Abstract:
A mobile communication terminal includes a location information database storing location data and map data for each of the radio cell stations. When receiving a data request including an identification of a second mobile terminal from a first mobile terminal through a first radio cell station, the database is searched for first location data of the first radio cell station, second location data of a second radio cell station forming a micro cell in which the second mobile terminal is located, and map data for at least one of the first and second radio cell stations. Then the first and second location data and retrieved map data are transferred to the first mobile terminal through the first radio cell station and thereby a map and two locations corresponding to the first and second mobile terminals are displayed on screen based on the retrieved map data and the first and second location data.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a mobile communications system, and in particular to a micro-cellular communications system which performs call connections between mobile terminals. 
     2. Description of the Related Art 
     In mobile communications, a user having a mobile terminal therewith may move from one cell to another or between different service areas. Therefore, it is important to inform the user through the mobile terminal where it is located. A navigation system using GPS (Global Positioning System) has been known as such a location displaying system. 
     Further, a mobile navigation system combining a mobile communications system with the navigation system has been proposed in Japanese Patent Unexamined Publication No. 1-142899. More specifically, in the mobile navigation system, a mobile switching center is provided with a map information memory. When receiving the location information of a mobile terminal, the mobile switching center reads map information based on the location information from the map information memory and transmits it to that mobile terminal. Therefore, the mobile terminal can display the map information appropriate for the location on screen and the user can easily be informed where the user is. 
     SUMMARY OF THE INVENTION 
     In the case of calling, however, the calling user cannot know where the destination terminal is located. In other words, the conventional system cannot provide the location information of both sides of connection. Therefore, the calling and called users cannot be informed whether they are near. Further, the conventional mobile terminal needs the GPS receiver, resulting in increased amount of hardware and complicated circuit in the mobile terminal. 
     An object of the present invention is to provide a mobile communications system and a mobile terminal which can provide the location information of both the mobile terminal and another mobile terminal with reduced size and weight. 
     Another object of the present invention is to provide a mobile terminal which can receive and display the map information including the location of another mobile terminal. 
     According to the present invention, in a mobile communications system comprising a plurality of radio cell stations each forming a micro cell and performing call connections between mobile terminals, location data and map data for each of the radio cell stations are stored onto a database. When receiving a data request from a first mobile terminal through a first radio cell station, the data request including designation of a second mobile terminal, the database is searched for first location data of the first radio cell station, second location data of a second radio cell station forming a micro cell in which the second mobile terminal is located, and map data for at least one of the first and second radio cell stations. Then the first and second location data and retrieved map data are transferred to the first mobile terminal through the first radio cell station. 
     The first mobile terminal, when receiving the first and second location data and retrieved map data from the mobile communications system through the first radio cell station, displays a map and two locations corresponding to the first and second mobile terminals on screen based on the retrieved map data and the first and second location data. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing a mobile communications system according to an embodiment of the present invention; 
     FIG. 2 is a diagram showing an example of a table stored in the location information database; 
     FIG. 3 is a block diagram showing a mobile terminal of the embodiment; 
     FIG. 4 is a sequence diagram showing an operation of the mobile communications system of FIG. 1; 
     FIGS. 5A-5D are signal formats of data request messages used in the mobile communications system; 
     FIG. 6A is a schematic diagram showing an example of display screen in the mobile terminal PS 2 ; 
     FIG. 6B is a schematic diagram showing an example of display screen in the mobile terminal PS 3 ; in the case as in FIG. 6A; 
     FIG. 6C is a schematic diagram showing an overlapped area of two adjacent map areas; 
     FIGS. 7A and 7B are signal formats of map data request messages used in the mobile communications system; 
     FIG. 8A is a schematic diagram showing another example of display screen in the mobile terminal PS 2 ; 
     FIG. 8B is a schematic diagram showing another example of display screen in the mobile terminal PS 3 ; in the case as in FIG. 8A; and 
     FIG. 9 is a schematic diagram showing a map area arrangement to be retrieved in the case where two map areas are separated. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a micro-cellular communications system is composed of a location information database  101 , a plurality of mobile switching centers  102 ,  103 , . . . , each having a plurality of radio cell stations connected thereto. Each radio cell station CS forms a micro cell of the order of 100 to 500 meters in which a mobile terminal (or a personal station) communicates with that radio cell station by radio. The radio cell stations are placed to cover the service area with their micro cells and each mobile terminal can move freely between micro cells. As will be described later, the location of a mobile terminal can be detected depending on which micro cell the mobile terminal is located in. Since each micro cell is of 100 to 500 meters diameter, the detected location of the mobile terminal has an error of 100-500 meters at the maximum. 
