JP2006254063A - Communication media selecting method by area information, communications terminal and communications system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communications terminal, system and method for appropriately selecting communication medium to be used for connection to a communications network without having to periodically transmitting position information to the communications network and without making all the communication media mounted on the communications terminal active at all times. <P>SOLUTION: The communications terminal having a plurality of communication media to be used for connection to a radio system has a position acquiring means for acquiring position information of the communications terminal, a storing means for storing area information, showing the information of a radio system that can be used for connection to the communications network for each area that is a region with a prescribed range, and a medium selecting means for selecting a communication medium to be used for connection to the communications network, based on the positional information. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method and a communication terminal for selecting a communication medium used for connection to a wireless system based on area information of the wireless system, and a communication system including the communication terminal.

  In Non-Patent Document 1, the available area of each of a plurality of wireless systems used to access a communication network is managed on the communication network side, and the communication terminal is currently based on position information transmitted to the communication network by the communication terminal. A configuration is described in which a communication network notifies a communication terminal of a list of available wireless systems, and a wireless system to be used by the communication terminal is selected. Note that the communication terminal acquires the position information from a GPS (Global Positioning System) or the like.

  According to Non-Patent Document 1, on the communication network side, detailed geographic information, location information management of the communication terminal, communication processing with the communication terminal as needed, and location information of the base station that communicates directly with the communication terminal by radio It is required to perform management, estimate a propagation pattern based on the transmission output of each base station, and determine whether or not each wireless system can be used based on these.

  Further, Non-Patent Document 2 describes a handover procedure in the configuration of Non-Patent Document 1, that is, a procedure for switching a radio system used by a communication terminal during communication.

  According to Non-Patent Document 2, the communication terminal periodically transmits position information to the communication network, and the communication network includes the communication area of the wireless system currently used by the communication terminal, the position information of the receiving communication terminal, and Based on the above, the necessity of handover is determined, and if necessary, a list of wireless systems that are candidate switching destinations is transmitted to the communication terminal.

  In the configurations of Non-Patent Documents 1 and 2, the control information is exchanged between the communication terminal and the communication network by a predetermined wireless system. Therefore, the communication terminal only needs to start the communication medium for the predetermined wireless system while not communicating, and is used for communication with the communication medium for the predetermined wireless system even during communication. It is only necessary to start up the communication media that are being used, and other communication media are stopped to reduce power consumption.

  Non-Patent Document 3 also describes a communication terminal handover procedure. According to Non-Patent Document 3, each radio system selects a plurality of points from the extension of the communication area and transmits the positions of the selected plurality of points to the communication terminal in order to notify the communication terminal of the communication area. . The communication terminal recognizes the communication area of the wireless system from a plurality of points received from the wireless system, and acquires its own position information from GPS or the like, thereby grasping the relationship between the communication area and its own position.

  If the communication terminal can communicate with other wireless systems that it is currently using and receives information on multiple points indicating the communication area from other wireless systems that are capable of communicating, The necessity of switching is determined based on the communication area and the moving direction that can be determined from the change history of the own position information, and switching is performed if necessary.

Murakami, Hasegawa, Muhammad, Inoue “Development of MIRAI Demonstration System (2) Resource Manager and Signaling Procedure”, IEICE Communication Society, B-5-118, 2002, pp.415 M.Inoue, K.Mahmud, H.Murakami, M.Hasegawa “NOVEL OUT−OF−BAND SIGNALING FOR SEAMLESS INTERWORKING BETWEEN HETEROGENEOUS NETWORKS”, IEEE Wireless Communications, April 2004, pp.56-63 C.Bouras, Y.Siahos, P.Spirakis “AN EFFICIENT ALGORITHM TO IMPROVE HANDOFF IN MOBILITY SUPPORT FOR IPV6 PROTOCOL”, 2000 International Conference on Software, Telecommunications and Computer Networks (SoftCom2000), October 2000

  In the configurations described in Non-Patent Documents 1 and 2, each time communication is started, position information is transmitted to the communication network, a list of wireless systems that can be used from the communication network is received, and a wireless system to be used by the communication terminal is selected. That is, it is necessary to select a communication medium to be used, and the time required to actually start communication becomes long.

