JP2006270629A - Mobile terminal for relaying search, searching method, and searching program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mobile communication system capable of widely searching the position of a mobile phone without the medium of a base station, by relay operations only by mobile stations. <P>SOLUTION: A mobile terminal having a means of communication which enables direct communication between mobile terminals, relays an encrypted search signal comprising information on a target terminal to be a searching object from a searching terminal, and performs its broadcast transmission. A terminal having received the search signal decodes the search signal and collates key information, and if the terminal itself is not a target terminal, the transmission of the search signal is continued further until reaching the target terminal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention provides a wide range of distress locations by searching only for mobile stations using mobile terminals such as mobile phones and PDAs (Personal Digital Assistants) without going through a base station in searching for victims due to disasters. Provided is a mobile communication system that searches in a short time.

  When searching for a rescuer in a disaster rescue operation or the like, finding rescuer position information in a short time can lead to early rescue. If it is within the base station area, it is possible to communicate with the base station and thus the position information can be specified. However, in the case of the out-of-service area, the search using the communication system based on the base station cannot be performed.

  Conventionally, search methods using portable communication devices have been proposed for the purpose of searching and communication under such conditions (see Patent Documents 1 and 2).

  Japanese Patent Laid-Open No. 2003-143048 is a method of searching for a mobile body capable of communication and securing a communication path with a target mobile body. When a connection source mobile phone establishes communication with the target mobile body, This is a technique for communicating with a target mobile body by searching for nearby relay cellular phones and establishing communication.

  However, in such communication between mobile stations, the search range does not widen. Furthermore, when communication cannot be established due to deterioration of radio wave conditions during communication or weak radio waves, there is a problem that communication with a mobile object for search cannot be performed.

  Japanese Patent Application Laid-Open No. 2004-297201 is a method of performing communication by directly communicating between portable terminals, in which the search side periodically transmits a signal including target portable information, and the received information is received on the target portable side. Searching is possible by returning a response when it matches the own terminal.

However, although it is a proposal of a method of searching without going through the base station, it is limited to a case where direct communication is possible and is restricted by communication conditions.
JP 2004-143048 A Japanese Patent Laid-Open No. 2004-297201

  Even when the rescue activity target area is within the base station area, it is assumed that communication may be difficult due to a failure of the base station or the like in the event of a disaster. Similarly, when the target range is an out-of-service area, a search using a communication system based on a base station cannot be performed.

  On the other hand, a system that does not use a base station (hereinafter referred to as a mobile communication system) has the advantage that it is less affected by a base station failure or traffic increase during a disaster. However, the search method using the rescuer's mobile terminal by the conventional mobile communication system has a problem that the search range is narrow because the communication distance is short.

  In the present invention, in order to solve the above problem, the search range is expanded via the relay terminal even when radio waves do not reach the target terminal directly from the search terminal by using another terminal existing in the out-of-service area as the relay terminal. Provide a method.

  A first invention is a relay terminal configured by a mobile terminal provided with a communication means capable of direct communication and relaying search information from a search source, which is transmitted from the search source terminal and uses the unique information of the target terminal as a key. Search signal receiving means for receiving a search signal encrypted as: decryption means for decoding the search signal received by the search signal receiving means using the unique information of the mobile terminal as a key; and the decryption When the search signal cannot be decoded by the means, a signal retransmission means for retransmitting the search signal; and when the search signal can be decoded by the decoding means, And a search response means for transmitting a search response signal including position information based on the determination.

  That is, according to the first invention, the search signal received by the search signal receiving means is received from the search source terminal, the search signal received by the decoding means is decrypted, and as a result of the decryption, decryption is performed. If not established, the search signal is transmitted to the other portable terminal as it is by the search signal retransmitting means, and when the decoding is established, the search response means determines that the terminal is the target terminal and By adopting a configuration that returns a search response signal to which data such as information is added, the search signal from the search source can be captured even if the target terminal is in a place where radio waves do not reach directly.

  In addition, as a result of the relay terminal receiving the search information decrypting with the unique information of its own terminal as a decryption key, it is possible to easily and quickly determine whether the terminal is the target terminal while ensuring security.

  The second invention includes transmission information storage means for holding these signals in a storage unit when the search signal or the search response signal is transmitted and received, and signals received within a predetermined time are stored in the transmission information storage unit. The present invention relates to the relay terminal according to the first aspect of the invention, wherein when the search signal or the search response signal that is held matches the search signal, the signal is discarded.

