METHOD FOR DOPPLER-REPLICA HARMONIC AVOIDANCE

摘要

A DIRECT SEQUENCE SPREAD SPECTRUM RECEIVER RECEIVES AN INPUT SIGNAL ON A SIGNAL CARRIER FREQUENCY. THE RECEIVER GENERATES A LOCAL OSCILLATOR SIGNAL (214) WHICH IS OFFSET FROM THE CARRIER FREQUENCY. THE INPUT SIGNAL AND THE LOCAL OSCILLATOR SIGNAL (214) ARE MIXED PRODUCING AN IF SIGNAL WHICH IS CONVERTED TO A DIGITAL SAMPLE AND STORED IN MEMORY. A CORRESPONDING REPLICA SIGNAL IS GENERATED AND CORRELATED WITH THE DIGITAL SAMPLE. THE OFFSET OF THE LOCAL OSCILLATOR FREQUENCY FROM THE CARRIER FREQUENCY IS SUFFICIENTLY LARGE TO CAUSE THE HARMONICS OF THE REPLICA SIGNAL TO FALL ABOVE THE HIGHEST FREQUENCY OF THE IF SIGNAL. SUCH A RECEIVER IS USEFUL IN GLOBAL POSITIONING SATELLITE (GPS) SIGNAL PROCESSING WHERE A REPLICA GENERATOR MUST BE USED TO ACQUIRE THE INCOMING SATELLITE TRANSMISSIONS.