Fast doppler tracking DSP-based earth station modem for LEO satellite applications

A fast Doppler (carrier frequency drift) tracking earth station modem is presented in this paper. The modem is designed to track high carrier frequency offsets for low-earth orbital (LEO) satellite applications. LEO satellites have very high Doppler offsets with considerable Doppler rates (rate of change of frequency). The earth station modem tracks Doppler offsets at a data rate of 128ksym/s for QPSK modulation. The synchronisation circuit of the modem consists of, frequency synchronisation, symbol timing synchronisation and phase synchronisation. We look into the design and performance analysis of the modem, in particularly the synchronisation system of the modem.