Importance

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Abstract

A direct sequence spread spectrum receiver for receiving an RF carrier radio signal modulated with a message signal in accordance with a code having a fundamental frequency converts the received signal to an IF signal centered about a frequency f.sub.o corresponding to the code fundamental frequency offset by a Doppler shift. The IF signal is digitized and sampled at a local clock frequency to develop N-bit digital signals. Locally generated digital phase shifted sine and cosine signals at frequency f.sub.o are multiplied by a local code to obtain local 1-bit IF signals which are then correlated with the digitized IF signals to develop in phase and quadrature component signals. A tracker uses the component signals to translate the frequency of the digital local IF signal to track the Doppler shift, to maintain the local sampling frequency at 4f.sub.o, and to maintain the local code generator in synchrony with the code of the received signal. Except for the IF down conversion, the receiver employs all digital circuitry. The receiver architecture is adapted to a low power sequential tracking microreceiver.

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First Claim