     It is assumed for simplicity that the location information database  101  can be shared between the mobile switching centers  102  and  103  and that radio cell stations CS 1  and CS 2  are connected to the mobile switching center  102  and radio cell stations CS 3  and CS 4  are connected to the mobile switching center  103 . Further, it is assumed that mobile terminals PS 1 , PS 2  and PS 3  are located in the micro cells of the cell stations CS 1 , CS 3  and CS 4 , respectively. 
     Referring to FIG. 2, the location information database  101  stores a location information table containing the location data, the map data, and the located terminal data for each cell station. In this embodiment, the location data is absolute location data of each cell station, such as a set of Longitude and Latitude, the map data is bitmap data of a predetermined area map on a scale of 1 to 50,000 in the vicinity of each radio cell station, and the located terminal data is the identification list of mobile terminals which are located in the micro cell of each radio cell station. For example, the absolute location of the radio cell station CS 1  is Longitude 140° 6′ 52″ E and Latitude 34° 56′ 50″ N, the map in the vicinity of the radio cell station CS 1  is formed with the bitmap data MAP 1 , and the mobile terminal located in the micro cell of the radio cell station CS 1  is the mobile terminal PS 1 . 
     The area size of each map is preferably set to more than 50 times the radius of each micro cell so as not to influence the error of location of each mobile terminal. As shown in FIG. 2, the radio cell stations CS 3  and CS 4  are relatively close to each other and the radio cell station CS 1  is far away from the radio cell stations CS 3  and CS 4 . Therefore, the map areas of the radio cell stations CS 3  and CS 4  are overlapped and those of the radio cell station CS 1  and the radio cell station CS 3  or CS 4  are separate from each other. 
     Referring to FIG. 3, a mobile terminal PS is comprised of an antenna and a radio transceiver  201  which transmits and receives a radio signal to and from a nearby radio cell station through the antenna. A processor  202  performs the operations of the mobile terminal including coding/decoding and other necessary operations for radio communication. An ID ROM (read-only memory)  203  stores an identification number such as a subscriber telephone number which is used to received data from the nearby radio cell station. A RAM (random access memory)  204  stores the map data and the absolute location data received from the location information database  101  through the mobile switching center and the nearby radio cell station. 
     As will be described later, the processor  202  performs the calling and called operations using the ID ROM  203  and the RAM  204  according to instructions received from a telephone section  205 . The telephone section  205  includes a speech encoder/decoder, a speaker, a microphone and a keypad for dialing. The processor  202  further controls a display driver  206  to display the received map data and absolute location data on a display  207  such as a liquid-crystal display (LCD). 
     Operation 
     The respective radio cell stations CS 1  to CS 4  broadcast control signals in their micro cells at all times. The control signals include cell station identification numbers (CD-ID 1  to CS-ID 4 ) which are previously assigned to the radio cell stations CS 1  to CS 4 , respectively. 
     Referring to FIGS. 4 and 5, when a mobile terminal (here, PS 1 ) moves from outside the service area into the micro cell of the radio cell station CS 1  or when the mobile terminal is powered on within the service area, the mobile terminal PS 1  receives the control signal from the radio cell station CS 1  and then transmits a location registration request message to the radio cell station CS 1 . As shown in FIG. 5A, the location registration request message conveys the cell station ID number CS-ID 1  and the self ID number PS-ID 1 . 
