The Study Of Cooperative Protocols In Wireless Cooperative Communication

Multi-path fading is a serious problem that affects reliability of system. Diversity techniques are effective ways that combat fading induced by multipath propagation in wireless networks. Multiple-Input Multiple-Output (MIMO) technique as a typical space diversity technique can improve the capability of the wireless system. However, MIMO is difficultly implemented to practical system directly due to physical limitations of terminal, such as size and power's cost. Cooperative diversity as a new space diversity technique creates a way to apply MIMO in practical system. The central idea of cooperative communication is like this: in multi-user communication environment, the adjacent mobile terminals with single antenna share their antennas in a special way to transmit their information. In this situation, it will create a"Virtual Array", which is like the physical multi-antenna, and achieve diversity gain.The major efforts of this thesis are focused on the design of cooperative diversity protocols. First, the system model and fundamental principles of cooperative communication are illustrated. Then, the existing cooperative diversity protocols are classified and illustrated. Of these protocols, this thesis deeply researches the amplify-and-forward (AF) and decode-and-forward (DF) protocols in fading channel, and compares with direct transfer protocol. The field of research covers the protocols'principles, outage probability, advantages and disadvantages. Finally, theoretical analysis and system simulation of estimated-and-forward (EF) protocol are researched. And then, a new cooperative diversity protocol called"Adaptation estimated-and-forward (AEF)"is proposed considering the advantages of AF and EF. The central idea of this protocol is like this: the relay forwards what it received from the source, using either amplify-and-forward or estimated-and-forward which is more efficient according to the inter-user channel situation information (CSI). That is to say, if I SR> R, the relay turns to EF cooperative diversity protocol. Contrarily, the relay turns to AF cooperative diversity protocol. Outage probability analysis and simulation results show that the AEF protocol has better performance than AF and DF.