Performance Comparison of OTFS and MC-CDMA with Channel Estimation and Power Back-Off

To ensure robust communication in doubly dispersive channels, Orthogonal Time Frequency and Space (OTFS) modulation has been proposed to exploit the channel in the Delay-Doppler domain. OTFS is expected to outperform conventional Orthogonal Frequency Division Multiplexing (OFDM) especially in high Doppler environments. In this work, we revisit Multi-Carrier Code Division Multiple Access (MC-CDMA) waveforms and compare them with OTFS in practical downlink Single Input Single Output (SISO) scenario with channel estimation and Peak to Average Power Ratio (PAPR) input back-off. Both the modulation schemes are compared for the same information rate, transmit power per symbol and block size MN, where M and N represent the number of Delay and Doppler bins in OTFS respectively. Simulation results highlight the fact that with channel estimation of OTFS, for constant M N with larger M and N, OTFS performs better than MC-CDMA in medium SNR links with less PAPR. In less noisy environments, both OTFS and MC-CDMA perform similarly, with OTFS having an upper hand at very high Dopplers. However, in low SNR links, MC-CDMA with grid boosting outperforms OTFS for any Doppler. Our work shows that both MC-CDMA and OTFS are good contenders for the present needs of high-speed wireless communication links, and the choice of waveform can be made based on the operating environment and system requirements.