Low-complexity improved schemes for ACO-OFDM based on hartley transform or real-fourier transform over AWGN channel

As a widely used Intensity Modulation and Direct Detection (IM/DD) system, Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing (ACO-OFDM) is considered one of the most promising modulation techniques for high-speed optical communications. Conventional ACO-OFDM uses Hermitian Symmetry (HS) to guarantee a real signal, which results in high computational complexity. The Real Discrete Fourier Transform (RDFT) and Discrete Hartley Transform (DHT) offer alternative approaches to generating real-valued OFDM signals without the need for HS. In the existing literature, various modified techniques have been proposed to enhance ACO-OFDM in terms of bit error rate (BER) or spectral efficiency. However, these methods often suffer from high computational complexity or poor BER performance due to DC offsets and low-frequency noise. To the best of our knowledge, few studies have explored low-complexity yet improved ACO-OFDM schemes that use alternatives to the conventional Discrete Fourier Transform (DFT). In this context, this paper investigates the implementation of Diversity-Combining (DC) and Improved Noise Cancellation (INC) techniques using the Discrete Hartley Transform (DHT) and Real-DFT in an ACO-OFDM scheme over an Additive White Gaussian Noise (AWGN) channel. Simulations conducted in MATLAB 2021 show that both DHT-based and Real-DFT ACO-OFDM achieve similar BER performance compared to conventional ACO-OFDM. Furthermore, the proposed schemes demonstrate a 3 dB power gain in an AWGN channel over traditional ACO-OFDM. Given their low complexity and high performance, DHT-based and Real-DFT INC-ACO-OFDM emerge as promising candidates for optical network systems. Among them, DHT-based solutions are particularly advantageous due to their lower computational complexity.