Low-Complexity MMSE Receiver Design for Massive MIMO OTFS Systems

We design a low-complexity minimum mean square error (MMSE) receiver for a practical rectangular pulse-shaped orthogonal time frequency space (OTFS) massive multiple-input multiple-output (mMIMO) system. The proposed receiver is designed by exploiting the OTFS channel sparsity, and the structure of matrices involved in the MMSE receiver. We show that the sparse OTFS channel matrix is multi-banded, and has a high bandwidth. This is because its non-zero elements, which occur in multiple bands, are scattered throughout the matrix. We reduce its bandwidth by using the Reverse Cuthill-Mckee algorithm. The proposed MMSE receiver does not use any approximation, and thus has the same bit error rate (BER) as that of its conventional counterpart. We show that the proposed receiver, without any BER loss, achieves significantly lower complexity than the existing state-of-the-art receivers.