Orthogonal Time Frequency Space (OTFS) with Tri-Mode Index Modulation

Orthogonal time frequency space with index modu-lation (OTFS-IM) has been considered a promising technique for improving the bit error rate (BER) in high mobility environments. To further improve the BER and spectral efficiency, here, tri-mode index modulation is proposed with OTFS modulation (TM-OTFS-IM). A portion of information bits is modulated with two distinguishable constellations, and the rest of the delay Doppler resource blocks (DDRBs) remain inactive in the DDRB grid. Through this approach, extra bits can be transmitted by the DDRB indices that correspond to the two constellation sets. The TM-OTFS-IM presented has the ability to improve both the spectrum and energy efficiency when compared to previous OTFS-IM, dual mode OTFS-IM and OTFS methods. Simulation results show the reduction in BER using TM-OTFS-IM as compared to DM-OTFS-IM and traditional OTFS-IM.