Performance Comparison of DFT and RDFT Systems Based on Optical-OFDM in PAPR Reduction

Abstract

This study investigates an advanced Visible Light Communication (VLC) system employing Real Discrete Fourier Transform (RDFT)-based DC-biased Optical OFDM (DCO-OFDM), focusing specifically on the reduction of Peak-to-Average Power Ratio (PAPR) via the Walsh-Hadamard Transform (WHT). This study aims to reduce the substantial computational complexity and power inefficiency of traditional DFT-based DCO-OFDM systems, while preserving comparable spectral efficiency and Bit Error Rate (BER) performance. The RDFT is a superior mathematical approach compared to the DFT as it eliminates the need for costly Hermitian symmetry calculations. This reduces the quantity of real multiplications and real additions by 50%. We simulated a system with N=256 in MATLAB over an AWGN channel utilizing 16-PSK and 16-QAM modulation techniques. The results demonstrate that DCO-OFDM with RDFT shows a BER performance akin to that of DFT-based systems. At an SNR of approximately 33.5 dB, 16-PSK has a BER of 10⁻⁴. At an SNR of approximately 29.5 dB, 16-QAM exhibits an equivalent BER. The application of WHT pre-coding reduces PAPR; for example, RDFT-WHT demonstrates a decrease of around 0.5 dB at a CCDF of 10⁻⁴ in comparison to the exclusive use of RDFT. Upon examining complexity, it is evident that both addition and multiplication have been simplified. The findings indicate that the RDFT-WHT-based system is the optimal choice for future optical wireless communication systems due to its user-friendliness, energy efficiency, and superior performance compared to alternative systems.