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tors that deploy and operate microcells with a limited communication range, but do not necessarily carry out subscriber management) are facility managers and com-munications service providers, which provide mobile communications services to supplement coverage areas that cellular mobile operators cannot fully cover. Devices sub-scribed to a cellular mobile operator’s service connect to and communicate via not only macrocell base stations or microcell base stations operated by the mobile operator to which they are subscribed, like Device A and Device B in Fig. 1, but also microcell base stations operated by micro-cell mobile operators (the Microcell Mobile Operator shown in green in Fig. 1). In addition, there are devices that microcell mobile operators manage themselves, which are not subscribed to the services of a cellular mobile op-erator and which only connect to and communicate via the microcell base stations managed by the microcell mobile operator in question, like Device C.e cell deployment sites in mobile communications systems are examined on the basis of classication into two operational categories — public areas and private areas — as shown in Fig. 2[10]. Public areas are areas in which cellular mobile operators deploy communications services. Private areas, on the other hand, are areas in which cells managed by specic individuals or organizations are de-ployed; microcell mobile operators deploy cells in private areas. In private areas, the owner or manager of the facil-ity is likely to have the best understanding of the features and performance requirements of the wireless communica-tions needed, so microcell deployment is based on the wishes of the owner. Conceivable examples of managed areas include companies, train stations, factories, under-ground shopping malls, universities, commercial facilities, and homes. Public areas cover the whole area, so public areas and private areas will usually overlap.Private area microcells use the minimum necessary interface to connect to control devices belonging to cellular mobile operators. In addition, they provide cellular mobile operators with information about the location, capabilities (transmission speed, latency, etc.), frequency, and band-width of microcell base stations operating in private areas. is information is broadcast within the transmission area using the control channels of cellular mobile operators’ macrocells. Devices gain information about the cells de-ployed by microcell mobile operators by receiving this information. Based on information about such matters as the type and status of the applications used, the load on network equipment, and wireless communication quality, devices then select and connect to the optimal cell from among those of both cellular mobile operators and micro-cell mobile operators in order to begin communicating.FiF1　Cell deployment and terminal topology in future mobile communications systems(Devices subscribed to either A or B can connect to the green cells)(Facility Manager / Service Provider, etc.)Device A(Used as a subscriber toCellular Mobile Operator A)Device B(Used as a subscriber to Cellular Mobile Operator B)Device C(Used solely on theself-operated system)MacrocellMicrocell52-1 Next Generation Mobile Communications System to Realize Flexible Architecture and Spectrum Sharing