  In addition, it is necessary to periodically transmit location information to the communication network for handover, that is, to change the selection of communication media during communication. However, if the transmission interval of location information is shortened, the location information If the communication amount increases, and conversely increases, the switching determination cycle also becomes longer, resulting in a problem that switching cannot be performed at an appropriate timing.

  In the configuration described in Non-Patent Document 3, the communication terminal does not need to periodically transmit the position information. However, the communication terminal can recognize the communication area of the wireless system only after it can communicate with the wireless system. Therefore, the communication terminal needs to keep all installed communication media in the activated state. As a result, the power consumption of the communication terminal increases.

  Therefore, an object of the present invention is to provide a method, a communication terminal, and a communication system for selecting a communication medium used for accessing a communication network at an appropriate timing.

  Also, there is no need to periodically transmit control information such as position information to and from the communication network, and there is no need to constantly activate all communication media implemented by the communication terminal, communication terminal and communication The purpose is to provide a system.

According to the communication terminal of the present invention,
A communication terminal having a plurality of communication media to be used for connection to a wireless system, a position acquisition unit for acquiring position information of the communication terminal, and a connection to a communication network for each area that is a predetermined area. It comprises storage means for storing area information indicating information of possible wireless systems, and media selection means for selecting a communication medium to be used for connection to a communication network based on position information and area information.

According to another embodiment of the communication terminal of the present invention,
It is also preferable that the media selection unit puts communication media other than the selected communication media in a stopped state.

According to another embodiment of the communication terminal of the present invention,
A communication terminal having a plurality of communication media to be used for connection to a wireless system, a position acquisition unit for acquiring position information of the communication terminal, and a connection to a communication network for each area that is a predetermined area. Storage means for storing area information indicating the information of the wireless system that can be used, and while the communication terminal is communicating, communication media other than the communication media being used are stopped, and the possibility of area change is determined based on the position information. When there is a possibility of area change, based on the area information of the change destination, the communication medium used for connection to the communication network is selected in the change destination area, and the selected communication medium is activated. And

Furthermore, according to another embodiment of the communication terminal of the present invention,
The area information preferably includes frequency information used by the wireless system.

According to the communication system of the present invention,
A communication system comprising the communication terminal and a communication network, wherein the communication network has a roaming support server having area information of a plurality of areas, and the communication terminal has area information stored in position information and storage means The roaming support server transmits an area information request signal to the roaming support server, and the roaming support server transmits the area information to the communication terminal when the area information request signal is received.

According to another embodiment of the communication system of the present invention,
The area information request signal includes the position information of the communication terminal and the information on the moving speed of the communication terminal determined from the history of the position information, and the roaming support server transmits the area information from the position information and the information on the moving speed. It is also preferable to determine the range of the area.

Further, according to another embodiment of the communication system of the present invention,
The area information request signal further includes information on the moving direction of the communication terminal determined from the history of position information. The area range in which the roaming support server transmits the area information is the moving speed in the moving direction of the communication terminal. It is also preferable to increase the size depending on.

Furthermore, according to another embodiment of the communication system of the present invention,
The area information has a location history of the communication terminal for each area. When the communication terminal receives the area information from the roaming support server and deletes the area information already stored in the storage means, It is also preferable to delete from area information of an area with a small history.

According to the method of the present invention,
Communication media in a communication terminal that stores area information indicating information of a wireless system that can be used for connection to a communication network and has a plurality of communication media that are used for connection to the wireless system for each area that is an area of a predetermined range A selection method comprising the steps of obtaining current position information and selecting a communication medium to be used for connection to a communication network based on the position information and area information.

According to another embodiment of the method of the present invention,
Communication media in a communication terminal that stores area information indicating information of a wireless system that can be used for connection to a communication network and has a plurality of communication media that are used for connection to the wireless system for each area that is an area of a predetermined range A selection method, during communication with the first communication medium, a step of acquiring position information, a step of determining the possibility of area change based on the position information, and a change if there is a possibility of area change Selecting a second communication medium to be used for connection to the communication network in the change destination area based on the previous area information, and when the first communication medium and the second communication medium are different, After the second communication medium is connected to the wireless system, the communication medium to be used is changed to the second communication medium.

  The communication terminal identifies an available wireless system based on the area information held by itself and the position information acquired by itself. Therefore, at the start of communication, it is possible to select a communication medium to be used without causing a delay.

