In the field of radio communication systems including mobile phone systems and the like, it is known that environmental effects (e.g., reflection of radio waves by buildings, etc., and consequent radio wave interference) around a mobile terminal cause a defective area in which a radio communication service is not available, even within a coverage area (e.g., cell or sector) of a radio base station. Furthermore, especially in urban areas, construction of new buildings changes a surrounding environment around mobile terminals, which may cause a situation that an area to which the radio communication service was previously reachable turns into a new defective area. For this reason, from view points of configuration management, performance optimization, and automation of troubleshooting of a system based on a self-optimizing network (SON) on which much attention has been recently focused, it is preferable the location of a defective area is recognized by a radio base station.
As one example of approaches for a radio base station to recognize a defective area location, it is contemplated, for example, that when an increase in the occurrences of radio link disconnection on a cell level is detected or when an unusual load condition is detected, the action of detecting and locating a defective area is carried out, through investigation of communication quality conditions at some points within a cell, based on radio communication quality measured by mobile terminals (a measurement result in a so-called Measurement Report). Alternatively, it is also contemplated that detection of a defective area and recognition (identification) of the location of the defective area are carried out on a regular basis, through investigation of communication quality condition at some points within a cell based on radio communication quality measured by mobile terminals. Please see, for example, the following documents: Japanese Laid-open Patent Publication No. 2002-271833; 3GPP TS36.305 “Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Stage 2 functional specification of User Equipment (UE) positioning in E-UTRAN”; and 3GPP TR36.902 version1.2.0 “Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Self-configuring and self-optimizing network (SON) use cases and solutions”. 
In order to perform the aforementioned approaches, a radio base station may have to cause a mobile terminal located at a specific point within a cell to measure and report communication quality. Thus, the radio base station may have to recognize the respective individual locations of a number of mobile terminals within a cell. Furthermore, the radio base station may also have to issue an instruction to selectively cause some mobile terminal located at a specific point to perform measurement and report of communication quality. However, a commonly-available communication quality measurement and report operation (Measurement Report) for mobile terminals has no mechanism to selectively cause a mobile terminal located at a specific point to measure and report communication quality. For this reason, the radio base station may have to recognize the individual locations of a number of mobile terminals by use of a so-called “location tracking service” or the like for a purpose other than originally intended (i.e., enabling parents to know the location of their children having a mobile phone). In this case, however, the radio base station may have to perform operations for the location tracking service with respect to every mobile terminal within its own cell. This could cause the technical problem that a processing load considerably increases. This may in turn cause an increase of processing load in the radio communication system. As a result, the technical problem that the whole radio communication system goes into a state of congestion could be caused.