Costas序列短波MFSK通信时频联合同步方法

针对低信噪比与强多径传播导致短波MFSK信号捕获困难、同步精度低的问题，提出一种基于Costas序列的短波MFSK信号时频联合同步方法。利用Costas序列二维图案优异的自相关特性进行信号检测与同步，将传统的滑动窗口法由时域扩展到时频域，同步获得时间和频率的估计值;为了降低计算量，给出了频偏与时延的精估计方法。仿真结果表明，与传统伪随机码(PN码)同步方法相比，提出的方法具有更好的抗噪声和抗频偏性能。在信号带宽为50 Hz、同步序列长度为1.28 s的ITU-R中纬度短波信道上，该同步方法能够达到98%的捕获率，虚警概率低于10^-2;时间同步误差低于12 ms;频率估计误差低于1 Hz。

Time-frequency joint synchronization method of HF MFSK communication based on Costas sequence

Aiming at the problems of low signal-to-noise ratio and strong multipath propagation that cause HF MFSK signal acquisition difficulties and low synchronization accuracy, we propose a time-frequency joint synchronization method of HF MFSK signals based on Costas sequence. This method uses the excellent autocorrelation characteristics of Costas sequence two-dimensional patterns for signal detection and synchronization, and extends the traditional sliding window method from the time domain to the time-frequency domain, which can obtain time and frequency estimates simultaneously. In order to reduce the amount of calculation, a precise estimation method of frequency offset and time delay is given. The simulation results show that, compared with the traditional PN code synchronization method, the proposed method has better anti-noise and anti-frequency offset performance. On the ITU-R mid-latitude HF channel (signal bandwidth is 50 Hz, synchronization sequence length is 1.28 s), this synchronization method can achieve a capture rate of 98%, and false alarm probability is less than 10^-2. The time synchronization error does not exceed 12 ms. The frequency estimation error is less than 1 Hz.