  During communication, when the communication media other than the communication media being used are stopped and it is determined that the communication area is close to the adjacent area, the necessary communication media is activated to reduce the power consumption of the communication terminal and It is possible to quickly switch communication media when moving to a communication area. In particular, the effect of reducing power consumption is greatly advantageous for a wireless terminal that consumes a large amount of power when starting up the communication medium or a communication terminal that has a communication medium of a wireless system with a limited area.

  Furthermore, not only the radio system information but also the frequency information is held as the area information, so that it is possible to connect to the radio system without performing a frequency search, and quick switching is possible.

  The range of the area where the communication terminal can hold the area information is limited by the capacity of the storage unit. However, by installing a roaming support server, the communication terminal can use the area information of the area not held by the communication terminal as necessary. The media selection method of the present invention can be used widely. In addition, it is possible to flexibly cope with changes in area information due to the establishment or removal of a wireless system.

  Moreover, the frequency of area information download can be appropriately adjusted by changing the area range of the area information transmitted by the roaming support server according to the moving speed and the moving method.

  Furthermore, the area information is included in the area information, and is deleted from the area information of the area having a small area history, so that the area information of the place where the user stays temporarily is preferentially deleted. Therefore, the area information can be managed efficiently by the mobile terminal, and the communication amount with the roaming support server can be reduced.

  The best mode for carrying out the present invention will be described in detail below with reference to the drawings.

  FIG. 1 is a block diagram of a communication terminal 1 according to the present invention. According to FIG. 1, the communication terminal 1 includes communication media 11 and 12, a communication processing unit 13, a media selection unit 14, a position acquisition unit 15, and a storage unit 16.

  Each of the communication media 11 and 12 has a corresponding wireless system, and performs transmission / reception of a signal conforming to the standard of the corresponding wireless system with a base station or an access point device of the wireless system. In FIG. 1, the communication terminal 1 has two communication media, but it is naturally possible to implement two or more communication media.

  The communication processing unit 13 is located between the application unit of the communication terminal 1 (not shown) and the communication media 11 and 12, and performs processing necessary for communication. At this time, based on the notification from the media selection unit 14, a transmission signal is output to the communication media being used.

  The position acquisition unit 15 acquires the current position of the communication terminal 1 using GPS or the like, and notifies the media selection unit 14 of the current position.

  The storage unit 16 stores area information. FIG. 2 is a diagram illustrating areas, and FIG. 3 is a diagram illustrating area information corresponding to the state of FIG. In FIG. 2, each area is expressed as a square having a side of 100 m, but can be expressed in an arbitrary shape such as a regular hexagon or a circle and an arbitrary size. In FIG. 2, the position of each area is expressed as a relative position with respect to a predetermined reference position, but may be expressed as an absolute position such as latitude and longitude. In FIG. 2, the coordinates of the upper left corner are used to indicate the position of each area, but it is also an arbitrary matter which position in the area can be represented.

  In FIG. 2, BS1 and BS2 represent base stations for connecting to the wireless system. Each area is classified into an area where only BS1 can be used, an area where only BS2 can be used, and an area where both can be used. FIG. 3 (a) shows the correspondence between the areas represented by these squares and the available base stations, and FIG. 3 (b) shows the radio system used by each base station. It shows the specifications and information about the carrier frequency in the wireless system. That is, the base information that can be used in each area is recognized based on the area information, and the base station corresponds to the radio system. Therefore, the radio system that can be used in each area can be recognized based on the area information.

  Based on the location information of the communication terminal 1 acquired by the location acquisition unit 15 and the area information held by the storage unit 16, the media selection unit 14 determines a wireless system that can be used at the current location and determines the communication media to be used. Make a selection. Further, the selected communication medium is activated, and the unused communication medium is controlled to be stopped. In addition, the communication processing unit 13 is notified of the selected communication media.

