Research On Optimized Design Of Cooperative Diversity In Wireless Communication

In wireless communication system, channel fading can decrease the reliability and quality of communication. Diversity technique, which is an efficient manner to combat fading and improve the communication performance, has been widely researched and used. Space diversity, which does not require extra time or frequency resource to transmit redundant signal, is more attractive than traditional time and frequency diversity techniques. However, it is difficult to deploy multiple antennas on some wireless equipments due to size, cost and energy constrains. Cooperative diversity, in which users share their antennas to obtain space diversity, solves this problem and becomes a new valuable diversity technique. There're still some problems to be solved on application of cooperative diversity. This dissertation develops the research on optimized design of cooperative diversity, to solve some of these problems.How to work together with other new technologies is an important problem of cooperative diversity. Amplify-and-forward cooperative diversity scheme is an important cooperative manner as its low complexity and full diversity orders. Network coding is an attractive technology to improve efficiency of communication networks. In this dissertation, an amplify-and-forward cooperative diversity scheme based on network coding is proposed. In this scheme, the cooperation users multiply local signals to the signals received from cooperation partner to realize network coding in analog domain. The network coding signals are transmitted by the user with better instantaneous channel condition, based on one bit feedback from the destination, to improve the spectral efficiency. The theoretic bound of average bit error rate is derived. Both of the theorem and simulation results prove that the proposed scheme has similar performance with plain amplify-and-forward, while achieving higher spectral efficiency.Space time cooperative diversity is a high-efficiency cooperative diversity manner. In this dissertation, space time cooperative diversity techniques are researched. An adaptive space time transmission scheme base on twice detections at base station is proposed, where the cooperation users adaptively arrange resource in retransmission based on the detection results fed back by base station. The theoretic bit error rate of the proposed scheme is derived. Both theorem and simulation results prove the proposed scheme can improve the bit error rate, while achieving higher throughput by saving some transmission slots.The adaptation capability in different kinds of channels is one of the key issues for cooperative diversity technologies to survive. However, the performance of plain decode-and-forward with cyclic redundant check cooperative diversity scheme is worse than non-cooperation scheme when the latter can achieve time diversity. In this dissertation a signal space diversity decode-and-forward scheme is proposed. In the propose scheme, cooperation users rotate and superpose local signals and the signals received from cooperation partner in signal space diversity manner, and the destination node detects the signals in iterative manner. Simulation results prove that the proposed scheme can achieve good performance in both two kinds of channels.Recent research shows that decode-and-forward without cyclic redundant check cooperative diversity scheme can approach to full diversity orders with low complexity, and consequently has a good prospect in application. However the performance analysis and optimization is difficult due to the wrong-bits-forward at relay nodes. In this dissertation, an outage probability model for decode-and-forward without cyclic redundant check cooperative diversity scheme is made up first, and based on this model an outage probability minimization algorithm with a few feedback bits in ergodic channel is proposed. The simulation results prove that a few feedback bits can heavily improve the outage performance in the proposed scheme.