为使现有遥测脉冲编码调制/调频(PCM/FM)系统中的定时同步环路可直接用于多符号检测(MSD)，从而降低系统的复杂度，提出了一种适用于遥测 PCM/FM MSD的位同步算法。该算法采用 MSD的似然比作为定时估计的统计变量，据此可直接利用传统 PCM/FM限幅鉴频接收机中的定时同步环路来实现位同步。与传统的基于“迟早门”的 MSD位同步算法相比，所提算法节省了一个 MSD支路的运算，极大降低了接收机存储和计算资源。此外，所提算法采用 Gardner算法作为定时误差检测单元，便于高速实现；所提算法的定时估计误差的归一化方差在低信噪比区仍小于 0.01，满足遥测接收机的要求，且误比特率 (BER)性能与理想同步情况相比，几乎没有损失。

Applying the timing recovering loop for PCM/FM to Multi-Symbol Detection(MSD) could reduce the complexity of the whole system. This paper proposes a symbol timing synchronization algorithm for MSD in telemetry Pulse-Code Modulation/Frequency Modulation(PCM/FM) system. The proposed algorithm uses the likelihood ratio of MSD as the statistical variable for timing estimation, and can adopt traditional timing synchronization loop in PCM/FM using limiting amplitude and frequency discrimination to achieve symbol synchronization. Compared with the traditional MSD symbol timing synchronization method based on the “early-late gate”，the proposed method saves the operation of a branch of MSD, which greatly reduces the storage and computing resources in receiver. In addition, the proposed algorithm adopts the Gardner algorithm as a timing error detection unit, which facilitates high speed implementation in practical systems. The normalized variance of the timing estimation error in the proposed method is still less than 0.01 in the low SNR region, which satisfies the requirements of the telemetry receiver. Compared with the ideal synchronization situation, the proposed algorithm has almost no loss in terms of Bit Error Rate(BER) performance, and has a promising prospect.