Fast acquisition burst mode spread spectrum communications system with pilot carrier

摘要

A high frequency code division multiple access spread spectrum (CDMA SS) communications system includes multiple transmitters and their associated receivers, and a pilot carrier source. In order to reduce errors in the receiver IF frequency due to unavoidable differences between the desired transmitted carrier and receiver local oscillator (LO) , the transmitted carrier ferquency is related to the pilot frequency. The receiver phase-locks the pilot carrier to the local oscillator, thereby providing an IF data signal with reduced frequency error. The IF data signal is multiplied by sine and cosine demodulating signals related to the local oscillator frequency to produce inphase (I) and quadrature (Q) components of the received data signal. The I and Q signals are applied to code matched filters, which produce filtered or decoded signals the amplitudes of which are related to the phase error between the demodulating signals and the IF carrier. A logic arrangement responds to the decoded signals to generate a control signal which step-corrects the demodulating signal to the correct phase. Correction can occur within one or a few bit intervals, thereby allowing burst mode communications while maintaining high throughput for the multiple users of the communication system.