FIG. 4 is a sequence diagram of media selection in the communication terminal 1. When the communication terminal 1 initially selects the communication medium 11 and switches to the communication medium 12 during communication using the communication medium 11. The sequence is shown.
(S41) The media selection unit 14 acquires the current position information of the communication terminal 1 from the position acquisition unit 15.
(S42) The media selection unit 14 acquires area information about the current position from the storage unit 16.
(S43) The media selection unit 14 selects a base station to be used from available base stations included in the acquired area information. As a selection method, any method such as bandwidth priority and cost priority can be used. Corresponding to the selected base station, the communication medium to be selected is determined. Here, it is assumed that the communication medium 11 is selected.
(S44) The media selection unit 14 activates the selected communication media 11, and the communication media 11 connects to the wireless system after activation, and notifies the media selection unit 14 of activation completion after the connection is completed.
(S45) During communication, the media selection unit 14 performs a change determination process. In this process, a determination is made as to the necessity of switching the wireless system that accesses the communication network. Here, it is assumed that it is determined that the communication medium 12 is changed due to movement of the communication terminal 1 or the like.
(S46) The media selection unit 14 activates the communication media 12. The communication media 12 connects to the wireless system after activation, and notifies the media selection unit 14 of activation completion after the connection is completed.
(S47) The media selection unit 14 instructs the communication processing unit 13 to switch the communication media to be used, that is, switching from the communication media 11 to the communication media 12. After receiving the switching completion notification from the communication processing unit 13, the media selection unit 14 The media 11 is stopped.

FIG. 5 is a flowchart of the change determination process in S45 in FIG. 4 and the process after determining that the switching is necessary. At the start of the flowchart, the communication terminal 1 determines 1 based on the current position information. Select one media to communicate.
(S51) The area information adjacent to the area to which the current position of the communication terminal 1 belongs is acquired from the storage unit 16.
(S52) The position information is acquired from the position acquisition unit 15.
(S53) Based on the current position, the moving direction and speed of the communication terminal 1 determined from the update history of the current position, the positional relationship with the adjacent area, and the base station information that can be used in the adjacent area, The possibility of change is determined. If there is a possibility of change, the radio system to be used in the change destination area is subsequently determined. Furthermore, it is determined whether or not the communication medium used in the change destination area needs to be changed by comparing the communication medium corresponding to the determined wireless system and the communication medium currently in use.
(S54) For example, when it is determined that the communication area is changed after a predetermined time and the communication medium needs to be changed accordingly, the communication medium to be newly used is activated. This step corresponds to the activation process in S46 of the sequence diagram of FIG.
(S55) The activation completion notification from the activated communication medium is monitored. This step corresponds to the state of waiting for reception of the completion notification in S46 of the sequence diagram of FIG.
(S56) When the activation completion notification is received from the activated communication media, communication media switching processing is performed. This step corresponds to the switching process in S47 of the sequence diagram of FIG.
(S57) After completion of switching, the communication media used before switching is stopped. This step corresponds to the stop process at S47 in the sequence diagram of FIG. 4 (S58) After the activation process at S54, when the moving direction is changed, the newly activated communication media is connected to the wireless system. Can not. Therefore, if there is no notification of connection completion from the activated communication media, the same determination as in S53 is performed again, and if it is determined that there is a change, a completion notification from the activated communication media is further waited.
(S59) In S58, when it is determined that it is no longer necessary to switch to the newly activated communication medium due to a change in the moving direction, the activated communication medium is stopped again.

  In the determination at S55, when the connection completion notification is received from the newly activated communication media, it is possible to immediately switch at S56, but the terminal enters the area predicted by the determination at S53. After switching, or after satisfying at least one of the conditions such as after the elapse of a predetermined time from the connection completion notification or after the reception level of the radio wave of the newly activated communication media exceeds a predetermined value, switching, that is, S56 It is desirable to proceed to the process. This is to prevent repeated switching of communication media at an area boundary or the like. For the same reason, it is desirable that the media stop process in S57 is not performed immediately after the switching in S56, but is performed after the position of the communication terminal 1 is separated to some extent from the area to which it previously belonged.

  As described above, the communication terminal identifies an available wireless system based on the area information held by itself and the position information acquired by itself. Therefore, at the start of communication, it is possible to select a communication medium to be used without causing a delay. During communication, when the communication media other than the communication media being used are stopped and it is determined that the communication area is close to the adjacent area, the necessary communication media is activated to reduce the power consumption of the communication terminal and It is possible to quickly switch communication media when moving to a communication area.

  In particular, for a wireless system such as a wireless LAN (Local Area Network), which consumes a large amount of power when starting up the communication medium, or a communication terminal having a communication system of a wireless system with a limited area, the power consumption can be reduced. Is greatly advantageous.

