Transmission over wireless channels suffers from multi-path fading, which is the biggest problem that affects the data rate and quality of service. Diversity is a powerful technique to mitigate fading, such as time diversity, frequency diversity, spatial diversity, and so on. Spatial diversity is particularly attractive since it provides diversity gain without incurring an expenditure of transmission time or bandwidth, and also can be combined with other diversity techniques. However, in practice, because of the size, weight, and energy, it's hard to equip multiple antennas at the mobile terminals. Thus a new diversity is proposed, which is called cooperative diversity. It means that mobile terminals share antennas of each other, which can be form a virtual antenna array to get the same gain as conventional MIMO technique does.In this dissertation, the concepts of diversity and cooperation are firstly discussed, subsequently the cooperative diversity is proposed. The relative background knowledge is introduced, mainly are wireless; relay channel; wireless channel and capacity. Cooperative diversity protocols are summarized, and the different performance between AF and DF is analyzed. The scenarios of cooperative diversity based upon Space-Time code and Turbo code are introduced. Also the simulation of cooperative diversity using a simple and based on delay diversity Space-Time Code was done. The results indicate that the cooperative diversity improves the performance over non-cooperative diversity in form of BER and throughput. Finally, the power control principle of cooperative diversity is studied.