A Low Complexity Code-aided Carrier Synchronization Algorithm
Yan Hui Tang Fa-jian Zhang Zhong-pei
National Key Laboratory of Science and Technology on Communications, University of Electronic Science and Technology of China, Chengdu, Sichuan 611731, China
Abstract:Considering the condition of low Signal to Noise Ratio (SNR), the Code-aided carrier recovery algorithm performs high computational complexity. Based on the analysis of the probability density function of posterior information, modified posterior information mean with three states and new Log-Likelihood Ratio (LLR) are proposed according a probability threshold that represents the information reliability. Then a new carrier synchronization algorithm is obtained when the new posterior information mean and log-likelihood ratio are separately applied into the expectation maximization and soft frequency sweep algorithm. There is a simplified expectation maximization algorithm and evaluation function. In last, the simulations by the Turbo code with 1/6 code rate verify that the new algorithm improves the performance of computational complexity, increases the synchronization range and achieves perfect synchronization with only 0.05dB loss when SNR exceeds -7.9 dB.