Process for searching for synchronization on reception of a spread spectrum modulated signal

A sequence synchronization and carrier frequency searching device included in a phase demodulator which demodulates a received signal resulting from a phase modulation of a digital pseudorandom sequence by a data signal, said digital pseudorandom sequence phase-modulating said carrier and having a predetermined length L of bits,

• said device comprising means for deriving a signal at a predetermined local frequency close of the frequency of said carrier, means for generating a local digital pseudorandom sequence identical to said sequence in said received signal, and a first correlator,
• said first correlator comprising first modulation means for phase-modulating said local frequency signal by said local sequence into a modulated signal, second modulation means for phase-modulating said received signal by said modulated signal into a mixed signal with intermediary frequency, means for filtering said mixed signal in a filtering band into a filtered signal, means for integrating said filtered signal for at least a predetermined integration period into an integrated signal, and means for comparing said integrated signal with at least one predetermined threshold thereby supplying a comparison signal,
• said device further comprising control means for modifying said integration period in said integrating means and a local sequence time shift in said generating means as a function of said comparison signal, and means controlled by said control means for modifying said local frequency in said deriving means to enable said local frequency to be equal to first discrete values and second discrete values,
• said first discrete values of said local frequency corresponding to first intermediary frequencies in said mixed signal substantially equidistributed in a band widely including said filtering band, said first local frequency discrete values being deriving in said deriving means under the control under said control means during plural successive series of integration steps respectively, each series of steps including at least 2L integration steps in said integrating means corresponding to 2L successive half-bit time shifts of said local sequence in said sequence generating means respectively, said control means stopping the discrete variation of said local frequency and the half-bit shifting of said local sequence responsive to said integrated signal exceeding said predetermined threshold, and
• said second discrete values of said local frequency being deducted from one another from a second frequency stepping increment that is lower than the difference between two first intermediary frequencies and which correspond to intermediary frequencies included in a second frequency band centered on said first found frequency and wider than said filtering band,
• said second local frequency discrete values being deriving by said deriving means under the control of said control means during last integration steps for which said local sequence does not undergo any time shift.