Process for searching for synchronization on reception of a spread

Abstract

In a phase demodulator is received a signal of which the carrier is phase-modulated by a digital pseudorandom sequence itself phase-modulated by a data signal. A frequency close to that of the carrier is locally modulated by a sequence identical to the received sequence. The received and local signals are mixed into a filtered signal with an intermediary frequency band. A repetitive double integration step of the signal filtered into an integrated signal is used and is compared with a threshold in order to quantify the correlation between the received and local signals. Firstly, the local frequency varies according to a few discrete values spread over the uncertainty range of the carrier corresponding to intermediary frequencies in the vicinity of the filtering band. At each discrete frequency value, integration steps are carried out for half-bit local frequency shifts. Synchronization of the sequences is acquired in response to an integrated signal exceeding said threshold at the end of an integration step. Then, the value of the carrier frequency is estimated by the average of numerous discrete local frequencies corresponding to favorable integration steps and included in a band centering on the frequency found during synchronization of the sequences. The invention also relates to the closed-loop controlling of the amplification gain in correlators of the demodulator.