     When receiving the location registration request message, the radio cell station CS 1  transfers it to the mobile switching center  102  which uses the location information database  101  to perform the location registration of the mobile terminal PS 1 . This causes the database  101  to be updated such that the mobile terminal PS 1  is added to the located terminal field for the radio cell station CS 1 . After that, the mobile switching center  102  reads the absolute location data of the radio cell station CS 1  from the database  101  and then transmits a location registration response message back to the mobile terminal PS 1 . The location registration response message includes the absolute location data (here, Longitude 140° 6′ 52″ E and Latitude 34° 56′ 50″ N) as shown in FIG.  5 B. When receiving the location registration response message from the radio cell station CS 1 , the processor  202  of the mobile terminal PS 1  stores the absolute location data included in the location registration response message as the location data thereof onto the RAM  204 . 
     In the case where a user wants to know the location of another mobile terminal, the user uses the keypad to designate the ID number of the mobile terminal (for example, PS 2 ) and start calling, which causes a location data request message to be transmitted to the radio cell station CS 1 . The first terminal is the calling terminal and the second terminal is the called terminal. As shown in FIG. 5C, the location data request message conveys the cell station ID number CS-ID 1 , the self ID number PS-ID 1 , and the designated ID number PS-ID 2 . 
     When receiving the location data request message, the radio cell station CD 1  transfers it to the mobile switching center  102  which in turn inquires from the location information database  101  whether the designated terminal PS 2  is now located in the service area, that is, the designated ID number PS-ID 2  is registered in the location information database  101 . 
     If the designated terminal PS 2  is located in the service area, the absolute location data of the designated terminal PS 2  (here, Longitude 139° 36′ 11″ E and Latitude 35° 43′ 58″ N) is read from the database  101  and then a location information response message is transmitted back to the mobile terminal PS 1 . The location information response message includes the absolute location data of the designated terminal PS 2  as shown in FIG.  5 D. When receiving the location information response message from the radio cell station CS 1 , the processor  202  of the mobile terminal PS 1  stores the absolute location data included in the location information response message as the location data of the designated terminal PS 2  onto the RAM  204 . If the designated terminal PS 2  is not located in the service area, another location information response message indicating that the designated terminal is outside the service area is transmitted back to the mobile terminal PS 1 . 
     After the location data of the self terminal and the designated terminal are received, the map data MAP 1  in the vicinity of the radio cell station CS 1  is downloaded from the database  101  to the mobile terminal PS 1 . In this case, the mobile terminal PS 1  may transmit a map data request message and receive a map data response message conveying the map data MAP 1  (see FIGS.  7 A and  7 B). The processor  202  of the mobile terminal PS 1  stores the received map data onto the RAM  204  and then displays the map together with the locations of the self terminal PS 1  and the designated terminal PS 2  on the display  207 . 
     The other mobile terminals can perform the same sequence as described above. In FIG. 4, the sequence performed by the mobile terminal PS 2  is shown as an example. The mobile terminal PS 2  can display the map in the vicinity of the radio cell station CS 3  together with the locations of the self terminal PS 2  and another terminal on screen. 
     FIG. 6A shows a displayed map in the mobile terminal PS 2  when it designates the mobile terminal PS 3  and FIG. 6B shows a displayed map in the mobile terminal PS 3  when it designates the mobile terminal PS 2 . In the displayed map of the mobile terminal PS 2  as shown in FIG. 6A, the location of the mobile terminal PS 2  itself is displayed in the approximate center of the screen and the location of the designated mobile terminal PS 3  is displayed in the lower-right portion of the same screen. On the other hand, in the displayed map of the mobile terminal PS 3  as shown in FIG. 6B, the location of the mobile terminal PS 3  itself is displayed in the approximate center of the screen and the location of the designated mobile terminal PS 2  is displayed in the upper-left portion of the same screen. The displayed maps as shown in FIGS. 6A and 6B are obtained in the case where both the mobile terminals PS 2  and PS 3  are located in the overlapped area of the respective map areas of the radio cell stations CS 2  and CS 3  as shown in FIG.  6 C. 
