Orthogonal Time-Frequency Multiplexing With 2D Hermitian Symmetry for Optical-Wireless Communications

Jie Zhong,Weiping Liu,Ji Zhou,Jiayin Qin

doi:10.1109/jphot.2020.2972587

Abstract

Orthogonal time-frequency-space (OTFS) modulation is a promising two-dimensional (2D) signal technique to tackle high mobility time-varying wireless channels. However, its good performance on time-frequency plane multiplexing for optical-wireless communications (OWC) has never been fully investigated. In this article, we take advantage of OTFS and propose a new orthogonal time-frequency multiplexing (OTFM) scheme for DC-biased OWC. We first design a 2D Hermitian symmetry in the DC-biased optical OTFM (DCO-OTFM) system to generate the real-valued signal. The bit error rate (BER) of a DCO-OTFM system is studied on the OWC channel. Numerical results demonstrate that the proposed scheme outperforms the conventional DC-biased optical orthogonal frequency division multiplexing scheme.

Highlights

Orthogonal time-frequency-space (OTFS) modulation is an emerging solution to handle high Doppler shifts in time-varying multipath wireless channels [1]–[3]
The required SNRs of DCO-orthogonal time-frequency multiplexing (OTFM) to achieve the threshold of bit error rate (BER), i.e, BER of 1 × 10−3, are lower than for DCO-orthogonal frequency division multiplexing (OFDM) in both 4QAM and 16QAM
A DCO-OTFM scheme was proposed for an optical-wireless communications (OWC) system

Summary

Introduction

Orthogonal time-frequency-space (OTFS) modulation is an emerging solution to handle high Doppler shifts in time-varying multipath wireless channels [1]–[3]. The data can be transformed to the time-frequency domain with conventional modulation schemes, such as orthogonal frequency division multiplexing (OFDM). This promising technology, resulting in an improved bit error rate (BER), simplified channel estimation and signal detection in high-mobility scenarios, was first proposed in [1]. A hybrid system for VLC combined asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) and onoff keying modulation was proposed, which can accommodate various receivers with high spectral efficiency [22]. Our proposed DC-biased optical OTFM (DCO-OTFM) system utilizes proper channel estimation and equalization method at the receiver side, which enables the demodulated signals to achieve better performance on BER and PAPR compared to an OFDM system. We denote M-point discrete Fourier transform (DFT) and the inverse discrete Fourier transform (IDFT) operation matrices by FM and FHM

Optical-Wireless Channel Model

Real-Valued OTFM Signal Generation

Receiver-Side Processing for OTFM Signal

Simulation Setup and Results

Conclusion