AUTOMATIC FREQUENCY CONTROL UNDER LOW SIGNAL-TO-NOISE CONDITIONS

摘要

A method for determining the carrier frequency offset and the corresponding sample-to- sample phase shift present in the sampled digital signal from the radio of a wireless transceiver is specified. The method divides the CFO range to be covered into a number of intervals and creates, from the received signal, as many parallel derived streams as there are interval endpoints, pre -compensating ("back rotating") the input by the sample-to-sample phase shift corresponding to the particular endpoint. It computes the magnitude and phase values of the correlation of a preamble pattern period with the preamble segment of each derived stream in parallel and uses the largest resulting magnitude value(s) to zoom in on the actual CFO present in the input stream. In order to improve accuracy in the presence of noise and provided there is still input preamble left to work on, it repeats the search for a shorter interval centered on the CFO value located in the first run. The finally located CFO value and the phase value from the corresponding correlation computation then determine the actual CFO and the corresponding sample-to-sample phase shift to be applied for pre- compensation ("back rotation") in an open-loop AFC.