Mobile communication terminal, method for registering locatio thereof and computer readable recording medium

0001The present invention relates to a mobile communication terminal in a radio communication system, a method for registering location information in the mobile communication terminal and the like.

0002In a region such as a railway station or a downtown that is crowded with many people, a large number of mobile communication terminals (mobile units and mobile stations) are used at the same time for a radio communication system such as a mobile phone system. In such a region, compared with a non-crowded region, communication traffic is always heavy so that a large load tends to be put on a radio base station. If a large load is put on the radio base station, a mobile communication terminal located close to the radio base station may not be able to communicate.

0003Furthermore, many mobile communication terminals may be turned on at the same time in a facility such as a concert hall just after an event has been finished or at an arrival gate in an airport just after an airplane has arrived. Then, communication traffic may increase rapidly so that the mobile communication terminals cannot communicate.

0004In order to solve this problem, a countermeasure is taken to increase the number of radio base stations mainly in the region crowded with many people or in the region in which many mobile communication terminals are apt to be turned on.

0005However, it is necessary to make a large amount of investment for the countermeasure as well as management and maintenance after that. From a viewpoint of preserving the natural environment, it is desirable not to install too many radio base stations for saving energy.

0006In addition, there is a case where it is difficult to secure a space for installing additional radio base stations in the crowded region such as a city center.

0007Therefore, it is desirable to realize a comfortable communication service without adding so many radio base stations. As one method for realizing it, there is a method of preventing concentration of requests for registering location information (location registration) made by many mobile communication terminals with respect to the same radio base station at one time, i.e., a method of distributing the requests for location registration to many radio base stations.

0008<patcit id="pcit0001" dnum="JP4213234A"><text>Japanese unexamined patent publication No. 4-213234</text></patcit> describes a method of making a mobile communication terminal select a radio base station. According to this method, a mobile station (the mobile communication terminal) receives notice information from a notice channel from each radio base station and selects a radio base station having the largest number of available channels based on the received notice information.

0009However, the conventional method as described in <patcit id="pcit0002" dnum="JP4213234A"><text>Japanese unexamined patent publication No. 4-213234</text></patcit> may not be able to distribute requests for location registration to radio base stations appropriately if many mobile communication terminals request location registration at one time like the case just after an event has been finished or just after an airplane has arrived.

0010It is therefore desirable to distribute requests for location registration issued from many mobile communication terminals located in a neighborhood at the same time to radio base stations appropriately.

0011According to one aspect of the present invention, a mobile communication terminal for performing radio communication includes a received radio wave intensity measuring portion measuring intensity of received radio waves that are radio waves received from radio base stations, a radio base station selecting portion selecting one of the radio base stations to which a request for location registration of the mobile communication terminal should be sent, and a location registration requesting portion sending the request to the radio base station selected by the radio base station selecting portion. When the request is sent, the radio base station selecting portion initially selects a first radio base station of the radio base stations whose received radio wave has the highest intensity measured by the received radio wave intensity measuring portion, and, subsequently if the location registration in accordance with the request sent to one of the radio base stations has failed, the radio base station selecting portion selects a second radio base station of the radio base stations whose received radio wave has intensity lower than the intensity of the received radio wave from the one of the radio base stations.

0012According to another aspect of the present invention, a mobile communication terminal for performing radio communication includes a radio wave receiving portion receiving radio waves from radio base stations, a radio base station selecting portion selecting at random one of the radio base stations that send the radio waves received by the radio wave receiving portion, and a location registration requesting portion sending a request for location registration of the mobile communication terminal to the radio base station selected by the radio base station selecting portion.

0013According to the present invention, it is possible to distribute requests for location registration issued from many mobile communication terminals located in a neighborhood at the same time to radio base stations appropriately.

