Abstract: A micro-cellular radio communications system (microsystem) is arranged to re-use radio frequency channels which are assigned for use in a cellular radio system (macrosystem) in the same vicinity. The microsystem maintains a list of each frequency channel which is in current use in any microcell of the microsystem. In each microcell of the microsystem a signal characteristic, for example received signal strength, of each frequency channel, is repeatedly measured when the channel is not in current use in any microcell of the microsystem, and the measurements are used to determine a long-term statistical preference for re-use of a favoured set of the frequency channels in that microcell. For each microcell, the frequency channels in the favoured set are given a short-term order for actual use in dependence upon frequent measurements of the signal characteristic for the microcell regardless of whether or not the channel is in current use in any other microcell of the microsystem.