| As virtual multiple-input multiple-output(MIMO) techniques, cooperative diversity techniques have a vast application prospect in wireless communications, thanks to their abilities to not only reap the benefits of MIMO in data rate and transmission reliability improvement without requiring the equipment of multiple antenna, but also increase the coverage of wireless networks, cover the shadow and reduce energy consumption. However, due to the use of half-duplex relay, conventional one-way relaying based cooperative systems suffer from a significant loss in spetrum efficiency(SE). Therefore, the so called two-way relaying techniques, which allow the relay forward simutaneously a signal to the two terminals in a single time slot, have recently emerged as a promising approach to increase the sum rate and mitigate the spectrum efficiency loss of cooperatieve systems. Afterwards, more and more studies for two-way relaying systems are inspired. Of particular interest is the amplify-and-forward(AF) based two-way relaying, which is characterized by low-complexity and high SE. Focusing on two-way AF relaying cooperative communication systems, this dissertation mainly investigates the following problems: outage probability performance, asymmetric traffic requirement, SE and Energy Efficiency(EE) tradeoff and imperfect channel state information(CSI), through three aspects: performance analysis, design of node selection schemes and power allocation schemes. The main contribution of this dissertation can be summarized as follows.Given the limitations of the existing outage performance analysis for two-way AF relaying systems, the first part focuses on deriving unified outage probability expressions regardless of different channel fadings. A more generalized fading channel is considered, where the two source-relay channels are independent and allowed to be subject to all kinds of fading distributions. To this end, a visual integral region based geometric analysis(IRGA) approach is introduced, which does not depend on the specific functional forms of the channel fading distributions. For three-node two-way AF relaying systems, the unified expressions and closed-form low bounds of both individual and system outage probability are presented. Importantly, our analysis is then extended to multi-user and multi-relay scenario and unified expression and concise lower bound of system outage probability are achieved. All the presented expressionsare in concise forms as functions of the CDF of the channel gain squared and apply to different channel fadings. The biggest advantage of the bound is that the expression is quite concise and can be utilized to study the system performance fast and efficiently, such as diversity order or other asymptotic studies. Simulation results show that, compared with the existing work, our derived expressions are efficient, accurate and generalized.Given the asymmetry of data rate requirements for multi-relay two-way AF relaying systems, the second part focuses on the design of optimal relay selection schemes, after a full analysis of the impact of asymmetric traffic requirements on the system performance. According to the asymmetry of data rate requirements, a novel traffic-knowledge based relay selection is proposed. To gain more insights into the proposed relay selection criterion, performance analysis is performed over Rayleigh and Rician channel. For Rayleigh fading channel, the exact system outage probability, diversity gain and coding gain are investigated, and closed-form expressions are presented. For Rayleigh fading channel, lower bound, diversity gain and coding gain for system outage probability are presented. Simulation results verify the accuracy of our derived expressions and highlight the performance of the proposed relay selection policy especially for asymmetric two-way relaying systems.Given the fact that energy efficiency(EE) and spectral efficiency(SE) can hardly be achieved simultaneously, the third part studies the tradeoff problem of EE and SE for asymmetric two-way relaying systems. Utilizing the knowledge of only statistical CSI, the statistical SE model and the statistical EE model are first built, based on which an optimal power allocation problem that optimizes the EE and SE simultaneously is then formulated. Through the exploitation of theorem of nonlinear fractional programming, a unique closed-form optimum solution is obtained. It has been proved that the provided optimal solution is Pareto-optimal for EE-SE optimization. Finally, our solutions are extended to multi-relay scenario and an EE-SE based relay selection criterion is presented. Applying these results, one can flexibly make the tradeoff between EE and SE by simply setting the tradeoff factor.Given the fact that the obtained CSI is hardly perfect, the fourth part analyzes the impact of imperfect CSI on system performance, and formulates power allocationschemes to mitigate the performance loss for two-way AF relaying systems. Individual outage probability, average symbol error rate(SER) and system outage probability are investigated, and their exact expressions, high Signal-to-Noise Ratio(SNR) asymptotic expressions and error floor(EF) introduced by imperfect CSI are presented. The analytical results and simulation results indicate that imperfect CSI has a significant impact on the two-way relaying systems. Therefore, two dual power allocation optimization problems are formulated: the first power allocation optimization problem aims to minimize the system outage probability while satisfies the total energy consumption constraint; the second power allocation optimization problem aims to minimize the total energy consumption while satisfy the outage performance requirements. Closed-form optimal solutions to both problems are finally achieved. Simulation results show that the proposed power allocation can mitigate the negative impact of imperfect CSI effectively, and more than 50% energy on average is saved when power allocation is adopted for each node compared with uniform power allocation scheme.
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