A Weighted Combining Algorithm for Spatial Multiplexing MIMO DF Relaying Systems

Jointly detecting signals from the source and relay in a multi-input multi-output (MIMO) relaying system can achieve lower symbol error probability (SEP) and higher diversity order. In the literature, the best detector for spatial multiplexing decode-and-forward (DF) MIMO relaying systems is the near maximum likelihood (NML) decoder. However, both NML decoder and its variation are computationally intensive, especially when high-order modulations and multiple data streams are adopted. In order to develop a more efficient detection scheme, we propose a weighted combining (WC) algorithm which is applied before the final detector. The proposed algorithm merges the signal vectors from the source and relay without expanding their dimension and formulates an equivalent MIMO channel matrix for the combined signal, resulting in a much lower complexity for the subsequent detection. Simulation results show that by using the proposed WC algorithm with the ML detector, the same diversity gain as that of the more complex NML detection scheme can be achieved. In particular, in a symmetric network topology, the performance of the proposed WC algorithm is comparable to that of NML.