Optimum decode-and-forward relay-assisted combining scheme with relay decision information

Diversity combining is a form of spatial diversity which is of primary importance in wireless communications. Maximum Ratio Combining (MRC) is known as the best combining scheme because it effectively uses the Channel State Information (CSI) at the receiver in the combining process. However, in cooperative relay-based systems employing relay detection, MRC performance is limited by the fact that the CSI is insufficient to optimize the combining process due to hard decisions performed by some signaling methods at the relay such as Decode-and-Forward (DF). In this paper, we propose a new optimum combining scheme for DF cooperative systems in which the performance gain is achieved through the use of relay decision information along with the CSI in the combining process. The proposed optimum combining is a general scheme, where MRC and other combining schemes are considered to be special cases of optimum combining. Results show that optimum combining significantly improves the system throughput and reduces the error probability. Moreover, it enhances the system robustness due to the adaptivity of the combiner with the change in cooperative channel conditions and packet size.