Orthogonal time chirp space modulation based upon fractional Fourier transform

Linear chirps play a significant role in communications because of their ability to spread spectrum and provide secure and robust communication. Orthogonal time frequency space (OTFS) modulation is suit-able for high-mobility transmissions over a stationary delay-Doppler channel. The advantages of linear chirps and OTFS modulation are combined in this study. Specifically, orthogonal time chirp space mod-ulation based on fractional Fourier transform (OTCS-FrFT) is proposed, which is obtained by replacing the two-dimensional (2D) sinusoidal carriers of OTFS modulation with 2D linear chirps. As the Fourier transform is the kernel of OTFS modulation, FrFT underlies the proposed OTCS-FrFT system for its com-plete and orthogonal linear chirp bases and its fast computation algorithms. The information symbols are originally placed on the delay-fractional Doppler plane, which is a rotation of the delay-Doppler plane, where the rotation angle is a free parameter that enables the OTCS-FrFT to adapt to different time-varying Doppler scenarios. It is proven that the OTCS-FrFT is robust to time-varying channels with linear de-lay/Doppler spreading functions. For other time-varying channels, simulations are performed to validate the superior performance of the OCTS-FrFT over other FrFT-based OTFS modulation methods, where the bit error rate is reduced by approximately 1 dB for both high-speed and high-acceleration terminals. (c) 2023 Elsevier B.V. All rights reserved.

Automated summary

This study proposes a novel orthogonal time chirp space (OTCS) modulation method based on fractional Fourier transform (FrFT) by replacing the two-dimensional sinusoidal carriers with two-dimensional linear chirps in orthogonal time frequency space (OTFS) modulation. The OTCS-FrFT method adapts to different time-varying Doppler scenarios by placing information symbols on the delay-fractional Doppler plane with a rotation parameter. The robustness of OTCS-FrFT is proven for time-varying channels with linear delay/Doppler spreading functions, and simulations demonstrate its superior performance over other FrFT-based OTFS modulation methods, reducing the bit error rate by approximately 1 dB for high-speed and high-acceleration terminals.