  In addition, in a wireless system developed in units of very small areas, represented by DSRC (Dedicated Short Range Communication), the period of staying in each area is short, and frequent communication media switching occurs. Since the communication terminal predicts the area change in advance, it is possible to perform switching accurately in these systems.

  Furthermore, as shown in FIG. 3, not only the system information of each base station but also the frequency information is held as area information, thereby enabling connection to a wireless system without performing a frequency search, and quick switching. Is possible.

  FIG. 6 is a block diagram of a communication system according to the present invention. According to FIG. The communication system includes a communication terminal 1, base stations 21 to 23, a communication network 4, and a roaming support server 5 installed in the communication network 4.

  The communication terminal 1 is as described above, and accesses the communication network 4 via the base station. Each of the base stations 21 to 23 performs transmission / reception of signals suitable for each wireless system with the communication terminal, and provides access means to the communication network 4 for the communication terminal. As described above, a base station means a device that transmits and receives radio signals to and from a communication terminal and provides access means to the communication network 4, and is equivalent to an access point device used in a wireless LAN or the like. A device having a function is used as a general term. In FIG. 6, reference numerals 31 to 34 denote areas.

  As shown in FIG. 6, the communication terminal 1 exists in the area 31 and moves in the direction of the area 32, but since the storage capacity of the storage unit 16 of the communication terminal 1 is finite, the communication terminal 1 The case where the information of the areas 32-34 is not hold | maintained may arise. For this reason, for example, a roaming support server 5 that manages area information for a wide area such as all of Japan or the Kanto region is installed in the communication network 4. The communication terminal 1 transmits an area information request signal to the roaming support server 5 in advance when determining that the communication terminal 1 enters an area that does not hold the area information based on the position information, the moving direction, and the speed. New area information is acquired from the roaming support server 5. At this time, the communication terminal 1 notifies the roaming support server 5 of not only the position information of the communication terminal 1 but also the moving speed and / or moving direction, and the roaming support server 5 Alternatively, it is desirable to change the area range of the new area information to be notified based on the moving direction.

  FIG. 7 is a diagram illustrating the area information that the communication terminal 1 acquires from the roaming support server 5. FIG. 7A shows an area range in which area information is acquired when the moving speed v of the terminal is less than the threshold Th, and one side centered on the current position of the communication terminal is a predetermined value A. Get a square range.

  (B) of FIG. 7 is an example of an area range in which area information is acquired when the moving speed v of the terminal is equal to or higher than the threshold Th, and one side centered on the current position of the communication terminal is a predetermined value B. A square range which is a value obtained by multiplying by the moving speed v is acquired.

  (C) of FIG. 7 is another example of the area range in which the area information is acquired when the moving speed v of the terminal is equal to or higher than the threshold value Th, and is moved in the moving direction by a predetermined value from the current position of the communication terminal. The center is shifted, and the side parallel to the moving direction is a value obtained by multiplying the predetermined value C by the moving speed v, and a rectangular range having a predetermined value A is obtained in the direction orthogonal to the moving direction. Yes.

  In this way, by installing the roaming support server 5, there is no limitation on the area range of storable area information due to the storage capacity of the storage unit 16 of the communication terminal 1, and the media selection method of the communication terminal 1 can be used over a wide range. And In addition, it is possible to flexibly cope with changes in area information due to the establishment or removal of a wireless system.

  Further, by changing the area range of the area information notified by the roaming support server 5 according to the moving speed, the frequency of downloading the area information can be adjusted appropriately. In particular, when the mobile terminal is mounted on a vehicle, it is effective to acquire area information in a range in which the vector component in the moving direction is increased.

  The communication terminal 1 may need to delete the stored area information by acquiring new area information. For this reason, it is desirable to include the acquisition time and / or the location point in the area information. FIG. 8 is a diagram illustrating another example of area information, and each area information has an acquisition time and a location point. As an example of calculating the location points, there is a method in which the mobile terminal sequentially performs addition processing with 3 points in the communication area to which the mobile terminal currently belongs, 2 points in the adjacent area, and 1 point in the adjacent area. Conceivable. When the communication terminal 1 deletes the area information, the communication terminal 1 deletes the area information from the area with the lower location point.

