A base station in a wireless communications network is configured to transmit signals including a plurality of data units, and selecting for transmission a signal configuration including a distribution pattern of reference signals arranged in a predetermined pattern in the data units with a predetermined density. The signal configuration also includes control data indicative of the reference signal density and distribution. A mobile terminal uses the control data to identify the reference signal density and distribution in use by the base station to which it is working or about to hand over, so that it can identify which symbols are appropriate to estimate the channel characteristics. By adapting the symbol density to local circumstances, in particular the likelihood of Doppler spreading, a more reliable acquisition of the base station can be obtained. The symbol density is reduced in the subcarriers remote from the control block, as these are less likely to be used by a mobile terminal in the circumstances in which density can be reduced.