0014Reference will now be made, by way of example, to the accompanying drawings, in which: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a diagram showing an example of a general structure of a mobile phone system;</li><li><figref idref="f0002">Fig. 2</figref> is a diagram showing an example of a hardware structure of a mobile phone terminal;</li><li><figref idref="f0003">Fig. 3</figref> is a diagram showing an example of a functional structure of the mobile phone terminal;</li><li><figref idref="f0004">Fig. 4</figref> is a diagram showing an example of a registration target table;</li><li><figref idref="f0005">Fig. 5</figref> is a flowchart explaining an example of a flow of a location registration process;</li><li><figref idref="f0006">Fig. 6</figref> is a diagram showing an example of cells in a neighborhood of a facility and states of the mobile phone terminals when a mobile phone terminal is turned off;</li><li><figref idref="f0007">Fig. 7</figref> is a diagram showing an example of the cells in the neighborhood of the facility and states of the mobile phone terminals after the mobile phone terminal is turned on;</li><li><figref idref="f0008">Fig. 8</figref> is a diagram showing a variation of the functional structure of the mobile phone terminal; and</li><li><figref idref="f0009">Fig. 9</figref> is a flowchart explaining a variation of the flow of the location registration process.</li></ul>

0015The invention will now be described in detail with reference to the attached drawings.

[First embodiment]

0016<figref idref="f0001">Fig. 1</figref> is a diagram showing an example of a general structure of a mobile phone system 1, <figref idref="f0002">Fig. 2</figref> is a diagram showing an example of a hardware structure of a mobile phone terminal 2, and <figref idref="f0003">Fig. 3</figref> is a diagram showing an example of a functional structure of the mobile phone terminal 2.

0017As shown in <figref idref="f0001">Fig. 1</figref>, the mobile phone system 1 is a radio communication system, which is made up of the mobile phone terminals 2 according to the present invention, a radio access network (RAN) 3, a core network (CN) 4 and the like.

0018Structures of the radio access network 3 and the core network 4 are the same as those of the conventional system. More specifically, the radio access network 3 is made up of radio base stations (BS's) 31 and base station controllers (BSC's) 32 and the like. The core network 4 is made up of gateway mobile services switching centers (GMSC's) 41, mobile services switching centers (MSC's) 42, home location registers (HLR's) 43 and the like.

0019Note that the radio base station 31 may be called a "Node B" or a "base station" or the like. In addition, the base station controller 32 may be called an "RNC (Radio Network Controller)". Hereinafter, each of the radio base stations 31 may be referred to as a "radio base station 31A", a "radio base station 31B", a "radio base station 31C" or the like in a distinguishable manner.

0020The mobile phone terminal 2 can perform voice communication with another mobile phone terminal or a fixed telephone or perform data communication of electronic mail or image data with another mobile phone terminal or a personal computer via the radio access network 3, the core network 4 and the like in the same manner as the conventional one.

0021The mobile phone terminal 2 is made up of a CPU 20a, a memory 20b, a radio frequency circuit 20c, a liquid crystal panel 20d, an operating button 20e, an antenna 20f, a microphone 20g, a speaker 20h, an input and output interface 20i and the like as shown in <figref idref="f0002">Fig. 2</figref>. In this way, the hardware structure of the mobile phone terminal 2 is the same as the hardware structure of the conventional mobile phone terminal.

0022In addition, software stored in the memory 20b is also basically similar to the conventional mobile phone terminal. However, as software for selecting the radio base station 31 that relays communication with the core network 4, software for realizing the functions as shown in <figref idref="f0003">Fig. 3</figref> is stored, which includes a field intensity measuring portion 201, a registration target base station selecting portion 202, a location registration executing portion 203, an execution timer activating portion 204, an execution timer end decision portion 205, a location registration frequency recognizing portion 206, a location registration completion decision portion 207, an execution frequency counter 2CR, an execution timer 2TR and the like. The software is executed by the CPU 20a.

0023<figref idref="f0004">Fig. 4</figref> is a diagram showing an example of a registration target table TL. Next, process contents performed by the individual portions of the mobile phone terminal 2 shown in <figref idref="f0003">Fig. 3</figref> will be described.

0024The field intensity measuring portion 201 measures intensity of the radio wave received from the radio base station 31 with the antenna 20f of the mobile phone terminal 2 itself (i.e., field intensity in the mobile phone terminal 2 due to the radio wave from the radio base station 31) by the method similar to a conventional method.

