Apparatus for the acquisition of a carrier frequency and symbol timing lock

摘要

Acquisition of a carrier frequency lock and a symbol timing lock is efficiently achieved during the preamble of a data signal in a time division multiple access communication system by first operating the system in an acquisition mode and subsequently switching to a data recovery mode. In the acquisition mode, an input signal is passed through a transversal correlator and frequency multiplied by a factor of two. The multiplied signal is used to control a local oscillator for demodulating the carrier signal. Also in the acquisition mode, the output of the transversal correlator is envelope detected and applied to a symbol timing loop that produces a symbol timing signal. Upon the detection of a symbol timing lock, a lock detector switches the system to the data recovery mode. In the data recovery mode, the input signal is frequency multiplied by 4 and used to control the local oscillator for demodulating the input signal. The demodulated input signal is now applied to the symbol timing loop to maintain a symbol timing lock condition.