This invention relates to a radio mobile communication system and, in particular, to a communication system for use in communicating with a land mobile or mobiles. 
A conventional mobile communication system of the type described comprises a control station and a plurality of base stations controlled by the control station.  Each of the base stations defines a service area which partly overlaps at least one adjacent service area.  Each mobile station is communicable with a selected one of the base stations in a selected one of the service areas that is allotted to the selected base station, unles traffic congestion occurs in the selected base station.  This applies to the case where each mobile station enters the selected service area from a neighboring service area. 
Each base station has a capacity of equipment designed in accordance with an estimated traffic predetermined in consideration of probability of loss of calls.  This means that traffic congestion takes place in the selected base station when an actual traffic is concentrated on the selected base station over the capacity of equipment.  During the traffic congestion, the selected base station cannot handle any other calls in the selected service area longer.  Moreover, it is not possible for the selected base station to track a mobile station that has entered the selected service area.  The probability of loss of calls is, therefore, high with the conventional system.  In addition, a difference between the actual traffic and the estimated traffic brings about a shortage or a surplus of equipment in each base station.  Anyway, such conventional system lacks the flexibility of equipment.