Sync acquisition and tracking circuit for DS/CDMA receiver

DETAILED DESCRIPTION It is therefore an object of the present invention to provide a precision sync acquisition and tracking circuit for a direct sequence spread spectrum receiver.
According to the present invention, there is provided a sync acquisition and tracking circuit for a direct sequence spread spectrum receiver which receives in-phase and quadrature data signals and in-phase and quadrature pilot signals.
The sync acquisition and tracking circuit comprises a register for storing a plurality of phase position signal.
A first selector cyclically selects each one of the phase position signals in response to a shift command signal which is generated at a rate higher than the rate at which Rayleigh fading occurs.
A pseudo-random number (PN) generator is provided for producing orthogonal PN sequences in accordance with the selected phase position signal.
A correlator takes correlation between the in-phase and quadrature spread pilot signals and the PN sequences at a chip rate to produce in-phase and quadrature despread pilot signals and integrating the in-phase and quadrature despread pilot signals at predetermined intervals to produce a correlation value.
A plurality of accumulators are provided.
A second selector responds to the shift command signal by cyclically selecting each one of the accumulators and applying the correlation value from the correlator to the selected accumulator to thereby cause it to produce a total sum of the correlation values which are produced by the correlator during the time the phase position signals are being repeatedly selected and applied to the PN sequence generator.
At least the highest total sum is selected from the outputs of all accumulators, and a corresponding phase position signal is identified.
Despreading sequences are generated corresponding to the identified phase position signal and applied to the direct sequence spread spectrum receiver to despread incoming signals.
For applications wherein signals are received through multipath fading channels and a plurality of demodulators are provided respectively for the multipaths, a plurality of higher total sums are selected from the outputs of all search accumulators, and corresponding phase position signals are identified