  That is, according to the second invention, the search and response signal transmitted and received by the transmission information storage means is held in the storage unit, and the signal received within a predetermined time is stored in the storage unit and the search and response signal information. If the received signals are matched, the received signal is discarded, so that the information transmitted by itself can be received in the search signal and the same signal between the mobile terminals can be prevented from being transmitted twice.

  According to a third aspect of the present invention, the search signal includes a relay counter indicating the number of relay terminals. Each time the relay signal passes through the relay terminal, the number of relay terminals is subtracted, and the search signal with the relay counter reaching zero is received. In this case, the present invention relates to the relay terminal according to the first or second invention, wherein no subsequent transmission is performed.

  That is, according to the third aspect of the invention, counter information indicating the maximum number of relay terminals is added to the search signal information, and the counter value is reduced every time it passes through the relay terminal. By adopting a configuration in which the above transmission is stopped, the range of the maximum search area can be specified, and the search area can be prevented from spreading indefinitely.

  As described above, according to the present invention, from a search terminal to a target terminal by using a mobile terminal provided with communication means capable of directly communicating with each other and having another mobile terminal existing in the out-of-service area as a relay terminal. Even when radio waves do not reach directly, it is possible to greatly expand the search range via a plurality of relayed mobile terminals without using a base station.

  In addition, by storing search and response signals sent and received in the storage unit, by collating with signals received within a certain time, and by discarding if the same signal, information transmitted by itself Can be received mixed with the search signal, and the same signal between the relay terminals can be prevented from being transmitted twice.

  Furthermore, the maximum search area can be set by setting the maximum value of the number of relay terminals to be passed as the value of the relay counter, adding it to the search signal information, and checking the counter value, Transmission beyond the maximum area can be stopped, and inefficiency that the search area can be expanded infinitely can be prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a basic configuration of a portable search system according to an embodiment of the present invention.

  In the following embodiment, in order to search for a lost person who is missing in the discovery of a victim at a disaster occurrence point, the lost person is possessed by the lost person from the search source terminal. It is assumed that a search signal is transmitted to the surroundings using a mobile terminal as a target terminal.

  In the present embodiment, it is assumed that the conventional function is guaranteed in a range where radio waves reach from the search source terminal 1. Also, in the event of a disaster such as a mountain distress or an earthquake, assuming that the mobile terminal held by the rescue waiting side and the rescue side each possesses a mobile terminal, the searcher terminal 1 is rescued as the mobile terminal possessed by the rescuer. The mobile terminal on the other side is defined as the target terminal 3, and the other mobile terminals are defined as the relay terminals 2 (2-1, 2-2... 2-n).

  In this mobile search system, a search source mobile terminal is a search source terminal 1, a mobile terminal that relays search data is a relay terminal 2 (2-1, 2-2,..., 2-n), and a search target. The target portable terminal is configured by the target terminal 3. Each mobile terminal is assumed to have a configuration capable of direct communication between terminals without using a base station, and the number of relay terminals 2 may be any number.

  Area 1 indicates an area where direct communication with the search source terminal 1 is possible, Area 2 indicates an area where direct communication with the relay terminal is possible, and Area 3 indicates an area where direct communication with the target terminal 3 is possible. In addition, the search source terminal 1 and the target terminal 3 are in a state where direct communication is not possible.

  The outline of the portable search system of the present invention shown in FIG. 1 will be described below.

A processing procedure in which the search source terminal 1 transmits a search signal including information on the target terminal 3 using a mobile terminal (typically a mobile phone) having communication means capable of directly communicating with each other between mobile terminals is shown below.
(1) When the target terminal 3 is not in the reception range: When the relay terminal 2 (2-1, 2-2... 2-n) exists, the received signal is transmitted in the same manner.
(2) When the relay terminal 2 determines that the terminal itself is not the target terminal 3 by decoding the received signal, the relay terminal 2 further transmits the received signal in the same manner.
(3) The search source terminal 1 or the relay terminal 3 stores the information transmitted by the search source terminal 1 or the relay terminal 3 in its own terminal, ignores the same information within a certain period of time, and transmits no more.

As a result, even when a plurality of relay terminals exist in the corresponding area, double transmission of the same-purpose signal is prevented.
(4) Since there is a possibility that the search range extends infinitely, it is prevented by adding additional information to the transmission information.

