On Cooperative Diversity Technology In Wireless Communication Systems

Cooperative diversity has attracted much interest over the past few years, and hasbecome one of the most widely explored topics in wireless communications. The keyidea is that each user in wireless networks transmits its own data to the destination andserves as a relay for its partner as well. By sharing each other’ antenna, a virtualmultiple input multiple output (MIMO) system is formed to exploit spatial diversity.Recently, the focus on cooperative system has shifted from the basic single-antennatwo-user cooperative system (i.e., single-relay system) to multiple relays, multiplesources, and even multiple antennas scenarios. Meanwhile, cooperative diversitytechnology has also made its way toward next generation wireless standards, such asIEEE802.16(WiMAX) and long term evolution (LTE).Now, more and more researchers tend to concentrate on complex cooperative systems.However, many problems need to be solved even for the simplest single-relay system.Based on the comprehensive analysis of the bit error and outage performance of thetraditional adaptive decode-and-forward (ADF) system, this dissertation aims to copewith the drawbacks of the ADF system on effectiveness, reliability, and implementationsimplicity. The main contributions are as follows:1. For the repetition-based ADF cooperative system, assuming frame-by-frametransmissions, we first derive an accurate end-to-end bit error rate (BER) expression aswell as its asymptotic approximation. Also, we derive the closed-form power gain ofoptimum power allocation (OPA) over equal power allocation (EPA). Based on theanalysis, we study the impact of frame length on the BER, coding gain, diversity gain,and power allocation. Then, we derive the exact outage probability of the ADF systemand the power gain of OPA over EPA in terms of outage probability. Moreover, thelargest power gain of OPA over EPA, in the sense of either BER or outage probability, isproven to be1.5dB at high signal-to-noise ratio (SNR).2. Although the repetition-based ADF system can achieve full diversity, thebandwidth efficiency is only half of that of direct transmission. To improve theeffectiveness of the ADF system, signal space cooperative (SSC) system is designed,which can obain full diversity while maintaining full rate. Our main focus is on the BERand outage probability of the SSC system as well as the effect of power allocation onthe two performance measures, aiming to offer important theoretical guidance to systemdesigners. First, we derive the accurate end-to-end BERs and their asymptoticapproximations when the destination emplies three different detection schemes, which determine the achievable diversity and coding gains of the three schemes. Then, weobtain the exact outage probability and its asymptotic approximation of the SSC system.Moreover, theoretical analysis and simulation results show that EPA is a wise choice interms of either BER or outage probability.3. We incorporate signal space diversity (SSD) into the ADF cooperative system toreap high-order diversity, which can further improve the transmission reliability. Byusing constellation rotation, we propose a combined SSD and ADF (SSD-DF) scheme.Then, we analyze the BER of the SSD-DF scheme, and propose an OPA strategy.Moreover, asymptotic approximation analysis confirms that both the signal space andspatial diversities can be achieved. Simulation results show that an obvious BER gainover the traditional ADF system is obtained at no additional power or bandwidthexpense, which significantly improve the reliability of transmissions.4. From the perspective of implementation simplicity, we focus on the quadraturesignaling-based cooperative systems. Particularly, an enhanced quadrature signaling-based cooperative system is designed, which can harvest full diversity whilemaintaining full-rate transmissions. Then, we focus on the BER of the full-rate system,and obtain accurate BER expression in closed form as well as the asymptoticapproximation. Simulation results show that the proposed full-rate scheme significantlyoutperforms the traditional signaling-based scheme with the same complexity order.