Low-complexity Linear Equalization for 2×2 MIMO-OTFS Signals
G. D. Surabhi, A. Chockalingam
Abstract
Orthogonal time frequency space (OTFS) modulation is a two-dimensional modulation scheme which has superior performance compared to conventional multicarrier modulation schemes. In this paper, we propose low-complexity linear equalizers for a 2 × 2 multiple-input-multiple-output (MIMO) OTFS system. The proposed equalizers are designed by exploiting the structure of the effective delay-Doppler MIMO channel matrix in a MIMO-OTFS system. The channel matrix in a MIMOOTFS system is a block matrix composed of blocks which have a block circulant with circulant block structure. The proposed approach makes use of the properties of block matrices and block circulant matrices to reduce the computational complexity of linear equalizers. For a 2 × 2 MIMO-OTFS system that uses N ×M OTFS modulation, where N and M denote the number of Doppler and delay bins, respectively, the proposed linear equalizers provide exact solution with a computational complexity of O(MN logMN), whereas conventional linear equalizers require a complexity of O(M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ).