基于似然比的码辅助Turbo迭代同步算法

针对传统接收机在低信噪比环境中因同步损失而引起的Turbo码纠错性能恶化问题,结合Turbo迭代机制,提出基于对数似然比的最大似然比均值(MMLR)码辅助同步算法。首先采用改进的数据辅助方法,将定时误差控制在一个码元周期内;然后根据信号同步、失步时译码输出似然比分布差异,反馈误差信息,进行迭代相位估计。该算法充分发挥译码器的校正纠错功能辅助同步环节,有效地提高了同步精度。最后针对最小移频键控(MSK)信号建立Turbo-MSK仿真模型。仿真结果表明,在极低信噪比下,该算法能够准确完成定时和相位估计,获得与理想同步近似的可靠性能。

Code-Aided Turbo Iterative Synchronization Algorithm Based on Likelihood Ratio

In view of the error-correcting performance deterioration of Turbo codes due to the synchronization loss at low SNR environment, a code aided synchronization algorithm named maximum-mean likelihood ratio (MMLR) based on the log-likelihood ratio is proposed by combining with Turbo iterative mechanism. Firstly, improved data aided (DA) method is adopted to ensure the timing error less than one symbol period. And then error information is fed back according to the distribution of likelihood ratio. The iterative phase estimation is carried out. Since the decoder has the error correcting function, the synchronization accuracy of the algorithm is effectively improved. Turbo-minimum shift keying(MSK) simulation model is established. Simulation results show that the algorithm can accurately complete the timing and phase estimates and achieve the reliability close to that of ideal synchronization at very low SNR.