光无线通信中基于哈特莱变换的翻转OFDM技术

Flip-OFDM Based on Hartley Transform for Optical Wireless Communications

提出了一种新的基于快速哈特莱变换(FHT)的翻转光正交频分复用(OFDM)方案(Flip-FHT)。快速哈特莱变换为实三角变换,当用其处理傅里叶变换时,输入信号不需要厄米对称性。同时,与传统的基于快速傅里叶变换(FFT)的非对称限幅光OFDM(ACO-OFDM)中只有奇数子载波携带信息符号不同,该方案由于翻转了实双极信号的负数部分,使得偶数子载波也可以携带信息符号,故该方案适用于强度调制/直接检测(IM/DD)光无线通信(OWC)系统。与ACO-OFDM相比,Flip-FHT的频谱效率提高了1倍,计算复杂度在接收端降低了50%。仿真结果表明,与采用4QAM和16QAM(正交幅度调制)的ACO-OFDM相比,采用BPSK(二进制相移键控)和4PAM(脉冲幅度调制)的Flip-FHT可以在系统结构更简单、星座尺寸更小的情况下获得相同的性能。

We proposed a novel flip-optical orthogonal frequency division multiplexing(OFDM) scheme based on fast Hartley transform(FHT), namely Flip-FHT. FHT, as a real trigonometric transform, was used to process the Fourier transform. Therefore, Hermitian symmetry was not required for the input signal. At the same time, unlike the traditional fast Fourier transform(FFT)-based asymmetric clipped optical OFDM(ACO-OFDM), in which only odd subcarriers carried information symbols, the proposed scheme flipped the negative part of the real bipolar signal so that even subcarriers could also carry information symbols. Therefore, this scheme is suitable for intensity modulation/direct detection(IM/DD) optical wireless communication(OWC) systems. The spectral efficiency of the Flip-FHT system is 2 times that of the ACO-OFDM system, and the computational complexity at the receiver is 50% that of the ACO-OFDM system. Simulation results show that compared with the ACO-OFDM system under 4-quadrature amplitude modulation(4 QAM) and 16 QAM, the Flip-FHT system featuring binary phase-shift keying(BPSK) and 4-pulse amplitude modulation(4 PAM) achieves the same performance with a simpler system and a smaller constellation size.