FPGA Implementation of SFO for OFDM-based Network Enabled Li-Fi System

Light Fidelity (Li-Fi) is the complementary technology to the RF based communication in 6G. It uses optical spectrum which is completely free and unregulated. Sampling frequency offset (SFO) is an issue related to the mismatch between TX and RX clock oscillators. However, this issue is often assumed to be ideal in many Li-Fi research. In this work, we aim to address this issue by proposing an FPGA implementation of SFO compensator module for OFDM system. We optimize an SFO compensation method so that it can be implemented in FPGA efficiently in terms of resource usage. We evaluate the module by integrating it with the OFDM processor, Linux TCP/IP stack, and tested with TCP data. Real-time experiment results demonstrate that with our SFO compensator, the EVM of our Li-Fi system can be decreased up to 6.7% and 1.4% for QPSK and 16-QAM, respectively. Frame lost is decreased by 22.42% and TCP data rate is increased by 8.25x.

I. Introduction

It is shown that optical spectrum can be used in 6G [1], [2]. Li-Fi uses LEDs for transmitters (TX) and photodiodes for receivers (RX). It uses the visible light spectrum between 400 THz to 800 THz for downlink transmission. Hence, it is also called visible light communication (VLC). This spectrum is completely free and unregulated. Therefore, it has a potential to be used simultaneously for illumination and data transmission [3]. The uplink transmission can use the infrared spectrum. Li-Fi can be used for indoor positioning system [4], internet of things (IoT) [5], and industrial network [6]. Furthermore, Li-Fi can also be coordinated with Wi-Fi to form hybrid network [7], [8].