Research On Key Technologies Of Cooperative Relaying Communications In Wireless Networks

Multiple Input and Multiple Output (MIMO) is a breakthrough in the wireless communication field. It is a key technology which might be adopted by the next generation mobile communication systems, because it can greatly improve the spectrum utilization and channel capacity without increasing the bandwidth.As a practical measure of MIMO, cooperative relaying communication has attracted much attention due to its ability to explore the inherent spatial diversity in relay channels. Aiming at applying cooperative relaying communication technologies in the wireless communication networks, this dissertation has studied and analyzed cooperative relaying communication technologies from three aspects:relay selection strategies in distributed cooperative relaying communication networks and their performance analysis, joint resource optimization in Orthogonal Frequency Division Multiple Access (OFDMA) based cooperative relaying cellular networks and cooperative spectrum sharing in cognitive radio systems.The major contributions are outlined as follows.1.How to select relays from all potential relays to aid the transmission of the source is an important problem in cooperative relaying communication networks.For distributed multi-source cooperative relaying communication networks without a central control unit and with limitation on energy and capacity for each node, a proactive relay selection strategy (M-PRS) is proposed, and its high signal-to-noise ratio(SNR) outage probability is analyzed.Then it is compared with a reactive relay selection strategy (M-RRS) and a distributed space-time coding strategy (M-DSTC) in outage probability, diversity-multiplexing tradeoff (DMT) and implementation overhead and complexity. The theoretical analysis and computer simulations show that M-PRS is an appropriate cooperative relaying transmission strategy which is able to effectively lower the network implementation overhead with only a small performance loss in the outage probability.2.In OFDMA based cooperative relaying cellular systems, how to optimally allocate all kinds of limited resource under a specific system goal is one of the key problems which are under extensive investigation. By taking the weighted sum rate (WSR) as the system optimization goal, an optimal resource allocation algorithm based on optimization theory is proposed.The algorithm can jointly optimize subcarrier allocation, power allocation, relay selection and transmission mode selection. Compared with other optimal resource allocation algorithms which are also based on optimization theory, our algorithm is able to achieve stable convergence independent of system parameters which lowers its computational complexity accordingly in the long run. The implementation and performance of the algorithm under different relay strategies (including decode-and-forward (DF) and amplify-and-forward (AF)) are also discussed. Theoretical analysis and computer simulations illustrate that choosing the weighted sum rate as the system optimization goal is rational, because it is able to both simplify the implementation of different fairness criterions and reduce the computational complexity of the algorithm. We also validate that the algorithm has advantages in fully utilizing the capabilities of relays to improve the system capacity.3.The next generation wireless communication system should have the capability to guarantee users'lowest quality of service (QoS), and in some scenarios, the system should also have the capacity to guarantee fairness among users.Taking these notions into consideration, for OFDMA-based cooperative relaying cellular systems, a fair resource allocation problem that is able to guarantee users'lowest QoS is proposed. The problem also includes the joint optimization of subcarrier allocation, power allocation, relay selection and transmission mode selection. Due to the high complexity involved in optimally solving the problem, a suboptimal algorithm based on equal power allocation is developed. To make sure that there is a feasible solution to the problem, and the algorithm is integral and practical, call admission control (CAC) mechanisms are introduced and three CAC strategies are discussed. Research results indicate that our algorithm obtains a performance close to the optimal exhaustive search when equal power allocation is applied with a much lower computational complexity, and achieves an effective tradeoff between system efficiency and fairness among users.4.As a promising technology to deal with the scarcity of spectrum resource and improve the spectrum utilization, cognitive radio (CR) has attracted more attention in recent years.It is necessary to apply cooperative communication technologies into CR systems because they also suffer adverse impacts from multipath fading. Based on the property-right model of spectrum sharing, the strategy by which a primary user (PU) with QoS requirement shares its spectrum with secondary users (SUs) in a cooperative way is studied. By assuming the PU is able to lease some of its channel usage time to the SU in order to exchange the cooperative transmission of the SU and improve its QoS when it does not have a good direct link, a spectrum leasing model based on selective cooperation and cooperative game framework is proposed.The solution to this model is discussed and a distributed implementation strategy with low complexity and overhead is developed. Theoretical analysis and computer simulations show that our strategy can greatly reduce PU's service outage probability, and hence guarantee its QoS and improve its transmission capability. At the same time, the strategy makes it possible for the SU to acquire transmission opportunities. Therefore, the strategy is able to produce a win-win outcome for both the PU and the SU.