Co-existence Analysis of OTFS and OFDM Waveforms for Multi-mobility Scenarios

Abstract

Multiple waveforms should be supported by the new generation wireless communication systems, in order to satisfy the requirements for various mobility scenarios. Orthogonal frequency division multiplexing (OFDM) has been extensively adopted by various wireless communication systems, but it faces great challenges in high mobility scenarios due to large Doppler shift and Doppler spread effects. To overcome this challenge, orthogonal time frequency space (OTFS) has been recently proposed to exploit delay and Doppler diversities, which leads to superior performance to OFDM in high mobility scenarios. This excellent property empowers OTFS to become a promising waveform for high-mobility wireless communication systems (HMWCS). However, in low mobility scenarios, OTFS does not exhibit obvious performance superiority, and suffers from some additional processing complexity. In this paper, considering multi-mobility scenarios, we study the co-existence of OTFS and OFDM waveforms to achieve good tradeoffs between performance and complexity. By regarding OTFS as precoded OFDM, we design multi-waveform downlink transmission systems. We also study two schemes for the co-existence of OTFS and OFDM waveforms. The time division multiplexing (TDM) scheme enables OTFS users with high mobility and OFDM users with low mobility to be multiplexed in the time domain, while the frequency division multiplexing (FDM) scheme multiplexes OTFS users and OFDM users in the frequency domain. The simulation results show that both the FDM and TDM schemes improve the bit error rate (BER) performance of high mobility users. The results also show that the TDM scheme achieves superior BER performance to the FDM scheme.