DIGITAL COMMUNICATIONS SYSTEM WITH IMMUNITY TO FREQUENCY SELECTIVE FADING

摘要

DIGITAL COMMUNICATIONS SYSTEM WITHIMMUNITY TO FREQUENCY SELECTIVE FADINGAbstract of the DisclosureA digital communications system with increased resistanceto frequency selective fading. Digital signals to be transmittedare phase shift modulated upon a spectrum spreaded carrier.The carrier is generated by mixing the output of a band spreadoscillator with a locally generated IF oscillator signal.The signal thus obtained is divided into transmission periods,each of which is longer than the maximum spreading time ofthe nonlinear transmission medium. The increased bandwidthoccupancy thus obtained increases the immunity of the trans-mitted signals to frequency selective fades moving acrossthe allocated bandwidth. The signals are received by adifferentially adaptive receiver which automatically adjustsits response to the envelope of received signals.