The deijitaru demodulator and the differential phase deviation keying demodulator and it is low signal-to-noise ratio input signal demodulation manner

摘要

PURPOSE: To enable symbol synchronization in spite of the carrier phase or frequency of a low S/N ratio by adopting differential phase shift keying demodulation for a digital modem. CONSTITUTION: After the vagueness of carrier frequency is narrowed by a rough frequency estimation and lock detection module 14, filtering processing is performed by integrating and attenuating operation. Since integrators 22, 24, 26 and 28 are attenuated at the end of respective symbol blocks, inter-symbol interference is decreased as a result. Then, symbol timing is estimated in spite of the carrier phase by a digital data tracking closed loop inside a symbol timing module 30 and the symbol timing module 30 adjusts integration windows so as to line up integrators and attenuation filters 22, 24, 26 and 28 on the received data symbol boundary before automatic frequency control closed loop lock. Thus, the symbol synchronization of low S/N is enabled in spite of the phase and frequency of carrier wave.