A ranging code present in a transmission from a transmitter to a receiver can be detected, and hence a time offset can be determined. For each of the possible ranging codes in a transmitted signal, a correlation is formed between a received signal and the ranging code for multiple subcarriers in the received signal. For multiple adjacent ranging subcarriers, the correlation is multiplied by a conjugate of the correlation of an adjacent ranging subcarrier in order to form a differential phase value. At least one ranging code in the transmitted signal can then be determined based on the differential phase values for said plurality of subcarriers. A time offset in the transmission from the transmitter to the receiver can then be determined, based on the differential phase values for the subcarriers, and based on the determined ranging code.