一种基于APPA的码辅助载波同步算法

在低信噪比环境下，小的频偏和相偏的存在会使Turbo编码系统的译码性能恶化，所以必须结合迭代译码系统，对信号的残留频偏和相差进行估计。该文提出一种改进的残留频偏载波相位估计算法后验概率辅助(APPA)相位估计，该算法将译码器输出的外信息用于辅助迭代的相位估计。环路滤波器将相位误差信号转换成控制信号，控制数控振荡器的输出，这样可以得到待估计的相位误差。仿真表明，在极低信噪比下(比如，SNR-7.8 dB)该算法在同时存在频偏和相偏的时候能正常工作，其性能非常接近理想同步条件下的性能。

A Code-Aided Carrier Synchronization Algorithm Based on APPA

The residual frequency and phase offset will make obvious degradations on the Turbo decoding performance under low SNR conditions, and it must introduce some coded-aided carrier synchronization algorithm for the phase estimation. In this paper, an improved residual carrier frequency offset estimation algorithm based on APPA(A Priori Probability Aided)phase estimation is proposed. It uses the extrinsic information obtained from the turbo decoder to aid an iterative phase estimation process. And the loop filter converts the phase error signal to a control word that is used to bias the numerically controlled oscillator. The simulation results show that the algorithm performs successfully with small frequency offset and phase offset at very low SNR(for example, SNR<-7.8 dB) and its performance is very close to the optimally synchronized system.