Research On Cooperative Relay Technique In Wireless Networks

Compare with wired channels, there exist fading effects in wireless channels due to the open and time varied characteristic of propagation space. The signal usually has been se-verely degrade when it reached at the receiver. Spatial diversity and MIMO technologies can significantly deal with the fading effects by transmitting multiple signals in different spatial paths, which improve the reliability of information transmission and the system capacity. In order to guarantee the irrelevant of multi-signals, it is necessary to set multiple antennas which was separated from enough distance at the transmitter or receiver. But it is difficult to set multiple antennae in mobile equipments which should be portable, and it limits the prac-ticability of spatial diversity. The technique of cooperative relay has been widely studied in academia. It can improve the transmission reliability and system capacity via sharing each antenna by different users to form virtual spatial diversity.In the thesis, several common diversity techniques and combining techniques are dis-cussed firstly, and the bit error rate performance of QPSK modulation signal is simulated in different number of paths and in different methods, which refers to MRC and EGC and SC, and compare the performance with that in non-diversity system. Sencondly, the analysis of cooperative relay system which contains three nodes is described, and the performances of bit error rate in AF, DF, SDF and IR mechanism are simulated. Thirdly, two-way decod-ed-and-forward relaying system is discussed due to the low efficiency of frequency spectrum in one-way system; both DF-Xor mechanism and DNF mechanism are introduced. The per-formances of symbol error rate are simulated in both DF-Xor mechanism and DNF mecha-nism. At last, an optimized power allocation scheme is proposed to minimize the symbol er-ror rate in the system under fixed total power of three nodes. The scheme can adapt the dif-ference of two channels in the system. The simulation results show the optimized power al-location scheme can reduce the symbol error rate and improve the capacity of system.