Research On Cooperation Diversity In Wireless Networks

With the increasing demands of wireless communication service, people needs wireless transmission with higher speed and better quality. Signal fading arising from multipath propagation is the main problem to improve speed and quality of wireless transmission, so many methods are introduced to mitigate the impairment of multipath fading among which diversity technique is one of most useful ways to conquer multipath fading. Diversity, sorted by ways of Multiplex, includes time diversity, frequency diversity and space diversity, among which space diversity is particularly attractive for its dramatic performance without sacrificing delay and bandwidth. In recent years, multiple-input multiple-output (MIMO) technique as a typical space diversity technique has been shown to be significantly beneficial for wireless communication, as it can offer both an increase in reliability also an increase in rate.However, MIMO is hardly implemented to real system directly, due to the physical constraints of mobile unit, such as size, power cost and settings of multiple antennas. Thus, the idea of cooperation diversity motivated by relay channel is proposed by Sendonaris. Cooperation diversity involves a pair of users employing signaling schemes that allows each to send information using both of their antennas, so it provides transmit diversity even when each mobile user is set with single antenna in multiple user communication system. Cooperation diversity includes amplify-and-forward, decoded-and-forward and coded cooperation, among which coded cooperation employing channel coding has a better performance due to its effective use of bandwidth.Firstly, this paper introduces the diversity techniques which are widely used in wireless networks, emphasized on the space diversity technique involved in my work, then the performance of diversity system and non-diversity system is compared.Secondly, this paper introduces the development and performance improvement of previous cooperation diversity techniques. It investigates the cooperation ways and performances on three kinds of cooperation diversity techniques, i.e. amplify-and-forward, decoded-and-forward and coded cooperation, emphasized on coded cooperation.Finally, a new coded cooperation scheme based on coded cooperation is proposed, and its performance compared to coded cooperation scheme without improvement is investigated through simulation.