Research On Cooperative Diversity And Relay-Selection Algorithms

With the development of wireless communication, the demand for wireless applications increases rapidly, however QOS of wireless communications is badly degradated by multi-path fading channel. Research shows that diverstiy is a valid technology to overcome degradation. Space diversity technology attracts broad attention owing to no extra bandwith and tme slots occupied. However the multi-antenna system with space diversity is restricted by the cost and the size. Sendonaris and Laneman studied a system that source node can resort to one or more neighboring nodes who can help source retransmit the received signal from the source to the destination node, called cooperative diversity.The present research on cooperative diversity exists following questions:(1) most literatures assume that both the transmitter and the receiver know ideal CSI for cooperative diversity. Few studied the performance of cooperative communication with channel estimation errors. (2) Research on "best selection" most assumes that cooperation is'all-participate-in'cooperative scenes, seldom studied trade-off between diversity and bandwith efficiency. (3) While the "best" relay is completely scheduled by other users, the source must resort to sub-optimal or kth optimal-relay, this model remains intensive study for future. (4) Multi-user cooperation can achieve not only multi-user diversity but also cooperative diversity, the exact theoretical expressions awaits deep research.In order to answer these questions, serveral cooperative models and algorithms are studied. The contibution of the thesis is listed as follows:(1) We study the mathematical model for performance analysis of cooperative diversity with channel estimation errors. The impact of channel estimation errors on cooperation is analyzed.â‘ As for DF cooperation, we obtain the average symbol error probability(SEP) and its upper bound expressions for Rayleigh fading channel with estimation errors. For the case of cooperative diversity with total power constraint, we analyse the performance of the average SEP with optimal power allocation. As for Nakagami-m fading channel, we also obtain the average SEP expressions and analyse different m parameters how to affect the performance of cooperative diversity.â‘¡As for AF cooperation, we analyse the performance of AF cooperative diversity with channel estimation error and derived PDF,CDF and MGF expression of End-to-End signal-to-noise ratio based on non-direct link with approximation bound. Then we derive the average SEP and outage probability expressions.(2) We study relay-selection system and relay-selection algorithms:â‘ in order to implement the trade-off between diversity gain and bandwidth efficiency for AF relay selection system, we propose S-D SNR threshold-ruler relay-selection algorithm and S-R-D /S-D SNR threshold-ruler relay-selection algorithm, and derive the average SEP and bandwidth efficiency expressions respectively. We also analyse different threshold value how to impact on the performance of SEP and bandwidth efficiency. Theoretics and simulation show that,as for S-D SNR ruler, raising diversity gains can be resolved by decrease threshold value, at the same time enhancing bandwidth efficiency can be resolved by increasing threshold value. As for S-R-D/S-D ruler, we can achieve the better diversity gains by decreasing threshold value when channel is under low SNR condition, and we can also enhance bandwidth efficiency by increasing threshold value when channel is under high SNR condition. So we can implement trade-off between diversity gain and bandwidth efficiency. Not only can we solve the problem of "Whom to cooperation"but also solve the problem of "When to cooperation".â‘¡As for multi-source multi-relay cooperation with centralized scheduling, we study sub-optimal or Kth optimal cooperative models with Order Statistic, and derive PDF,CDF and MGF expressions of End-to-End SNR, then apply these expressions to derive the Average SEP and the Average SNR gains for non-idential distributed parameters.(3) We investigate the model of joint multi-user diversity and cooperative diversity for i.i.d Rayleigh fading channel, and derive the average SEP and the average channel capacity expressions. Then we analyse the number of users K how to impact on cooperative system. Theoretics and simulation show that,as for single-relay multi-user AF cooperation,, the diversity order is no longer 2 but 2K for joint multi-user diversity and cooperative diversity system. That is to say that diversity-order double increases along with the number of users K.