基于导频辅助的预编码连续相位调制(CPM)信号精确同步算法

Precise synchronization algorithm for CPM signal based on pilot-aided pre-coding

针对连续相位调制(continuous phase modulation,CPM)信号同步问题,提出一种基于导频辅助的位定时与载波同步算法。导频信号由伪随机码构成,采用二进制预编码连续相位调制,在不破坏恒包络特性的基础上同时保留其伪随机特性。利用该导频信号可以实现位定时误差、载波频偏、相偏各参数并行独立估计。算法首先推导出同步头相关函数的闭合表达式;然后利用相关函数的单峰特性,通过搜索第1大和第2大采样值,实现对定时误差、相位误差的精确估计,并利用相位估计值通过差分计算实现对频偏的估计;最后通过计算机仿真,给出了该算法关于定时、相位、频偏估计的抗噪性能和估计范围。结果表明,该算法在加性高斯白噪声信道中具有良好的性能,各同步参数在估计范围内和较低信噪比条件下能够接近修正的克拉美罗界(modified Cramer-Rao bound,MCRB)。

For the continuous phase modulation （CPM） signal synchronization problem, this paper proposes a symbol timing and frequency offset estimation algorithm based on pilot symbols. The pilot is constituted by pseudo random sequence ; by means of binary pre-coding CPM, which reserves the pseudo random trait without destroying the constant envelop. The pilot is used for independence estimate of synchronization parameters such as timing, frequency offset and phase offset, Firstly, the close expression of the correlation function for the synchronous head is derived. Then by employing the single peak characteristic of the correlation function, the first and second largest sample values arc searched to realize accurate estimation of timing error and phase error. Estimation of the frequency offset is achieved according to the estimated phase. Through computer simulation, anti-noise performance and estimation range are obtained of the timing and phase as well as frequency offset estimation of this algorithm. Simulation shows that the algorithm has a favorable estimation performance in the AWGN channel, the synchronization parameters in the condition of estimation range and low SNR can approximate mod- ified Cramer-Rao bound（MCRB）.