Efficient Network Coding Technology Under Wireless Relay Networks

In recent years, the performance of mobile terminals improved and the cost lowered day by day. As a result, Internet services migrate from personal computer to mobile terminals massively, and the amount of mobile terminals continues to surge. On the other hand, as the big data services, such as stream media, popularized and developed on mobile terminals, the amount of mobile data traffic continues to surge. With regard to the limited and precious wireless spectrum resources, these trends are severe tests.With the emergence of network coding (NC) technology, traditional transmission model is completely overhauled. Through encoding transferred data on intermediate nodes, NC is able to achieve the maximum capacity of network. The relay cooperative and wireless broadcast characteristics of wireless relay networks fit with the based idea of network coding naturally. Applying network coding to wireless network brings huge and significant performance gains. This dissertation focus on wireless relay network to explore efficient network coding technologies.This dissertation deals with the algorithm complexity problem and radio interference problem which appears when carrying out network coding in wireless relay network, and proposes corresponding innovative solutions. The performance of proposed algorithms is proved through theoretical analysis and computer simulation. The main contributions of this dissertation are concluded as the following:1) Propose a low decoding complexity code construction method of network coding, refered as segment linear network coding (SLNC).By dividing a generation into several segments and restraining the coding coefficients of the symbols within the same segment, SLNC splits a high-rank matrix inversion into several low-rank matrix inversions, therefore reduces the decoding complexity dramatically; proposes two coefficient selection strategies for both centrally controlled networks and distributed networks respectively in order to reduce the extra data cost introduced by SLNC; proves the performance of SLNC by theoretical analysis and simulation.2) Propose an optimal pre-coding algorithm for complex field network coding (CFNC) based on the rule of maximizing the minimum Euclidean distance.Model the optimization of the decoding performance of CFNC based on the equivalent superpositioned (ESP) constellation; find the pre-coding algorithm which maximizes the minimum Euclidean distance of the ESP constellation; deduce the expressions of the optimal pre-coding coefficients when M-PSK modulation is adopted at sources and the number of sources is2; give related numerical results when the number of sources is larger than2; compare and verify the proposed algorithm through simulation.3) Propose a joint network coding and modulation (JNCM) technology which achieves joint optimization of effectiveness and reliability.Prove that if rotate the modulation constellations on multiple sources by proper angles, the points of the equivalent superpositioned constellation at the receiver would cluster, with each cluster center corresponding to a different sum of the source symbols. Utilizing this nature, this dissertation designs layered demodulation to the superpositioned signal, which enables the receiver to adapt the throughput and symbol error probability according to channel conditions; for (N,1,1) and (N,NR,1) two-hop relay network, this dissertation gives linear independent pre-coding mechanism and corresponding transmission strategies based on JNCM; proves the performance by theoretical analysis and simulation.