Implementation of wavelet transform based non-Hermitian symmetry OFDM for indoor VLC system using Raspberry Pi

Abstract

Abstract Optical orthogonal frequency-division multiplexing (OFDM) has proven to be an effective technique for the visible light communication (VLC) system in which data is sent and received through the intensity-modulated/direct-detected optical channel. However, OFDM exhibits high peak-to-average power ratio (PAPR) and for the generation of real-valued signal employs Hermitian symmetry (HS) of the frequency symbols which in turn boost the computational complexity (CC) and deteriorates the performance of the system. Besides, OFDM also included cyclic prefix (CP) as redundancy that reduces the spectral efficiency. This paper aims to target the aforesaid OFDM issues and introduce a novel technique in the form of wavelet transform (WT) based on non-HS OFDM (NHS-OFDM). In the proposed technique, an N-point complex OFDM signal is generated by utilizing wavelets as basis function, from which real and imaginary components are extracted and then concatenated to form a 2N-point real signal. The work also confirmed that the CC of the proposed technique is about 83% less than the conventional Fourier transform (FT) based NHS-OFDM technique due to which reduction in PAPR and bit error rate (BER) improvement is also noticed from the simulated results. The superior performance of WT based NHS-OFDM technique is further verified via experiments conducted by interfacing the computer terminal with Raspberry Pi (RPi) 3b+ modules. In the designed VLC prototype, the NHS-OFDM modem work as the software-defined radio (SDR) on a stand-alone computer. The experiment results reveal that real-time text message is transmitted and received without error at the communication range of 1.75 m while the data rate attains from the prototype is 3.921 Mbps.