||In recent years, the productivity for mobile devices has astonishing increase, and almost everyone has one hand-held device, which results in large demand of wireless bandwidth. However, spectrum resource is scarce and expensive. Thus, how to increase the number of served users and per-user throughput becomes an important issue, especially for those users located at cell-edge. In this thesis, we propose two-way relaying scheme to deal with aforementioned challenges because two-way relaying systems require half transmission-time compared with one-way relaying systems. Besides, we adopt amplify-and-forward relaying protocol to assist message exchange between two nodes. Under the assumption that instantaneous CSI is known globally, we can employ various cooperative strategies to exploit spatial diversity such as transmit beamforming, antenna selection. Most existing works on two-way relaying scheme adopt assumption of perfect CSI. Nevertheless, it demands great amount of information exchange between nodes, which leads to huge system overhead. To be more practical, we consider that channel information is first quantized and exchanged with limited bits through feedback channel-. Based on the quantized CSI, we design precoder of relays to maximize sum-rate of two source users. However, this optimization problem is neither convex nor concave, and it can’t be solved by existing CVX tool. Therefore, we adopt branch-and-bound algorithm to approach optimal precoder iteratively. More specifically, channel information can be decomposed into channel quality information(CQI) and channel direction information(CDI), where the former represents the magnitude of channel vector, and the latter indicates the direction of channel vector, and both are quantized accordingly. We will explore statistical properties of quantization error to take expectation on the sum-rate, and adopt branch-and-bound algorithm to perform precoder optimization. Finally, we will demonstrate system performance through computer simulations.|
Index Terms-Cooperative communication, Two-way relaying, Branch-and-bound algorithm, Quantized channel state information, Feedback channel.