Timing Offset Estimation of PPM Signal for Deep Space Optical Communications

Abstract

In the uplink of deep space optical communications, a single-photon detector array is usually used on the flight optical terminal to receive data at the power level of several pW per square meter. The nested format of pulse position modulation and the inter-symbol guard times are usually used in this application. The timing information needed by the demodulator is also carried in this format. It is very crucial to obtain the timing information for demodulating and decoding the signal. An estimation scheme of timing offset for this modulation format is proposed in this article. This method is combined with the photon detecting technique of the up-down counter, providing synchronization as well as reducing the impact of the Earth and ambient background illumination. The method and algorithms for timing offset estimation are given and statistical models of signal processing algorithms are presented on the condition of the Earth background illumination.