Low-Complexity Linear Equalization for OTFS Systems with Rectangular Waveforms

Orthogonal time frequency space (OTFS) is a promising technology for high-mobility wireless communications. However, the equalization realization in practical OTFS systems is a great challenge. In this paper, we first investigate the structure of the delay-Doppler domain effective channel matrix for more practical full-cyclic-prefix OTFS systems, and then reveal the block-circulant property and quasi-banded sparse structure of equalization matrices for the two typical linear equalization methods, i.e., zero-forcing and minimum mean square error. Then, two low-complexity linear equalizers are proposed, where Fast Fourier Transform and lower-upper (LU) factorization are efficiently leveraged to reduce the complexity. Compared with the existing low-complexity linear equalizers, the proposed equalizers improve the performance without additional complexity.