Research On Key Techniques Of Cooperative Transmission In Wireless Networks

Next generation mobile communication has the requirement of high transmission rate and high frequency efficiency. Recently, cooperative communication is considered as one of the key characteristics of future mobile communication system. It offers user diversity and spatial diversity gains, increases the transmission rate as well as extends the coverage of the system. Besides, cooperation technique can also be use to save energy for the system.Several key techniques of cooperative communication in wireless networks are studied. They include relay selection, resource allocation and cooperative protocols. Research covers different cooperative transmission schemes for different wireless networks. For the infrastructure mode network, which has a center controller, for example, the base station of cellular system, usually relay stations are introduced to cooperative cellular system for cooperative communication. For ad hoc mode network, in which all the nodes have same capability and transmission strategy, cooperative protocol made nodes with good channel state help nodes with poor channel state to transmit data. To improve performance such as throughput, outage, energy efficiency and lifetime for these networks, proper cooperative transmission schemes are proposed.An adaptive resource allocation algorithm for OFDMA (Orthogonal Frequency Division Multiple Access) cellular system with relay stations is proposed. Relay stations help base station to allocate resource in the cell. This decrease the control signal exchanged in the system. Besides, the algorithm adjusts the frame structure adaptively according to the channel state and the real-time system throughput to achieve higher throughput and lower outage probability.For Ad hoc mode of IEEE 802.11 WLAN (Wireless Local Area Network), a lifetime extended cooperative MAC (Media Access Control) protocol is proposed. Both throughput and energy information are taken into consideration during relay selection. A scoring scheme is developed to align all the station's lifetime, so that the lifetime of the network is extended. The throughput, power, energy efficiency and lifetime of the network are analyzed and simulated.