Correlation detectors for use in direct sequence spread spectrum signal receiver

In a direct sequence spread spctrum code division multiplex system, including a plurality of transmitters synchronized to a common timing signal and each transmitting a data signal s(t) spread by a bipolar pseudo-random code which is a different assigned shift of a common bipolar sequence;

• a receiver synchronized to said timing signal for receiving said data signals and discriminating the signal transmitted by a predetermined transmitter spread by a bipolar pseudo-random code having a predetermined assigned code sequence shift from the signals transmitted by the other transmitter, said receiver including a plurality of correlation detectors and means for developing (1) a first reference bipolar sequence r(t) that is a replica of the common bipolar sequence and has a code shift that is within one code chip of the assigned shift of the predetermined transmitter and is displaced from the common bipolar code sequence applied to the other correlation detectors by a common fraction of a code chip less than unity, and (2) a second reference bipolar sequence e(t) that is a replica of the common bipolar sequence and has an unassigned code sequence shift,
• each of said correlation detectors including first means for obtaining the product of the transmitted sequences s(t) and the first reference bipolar sequence r(t);
• second means for obtaining the product of the transmitted sequences s(t) and the second reference bipolar sequence e(t) and third means for obtaining a difference between the products obtained by the first and second means;
• synchronous integrator means for integrating the difference;
• means for synchronously sampling an output of the integrator means and signal processor means responsive to outputs of said correlation detectors to synchronize said receiver to said predetermined transmitter.