DEVICE FOR DEMODULATING A SPREAD SPECTRUM SIGNAL

Circuitry for receiving and demodulating a spread spectrum signal integrates signal acquisition and tracking functions and also accommodates signal drift. Two data decoding signals are generated which correspond to the pseudo noise code used to modulate the received signal and which are phase-shifted by a half-chip interval. Two correlators use the decoding signals to demodulate the received signal, both during acquisition and tracking, producing two data signals. A summer combines the two data signals to produce a signal whose strength is less dependent on the degree of synchronization of each data decoding signal with the received signal. Tracking error circuitry periodically compares the two demodulated data signals and incrementally phase shifts the two data decoding signals, the magnitude of the increment being one-quarter chip and the polarity being selected to strengthen the weaker of the two data signals. This causes the circuitry to track the received signal despite gradual signal drift. A bank of correlators also demodulate the received signal using test decoding signals having different phase angles. The phase angles of the test decoding signals are periodically adjusted to locate stronger signals. Control circuitry constantly compares the strength of the demodulated test signals and of the two data signals and adjusts the phase of the two data decoding signals to correspond to that phase producing the strongest demodulated signal.