Channel Estimation for MIMO Space Time Coded OTFS under Doubly Selective Channels

TL;DR

This paper introduces a UW-based channel estimation method for MIMO OTFS systems with space time coding in doubly selective channels, demonstrating improved performance over OFDM in high-order modulation scenarios.

Contribution

It develops a novel UW-based channel estimation scheme for MIMO OTFS with space time coding, extending previous SISO frame optimization to MIMO systems.

Findings

OTFS outperforms OFDM in high-order MIMO systems.

UW-based estimation effectively tracks doubly dispersive channels.

Higher modulation and code rates benefit more from OTFS advantages.

Abstract

In this paper, we present a unique word (UW)-based channel estimation approach for multiple-input multiple-output (MIMO) systems under doubly dispersive channels, which is applied to orthogonal time frequency space (OTFS) with space time coding (STC). The OTFS modulation has been recently proposed as a robust technique under time varying channels due to its property of spreading the data symbols over time and frequency. Yet another relevant aspect is the employment of multiple antennas at the transmitter and receiver. Therefore, we consider an STC MIMO system with cyclic delay diversity at the transmitter and maximum ratio combining at the receiver, where we develop a UW-based channel estimation scheme for multiple transmit antennas. We show a recently proposed frame optimization scheme for SISO is directly applicable to MIMO. In addition, we evaluate numerically the frame error rate (FER) of OTFS and OFDM with 2x2 and 4x4 MIMO, where the time varying channel is estimated using the UW-based approach. The FER results reveal that OTFS becomes more advantageous than OFDM for MIMO-STC systems with higher order modulation and code rate.