0025More specifically, the radio base station 31 usually sends the radio wave that notifies identification information or the like of the radio base station 31 by using a predetermined frequency channel that is called a "perch channel", a "common channel" or the like. The field intensity measuring portion 201 measures field intensity due to the radio wave of the perch channel detected by the antenna 20f of the mobile phone terminal 2 itself in the same manner as a conventional method.

0026Hereinafter, the field intensity measured by the field intensity measuring portion 201 is referred to as "field intensity DK". In addition, the field intensity DK of the radio base station 31A, 31B, 31C and so on may be referred to as "field intensity DKa", "field intensity DKb", "field intensity DKc", and so on, respectively, in a distinguishable manner.

0027The location registration executing portion 203 sends a request for location registration of the mobile phone terminal 2 itself to the radio base station 31 selected by the registration target base station selecting portion 202 that will be described later.

0028Then, the radio base station 31 receives the request, and location information on the mobile phone terminal 2 is registered in the radio base station 31 and the upper home location register 43. After that, it can be connected to a terminal device such as another mobile phone terminal, a fixed telephone, a personal computer or the like via the core network 4 and the like for performing communication.

0029The registration target base station selecting portion 202 performs a process for selecting a radio base station 31 that will relay communication between the mobile phone terminal 2 itself and the core network 4, i.e., the radio base station 31 to be the registration target of the location information on the mobile phone terminal 2 itself. This process is performed based on a result of the measurement performed by the field intensity measuring portion 201 and the registration target table TL shown in <figref idref="f0004">Fig. 4</figref>.

0030Here, the registration target table TL will be described. As mentioned above in the description of background art, the conventional mobile phone terminal tries registration of location information (location registration) in the radio base station 31 related to the highest (strongest) field intensity DK, if there are a plurality of radio base stations 31 in the neighborhood. If the location registration fails, the field intensity DK of each of the radio base stations 31 is measured again after a predetermined time has passed, so that the location registration in the radio base station 31 related to the highest field intensity DK is tried.

0031However, the mobile phone terminal 2 according to the present embodiment does not always try the location registration in the radio base station 31 related to the highest field intensity DK but also tries the location registration in the radio base station 31 related to the second highest or lower field intensity DK in accordance with the number of tries for the location registration. As shown in <figref idref="f0004">Fig. 4</figref>, the registration target table TL shows the relationship between the ordinal number of a try for location registration and the ordinal number of field intensity DK. As described later, it is determined, based on the registration target table TL, which radio base station 31 with which order of field intensity DK among the radio base stations 31 should be subjected to the location registration tried by the mobile phone terminal 2.

0032The execution timer 2TR is a timer for adjusting a time interval between the above-mentioned tries for the location registration to a predetermined time (hereinafter referred to as "time Ta). The execution timer activating portion 204 activates (starts) the execution timer 2TR. The execution timer end decision portion 205 decides that the execution timer 2TR finished measuring the time Ta. Then, after the decision, the execution timer end decision portion 205 makes the field intensity measuring portion 201 measure the field intensity DK and makes the registration target base station selecting portion 202 select the radio base station 31 and makes the location registration executing portion 203 perform the process for the location registration.

0033The execution frequency counter 2CR counts the number of tries for the above-mentioned location registration. The location registration frequency recognizing portion 206 recognizes the number of times indicated in the execution frequency counter 2CR and controls the individual portions in accordance with the recognized number of times as follows. If the number of times is "2" or larger, the location registration frequency recognizing portion 206 gives instructions to the execution timer activating portion 204 so as to activate the execution timer 2TR. If the number of times is "1", the location registration frequency recognizing portion 206 does not activate the execution timer 2TR but makes the field intensity measuring portion 201 measure the field intensity DK, makes the registration target base station selecting portion 202 select the radio base station 31 and makes the location registration executing portion 203 perform the process for the location registration.

0034The location registration completion decision portion 207 decides whether or not the location registration in the radio base station 31 and in the home location register 43 has succeeded (has been completed).

0035<figref idref="f0005">Fig. 5</figref> is a flowchart explaining an example of a flow of the location registration process. Here, the flow of the process concerning the registration of location information performed by the mobile phone terminal 2 will be described with reference to <figref idref="f0005">Fig. 5</figref>.

