| Cooperative relaying as a promising technique has been recently developed to enhance coverage, reliability and throughput for wireless networks. However, due to the constraint of half-duplex, conventional one-way relaying suffers a significant performance loss in the use of spectral resources. To gain efficiency, a novel transmission scheme referred as two-way relaying has been recently proposed. Currently, two-way relay transmission has attracted lots of attention in the research community. This dissertation focuses mainly on the transmission problems of two-way relaying and investigates novel strategies for the implementation of power allocation, power control and opportunistic relay selection. The outline of this dissertation is described as follows:(1) The outage performace of the considered MABC protocl is analyzed under three different relaying schemes [i.e., AF, DF (including DF-SC and DF-NC) and DNF relayings]. First, closed-form outage probabilities are derived over Rayleigh fading channels. Then, simulation experiments are performed and performace comparisons are conducted. The simulation results demonstrate that1) the DNF scheme is superior to all the counterparts for low and moderately low target rate conditions regardless of symmetric or asymmetric channels;2) the DF-NC scheme performs well for asymmetric channels or low target-rate conditions, and with the increasing of the level of channel asymmetry or the decreasing of the target rates, the performance of the DF-NC scheme approaches to that of the DNF scheme;3) the performance of the DF scheme deteriorates significantly when target rates are high;4) similar to the DNF scheme, the AF scheme is robust to the variance of channel characteristics and to that of target rates;5) the AF scheme is suitable for high target-rate and SNR conditions;6) compared with the DNF, DF-NC and AF schemes, the DF-SC scheme is unefficient, however, its performance is close to that of the AF scheme for strong asymmetric channels, and it can approache to that of the DF-NC scheme when the target rates are high.(2) Novel algorithms for the implementation of power allocation and power control are proposed for the AF-MABC protocol. Considering a generic scenario with asymmetric channels and traffics, a closed-form asymptotic outage probability of the network scenario under consideration is formulated over Rayleigh fading channels. It is shown that the outage probability in the system is determined only by the one-way channel or related to the two-way links depending on the asymmetric level of the two senders’target rates and the terminals’average transmission powers. Following this analysis, the problems of optimal power allocation under a fixed total power constraint and ptimum power control subject to an individual power constraint are investigated. Next, with the aid of traffic-knowledge, novel power allocation (using statistical CSI) and power control (using instantaneous or statistical CSI) criteria are proposed. The simulation results show that the proposed power allocation method can achieve significant performance gains in terms of outage probability regardless of symmetric or asymmetric traffics and channels; the proposed power control methods perform better than the conventional scheme that always using peak-power to transmit, and the method using instantaneous CSI is superior to that of utilizing statistical CSI.(3) Novel traffic-knowledge based relay selection strategy and relay location algorithm are proposed for the AF-MABC protocol. Similarly, a generic network scenario having asymmetric channels and traffics is considered. To minimize the system outage probability, utilizing instantaneous CSI and with the aid of traffic-knowledge, opportunistic relay selection is studied. As a result, a novel selection policy is proposed. Then, by separating the system traffic into different parts, closed-form outage probabilities or the corresponding upper bounds are derived over Rayleigh fading channels. The simulation results demonstrate that the proposed method can significantly enhance the overall performanc of the network scenario under consideration and performs better than the conventional max-min policy when the traffic is strong asymmetric. Next, by utilizing the traffic-knowledge and statistical CSI, a new method for outage minimization through the selection of relay situation is examined. As a result, a novel traffic-knowledge based algorithm is proposed. The simulation results show that1) the outage performance is significantly improved when the proposed algorithm is applied;2) for a fixed target rate, the optimal relay situation is more closed to the source terminal with lower transmission power;2) for fixed transmission powers, the optimal relay situation is invariant with the target rates when the system traffic is strong asymmetric, while the optimal relay situation approaches to the source terminal with higher target rate when the system traffic is symmetric or moderately asymmetric. (4) A novel single-criterion based relay selection policy is proposed for the DF-NC scenario. First, the achievable rate region of conventional three-node DF-NC scenario is characterized. Then, two significant relay selection strategies, i.e., the max-min and the max-sum policies, are studied and analyzed in terms of outage probability from the viewpoint of asymmetric traffic. Accordingly, a closed-form outage probability of the max-min policy and the corresponding upper and lower bounds of the max-sum policy are formulated over Rayleigh fading channels. It is found that the max-min policy is suitable for the high SNR region, while the max-sum strategy is appropriate for low SNRs. Next, with the aid of instantaneous CSI, a single-criterion based relay selection policy is proposed, which only uses the harmonic mean of the two-hop squared links’trengths, thus in contrast to the hybrid scheme no additional overhead is required. The simulation results show that1) the proposed policy is an efficient and appropriate method to implement relay selection and can extract the maximum diversity gain;2) it always performs better than the max-min policy;3) it is inferior a bit to that of the max-sum policy only in the low SNR region and symmetric channels.(5) According to the traffic-knowledge of operating systems, two novel relay selection policies are proposed for the DF-SC scenario. First, the achievable rate region of conventional three-node DF-SC scenario is characterized. Then, utilizing the traffic-knowledge of operating systems, a novel modified max-min policy is proposed and analyzed in terms of outage probability. Accordingly, the corresponding closed-form expressions are formulated over Rayleigh fading channels. Next, by using the balance technique, a joint relay selection policy is proposed, which consider the joint implementation of relay selection and power allocation between the superposed signals at the relay. The simulation results demonstrate that the proposed modifided max-min policy and the joint selection strategy can significantly enhance the system performance, and the latter is superior to that of the former.(6) Based on the criterion of maximum sum rate, a novel relay selection policy is proposed for the DNF scenario. First, the achievable rate region of conventional three-node DNF scenario is characterized. Meanwhile, two equivalent forms of the maximum sum rate (MSR) criterion are presented. Then, a novel relay selection policy based on the MSR criterion is proposed and analyzed in terms of ouatge probability. Accordingly, a closed-form outage probability is formulated over Rayleigh fading channels. The simulation results show that1) the system outage performance is improved significantly when the proposed relay selection policy is applied;2) compared to the AF-MABC protocl with max-min relay selection, the DNF scenario with relay selection performs well at low SNRs. |
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