the system. As a new technology, Network Coding can achieve the theoretical upper bound of multicast transmission capacity, which makes up the lack of wireless cooperative relay technology. So the integration and complemention of wireless cooperative relaying and network coding can further enhance the transmission performances of system. There are broad research and development prospects in wireless cooperative relay technology based on network coding.Besides significantly increasing the network transmission capacity, network coding is also a good method to enhance the security and reliability of system. However, the network coding mechanism, which encodes and forwards information through intermediate nodes, will raise some new challenges to security due to the loss, tampering and failure of packets transmission; and the introduction of a large number of relay nodes will make the wireless cooperative relay networks more vulnerable to interference and eavesdropping. Neither the traditional key-based security mechanism nor network coding mechanism can ensure the wireless communication’s absolute security. Therefore, more and more researchers pay attention to the new security theory——wireless physical layer security, which is a kind of unconditional security based on information theory. The establishment of the theory has opened up a new research direction for the communication security.Based on the transmission schemes of wireless cooperative relay system using analog network coding (ANC), the following aspects are researched in this paper regarding the channel capacity and security capacity of the wiretap channel as two main objects.(1) The original purpose of integrating network coding technology in wireless cooperative relay system is to use its excellent feature to in-crease the the network transmission capacity. So firstly, regarded the ch-annel capacity as the main object, different transmission schemes of wireless cooperative relay system using ANC are designed for two typical wireless cooperative relay scenarios (Two way relay channel and Uplink multiple access relay channel). The process of signal transmission, encoding/decoding and how to reduce the transmission time slots are described; and then the channel capacity of different transmission schemes are derived; finally, the advantage of using ANC technology to improve the transmission capacity of wireless cooperative relay system is analyzed through numerical calculation and simulation.(2) Although the simulation results demonstrate that using the ANC technology in wireless cooperative relay system can significantly enhance the transmission capacity for different scenarios, the performan-ce gain is also influenced by the signal-to-noise ratio (SNR), the relay location and the cumulation of ANC noises. So, in order to reduce the influence of above factors on the ANC performance gain, the optimal power allocation schemes to maximize the channel capacity for two wireless scenarios are presented, using the resource optimization al-location method in the case of limited resources. Finally the gain of channel capacity by optimal power allocation schemes is analyzed through numerical calculation and simulation.(3) Network coding is also a good method to enhance the security and reliability of system, but it can not ensure the wireless communication’s absolute security. When the eavesdroppers locate at some special positions, it is not secure at all. So, regarded the wiretap channel’s security capacity as another object, the security capacity for ANC two way relay wiretap channel is derived; then the main factors influencing the security capacity are analyzed through numerical simulation, including eavesdropper’s distance from communication node, angle and power allocation strategy; finally two strategies to improve security capacity of ANC two-way relay wiretap channel are presented, including adjusting the nodes’power allocation and using the negative effect of noise cumulation. The gain of security capacity by adjusting the nodes’power allocation is analyzed through numerical simulation.(4) For the second strategy (using the negative effect of noise cumulation) to improve the security capacity of ANC two-way relay wiretap channel, according to the viewpoint of the wireless physical layer security and cooperative jamming mechanism, the different cooperative jamming schemes of ANC two-way relay wiretap channel based on relay and node are designed; then the process of signal transmission, encoding/decoding and how to introduce active interferen-ce to suppress the wiretap are described, and the security capacity of diff-erent schemes are derived; finally, the gain of security capacity by cooperative jamming schemes is analyzed through numerical simulation.