Comb-Search and Hierarchical-Clustering Based Doppler-Shift Acquisition for Space Communications

Abstract

In space communications, the signal quality generally suffers due to long-distance transmission and high dynamic movement. Long-distance transmission causes a very low signal-to-noise ratio (SNR) and high dynamic movement causes a dynamic Doppler-shift on carrier frequency. To boost the signal component in SNR, multiple symbols over a long duration of time are accumulated, which is termed as long-term accumulation. However, during the long-term accumulation, the large acceleration and jerk result in a time-varying Doppler shift, thus dispersing the energy over a wide frequency range. In this paper, we propose a comb-search and hierarchical-clustering (CSHC) based Doppler-shift acquisition scheme, including the Generic CSHC algorithm and Iterative CSHC algorithm, to address the energy dispersion problem for space communications. In the Generic CSHC algorithm, the comb-search (CS) decreases the noise energy by a narrower CS-range while the hierarchical-clustering (HC) increases the signal energy by clustering multiple signal elements into one signal cluster. Then, the Iterative CSHC algorithm, which builds on the iterations of CS and HC, further decreases the noise energy and increases the signal energy. Simulations results verify that our proposed CSHC scheme significantly improves the acquisition probability, as compared with the existing schemes.