0036When the mobile phone terminal 2 is powered on, the execution frequency counter 2CR is reset (#1 in <figref idref="f0005">Fig. 5</figref>). The location registration frequency recognizing portion 206 recognizes the number of times indicated by the execution frequency counter 2CR and controls the individual portions in accordance with the number of times. For the first time (Yes in #4), the location registration frequency recognizing portion 206 recognizes "1" and gives instructions to the field intensity measuring portion 201, the registration target base station selecting portion 202 and the location registration executing portion 203 without activating the execution timer 2TR.

0037Then, the field intensity measuring portion 201 measures the field intensity DK of each of the surrounding radio base stations 31 (#8). The registration target base station selecting portion 202 selects any one of the radio base stations 31 based on the registration target table TL shown in <figref idref="f0004">Fig. 4</figref> (#9). Since this is the first try, the registration target base station selecting portion 202 selects the radio base station 31 related to the highest field intensity DK. Then, the location registration executing portion 203 sends a request for location registration to the radio base station 31 selected by the registration target base station selecting portion 202 (#10).

0038If the location registration completion decision portion 207 decides that the location registration has succeeded (Yes in #2), the series of processes shown in <figref idref="f0005">Fig. 5</figref> are finished. Note that the location registration is performed with respect to the home location register 43 too, in the same manner as a conventional method.

0039If the location registration has failed (No in #2), the execution frequency counter 2CR counts up by "1" (#3) and the location registration is tried again. However, the retry should be performed after at least the time Ta has passed from the previous try for the location registration.

0040More specifically, when it is detected that the previous location registration has failed, the execution timer activating portion 204 activates the execution timer 2TR promptly (#5). If the execution timer end decision portion 205 decides that the time measured by the execution timer 2TR is beyond the time Ta (Yes in #7), the field intensity measuring portion 201 measures the field intensity DK of each of the radio base stations 31 in the neighborhood again (#8). The registration target base station selecting portion 202 selects any one of the radio base stations 31 based on the registration target table TL (#9). In the second time and after that, the radio base stations 31 related to lower field intensity DK are selected one by one. Then, the location registration executing portion 203 performs the location registration in the radio base station 31 selected by the registration target base station selecting portion 202 (#10).

0041Note that the execution timer 2TR is stopped and reset every time when the execution timer end decision portion 205 decides that the time Ta has passed. In addition, the activation (start) of the execution timer 2TR may be performed at timing other than the timing when it is detected that the previous location registration has failed. The execution timer 2TR may be activated during a period of time from the time point when the process of the previous location registration was started until the timing when it is detected that the previous location registration has failed.

0042<figref idref="f0006">Fig. 6</figref> is a diagram showing an example of cells in a neighborhood of a facility and states of the mobile phone terminals 2 when a mobile phone terminal 2X is turned off, and <figref idref="f0007">Fig. 7</figref> is a diagram showing an example of the cells in the neighborhood of the facility and states of the mobile phone terminals 2 after the mobile phone terminal 2X is turned on.

0043Next, a process for the location registration of the mobile phone terminal 2X of a guest X, in the case where the mobile phone terminals 2 are powered on at the same time by guests just after an event has been finished in a facility such as a concert hall or a stadium, will be described with reference to <figref idref="f0006">Figs. 6</figref> and <figref idref="f0007">7</figref>.

0044When the event is finished so that the guests are permitted to use their mobile phone terminals, the guests will turn on their mobile phone terminals 2 at the same time. Since the guests gather in a specific area, the location registration of their mobile phone terminals 2 will be concentrated in a specific radio base station 31. In the example shown in <figref idref="f0006">Fig. 6</figref>, the location registration of their mobile phone terminals 2 is concentrated in the radio base station 31A.

0045Here, if a certain guest X turns on his or her mobile phone terminal 2 (2X) later than other guests, the mobile phone terminal 2X measures the field intensity DKa, DKb and DKc of the radio base stations 31A, 31B and 31C in the surrounding area of the mobile phone terminal 2X as shown by the circled numbers in <figref idref="f0007">Fig. 7</figref>. Here, suppose that values of the field intensity DKa, DKb and DKc are in descending order. Hereinafter, for the sake of a simple description, suppose that the order of values of the field intensity DK is not changed in the following description. Note that the circle of the dashed-dotted line in <figref idref="f0007">Fig. 7</figref> indicates the range of the cell of the radio base station 31A, the circle of the dotted line indicates the range of the cell of the radio base station 31B, and the circle of the full line indicates the range of the cell of the radio base station 31C.

