提出了一种基于两个并行相位调制器产生正交频分复用(OFDM)矢量毫米波信号的实现方案。与已有的方案相比,所提方案仅需要两个相位调制器,既不需要复杂的电路来控制调制器的直流偏置,也无需采用预编码技术,大幅降低了发射机的复杂度和系统成本。OFDM矢量信号和射频(RF)信号均采用数字信号处理(DSP)模块产生,以保证RF信号频率的灵活调节。在DSP模块中,通过对上变频后的OFDM矢量信号和无调制RF信号进行希尔伯特变换得到双单边带电信号,并将其加载到相位调制器上。采用光交错滤波器滤除光载波,在接收端用一个高速的光电探测器通过拍频得到OFDM矢量毫米波信号。基于所提方案,采用MATLAB和商业光通信仿真软件搭建了仿真平台,得到了50 GHz正交相移键控调制的OFDM矢量毫米波信号,并分析了测量结果与接收光功率和相位差偏移的关系。结果表明,该传输系统的误码率小于硬判决前向纠错门限(3.8×10 -3),这说明OFDM矢量毫米波信号的产生方案是可行的。

We propose an implementation scheme for generating orthogonal frequency division multiplexing (OFDM) vector millimeter-wave (mm-wave) based on two parallel phase modulators (PMs). Compared with previous schemes, the proposed scheme only needs two PMs without complex circuits to control the direct current bias of the modulator and precoding technology, which greatly reduces the complexity of the transmitter and the system cost. The OFDM vector signal and radio frequency (RF) signal are generated by digital signal processing (DSP) module to ensure the flexible adjustment of RF signal frequency. In the DSP module, one up-converted OFDM vector signal and the unmodulated radio frequency signal are transformed by Hilbert transform to obtain the dual single sideband (SSB) signals, respectively, which drive phase modulators. An optical interleaver is used to filter out optical carriers, and a high-speed photodetector is used to obtain the OFDM vector mm-wave signal through beat frequency. Based on the proposed scheme, we demonstrate the generation of a 50-GHz quadrature phase-shift keying (QPSK)-modulated OFDM vector mm-wave signal by simulation with the MATLAB and the optical communication commercial software. The measured results versus received optical power and phase deviation drift are analyzed. The results show that the bit error rate of the transmission system is less than the hard decision forward error correction threshold of 3.8×10 ^-3, which shows that the scheme of OFDM vector mm-wave signal generation is feasible.