Closed-Form Semi-Blind Receiver For MIMO Relay Systems Using Double Khatri-Rao Space-Time Coding

In this letter, we consider a one-way two-hop AF relaying scheme employing two independent Khatri-Rao space-time (KRST) codings at the source and relay nodes. The signals received at destination form a fourth-order tensor whose dimensions correspond to four signal diversities, and which satisfies a nested PARAFAC model. Exploiting this nested structure, we derive two matrix unfoldings expressed in terms of two Khatri-Rao products which are used to propose a closed-form semi-blind receiver allowing to jointly estimate the information symbols and the individual channels. A numerical analysis shows that this new receiver achieves a substantial computational complexity reduction over an iterative (ALS-based) semi-blind receiver, especially in presence of a great number of source and/or relay antennas.