Research On Cooperative Communication With Coding

The fundamentals of cooperative communication technology is multiuser collaborating by sharing their resources to achieve space diversity gain, and thus improve the validity and reliability of the system. In addition, cooperative communication technology can also be used in sensor networks, wireless ad-hoc networks, and other occasions. Therefore, it has been become the research hot spot in communication field in recent years. This thesis focuses on the research for cooperative communication based on coding, and the main contributions are outlined as follows:An amplify-and-forward (AF) cooperative transmission protocol based on Alamouti code is proposed for down link of mobile communication system. Firstly, Exact closed-form expressions for the symbol error ratio (SER) are derived under M-PSK modulation over Rayleigh fading channel, and the asymptotic expressions at high signal-to-noise ratio are further obtained. The proposed scheme can achieve diversity gain, and the diversity order is4, effectively improve the reliability of the system. Secondly, the optimal power allocation close-form expressions are deduced to minimize the SER under the same total power constraint.We research cooperatve transmission based on fountain code with single relay and propose two coding methods. Aiming for reduction of computational complexity and delay, a distributed fountain code--decomposed Luby transform codes (DLT) is proposed, and two layers degree distribution function of DLT is designed. Then, a cooperative communication transmission protocol based on DLT code is proposed. When the packet loss rate of each link is bigger, the proposed scheme can effectively decrease complexity and system transmission delay, compared to the existing method. Aiming for erasure floor reduction, a novel encoding method for regularized variable node degree Luby transform (RLT) codes is proposed. The proposed scheme is lightweight due to the elimination of the sorting, seeking and updating operations involved in the traditional look-up table of RLT codes. Meanwhile, by modifying the degree distribution, the waterfall area in decoding RLT is improved. Then, a cooperative communication transmission protocol based on the modified RLT code is proposed, and the SER performance is analyzed. Simulation results show that the proposed method can save system encoding and decoding time, effectively reduce the SER erasure floor and decrease the required number of transmission.In order to increase frequency efficiency of multiple relay rateless transmission, a rateless cooperative transmission protocol based on network coding and relay selection is proposed. We establish a successful decoding relay set and select the best relay to collaborate using relay selection strategy. Meanwhile, the source broadcasts network coding packets of the current message block and next block, to obtain diversity gain and network coding gain. Then, through converting quasi-static Rayleigh fading channel into erasure channel, the performances are evaluated with regard to the required number of transmissions and the corresponding probability mass function (PMF). The impact of decoding relay set size on system performance is also discussed. The proposed method can effectively reduce the required number of transmission, therefore, it enhances the spectral efficiency.