This paper proposes a novel non-Hermitian symmetry ${2 \times 2}$ MIMO-OFDM (Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing) system based on fast Hartley transform (FHT) with unipolar encoding (referred to as HU-OFDM) for visible light communications. The new scheme uses FHT instead of FFT (fast Fourier transform) to process the complex-valued signals reducing the computational complexity and hardware cost and employs two LEDs (light-emitting diodes) to transmit the real and imaginary parts of a complex-valued OFDM signal respectively. Unipolar encoding is applied to the transmitted signal from each LED to ensure non-negative. The restrictions of Hermitian symmetry in traditional optical OFDM systems and real constellation mapping in FHT based optical OFDM systems can be removed simultaneously in the proposed system. Compared with MIMO-ACO/DCO-OFDM system, HU-OFDM has significant performance improvement along with a tremendous decrease in hardware cost and computational complexity. Compared with other non-Hermitian symmetry MIMO-OFDM systems, HU-OFDM has significant advantages in terms of power efficiency, system design flexibility, computational complexity, or hardware cost without losing reliability.

中文翻译：

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一种用于可见光通信的新型非厄米对称正交频分复用系统

本文提出了一种新的非厄米对称性 ${2 \times 2}$MIMO-OFDM（多输入多输出正交频分复用）系统基于快速哈特利变换（FHT）和单极编码（简称HU-OFDM），用于可见光通信。新方案使用 FHT 代替 FFT（快速傅立叶变换）来处理复值信号，降低了计算复杂度和硬件成本，并使用两个 LED（发光二极管）来传输复值 OFDM 的实部和虚部分别发出信号。对来自每个 LED 的传输信号应用单极编码以确保非负。在所提出的系统中，可以同时消除传统光 OFDM 系统中的厄米对称性和基于 FHT 的光 OFDM 系统中的实际星座映射的限制。与 MIMO-ACO/DCO-OFDM 系统相比，HU-OFDM 具有显着的性能提升，同时大幅降低了硬件成本和计算复杂度。与其他非厄米对称 MIMO-OFDM 系统相比，HU-OFDM 在不损失可靠性的情况下，在功率效率、系统设计灵活性、计算复杂度或硬件成本等方面具有显着优势。