A method of identifying frequency data for use in adjusting a frequency offset of a receiver, the method comprising: receiving a signal at the receiver, the signal comprising a set of slots, at least one of said slots comprising a preamble portion and being transmitted at a predetermined transmission frequency, wherein said predetermined transmission frequency is within a known range of frequencies; dividing the range of frequencies into a plurality of frequency bands; the method characterised by: for each data item contained within the preamble portion: identifying a magnitude of signal received within each of said frequency bands; identifying a plurality of pairs of frequency bands, each of said pairs of frequency bands comprising a first frequency band and a second frequency band, for at least some of the plurality of pairs of frequency bands, subtracting a first signal magnitude identified for said first frequency band from a second signal magnitude identified for said second frequency band, whereby to demodulate the signal within at least part of said preamble portion; combining the subtracted signal magnitudes corresponding to respective pairs of frequency bands with the output from an oscillator tuned to a fundamental of a period associated with said preamble portion; and for each pair of said first and second frequency bands, accumulating the combined signal magnitudes over the preamble portion, whereby to identify frequency data for use in adjusting a frequency offset of the receiver. receiving a signal at the receiver, the signal comprising a set of slots, at least one of said slots comprising a preamble portion and being transmitted at a predetermined transmission frequency, wherein said predetermined transmission frequency is within a known range of frequencies; dividing the range of frequencies into a plurality of frequency bands; the method characterised by: for each data item contained within the preamble portion: identifying a magnitude of signal received within each of said frequency bands; identifying a plurality of pairs of frequency bands, each of said pairs of frequency bands comprising a first frequency band and a second frequency band, for at least some of the plurality of pairs of frequency bands, subtracting a first signal magnitude identified for said first frequency band from a second signal magnitude identified for said second frequency band, whereby to demodulate the signal within at least part of said preamble portion; combining the subtracted signal magnitudes corresponding to respective pairs of frequency bands with the output from an oscillator tuned to a fundamental of a period associated with said preamble portion; and for each pair of said first and second frequency bands, accumulating the combined signal magnitudes over the preamble portion, whereby to identify frequency data for use in adjusting a frequency offset of the receiver. for each data item contained within the preamble portion: identifying a magnitude of signal received within each of said frequency bands; identifying a plurality of pairs of frequency bands, each of said pairs of frequency bands comprising a first frequency band and a second frequency band, for at least some of the plurality of pairs of frequency bands, subtracting a first signal magnitude identified for said first frequency band from a second signal magnitude identified for said second frequency band, whereby to demodulate the signal within at least part of said preamble portion; combining the subtracted signal magnitudes corresponding to respective pairs of frequency bands with the output from an oscillator tuned to a fundamental of a period associated with said preamble portion; and for each pair of said first and second frequency bands, accumulating the combined signal magnitudes over the preamble portion, whereby to identify frequency data for use in adjusting a frequency offset of the receiver. identifying a magnitude of signal received within each of said frequency bands; identifying a plurality of pairs of frequency bands, each of said pairs of frequency bands comprising a first frequency band and a second frequency band, for at least some of the plurality of pairs of frequency bands, subtracting a first signal magnitude identified for said first frequency band from a second signal magnitude identified for said second frequency band, whereby to demodulate the signal within at least part of said preamble portion; for at least some of the plurality of pairs of frequency bands, subtracting a first signal magnitude identified for said first frequency band from a second signal magnitude identified for said second frequency band, whereby to demodulate the signal within at least part of said preamble portion; combining the subtracted signal magnitudes corresponding to respective pairs of frequency bands with the output from an oscillator tuned to a fundamental of a period associated with said preamble portion; and for each pair of said first and second frequency bands, accumulating the combined signal magnitudes over the preamble portion, whereby to identify frequency data for use in adjusting a frequency offset of the receiver.