Collaborative Sub-set Of Performance Analysis And Coding Techniques In Wireless Communications

Wireless channel fading is one of the bottle necks that restrict the development of wireless communications, and diversity is an effective technique to combat fading in wireless communications. Comparing with the time diversity and frequency diversity, space diversity can achieve dramatic performance gain without consuming additional time or bandwidth. Because of high diversity gain and spectrum utilization, Multi-Input Multi-Output (MIMO), a typical space diversity technique which adopts multiple antennas at the transmitter and receiver at the same time, has been a hot research topic in recent ten years. However, some wireless devices are limited by power, size or hardware complexity. So cooperative diversity or cooperative communications was proposed, which enables single-antenna terminals in multi-user environment to share their antennas and generate a virtual multiple-antenna transmitter that allows them to achieve space diversity. At the same time it can extend the cell coverage and improve the cell edge performance, so cooperative diversity is currently a very active research direction. This dissertation will focus on the theoretical performance, space-time code design, signal design and performance analysis in multi-carrier system of cooperative diversity in wireless communications.This dissertation consists of five chapters. In chapter one, first of all, the background, current situation, foreground and existing problems of cooperative diversity are introduced. Moreover, the main works of this dissertation are summarized.In chapter two, we study the performance of uncoded cooperative communication systems in flat fading. We investigate the performance of cooperative communication systems with different number relays. The simulation results show that the system with one relay could achieve maximum average gain. Moreover, we derive exact average symbol error rate (SER) expression of a cooperative wireless transmission with adaptive decode-and-forward (DF) protocol, where the number of relays or cooperative user nodes, which can correctly decode the received signal, is a random variable subject to the Poisson distribution, the normal distribution, or the uniform distribution, respectively. Finally, we validate the optimal precoder of cooperative communication system with Quadrature Phase Shift Keying (QPSK) signal and get the optimal precoder for Binary Phase Shift Keying (BPSK) signal which will bring a gain of 8.5 dB.In chapter three, we study the performance of distributed space-time coded cooperative communication systems in flat fading. First of all, we derived approximative analytical SER expressions of amplify-and-forward (AF) method, analytical SER expressions of adaptive DF method in the cooperative communication system with distributed Alamouti code. Then optimal relay location of adaptive DF method with BPSK signal is derived and others are given through simulation.In chapter four, we study the performance of cooperative communication systems Orthogonal Frequency Division Multiplexing (OFDM) in frequency selective fading. Firstly, bit error rate (BER) expressions of two hop OFDM cooperative transmission system with BPSK and 16-QAM signals are derived. Moreover, a new OFDM cooperative transmission scheme with distributed Almouti code is proposed, which improves SER performance by 2 dB when SER equal to 10-3.Finally, some conclusions of the dissertation are drawn, and the further research issues are pointed out.