Comparing Precoded MC-CDMA and OTFS for High-Speed V2X Communications

High-Speed Vehicle-to-Everything (V2X) communications is an important aspect of 5G NR technology that requires Ultra-Reliable Low-Latency Communication (URLLC) under highly dispersive channel conditions. In this context, Orthogonal Time Frequency and Space (OTFS) modulation is known to achieve time and frequency diversity, especially in time-dispersive channels with large Doppler frequencies. Literature suggests that Multi-Carrier Code Division Multiple Access (MC-CDMA) can also achieve high diversity gain due to spreading in frequency and time. In this paper, we consider two MC-CDMA schemes, one in which the symbols are spread only along frequency (MC-CDMA-FS) and one where the spread sequence is mapped over both time and frequency (MC-CDMA- TFS). Also, two different precoders based on Walsh-Hadamard (WH) and Zadoff-Chu (ZC) sequences are considered for both of these schemes. We present a comparative performance study of OTFS with MC-CDMA-FS and MC-CDMA-TFS using both the precoders for a single user case, in doubly dispersive channels. Our simulation results show that MC-CDMA-TFS and MC-CDMA-FS schemes with ZC precoding resembles OTFS and even performs better in channels with larger delay and Doppler spreads in this framework.