Carrier wave recovery system.

摘要

A carrier wave recovery system for a slotted ALOHA system is disclosed. A reference carrier wave is provided by a voltage controlled oscillator (20) whose control signal (S4) is formed (adder 18) as the sum of a mean error signal (S6) and the current error signal (S3) derived by a phase comparator (12) from the input (S1) and reference (S2) signals. An averaging circuit (16) provides the mean error signal (S6) as the mean of the current control signal (S4) and the previous control signal stored in a register (28). In a time slot where no burst is input, the frequency of the oscillator (20) is locked to the mean value of carrier wave frequencies of bursts which were received in the past, thereby allowing a minimum of initial frequency offset to occur. In an alternative embodiment, the mean error signal is derived from stored maximum and minimum values of the control signal so that the oscillator frequency is controlled at initial pull-in to an average frequency of the highest and lowest carrier wave frequencies of an input burst signal.