The Research Of Cooperative Strategy In Cooperative Wireless Networks

In recent years, with the development of wireless communication technology, the demands for high communication quality and performance are growing. The next-generation wireless communication system should not only improve the data transfer rate, but also to ensure the system can meet the required by different media service. The fading of wireless channel greatly limits the performance of wireless communication, and diversity technology can well against fading, based on diversity technology many technologies appear like MIMO, cooperative communication and so on. It is believed that the wireless MIMO technology will be one of the key technologies that achieve the high-speed broadband mobile communication systems in the future with the high data rate, the high transmission performance and the high capability. The MIMO technique is well researched as its improvement in the spectral efficiency and link reliability. Comparatively speaking, the cooperative communication system can get diversity gain with lower hardware complexity and develop rapidly now. And for cooperative communication system, collaborative relay strategy is a hot issue of the current research.Based on AF relay protocol, we consider a two hop half-duplex wireless communication network with multiple antennas and multiple relays. For such a relay network, the problem of relay strategy has been analyzed in lots of papers, and many corresponding distributed relay schemes has been proposed including the schemes that do QR decomposition at the relay nodes such as QR-P-QR, QR-P-ZF, ZF-P-QR and the schemes that do QR decomposition at the destination node such as MF and MF-RZF. First, we do research to QR-P-QR, QR-P-ZF and ZF-P-QR relay schemes. The analysis shows that both QR-P-ZF and ZF-P-QR relay scheme cannot fully exploit the freedom degree of the MIMO multi-relay system because the QRD is not unique. However, the correspondence between the antennas of the source node and the antennas of the destination node is not consistent. So if the column or row permutation is utilized, the system capacity of traditional hybrid QRD-ZF schemes QR-P-ZF and ZF-P-QR can be further improved. Finally, two new improved QRD-ZF schemes called Permutation QR-P-ZF and Permutation ZF-P-QR based on traditional QRD-ZF schemes are proposed for this relay system. Last, we do research to MF and MF-RZF relay schemes. The simulation result shows that MF and MF-RZF achieve good performance in the Rayleigh channel but bad performance in the Rice channel. Taking into account of the feature of Rice channel, we proposed two new distributed relay beamforming schemes named IRZF-MF and RZF for this system. The RZF scheme uses RZF technique for both receive and transmit beamforming while the IRZF-MF scheme uses IRZF and MF technique for receive and transmit beamforming respectively. The simulation result of the Rayleigh and the Rice channel shows that the proposed two schemes are suitable for both Rayleigh and Rice channel.