Patent ID: 9729366
Date: 2017-08-08
CPC Classifications: H04L

Claim:
1. A digital radio receiver adapted to receive radio signals modulated using continuous phase frequency shift keying, the receiver comprising a radio reception portion for receiving an analogue radio signal having a carrier frequency, a correlator arranged to estimate a frequency offset between said carrier frequency and a nominal carrier frequency, a correction portion for correcting for said frequency offset and a matched filter bank (MFB) comprising a plurality of filters each of which corresponds to a different bit pattern for determining a bit sequence from said analogue radio signal, wherein the digital radio receiver further comprises a drift estimator arranged to estimate a frequency drift in said carrier signal by comparing a phase determined by a given filter of the MFB when it is the matched filter with the phase determined on a subsequent matching occasion after a period in which there are an equal number of high and low bits received, said receiver being arranged to record the phase with a timestamp each time a filter is matched, and the next time said filter is matched, to perform a check to see whether an equal number of high and low bits has been identified since the previous match.