PROCESS FOR CARRIER AND TIMING RECOVERY

摘要

Extremely stringent demands are made on the reliability of the frequency and phase synchronism of the demodulated digital signals in the synchronisation of reception of OQPSK signals. In the absence of direct coupling with the transmitter, coherent demodulation must be attained with the carrier obtained from the received signal. In order to attain highly precise phase synchronism and hence reception synchronism, the I/F signal is demodulated in a frequency control loop into a complex quadrature signal with in-phase and quadrature components. The digitised and filtered quadrature signal is subjected to particularly efficient frequency detection to generate the thereby necessary carrier frequency. In the downstream phase control loop, a QPSK signal is generated from the OQPSK signal by T/2 delay and, in phase detection, a proportional signal component is obtained for fast regulation within the phase control loop and an integral signal component for the overriding control of the frequency control loop. The synchronisation rate here depends essentially on the phase control which is not affected here by interference suppression filter time constants. Such process and device are applicable in particular to the reception synchronisation of satellite communication systems.