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网格编码调制(TCM)与脉冲幅度调制(PPM)相结合的T-PPM编码具备了双方在纠错能力和发射功率效率方面的优点,在空间光通信中有广阔的应用前景。而传统的T-PPM编码调制技术在映射方面存在缺陷,制约了系统的可靠性。为改善大气湍流光通信系统的误码性能,提出一种适用于单载波弱湍流空间光信道的改进型T-PPM技术。这种方法采用格雷映射取代传统TCM中的“子集划分”映射,降低接收时的误判可能性。仿真结果表明,格雷码映射能显著改善误码性能;在误码率为10-3处,格雷码映射相比子集映射提高了约0.2 dB增益,有效改善系统的差错性能;在1 ps和2 ps展宽量条件下误码率(BER)分别减少至传统方案的约1/2和4/5,从而验证了格雷码映射的优越性。
T-PPM coding, which combines TCM with pulse width modulation (PPM), has the advantages of both error correction capability and transmission power efficiency, and has broad application prospects in space optical communications. However, the traditional T-PPM coding and modulation technology has defects in the mapping and restricts the reliability of the system. In order to improve the error performance of atmospheric turbulent optical communication system, an improved T-PPM technique is proposed for single-carrier weak turbulence spatial optical channel. This method uses Gray mapping instead of “subset ” mapping in traditional TCM to reduce the possibility of false positives when receiving. The simulation results show that Gray code mapping can significantly improve the error performance. At the bit error rate of 10-3, Gray code mapping improves the error performance by about 0.2 dB compared with the subset mapping. At 1 ps and The bit error rate (BER) of 2 ps bandwidth is reduced to about 1/2 and 4/5 of that of the traditional scheme, which verifies the superiority of Gray code mapping.