Research On The System Enhancement Technology Of Two-way Relaying For Cooperative Communications

With the rapid development of mobile communication, people’s requirements on the data rate and quality of service are also increasing. However, due to the limitations of conventional wireless communication technology, people’s communication experience has not been satisfied very well. In order to address this obvious contradictions, experts in the field of communication have been exploring and continuing to propose efficient communication technologies to improve the user experience, such as OFDM(Orthogonal Frequency Division Multiplexing),MIMO(Multiple-Input Multiple-Output), and cooperative relaying. Among them, the relay technology, which can be used to expande cell coverage, improve system capacity and cell-edge user performance, has attracted a widespread concern.Cooperative relaying technology is divided into two categories, i.e., unidirectional(one-way) and bidirectional(two-way). Compared with the one-way relaying technology, two-way relaying has higher spectral efficiency, and thus it has more practical value. Therefore, mainly focusing on the bidirectional AF(amplify-and-forward) relaying systems, this paper studies the opportunistic relay selection mechanism in the single-antenna scenario and the OSTBC(Orthogonal Space-Time Block Codes) transmission scheme in the multi-antenna scenario respectively. The main contribution of our work can be summarized as follows:1.As for the bidirectional multi-relay scenario, a centralized relay selection algorithm based on the classical max-min criterion is presented to minimize the overall outage probability, which is shown to be outage-optimal. To reduce the complexity of the algorithm, we present a simple distributed relay selection algorithm, which is sub-optimal and ensures high system performance while reducing implementation complexity. When channel estimation error, feedback delay and other factors are taken into account in the actual system, imperfect CSI(Channel State Information) has a great impact on system performance. Therefore, the system performance with imperfect CSI is analyzed, and the closed-form expression of outage probability is given. Finally, the impact of imperfect CSI on relay selection mechanism is simulated and analyzed.2.Orthogonal STBC transmission scheme in two-way relaying system with multiple antennas is studied. First, we present tight upper and lower bounds for the average sum rate of two-way AF half-duplex relaying, which shows that it can significantly mitigate the spectral efficiency loss of conventional one-way AF half-duplex relaying.We then extend the analysis to the scenario where two sources configured with two antennas exchange information via a single-antenna AF relay by using Alamouti’s OSTBC. We introduce both upper and lower bounds for the average sum rate as well as an upper bound for the pair-wise error probability(PEP) for this scheme. We also find the optimal power allocation for both two-way relaying schemes. Our theoretical analysis and simulation results show that compared to the single antenna case, higher average sum rate and diversity order of two can be achieved by the Alamouti OSTBC scheme. Then, we extend the Alamouti scheme to the two-way relay system with arbitrary number of antennas in the source and relay nodes, and investigate how to incorporate orthogonal space-time block code. The symbol error rate performance of the system is also analyzed, which is verified by the simulation results.