Joint Delay-Doppler Index Modulation for Orthogonal Time Frequency Space Modulation

Orthogonal time frequency space (OTFS) is a promising waveform with outstanding performance in doubly-selective channels. Spreading information symbols across the entire delay-Doppler plane enables OTFS to exploit full diversity. Nevertheless, there is a need for enhanced reliability in OTFS systems to satisfy the rigorous requirements of forthcoming communication systems. To tackle this concern, we propose a scheme called joint delay-Doppler index modulation OTFS (JDDIM-OTFS). This scheme activates delay or Doppler resource elements in a subframe, and in order to obtain higher spectral efficiency, we use different constellations for each active resource block. Furthermore, we utilize a low-complex detector with the help of a greedy approach. Moreover, a theoretical upper bound is derived for the bit error rate (BER). Simulation results validate that JDDIM-OTFS outmatches classical OTFS and other benchmark schemes in terms of BER under perfect and imperfect channel conditions.