Semi-blind parallel factor based receiver for joint symbol and channel estimation in amplify-and-forward multiple-input multiple-output relay systems

In this study, the authors consider a new space-time coding scheme for two-hop amplify-and-forward (AF) relay multiple-input multiple-output (MIMO) relay communication systems. This scheme, called multiple Khatri-Rao space-time coding, which combines symbol stream blocking, spatial precoding and time-domain spreading. The authors show that the received signals at the destination node can be formulated as two parallel factor (PARAFAC) models, and then a novel semi-blind receiver is derived using a two-stage iterative fitting algorithm for joint symbol and channel estimation. Under the assumption that channel state information (CSI) is not available neither at the relay nodes nor at the destination node, the proposed semi-blind receiver operates close to the zero forcing receiver with perfect CSI. Moreover, without any channel training sequence, the proposed semi-blind receiver provides the destination node with full knowledge of all channel matrices involved in the transmission. Simulation results illustrate the performance of the proposed semi-blind receiver in comparison with alternative approaches.