As the additional information, for example, a maximum relay count value configured by the number of relay terminals is set. The relay terminal 2 decrements the number of relay terminals in the additional information at the time of reception and retransmits it. When the relay terminal number is 0, no further transmission is performed.
(5) The target terminal 3 has, for example, a navigation device that detects a current position based on a GPS (Global Positioning System) reception signal. When the search signal is received, the target terminal 3 is obtained by the navigation device. A response signal including the position information is output.
(6) When the relay terminal 2 receives the response signal, it further transmits in the same manner as (1), (3), and (4).

In addition, regarding the security of this function and information, since misuse by receiving this search signal can be considered, the transmitted signal is encrypted. The search signal is encrypted / decrypted by the following process.
(7) The search source terminal 1 performs encryption processing on the search information including the information of the own terminal in the search signal to be transmitted, using the unique information of the target terminal 3 as a key.
(8) The relay terminal 2 (or the target terminal 3) decrypts the received signal using the unique information of the terminal as a key.
(9) If the decoding process cannot be performed, the terminal determines that it is the relay terminal 2 and retransmits it.
(10) When the decoding process is completed, the terminal determines that it is the target terminal 3 and transmits a response signal.

  As described above, a mechanism is provided in which the search information transmitted from the search source terminal 1 can be decoded only by the target terminal 3.

  FIG. 2 shows a configuration example of search data according to the embodiment of the present invention. The search data 100 transmitted from the search source terminal 1 is a search function ID 101 (identifier: Identifier) for identifying that it is a search signal, a search signal identification ID 102 used for distinction from other search data, a relay counter 103, and It is composed of items of search information 106 including the telephone number 104 of the search source terminal 1 and the notification information 105 of the target terminal 3 such as a telephone number and position information for which arbitrary information can be set.

  The relay counter 103 is a counter that designates the maximum number of relays by the relay terminal 2, and the search effective range can be designated by this set value. For example, when the communicable distance of the direct communication means possessed by the terminal is r and the value of the relay counter 103 is N, the effective search range is the maximum radius distance (r × N) centered on the search source terminal 1 It is possible to specify within the circle area. In this embodiment, as an example, the value of the relay counter 103 is decremented by each relay terminal 2, and when the value of the counter is 0, the relay process is not performed.

  FIG. 3 shows a functional block diagram in the portable terminal according to the embodiment of the present invention.

  The mobile terminal for performing the search includes a search request accepting unit 11, a local terminal information obtaining unit 12, a search data creation and analysis unit 13, a timer management unit 14, a transmission information storage unit 15, and a direct communication device interface control unit 16. Consists of.

  Further, the search data creation and analysis unit 13 creates search data 100 for searching for the target terminal T and transmits the data to the relay terminal 2 existing in the vicinity. Encryption / decryption means 22 for encrypting / decrypting the search information 106 (search source telephone number 104 and target terminal 3 notification information 105), receiving the search data 100, and decrypting the encrypted information, Search data analysis means 23 for analyzing the success or failure of the decoding, signal retransmission means 24 for retransmitting the received signal when the decoding is not established as a result of the analysis, and when the decoding is established The search response means 25 is configured to generate the notification information 105 including its own position information and send a response using means such as GPS.

  Furthermore, the relationship between the functional units in the mobile terminal in FIG. 3 will be described below. The search is started when the search request receiving unit 11 receives a search request event from outside the functional block in the search source terminal 1.

  The search request event includes the telephone number of the target terminal 3, and the search data creation and analysis unit 13 obtains the telephone number 104 of the search source terminal 1 from the own terminal information acquisition unit 12, and the telephone number 104 In addition to the notification information 105 in which arbitrary information can be set, encryption is performed using the encryption / decryption control means 22 using the telephone number of the target terminal 3 as a key, and a search indicating that this is a search signal The search data 100 is created by adding the search signal identification ID 102 and the relay counter 103 having a unique content used for distinguishing the function ID 101 from the other search data 100, and between the communication devices having the direct communication device and the interface. The interface unit 104 is requested to transmit. Thereafter, a search signal including the search data 100 described above is transmitted from the search source terminal 1 by a normal process of direct communication.

  The search data information 106 created here is managed in the transmission information storage unit 15 in association with a timer that manages the effective search time. The timer management unit 14 manages those timers, and when a timeout occurs, a process of deleting the associated search data information 106 from the transmission information storage unit 15 is executed.

