Semi-blind Channel Estimation for Amplify-and-Forward Cooperative Relay Networks

We consider channel estimation in amplify-andforward wireless relay networks when coherent distributedspacetime coding is performed at the relays. Employing minimum mean-square-error signal detection at the destination, wefirst bring clearance on the detector formulation when only partial channel state information is available. We then consider ch annel estimation and propose to use a semi-blind (SB) estimation method based on the expectation maximization algorithm. Implementing the SB estimator in an iterative scheme, we show that a considerable improvement can be achieved in the recei ver performance after processing only few iterations. We discu ss the optimality of the proposed estimation scheme and further pr opose modifications to it in order to obtain an unbiased estimate to improve the receiver’s performance. Moreover, we show thathis way, we can obtain an interesting improvement in the receive r performance for large signal constellations.