| With the development of wireless communication, requirements for wireless data transmission speed and quality of service are also increasing. In wireless communications, due to the fading of propagation channels, the poor wireless link may result in the failure of date recovery. Diversity techniques are available in reducing detrimental effects of multi-path fading. However, transmitting diversity generally requires more than one antenna, so it would be limited by transmitter's size or other constraints. Prior work has shown that cooperative diversity enables single-antenna terminal to form a virtual multiple-antenna array, to get a spatial transmitting diversity.Firstly, this paper describes the cooperative diversity from the basic concepts and principles of technology. Then the basic protocols were simulated and compared. The advantages and disadvantages of various protocols were got through detailed analysis.Secondly, this paper discusses the Alamouti space-time codes in cooperative system. With the perspective of Alamouti space-time code in the AF system, in the analysis of the traditional Alamouti space-time code in AF system model, we propose a modified Alamouti space-time code with a combination of AF protocol model. With the perspective of Alamouti space-time code in the MIMO system, we propose a cooperative space-time system which was effective in overcoming the shortcomings of the MIMO system and was also received a MIMO system with the same diversity gain.Finally, we proposed two optimal power allocation algorithms, optimal power allocation implemented only among relays (OPA-RR) and among source and relays (OPA-SR) in in the two-relay collaborative system. The OPA-RR algorithm is simple and easy to spread to the multi-relays system. And the OPA-SR algorithm was to maximize the reduction in system symbol error rate, so that the whole system could have performance improvement. |
