相对于传统的光空间调制, 光广义空间调制在传输速率和频谱效率上虽然有了较大的提升, 但其误码性能不够理想。本文利用脉冲位置调制(PPM)和脉冲幅度调制(PAM), 通过每次同时激活两个激光器而提出了一种双空间调制(DSM)。采用联合界技术推导出了DSM的误码率理论上界, 分析了其频谱效率、传输速率和复杂度的影响因素, 并与已有光空间调制的性能进行了对比。仿真结果表明: DSM不仅提升了系统的频谱效率和传输速率, 而且有效地改善了系统的误码性能。在相同的传输速率下, 当误码率为1×10－3时, 相对于(4, 4)-8PPM SPPM 和(3, 4)-4PPM GSPPM方案, (3, 4)-8PPM-2PAM DSM的信噪比分别改善了约2.5 dB和6 dB, 频谱效率分别提高了2.335 bits/(s·Hz)和0375 bits/(s·Hz)。DSM方案为未来大气激光通信传输速率的提高提供了一种有效手段。

Compared with traditional optical spatial modulation, optical generalized spatial modulation has a significant improvement in transmission rate and spectral efficiency. However, its bit error rate (BER) is not ideal. In this paper, a double spatial modulation (DSM) is proposed to simultaneously activate two lasers, using pulse position modulation (PPM) and pulse amplitude modulation (PAM). The theoretical upper bound of the bit error rate of DSM is then derived using union bound technology. Furthermore, the effect factors of spectral efficiency, transmission rate, and complexity are analyzed. The performance of DSM is compared with that of the proposed optical spatial modulation. The simulation results show that the DSM improves the spectrum efficiency and transmission rate of the system, and efficiently reduces its BER. When the transmission rate is the same and the bit error rate is 1×10－3, the signal-to-noise ratio of (3, 4)-8PPM-2PAM DSM is improved by approximately 2.5 and 6 dB compared with (4, 4)-8PPM SPPM and (3, 4)-4PPM GSPPM, respectively. Further, its spectral efficiency is increased by 2.335 and 0.375 bits/(s·Hz), respectively. Therefore, DSM scheme can effectively improve the transmission rate of atmospheric laser communication in the future.