A constrained tensor-based approach for MIMO NL-CDMA systems

In this paper, we propose a deterministic tensor-based approach for joint channel and symbol estimation in the context of multiuser multiantenna (MIMO) CDMA communication systems. We use a new nonlinear (NL) coding allowing to obtain a third-order block-Tucker2 model for the signals received by multiple receive antennas, with a constrained structure for the core tensors that ensures the uniqueness of the tensor model. Two types of receiver are developed. First, assuming that the users´ code matrices are mutually orthogonal and known at the receiver, we derive a blind algorithm composed of two steps: a separation of users´ contributions in the received signals, with decoding, followed by a blind channel and symbol estimation for each user separately. Then, when the code matrices are unknown, a semi-blind receiver is proposed for jointly estimating the channels, codes and symbols of all the users. Some simulation results are provided to illustrate the performance of the proposed receivers.