  In the encryption performed by the encryption / decryption control means 22, the telephone number of the target terminal 3 is used in this embodiment. However, the telephone number may not be used as long as it is unique information that can identify the terminal. .

  FIG. 4 shows a configuration example of search information data managed by the transmission information storage unit according to the embodiment of the present invention. The search data information 200 managed by the transmission information storage unit 15 includes items of a search signal identification ID 201 for uniquely identifying a search signal, a timer identifier 202 indicating a search effective time, and a target terminal telephone number 203.

  Next, a processing flow for the search data 100 from the search source terminal 1 to the target terminal 3 via the relay terminal 2 will be described with reference to FIGS.

  FIG. 5 shows a search data reception process flow (reception main process) used in common between portable terminals according to the embodiment of the present invention. This flow shows a processing flow in the case where the search signal transmitted from the search source terminal 1 is subjected to reception processing via a number of relay terminals 2 and further retransmitted to other relay terminals 2.

  First, in step S11, when search data 100 is received from another relay terminal 2 that is a portable terminal, the search data 100 extracted from the search signal by the normal processing of direct communication is transmitted via the inter-communication device interface unit 16. The data is input to the search data creation and search data analysis unit 113.

  Next, in step S12, the search data creation and analysis unit 13 checks whether the search function identification ID 101 and the search signal identification ID are the search signals. If the check result is NG, the search is performed. The data 100 is discarded and the search process is terminated. Such a check can prevent malfunctioning of signals other than the search signal.

  If the above check result is OK, in step S13, a collation check between the search signal identification ID 102 and the search signal identification ID 201 of the transmitted search data stored in the transmission information storage unit 15 is performed. If a matching ID is found by collation, it can be determined that the search signal has been relayed or has been issued by the terminal itself, and the search data 100 is discarded without performing subsequent relay processing or search data analysis processing. To complete the search process. Search signal loop ID transmission can be prevented by checking the search signal identification ID 102.

  In this verification check, the target terminal telephone number 203 is set, so that it is possible to distinguish between the search signal transmitted from the own terminal or the relayed search signal, and the search signal transmitted from the own terminal. If it is, the peripheral relay terminal 2 knows that the search signal of its own terminal has been relayed.

  If the above-described verification check result is OK, in step S14, the encryption / decryption means 22 decrypts the search information 106 using the telephone number of the terminal as a key.

  In step S15, it is determined whether or not the decryption is successful. If the decryption fails, the process proceeds to the relay processing flow in FIG.

  If the decoding is successful, in step S16, the search data analysis means 23 refers to the search information data 200 stored in the transmission information storage unit 15 and collates with the search data 100. It is determined whether the terminal corresponds to the target terminal 3 of interest.

  In step S17, when the own terminal is the target terminal 3 to be searched, the process proceeds to the search response reception process flow of (b).

  On the other hand, when the response is not a response to the search signal transmitted from the own terminal, the response signal is returned because the target terminal 3 is a search signal intended for the search. The response reply operation is an operation of transmitting the search data 100 in which the search source terminal 1 and the target terminal 3 are switched in the operation in which the search source terminal 1 transmits the search data 100 described above. The search data 100 is created using the number 104 as an encryption key, and processing for transmitting a search signal to the surroundings is performed as follows.

  That is, if the terminal is not the target terminal 3 to be searched in step S17, the position information of the terminal is set in the notification information 105 in step S18, and encryption is performed using the unique information of the search source as a key. Search data 100 is created.

  Next, in step S19, the created search data 100 is transmitted to the next relay terminal 2. In step S20, the transmitted information is stored in the transmission information storage unit 15 in association with the timer, and the main reception process is terminated.

  Note that, as described above, the search signal transmitted by the response return operation is transmitted to the search source terminal 1 by the above-described direct communication chain between the terminals.

  FIG. 6 shows a flow of search data relay processing commonly used between portable terminals according to the embodiment of the present invention. This flow describes the operation of the relay terminal 2 (2-1, 2-2,..., 2-n) after failure in decoding the search information 106 in step S15 of the reception main process in FIG.

