Patent ID: 7027535

Claim:
A frequency tracking loop for a digital radio communications system, said frequency tracking loop comprising: (i) a means for correcting frequency offset, said means for correcting frequency offset receiving an input radio signal comprising bursts of known data at a first input, and supplying an output signal; (ii) a frequency offset estimator, supplied with said output signal from said means for correcting frequency offset, for providing an estimate of a frequency offset of said output signal; (iii) a variable bandwidth filter, supplied with said estimate of the frequency offset from said frequency offset estimator, for providing a filtered signal; (iv) a signal generator, supplied with said filtered signal from said variable bandwidth filter, for generating an output signal with a frequency dependent on said filtered signal, said output signal from said signal generator being supplied to a second input of said means for correcting frequency offset, wherein said frequency tracking loop is adapted to change a bandwidth of said variable bandwidth filter in dependence on at least one characteristic of a currently received burst of known data and wherein said frequency tracking loop is further adapted to provide said variable bandwidth filter with a wide bandwidth on receiving a burst of known data having a first length, and to provide said variable bandwidth filter with a narrow bandwidth on receiving a burst of known data having a second length that is shorter than the first length.