OTFS: Interleaved OFDM with Block CP

Abstract

Orthogonal time frequency space (OTFS) modulation is a recently proposed waveform for reliable communication in high-speed vehicular communication scenarios. It has better resilience to inter-carrier interference (ICI) than orthogonal frequency division multiplexing (OFDM). In this work, we describe OTFS as block-OFDM with a cyclic prefix and time interleaving. This interpretation helps one visualize OTFS in the light of OFDM as well as it also helps in analyzing the gain obtained by OTFS over OFDM. Further, we compare the performance of OTFS with its contender 5G new radio (NR)'s OFDM configuration of variable subcarrier bandwidth (VSB-OFDM) while considering practical forward error correction codes and 3GPP high-speed channel model. This provides realistic performance comparison, which is highly desired for technology realization. Considering practical channel estimation, we find that OTFS outperforms VSB-OFDM with 5G NR parameter by about 5dB. We also present results on peak to average power ratio (PAPR) due to specific pilot structure used in OTFS for channel estimation.

Time Domain Channel Estimation and Equalization of CP-OTFS Under Multiple Fractional Dopplers and Residual Synchronization Errors

“…y(k , L p +l ) = . Also, as explained in the [32], the time domain signal can be viewed as the interleaved OFDM, in which an N-point FFT is taken along the Doppler axis and then interleaved to get the time domain signal. If this is applied to the received delay-Doppler signal y(k , l ), then the signal without CP can be given as,…”

“…Such modifications not only improve the immunity of OFDM to inter-carrier interference (ICI), which is caused by high Doppler in high mobility conditions and phase noise at high carrier frequencies, but also allow a smooth transition from 4G (IMT-Advanced [9]) to 5G with minimal changes. In a recent work by the authors [10], it VOLUME 4, 2016 i This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License. For more information, see https://creativecommons.org/licenses/by-nc-nd/4.0/ This article has been accepted for publication in a future issue of this journal, but has not been fully edited.…”

On the Characterizations of OTFS Modulation over multipath Rapid Fading Channel

“…The above channel diagonalization will enable a one-tap detector and equalizer in accordance with the pretty simple input-output relation, so (5) produces an ideal communication system.…”

“…Because of the enormous advantage against Doppler spread, OTFS has attracted widespread attention as a next generation modulation scheme. To analyze the gain obtained by OTFS over OFDM, OTFS was described as block-OFDM with a cyclic prefix and time interleaving [5].…”

Estimation and Equalization of residual synchronization errors in CP-OTFS

“…Such modifications not only improve the immunity of OFDM to inter-carrier interference (ICI) caused by high Doppler in high mobility conditions and phase noise at high carrier frequencies but also allow a smooth transition from 4G (IMT-Advanced [9]) to 5G with minimalistic changes in the system configuration. In a recent work by the authors [10], it is shown that orthogonal time frequency space (OTFS) [11]- [13] outperforms adaptive OFDM used in 5G-NR in such high ICI conditions.…”