  If the decoding fails in step S21, the relay terminal 2 refers to the relay counter 103 of the search data 100. If the value of the relay counter 103 remains 1 or more, the relay terminal 2 decrements the relay counter by 1 in step S22. Otherwise, the search data 100 is transmitted as received. Thereafter, in step S23, the received information is stored in the transmission information storage unit 15 in association with the timer.

  If the value of the relay counter 103 is 0 in step S21, the search data 100 is discarded and the search process ends.

  The operation until the search data 100 is transmitted as a search signal is the same as the operation in which the search source terminal 1 transmits the search data 100 described above.

  Accordingly, the search data information 200 handled by the relay terminal 2 is also stored in the transmission information storage unit 15 in association with the timer that manages the search effective time. However, since there is no information on the target terminal telephone number 203, no setting or dummy information is set for the target terminal telephone number 203.

  FIG. 7 shows a flow of response reception processing for search data used in common between portable terminals according to the embodiment of the present invention. This flow shows a process in the case of receiving a response when it corresponds to the target terminal 3 in step S17 of the reception main process flow of FIG.

  In step S31, position information is acquired from the notification information area using, for example, GPS. Next, in step S32, the transmission information related to the search is deleted from the transmission information storage unit 15, and the process ends.

  The embodiments of the present invention described above are as shown in the following supplementary notes.

(Supplementary Note 1) A relay terminal configured with a mobile terminal provided with a communication means capable of direct communication and relaying search information from a search source,
Search signal receiving means for receiving a search signal transmitted from the search source terminal and encrypted using the unique information of the target terminal as a key;
Decoding means for decoding the search signal received by the search signal receiving means with the unique information of the mobile terminal as a key;
A signal retransmission means for retransmitting the search signal when the search signal cannot be decoded by the decoding means;
A search response means for determining that the search signal is a target terminal to be searched and transmitting a search response signal including position information when the search signal can be decoded by the decoding means;
A relay terminal characterized by comprising:

(Additional remark 2) When the search signal or the search response signal is transmitted and received, a transmission information storage unit that holds these signals in a storage unit is provided,
The signal is discarded when a signal received within a predetermined time is matched with the search signal or the search response signal held in the transmission information storage unit. Relay terminal.

  (Supplementary Note 3) When the search signal includes a relay counter indicating the number of relay terminals, the number of relay terminals is subtracted every time the relay terminal is passed, and a search signal in which the relay counter becomes zero is received. The relay terminal according to claim 1 or 2, wherein no subsequent transmission is performed.

(Supplementary Note 4) A search method for searching for a target terminal via a relay terminal configured by a mobile terminal provided with a communication means capable of direct communication,
On the computer,
A search signal receiving step for receiving a search signal transmitted from the search source terminal and encrypted using the unique information of the target terminal as a key;
A decoding step for decoding the search signal received in the search signal reception step using the unique information of the mobile terminal as a key;
A signal retransmission step for retransmitting the search signal if the search signal could not be decoded in the decoding step;
A search response step of transmitting a search response signal including position information by determining that the search target signal is a target terminal when the search signal can be decoded in the decoding step;
A search method characterized by causing to execute.

(Supplementary Note 5) A search program for searching for a target terminal via a relay terminal configured by a mobile terminal provided with a communication means capable of direct communication,
On the computer,
A search signal receiving step for receiving a search signal transmitted from the search source terminal and encrypted using the unique information of the target terminal as a key;
A decoding step for decoding the search signal received in the search signal reception step using the unique information of the mobile terminal as a key;
A signal retransmission step for retransmitting the search signal if the search signal could not be decoded in the decoding step;
A search response step of transmitting a search response signal including position information by determining that the search target signal is a target terminal when the search signal can be decoded in the decoding step;
Search program that executes

(Additional remark 6) It is the search system comprised by the portable terminal provided with the communication means in which each of a search origin terminal, a relay terminal, and a target terminal can communicate directly,
The search source terminal comprises search signal transmission means for transmitting a search signal encrypted using the unique information of the target terminal as a key,
When the relay terminal receives the search signal, the relay terminal decodes the search signal using the unique information of the terminal as a key, and the decoding of the search signal by the decoding means is not established And a search response signal including position information by determining that the terminal is the target terminal when the decoding of the search signal by the decoding unit is established, and a signal retransmission unit that transmits the search signal again Search response means for transmitting
The target terminal includes a decoding unit that receives the search signal and decrypts it using the unique information of the terminal as a key, and a search response unit that transmits a search response signal including position information,
A search system, wherein a search signal transmitted from the search source terminal is received by a target terminal via a relay terminal.