0046Then, the mobile phone terminal 2X first tries the location registration in the radio base station 31 related to the highest field intensity DK, i.e., the radio base station 31A based on the registration target table TL (see <figref idref="f0004">Fig. 4</figref>).

0047If the location registration in the radio base station 31A has failed, the mobile phone terminal 2X remeasures each field intensity DK and tries the location registration based on the registration target table TL. According to the registration target table TL shown in <figref idref="f0004">Fig. 4</figref>, the mobile phone terminal 2X tries the location registration in the radio base station 31B for the second through fourth times and tries the location registration in the location registration in the radio base station 31C for the fifth through seventh times.

0048According to the first embodiment, if the location registration has not succeeded, the mobile phone terminal 2 shifts the transmission target of the request for location registration one by one to the radio base station 31 that sends out a weaker radio wave. Therefore, the requests for location registration sent by many mobile phone terminals 2 located in the neighborhood can be distributed to the radio base stations 31 appropriately. Thus, reliability of the location registration can be improved.

[Second embodiment]

0049<figref idref="f0008">Fig. 8</figref> is a diagram showing a variation of a functional structure of the mobile phone terminal 2.

0050In the first embodiment, if the mobile phone terminal 2 fails in the location registration in the radio base station 31 related to the highest field intensity DK, it shifts the transmission target of the request for location registration one by one to the radio base station 31 related to weaker field intensity DK so as to retry the location registration. In the second embodiment, the mobile phone terminal 2 tries the location registration by selecting the radio base station 31 at random.

0051The hardware structure of the mobile phone terminal 2 according to the second embodiment is the same as that according to the first embodiment as shown in <figref idref="f0002">Fig. 2</figref>. The installed software is also the same as that in the first embodiment. However, as software for selecting the radio base station 31, software is stored for realizing functions, as shown in <figref idref="f0008">Fig. 8</figref>, that include a field intensity measuring portion 221, a registration target base station selecting portion 222, a location registration executing portion 223, an execution timer activating portion 224, an execution timer end decision portion 225, a location registration frequency recognizing portion 226, a location registration completion decision portion 227, a random number computing portion 228, an execution frequency counter 2CS, an execution timer 2TS and the like.

0052The field intensity measuring portion 221, the location registration executing portion 223, the execution timer activating portion 224, the execution timer end decision portion 225, the location registration frequency recognizing portion 226, the location registration completion decision portion 227, the execution frequency counter 2CS and the execution timer 2TS perform processes similar to the processes performed by the field intensity measuring portion 201, the location registration executing portion 203, the execution timer activating portion 204, the execution timer end decision portion 205, the location registration frequency recognizing portion 206, the execution frequency counter 2CR and the execution timer 2TR, respectively, according to the first embodiment.

0053The random number computing portion 228 generates a random number, which is a natural number, based on the number of field intensity DK detected (measured) by the field intensity measuring portion 221, for selecting one of the radio base stations 31 that send out the radio waves that can be received by the mobile phone terminal 2 at present. More specifically, if the field intensity measuring portion 221 detects the field intensity DK from N radio base stations 31, the random number computing portion 228 generates any one of "1" to "N" (N is a natural number larger than or equal to two) as the random number. It is possible to use a current value of the execution frequency counter 2CR as one of the arguments of a function for generating the random number. It is also possible to use another particular value as the argument.

0054The registration target base station selecting portion 222 performs a process of selecting the radio base station 31 that relays the communication between the mobile phone terminal 2 itself and the core network 4, i.e., the radio base station 31 to be a target of the location information registration of the mobile phone terminal 2 itself, similarly to the registration target base station selecting portion 202. However, the selection method is different from that in the registration target base station selecting portion 202.

0055More specifically, the registration target base station selecting portion 222 selects the radio base station 31 corresponding to the random number generated by the random number computing portion 228 as the target of the location information registration. The association between the random number and the radio base station 31 may be decided as follows. For example, the random number of "1", "2", "3" and so on may be associated in the descending order of the field intensity DK. Alternatively, the random number may be associated in the ascending order of the identification information.

