Orthogonal time frequency space (OTFS) modulation, which encodes information symbols in the delay–Doppler domain, offers a promising solution to the problem of high Doppler sensitivity of orthogonal frequency division multiplexing (OFDM) transmission. In this paper we study the diversity of OTFS assuming rectangular waveforms and a delay–Doppler channel with two paths. After introducing the concept of effective diversity (ED), which we argue to be more significant than “standard” diversity in the case of a large number of transmitted symbols, we examine the conditions under which OTFS achieves full ED for QAM symbols. We validate our analytical results through numerical simulations, which show that OTFS practically achieves full ED with sufficiently large signal constellations.

The work of the first three authors was supported by the Australian Research Council through the Discovery Project under Grant DP160100528. The work of Ezio Biglieri was supported by the European Research Council under the H2020 Framework Programme/ERC grant agreement 694974.