Orthogonal Time Frequency Space (OTFS) modulation is a candidate modulation technique for high-mobility links. It places data in the Delay-Doppler domain, where a fast-varying channel looks sparse and nearly time-invariant, and it is widely claimed to outperform OFDM. Recent work qualifies these claims. On the other hand, the asymptotic diversity of uncoded OTFS can be as low as one. On static channels, OTFS reduces to a known OFDM variant. And once channel estimation and pilot overhead are counted, a fair comparison looks different.

The work is to analyze what these claims actually say and under which conditions each one holds. This means comparing the definitions of diversity used in the literature (asymptotic versus effective) and the performance metrics used (uncoded error rate with perfect channel knowledge versus achievable rate with estimated channels). The result should be a balanced verdict on when OTFS offers a genuine advantage over OFDM, and if applicable, vice versa.

Prerequisites