0056<figref idref="f0009">Fig. 9</figref> is a flowchart explaining an example of a variation of the flow of the location registration process. Next, the flow of the process for the registration of location information performed by the mobile phone terminal 2 in the second embodiment will be described with reference to <figref idref="f0009">Fig. 9</figref>.

0057Contents of the process of the steps #21 to #28 are similar to the contents of the process of the steps #1 to #8 described above with reference to <figref idref="f0005">Fig. 5</figref> as the first embodiment. More specifically, when the mobile phone terminal 2 is powered on, the execution frequency counter 2CS is reset (#21 in <figref idref="f0009">Fig. 9</figref>). The location registration frequency recognizing portion 226 recognizes the number of times indicated by the execution frequency counter 2CS and controls the individual portions in accordance with the number of times. The location registration frequency recognizing portion 226 recognizes "1" for the first time (Yes in #24) and gives instructions to the field intensity measuring portion 221, the registration target base station selecting portion 222 and the location registration executing portion 223 without activating the execution timer 2TS.

0058Then, the field intensity measuring portion 221 measures the field intensity DK of the radio base stations 31 in the surrounding area (#28). After the measurement, the random number computing portion 228 is activated (#29) so as to generate the random number corresponding to the number of radio base stations 31 in the surrounding area (#30). The registration target base station selecting portion 222 selects the radio base station 31 in accordance with the random number (#31). Then, the location registration executing portion 223 makes a request for location registration to the radio base station 31 selected by the registration target base station selecting portion 202 (#32).

0059If the location registration completion decision portion 207 decides that the location registration has succeeded (Yes in #22), the series of processes shown in <figref idref="f0009">Fig. 9</figref> are finished. Note that the location registration is also performed on the home location register 43 as is with the case of the first embodiment.

0060If the location registration has not succeeded (No in #22), the execution frequency counter 2CS counts up by "1" (#23) and the location registration is tried again. Similarly to the first embodiment, the retry should be performed after at least time Ta has passed from the previous trial for the location registration (#25 to #27). However, in the second embodiment, the radio base station 31 for which the location registration has failed is excluded, so that one of the remaining radio base stations 31 that can perform communication is selected at random (#28 to #31). Note that it is possible to adopt another structure in which the radio base station 31 is not selected every time when location registration fails but is selected if the location registration has not succeeded after a predetermined number of times of tries.

0061According to the second embodiment, the mobile phone terminal 2 selects the radio base station 31 to be a target of transmission of the request for location registration at random. Therefore, the requests for location registration issued by many mobile phone terminals 2 located in the neighborhood at the same time can be distributed to the radio base stations 31 appropriately.

0062Although the radio base station 31 is selected at random from the first time for the process of the location registration in the second embodiment, it is possible to adopt another structure in which the radio base station 31 related to the highest field intensity DK is selected for performing the process of the location registration similarly to the first embodiment, and if the location registration has failed, one of the remaining radio base stations 31 is selected at random for performing the process of the location registration.

0063In the first and the second embodiments, it is desirable that the registration target base station selecting portions 202 and 222 do not regard every radio base station 31 related to the field intensity DK measured by the field intensity measuring portions 201 and 221 as a candidate for selection but exclude the radio base station 31 related to weak field intensity DK lower than a predetermined value from the candidates.

0064Although the first and the second embodiments exemplify the mobile phone terminals 2 (mobile stations) that are used in the radio communication system, the present invention can also be applied to mobile stations of other radio communication systems such as mobile stations of a so-called wireless LAN or mobile stations for PHS.

0065Other than that, the structure of the entire or the individual portions of the mobile phone system 1 or the mobile phone terminal 2, the process contents, the process order, the structure of the registration target table TL and the like can be modified variously in accordance with the spirit of the present invention.

0066While example embodiments of the present invention have been shown and described, it will be understood that the present invention is not limited thereto, and that various changes and modifications may be made by those skilled in the art without departing from the scope of the invention as set forth in the appended claims and their equivalents, as interpreted by the description and drawings.