A method of signalling in a Wireless Local Area Network, WLAN, includes transmitting a signal having a physical layer data unit via a wireless channel of the WLAN using plural subcarriers spaced across plural symbols, the physical layer data unit having a data packet and a preamble, wherein the preamble has a synchronisation part having a channel estimation part. The channel estimation part has N training symbols, where N is an integer greater than 1, the N training symbols have synchronisation information for synchronising a second wireless device with the first wireless device, the synchronisation information having an offset value, and synchronisation information transmitted in second and subsequent training symbols is transmitted using offset subcarriers, the offset subcarriers being frequency offset with respect to reference subcarriers used to transmit synchronisation information in a first training symbol, the frequency offset being equal to the offset value.