Two Types of Mixed Orthogonal Frequency Division Multiplexing (X-OFDM) Waveform for Optical Wireless Communication

TL;DR

This paper introduces two novel X-OFDM waveforms for optical wireless communication that are real, non-negative, and do not require DC bias, improving power efficiency by leveraging symmetric and antisymmetric properties of sub-carriers.

Contribution

The paper proposes two new X-OFDM waveforms based on Hermitian symmetry and sub-carrier properties, eliminating the need for DC bias and enhancing power efficiency in OWC systems.

Findings

Significantly reduces spectral efficiency to 1/3.

Enhances power efficiency under various noise conditions.

No DC bias needed for the proposed waveforms.

Abstract

The optical wireless communication (OWC) with the intensity modulation (IM), requires the modulated radio frequency (RF) signal to be real and non-negative. To satisfy the requirements, this paper proposes two types of mixed orthogonal frequency division multiplexing (X-OFDM) waveform. The Hermitian symmetry (HS) character of the sub-carriers in the frequency domain, guarantees the signal in the time domain to be real, which reduces the spectral efficiency to $1/2$. For the odd sub-carriers in the frequency domain, the signal in the time domain after the inverse fast fourier transform (IFFT) is antisymmetric. For the even sub-carriers in the frequency domain, the signal in the time domain after the IFFT is symmetric. Based on the antisymmetric and symmetric characters, the two types of X-OFDM waveform are designed to guarantee the signal in the time domain to be non-negative, where the direct current (DC) bias is not needed. With $N$ sub-carriers in the frequency domain, the generated signal in the time domain has $3N/2$ points, which further reduces the spectral efficiency to $1/3 = 1/2 \times 2/3$. The numerical simulations show that, the two types of X-OFDM waveform greatly enhance the power efficiency considering the OWC channel with the signal-dependent noise and/or the signal-independent noise.