     A mobile terminal can receive not only the map data in the vicinity of the radio cell station connected thereto but also the map data in the vicinity of another radio cell station connected to a designated mobile terminal. And a desired map can be selected and displayed on screen by a user&#39;s instruction. 
     As shown in FIGS. 7A and 7B, in the case where a user of the mobile terminal PS 2  wants to receive the map of another radio cell station connected to a designated mobile terminal PS 3 , the user uses the keypad to designate the ID number of the mobile terminal PS 3  and start calling, which causes a map data request message to be transmitted to the radio cell station CS 3 . The map data request message conveys the cell station ID number CS-ID 3 , the self ID number PS-ID 2 , the designated ID number PS-ID 3 , and a map data type. The map data type is used to select one of the self map, the designated terminal map, and a combination thereof. 
     When receiving the map data request message, the radio cell station CS 3  transfers it to the mobile switching center  103  which in turn inquires from the location information database  101  whether the designated terminal PS 3  is now located in the service area, that is, the designated ID number PS-ID 3  is registered in the location information database  101 . If the designated terminal PS 3  is located in the service area, the absolute location data of the designated terminal PS 3  and its map data MAP 4  are read from the database  101  and then are transmitted back to the mobile terminal PS 2 . The processor  202  of the mobile terminal PS 2  stores the absolute location data and the map data of the designated terminal PS 3  onto the RAM  204 . It is the same with the mobile terminal PS 3 . In this manner, the same map is displayed on the respective displays of the mobile terminals PS 2  and PS  3  as shown in FIGS. 8A and 8B. 
     FIG. 8A shows a displayed map in the mobile terminal PS 2  when it receives the map data MAP 4  in the vicinity of the radio cell station CS 4  connected thereto. FIG. 8B shows a displayed map in the mobile terminal PS 3  when it receives the map data MAP 4  in the vicinity of the radio cell station CS 4  connected to the designated mobile terminal PS 3 . 
     In this case, since the same map is displayed on the respective displays of the mobile terminals PS 2  and PS 3 , each mobile terminal can easily display route information such as required time and distance between these locations using the absolute location data with an error of 100-500 meters at the maximum. Needless to say, such concurrent displaying is obtained in the case where both the mobile terminals PS 2  and PS 3  are located in the overlapped area of the respective map areas of the radio cell stations CS 2  and CS 3  as shown in FIG.  6 C. Usually, these mobile terminals are located in different areas which are not overlapped. 
     Referring to FIG. 9, the mobile terminal PS 1  is away from the mobile terminal PS 3  and therefore the area map MAP 1  in the vicinity of the radio cell station CS 1  does not overlap with the area map MAP 4  in the vicinity of the radio cell station CS 4 . In this case, the mobile terminal PS 1  can display one selected from the area map MAP 1  and the area map MAP 4  on screen as described above. 
     Further, the mobile terminal PS 1  can display the reduced maps of the area map MAP 1  and MAP 4  on screen. Since the absolute locations of the radio cell stations CS 1  and CS 4  have been received, the processor  202  of the mobile terminal PS 1  can calculate route information such as a distance and a required time between them. 
     Furthermore, in the case where the location information database  101  stores the area maps between the radio cell stations CS 1  and CS 4  as shown in FIG. 9, the location information database  101  can reduce these area maps and transmit the reduced area map to the mobile terminal PS 1  together with the corresponding absolute locations. In this case, the mobile terminal PS 1  can display the reduced map between the area maps MAP 1  and MAP 4  on screen and further can calculate route information such as a traveling distance and a required time between them.