(Supplementary note 7) A search source terminal composed of a mobile terminal provided with a communication means capable of direct communication,
An encryption means for encrypting the search signal using the unique information of the target terminal as a search target as a key;
Search signal transmission means for transmitting the search signal encrypted by the encryption means to a plurality of relay terminals configured with mobile terminals provided with communication means capable of directly communicating;
A search source terminal characterized by comprising:

(Supplementary Note 8) A search destination target terminal including a mobile terminal provided with a communication means capable of direct communication,
Search signal receiving means for receiving an encrypted search signal transmitted from a search source via a relay terminal;
Decrypting means for decoding the search signal received by the search signal receiving means with the unique information of the terminal as a key;
A search response means for determining that the search signal has been transmitted to the own terminal when decoding is successful by the decoding means, and transmitting a search response signal including position information of the own terminal;
A target terminal characterized by comprising:

It is a figure which shows the basic composition of the portable search system which becomes embodiment of this invention. It is a figure which shows the structural example of the search data which becomes embodiment of this invention. It is a functional block diagram in the portable terminal which becomes embodiment of this invention. It is a figure which shows the structural example of the search information data managed by the transmission information storage part which becomes embodiment of this invention. It is a figure which shows the reception processing flow (reception main process) of the search data used in common between the portable terminals which become embodiment of this invention. It is a figure which shows the flow of the relay process of the search data used in common between the portable terminals which become embodiment of this invention. It is a figure which shows the flow of the response reception process of the search data used in common between the portable terminals which become embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Search origin terminal 2 Relay terminal 3 Target terminal 11 Search request reception part 12 Self-terminal information acquisition part 13 Search data preparation and analysis part 14 Timer management part 15 Transmission information storage part 16 Direct communication apparatus interface control part 21 Search signal transmission means 22 Encryption / Decryption Unit 23 Search Data Analysis Unit 24 Signal Retransmission Unit 25 Search Response Unit 100 Search Data 200 Search Data Information

Claims (5)

It is a relay terminal that consists of a portable terminal equipped with a communication means capable of direct communication and relays search information from a search source,
Search signal receiving means for receiving a search signal transmitted from the search source terminal and encrypted using the unique information of the target terminal as a key;
Decoding means for decoding the search signal received by the search signal receiving means with the unique information of the mobile terminal as a key;
A signal retransmission means for retransmitting the search signal when the search signal cannot be decoded by the decoding means;
A search response means for determining that the search signal is a target terminal to be searched and transmitting a search response signal including position information when the search signal can be decoded by the decoding means;
A relay terminal characterized by comprising: When transmitting or receiving the search signal or the search response signal, comprising transmission information storage means for holding these signals in a storage unit,
The signal is discarded when a signal received within a predetermined time is matched with the search signal or the search response signal held in the transmission information storage unit. Relay terminal.   The search signal includes a relay counter indicating the number of relay terminals, and subtracts the number of relay terminals each time the relay terminal is passed, and when the search signal is received when the relay counter becomes zero, The relay terminal according to claim 1 or 2, wherein transmission is not performed. A search method for searching for a target terminal via a relay terminal configured by a mobile terminal provided with a communication means capable of direct communication,
On the computer,
A search signal receiving step for receiving a search signal transmitted from the search source terminal and encrypted using the unique information of the target terminal as a key;
A decoding step for decoding the search signal received in the search signal reception step using the unique information of the mobile terminal as a key;
A signal retransmission step for retransmitting the search signal if the search signal could not be decoded in the decoding step;
A search response step of transmitting a search response signal including position information by determining that the search target signal is a target terminal when the search signal can be decoded in the decoding step;
A search method characterized by causing to execute. A search program for searching for a target terminal via a relay terminal configured by a mobile terminal provided with a communication means capable of direct communication,
On the computer,
A search signal receiving step for receiving a search signal transmitted from the search source terminal and encrypted using the unique information of the target terminal as a key;
A decoding step for decoding the search signal received in the search signal reception step using the unique information of the mobile terminal as a key;
A signal retransmission step for retransmitting the search signal if the search signal could not be decoded in the decoding step;
A search response step of transmitting a search response signal including position information by determining that the search target signal is a target terminal when the search signal can be decoded in the decoding step;
Search program that executes

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