A WALSH-QPSK CHIP MODULATION APPARATUS FOR GENERATING SIGNAL WAVEFORM IN A DIRECT SEQUENCE SPREAD SPECTRUM COMMUNICATIONS SYSTEM

摘要

In a direct sequence spread spectrum communications system wherein user binary information symbols are spread spectrum modulated and transmitted to the other party, a non-coherent Walsh QPSK and a coherent Walsh QPSK modulation methods, wherein the PN spreading sequences for inphase and quadrature data in a conventional QPSK PN modulation scheme are coded by Walsh sequences indexed by a special rule to reduce the envelope variation of the transmitted signal, can reduce the envelope variation of transmit signal. And, in a direct sequence spread spectrum communications system wherein several user binary information symbols are spread spectrum modulated, the information symbols of each user are covered by user-specified different Walsh codes and transmitted to the other party, a QPSK modulation methods, wherein the polarity of quadrature PN spreading sequence of a user is controlled by a system controller to make the number of users using the quadrature PN sequence equal to that of users using NOT of the sequence, can reduce the envelope variation of transmit signal.