An exemplary apparatus includes: means configured to obtain a set of plural samples of signals, the set comprising at least one sample for each of L antenna elements of a receiver, where L is an integer greater than two and where the samples are of an RF signal that has been downconverted by a downconversion frequency; means configured, for each antenna element, to perform autocorrelation on the samples relating to that antenna element; means configured to sum the results of autocorrelation for all antenna elements; means configured to convert the summed results into the frequency domain; means configured to determine a maximum value of the summed results in the frequency domain; and means configured to use the determined maximum value to provide an output indicative of an offset between a carrier of the RF signal and the downconversion frequency.