  By deleting from the area information of the area where the location point is low, for example, the mobile terminal 1 always holds area information of the area where the communication terminal 1 is frequently used such as the home, office, and commuting route of the user of the communication terminal 1 Thus, the area information of the place where the user stayed temporarily is deleted preferentially. Therefore, the mobile terminal 1 can efficiently manage the area information and can reduce the amount of communication with the roaming support server 5.

  In addition, based on the acquisition time information, it is possible to delete from old information, or to delete area information after a certain time while deleting based on the location point, regardless of the location point, etc. By deleting area information after a certain time has elapsed, it becomes possible to flexibly cope with changes in area information based on the establishment or removal of a base station or the like on the wireless system side.

It is a block diagram of the communication terminal by this invention. It is a figure explaining an area. It is a figure which shows the area information with respect to the state of FIG. FIG. 3 is a sequence diagram of media selection at the communication terminal 1. It is a flowchart of the change determination process in a media selection part. It is a block diagram of the communication system by this invention. It is a figure explaining the area information which a communication terminal acquires from a roaming assistance server. It is a figure which shows the other example of area information.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Communication terminal 11, 12 Communication media 13 Communication processing part 14 Media selection part 15 Position acquisition part 16 Storage part 21, 22, 23 Base station 31, 32, 33, 34 Area 4 Communication network 5 Roaming support server

Claims (10)

A communication terminal having a plurality of communication media used for connection with a wireless system,
Position acquisition means for acquiring position information of the communication terminal;
Storage means for storing area information indicating information of a wireless system that can be used for connection to a communication network for each area that is an area of a predetermined range;
A medium selecting means for selecting a communication medium to be used for connection to the communication network based on the position information and the area information;
A communication terminal comprising:   The communication terminal according to claim 1, wherein the media selection unit puts communication media other than the selected communication media into a stopped state. A communication terminal having a plurality of communication media used for connection with a wireless system,
Position acquisition means for acquiring position information of the communication terminal;
Storage means for storing area information indicating information of a wireless system that can be used for connection to a communication network for each area that is an area of a predetermined range;
While the communication terminal is communicating, communication media other than the communication media being used are stopped, the possibility of area change is determined based on the location information, and if there is a possibility of area change, the area information of the change destination Based on the above, a communication terminal that selects a communication medium to be used for connection to a communication network in a change destination area and activates the selected communication medium.   The communication terminal according to any one of claims 1 to 3, wherein the area information includes frequency information used by the wireless system. A communication system comprising the communication terminal according to any one of claims 1 to 4 and a communication network,
The communication network has a roaming support server having area information of a plurality of areas,
The communication terminal transmits an area information request signal to the roaming support server based on the location information and the area information stored in the storage means,
The roaming support server transmits the area information to the communication terminal when the area information request signal is received. The area information request signal includes the position information of the communication terminal and the information on the moving speed of the communication terminal determined from the history of the position information,
The communication system according to claim 5, wherein the roaming support server determines a range of an area to transmit area information from the position information and movement speed information. The area information request signal further includes information on the moving direction of the communication terminal determined from the history of position information,
7. The communication system according to claim 6, wherein the area range in which the roaming support server transmits the area information is increased depending on the moving speed in the moving direction of the communication terminal. The area information has a history of communication terminals in each area,
The communication terminal, when receiving the area information from the roaming support server, when deleting the area information already stored in the storage means, the communication terminal is deleted from the area information of the area with a small area history. 8. The communication system according to 7. Communication media in a communication terminal that stores area information indicating information of a wireless system that can be used for connection to a communication network and has a plurality of communication media that are used for connection to the wireless system for each area that is an area of a predetermined range A selection method,
Obtaining current location information;
Selecting a communication medium to be used for connection to the communication network based on the position information and the area information. Communication media in a communication terminal that stores area information indicating information of a wireless system that can be used for connection to a communication network and has a plurality of communication media that are used for connection to the wireless system for each area that is an area of a predetermined range A selection method,
Obtaining position information during communication on the first communication medium;
Determining the possibility of area change based on location information;
Selecting a second communication medium to be used for connection to the communication network in the change destination area based on the change destination area information when there is a possibility of area change;
When the first communication medium is different from the second communication medium, the communication medium to be used is changed to the second communication medium after the second communication medium is connected to the wireless system. Method.

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