Multiple-rate direct sequence architecture utilizing a fixed chipping

Abstract

A spread spectrum communication system is provided in which a receiver is adapted to despread multi-bit digital signals transmitted with a fixed chipping rate using two or more different spreading code lengths. As a result, a longer spreading code could be utilized to transmit at a lower data rate for conditions in which jamming resistance is more critical, such as over longer distances, and a shorter spreading code could be utilized to transmit at a higher data rate for conditions in which jamming resistance is less critical, such as over shorter distances. The receiver further comprises a digital matched filter adapted to correlate to the two different spreading codes. The digital matched filter comprises a digital delay line having a plurality of successive delay stages that propagate the received digital signal therethrough at a fixed rate corresponding to the chipping rate of the digital signal. A first correlator compares the digital signal to a first spreading code having a length M, and a second correlator compares the digital signal to a second spreading code having a length N, in which N is less than M. A multiplexer is adapted to select an output from one of the two correlators.