Carrier Frequency Synchronization of LDPC Coded Transmissions in High Dynamic Environments

Modern communication systems based on LDPC coded data transmission enable the operations at low signal-to-noise ratio (SNR) conditions, close to the Shannon limit, where strict synchronization is required to ensure the optimal performance of the receiver. Residual offsets left by imprecise synchronization would lead to SNR degradation at the decoder, yet its elimination remains an issue at low SNRs. In this paper we focus on the accurate estimation of carrier frequency offset, and propose a novel frequency estimator with moderate computational complexity, which has wider, signal-length-independent estimation range and lower variance close to the Cramer–Rao bound (CRB), compared to other existing methods. Based on the proposed estimator, we establish a new structure of iterative synchronization embedded decoder by utilizing the expectation-maximization (EM) algorithm. The presented decoder exhibits a capability to significantly alleviate the performance degradation caused by residual offsets and to achieve performance enhancement for both the decoder and synchronizer. Furthermore, we develop a general frequency estimation framework for joint acquisition and fine carrier synchronization, which shows superior performance of low error metric. The proposed frequency estimator and improved frameworks will be of great significance to the implementation of the signal reception in high dynamic wireless communication systems at low SNR conditions.