Spread spectrum codes for use in communication

Abstract

A technique for modulating and demodulating CPM spread spectrum signals and variations of CPM spread spectrum signals uses a set of codes or multiple sets of codes that reduce cross-correlation interference. A transmitter divides a signal data stream into I and Q data streams, independently modulates the I and Q data streams using CPM or a related technique, and superposes the plurality of resultants for transmission. A receiver receives the superposed spread spectrum signal, simultaneously attempts to correlate for I and Q chip sequences, and interleaves the correlated I and Q data streams into a unified signal data stream. In one embodiment the receiver separates the received spread spectrum signal into real and imaginary parts, attempts to correlate both real and imaginary parts for a plurality of chip sequences, and combines separate correlation signals into a unified signal data stream. In other embodiments single-bit or multi-bit digitization of the received spread spectrum signal is carried out prior to correlation. In another embodiment the transmitter differentially phase encodes the information to be transmitted, and the receiver decodes the phase-encoded information.