A base station receives measurement information from infrastructure units, and this measurement information in order to create a look-up table. Based on analysis of the measurement information, an indication of connections between a relay node and communications terminals in the network is transmitted, and communications resources are assigned to each of the infrastructure units in the network. The relay node in the network transmits channel sounding signals to be measured by other infrastructure units, in their assigned communications resource, and with a specified transmission power. The infrastructure units which detect the channel sounding signals can then use them to measure and estimate a state of the channel and determine which frequency resources to use when scheduling transmissions.