Orthogonal Time Frequency Space Modulation

TLDR

The authors introduce Orthogonal Time Frequency Space (OTFS) modulation, a two‑dimensional scheme operating in the delay‑Doppler domain. OTFS exploits full time‑frequency diversity to transform the fading, time‑varying channel into a quasi‑static channel with a nearly constant complex gain, eliminating the need for transmitter adaptation. Simulations show OTFS yields several dB better block‑error‑rate than OFDM across high Doppler, short‑packet, and large‑antenna scenarios, approaching channel capacity with MIMO scaling while OFDM performance collapses.

Abstract

A new two-dimensional modulation technique called Orthogonal Time Frequency Space (OTFS) modulation designed in the delay-Doppler domain is introduced. Through this design, which exploits full diversity over time and frequency, OTFS coupled with equalization converts the fading, time-varying wireless channel experienced by modulated signals such as OFDM into a time-independent channel with a complex channel gain that is roughly constant for all symbols. Thus, transmitter adaptation is not needed. This extraction of the full channel diversity allows OTFS to greatly simplify system operation and significantly improves performance, particular in systems with high Doppler, short packets, and large antenna arrays. Simulation results indicate at least several dB of block error rate performance improvement for OTFS over OFDM in all of these settings. In addition these results show that even at very high Dopplers (500 Km/h), OTFS approaches channel capacity through linear scaling of throughput with the MIMO order, whereas the performance of OFDM under typical design parameters breaks down completely.