V-BLAST receiver and performance in MIMO relay networks with imperfect CSI

Previous work demonstrated that the improvements in spectral efficiency and link reliability can be obtained in wireless relay networks employing terminals with MIMO capability. In order to take the advantage or MIMO relay networks while mitigate the complexity or decoding procedure, we propose a scheme that applies ZF relaying at the relay terminals and utilizes MMSE V-BLAST receiver at the destination terminal for two-hop half-duplex coherent MIMO relay networks. Considering the channel estimation is often imperfect due to the noise and interference, this paper extends the V-BLAST receiver design to the imperfect channel state information (CSI), assuming the channel estimation errors are independent complex Gaussian with zero mean and known second-order statistics. A robust MMSE nulling operator and its corresponding symbol detection ordering criterion is proposed for the MMSE V-BLAST receiver, which aims at providing, in each layer, the minimum average mean square error (MSE), over the random channel errors. The proposed ordering rule achieves global average MSE optimization which results in better performance than the previously proposed robust ZF V-BLAST. It has been shown that the proposed design exploits the characteristics of MIMO relay networks to provide good performance with respect to imperfect CSI while keeping a low complexity of the decoding procedure.