Mobile communication system and location registration method in mobile communication system

Claim 1

A portable radio telephone suitable for a portable radio telephone system composed of a plurality of base stations forming a plurality of zones adjacent to each other in a service area, each of said base stations communicating via a plurality of radio channels with a plurality of portable radio telephones each moving in the service area, comprising: a radio unit, having an antenna, for receiving control signals, each control signal includes an identification code of a base station that transmitted the control signal, from said plurality of base stations at a predetermined cycle via said antenna and for transmitting a location registration signal issued from the portable radio telephone to one of said plurality of base stations via said antenna to request registration of location information of the portable radio telephone at a memory unit for a call control; means coupled to said radio unit for repeatedly measuring channel quality of said radio channels between the portable radio telephone and said plurality of base stations based on said control signals received by said radio unit and for producing a base station information list every measuring cycle, said base station information list including identification codes of a predetermined number of base stations selected among said plurality of base stations based on a result of the measured channel quality, said identification codes being arranged in sequential order of base stations having better channel quality; a memory unit for storing a set of said base station information lists obtained through a predetermined number of measuring cycles; and a judging unit for judging a location of the portable radio telephone in said service area and for determining whether said location registration signal is to be transmitted or not by referring to said memory unit when said set of said base station information lists are prepared in said memory unit so that, if the order of said identification codes varies with each of said set of said base station information lists above a predetermined extent, then the transmission of the location registration signal is inhibited regardless of the location of the portable radio telephone.