MIMO multi-relay systems with tensor space-time coding based on coupled nested Tucker decomposition

In this paper, we propose a two-hop MIMO multi-relay system with tensor space-time coding (TSTC) at the source and the relays. The multiple relays use orthogonal channels (parallel relaying) to increase the diversity order, assuming that all the relays can communicate directly with the destination. The signals received at destination form a fifth-order tensor that satisfies a new tensor model, called coupled nested Tucker decomposition (CNTD). This model is a generalization of the nested Tucker decomposition (NTD) and extends the coupling concept, introduced for PARAFAC models, to Tucker-based decompositions. The CNTD consists of a coupling of NTD models that share a common factor, resulting in the concatenation of a generalized Tucker model with a Tucker one. This tensor modeling is exploited to derive a semi-blind receiver for jointly estimating the information symbols and the channels. The uniqueness property of the proposed tensor model and the identifiability conditions of the receiver are established. Monte Carlo simulation results are provided to illustrate the effectiveness of the proposed system and the advantage of exploiting cooperative diversity based on tensor modeling. (C) 2019 Elsevier Inc. All rights reserved.