The MIMO-OTFS Technique in the Next 6G Communications

The orthogonal time-frequency space (OTFS) technique is a promising method of waveform modulation that encodes data in the delay-doppler (DD) domain. OTFS distinguishes itself from conventional multiplexing methods by employing two-dimensional modulation to alternate between the time-frequency (TF) domain and the delay-Doppler domain. This feature enables the management of Doppler shifts induced by high-speed objects, which is not possible with conventional modulation schemes such as orthogonal frequency division multiplexing (OFDM). The main objective of this work is to provide a concise and comprehensive introduction of this emerging subject, emphasizing its system concept. In addition, we analyze crucial elements of OTFS modulation, including techniques for data detection, channel estimation, MIMO, and multiuser systems.