Layer Transmission for Cooperative Communication with Asymmetric Relay Channels

In downlink relay system, the conventional straightforward relaying scheme named decode-and-forward (DF) protocol is used at relay station (RS) to decode the data received from the base station (BS) and forward the decoded data to the mobile station (MS) to improve the spatial diversity gain. It is not spectrum efficient and capacity optimal since the wireless channels of BS-to-RS, BS-to-MS, and RS-to-MS links are asymmetric, i.e., different channel qualities are obtained in different links in the practical scenario. In this proposed scheme, layer transmission is used at BS and RS in two transmission phases to provide optimum spectrum efficiency based on different underlying channel situations. Specially, we discuss the capacity behavior of the proposed scheme and compare with the baseline, namely the capacity behavior of the conventional DF scheme. Our results are encouraging in that layer transmission scheme significantly improves the better capacity performance in downlink relay channels