Mobile Satellite TDMA Communications Robust Burst Repetition Despreading

Burst repetition spreading is a well known method for signal spreading in satellite communication systems. Frequency offsets cause a rotation in the repetition symbols, thus in the de-spreading process the repetitions are coherently combined by correcting their phase rotation. However, in low SNR conditions, conventional methods for phase offset estimation result in a large combining loss. In this paper, we developed a novel approximate Maximum Likelihood estimator for the repetition phase offset, and also show an efficient implementation of the estimator. Simulation results show that the combining loss of the developed estimator is significantly smaller than the combining loss of the conventional de-spreading method in low SNR conditions.