Mobile telephone systems

Claim 1

In a mobile telephone system comprising a plurality of basestations each of which has a respective plurality of frequency channels assigned to it, the assignments being such as to minimize or obviate the sharing of potentially interfering frequency channels between neighbour basestations, a method of testing the utility of potential frequency channels for a basestation, wherein a test channel is selected with a frequency which is disjoint with the frequency channels assigned to that basestation and neighbour basestations, and that basestation sends test messages on the test channel to mobiles in or near its cell and records for analysis the results returned from the mobiles; wherein the test messages are sent to active mobiles; wherein the frequency channels are divided into time slots and mobiles monitor a plurality of frequency channels and send to the basestation a frequency channel quality list of the strongest frequency channels, the basestation determining whether the test channel is included within the list received form the mobile; wherein the frequency channels monitored by a mobile are determined by a frequency channel list held within the mobile, where the basestation commands the test channel to be temporarily included in that list; wherein the basestation selects mobiles in dependence on the inclusion within their frequency channel quality lists of frequency channels assigned to particular neighbour basestaitons.