Recovery of frequency jumps in QPSK modulated microwaves radio links

摘要

The invention relates to a method for tracking Local Oscillators (LOs) phase hits and frequency clicks (fast frequency jumps) in Microwave Radio links using QPSK modulation. It consists of an AFC (Automatic Frequency Control) system, split into a "slow" carrier frequency recovery feedback subsystem (10) followed by a "fast" frequency tracking feedforward subsystem (11). The first subsystem is designed for recovering the average carrier frequency offset at the input of the demodulator, which is slowly varying with time, while the feedforward part of the AFC is designed for correcting fast frequency jumps, mainly due to microphonics of the local oscillators used in the up and/or down conversion of the modulated signal. A CTL (Carrier Tracking Loop) following the AFC system, will take care of all, if any, of the small frequency deviations introduced by the feedforward control.