In this letter, we investigate the problem of frame synchronization in a free-space optical (FSO) communications link, where a known synch pattern is periodically embedded in the transmitted bitstream. The modulation format is on-off keying (OOK) and the electrical signal provided by the photo-detector is plagued by a mixture of thermal and shot noise with signal-dependent power. Due to atmospheric turbulence, channel attenuation can exhibit large random fluctuations, so that no prior knowledge of the signal level and noise variances is assumed. These parameters, together with the start-of-frame, are jointly estimated using a simplified maximum likelihood (ML) approach. Numerical simulations indicate that the proposed scheme is able to effectively exploit the presence of shot noise to improve its detection capability, and outperforms the standard frame synchronization method tailored for an AWGN channel with signal-independent noise power.

中文翻译：

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信号幅度和噪声功率未知的 FSO 链路的帧同步


在这封信中，我们研究了自由空间光（FSO）通信链路中的帧同步问题，其中已知的同步模式周期性地嵌入到传输的比特流中。调制格式为开关键控 (OOK)，光电探测器提供的电信号受到热噪声和散粒噪声与信号相关功率的混合影响。由于大气湍流，信道衰减可能表现出较大的随机波动，因此无需假设信号电平和噪声方差的先验知识。这些参数与帧起始一起使用简化的最大似然 (ML) 方法进行联合估计。数值模拟表明，所提出的方案能够有效地利用散粒噪声的存在来提高其检测能力，并且优于针对具有与信号无关的噪声功率的AWGN信道定制的标准帧同步方法。