Research On Cooperative Diversity In Wireless Networks

The multi-input multi-output space diversity technology can reduce the impact ofwireless channel fading significantly and improve the quality of wireless communicationsystems, especially on the part of the capacity and spectrum utilization. However, thistechnology can be difficult for practical application due to the level of mobile devices. Butcompared with MIMO technologies, cooperative diversity has an big advantage of sharing thecooperative arrays of antenna and forming a virtual antenna array, it can also provide gains ofspace diversity. There are several relays among transmission equipment and receiver toimprove theperformance of the systems. Space diversity gain of the system can be extractedthrough cooperative diversity technology. But not all the cooperation relays is contributingfactor that can improve the performances of the system. A better selection of cooperationrelay can be accompolished by using the relay selection technologies which can not onlyenables the system to obtain the same diversity gains but also reduce the system powerconsumption. The green communication can be realized through the selection of cooperationrelays. Space-time coding technology makes the improvement of channel coding gain andsystem throughput possible. This thesis mainly illustrates the combination of cooperativerelay selection technology and space-time coding technology.Firstly, we analysis several traditional cooperative diversity mode which includingAmplify and Forward, Decode Forward、Coded Cooperation and Selective Decode Forward.The theoretical calculation of the outage probability for those system mode are listedrespectively.Comparing and analyzing of the systems are carried out through simulationsoftware.Secondly, two types of space-time coding scheme are introduced in this paper. One ofthem is Alamouti coding, which including its coding and decoding scheme and Bit ErrorRate(BER). By analyzing the1×1，2×1and2×2antenne systems, the results of simulationshows that the best performance is2×2antenna systems in the same channel condition. Theother is distributed space-time coding, coding scheme, system architecture and upper boundof pairwise error probability are analysised in this section.Thirdly, one or more cooperative relays between transmitter and receiver are selected.We discussed a better cooperative based on the receiving maximum signal-to-noise ratioguidelines at the receiver. In other words, this program is to choose some relays which makesthe receiver achieve the Max-SNR effects. Then using the the Minimum Mean Square Error(MMSE) between receiving signals and the transmitting signals to improve that program.Simulation and Comparison shows that the performance of the improved system is better than the former.Finally, A combination of space time coding technology and relay selection techniqueswhich base on above theoretical are proposed. In other word, selection of relay to participatein cooperation in the cooperative relay network is inevitable, then applies the STBCtechniques to the relay cooperative transmission process. Analysis justified that the two relaycooperative combine with distributed space-time coding program pairwise error probabilityChernoff upper bound to be much smaller than the two relay cooperative methods. Simulationresults proves that the BER of combined technologies is significantly lower than the separaterelay collaboration scheme, the validity and reliability of this system is improved greatly...