KR101950466B1 - Illegal passenger detection system, illegal passenger detection server and the method thereof - Google Patents

Abstract

The present invention provides an illegal passenger detection system for detecting an illegal passenger. The system includes a plurality of RFID antennas disposed in a predetermined area to acquire RFID tag signals, an RFID reader for communicating with a plurality of RFID antennas and collecting RFID tag signals, an RFID reader installed in an entrance or a passage of a predetermined area, A plurality of counter devices for counting the number of the counter devices; And a server for communicating with the RFID reader and the plurality of counter devices, and detecting an unauthorized person based on the RFID tag signal and the entry and exit count information.

Description

TECHNICAL FIELD [0001] The present invention relates to an illegal passenger detection system, an illegitimate passenger detection server,

And more particularly, to a system, a server and a method for detecting an unauthorized person in a system for collecting freight charges using an RFID (Radio Frequency Identification) tag. will be.

Conventional urban railway stations (or buses) use short range tags (within about 10 cm) based on smart card technology. Such a wicket system is expensive to install, and there is time consumed by users at the wicket for recognizing the near tag. This causes the traffic speed of users in the congestion time zone to decelerate rapidly, thereby increasing congestion. Due to the recent increase in the number of metropolitan railway lines and the increase in the number of transit stops, operating costs are increasing due to the addition of transit wickets to track transit routes and to set fare fare between operators. To this end, research is being conducted on a freight charge collection system that eliminates the installation of ticket gates.

In this regard, Korean Patent Laid-Open Publication No. 2013-0070011 (entitled "Bus or Subway High-pass System Using an RFID Tag") charges the fare for a ticket gate by calculating the fare using an RFID tag signal at the entry / The method comprising the steps of: In addition, Korean Patent Publication No. 2009-0128309 entitled " RFID based subway profit distribution system and method, subway access control system and method, and bus ride control system and method based on RFID) Thereby distributing the proceeds to each operating entity.

However, there is a disadvantage that it is difficult to detect unauthorized passengers in the fare collection system using RFID technology. While conventional wicket system can physically interfere with the user's pass to pass through the wicket without tagging the near tag, the freight bill collection system using the RFID technology prevents the movement of the rickety passengers Or warnings. Also, installing a wicket to detect unauthorized persons is not appropriate because it reduces the advantage of using RFID technology. Therefore, it is necessary to introduce a system capable of detecting an unauthorized person while omitting the installation of a ticket gate.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems of the conventional art, and it is an object of the present invention to provide an RFID reader, a counter device, a video device, and the like installed in a predetermined area while tracking riding information, transfer information, There is a need to provide a system for detecting an unauthorized person using a vehicle. It is to be understood, however, that the technical scope of the present invention is not limited to the above-described technical problems, and other technical problems may exist.

According to a first aspect of the present invention, there is provided an RFID tag, comprising: a plurality of RFID antennas disposed in a predetermined area to obtain an RFID tag signal; A reader, a plurality of counter devices installed in an entrance or a passage of a predetermined area to count the entry and advance of a user, and an RFID reader and a plurality of counter devices, And a server for detecting an unauthorized passenger detection system.

According to a second aspect of the present invention, there is provided a method of operating an illegal passenger detection server, comprising: receiving the RFID tag signal from an RFID reader collecting RFID tag signals acquired from a plurality of RFID antennas installed in a predetermined area; Or counting information of a user from a plurality of counter devices installed on a passage; And comparing the difference between the entry and exit count information and the normal number of users calculated based on the RFID tag signal to detect an unauthorized person.

In addition, the third aspect of the present invention provides a computer-readable recording medium on which a computer program for performing the method according to the second aspect is recorded.

On the other hand, the above-mentioned problem solving means is merely illustrative and should not be construed as limiting the present invention. In addition to the exemplary embodiments described above, there may be additional embodiments described in the drawings and the detailed description of the invention.

According to the above-mentioned problem solving means of the present invention, a fare fare is collected by recognizing RFID tags held by users via a plurality of RFID antennas and RFID readers installed in a certain area of a city railroad history (or a bus) It is possible to provide a system capable of efficiently detecting an unauthorized person through a counter device and / or a video device installed at an entrance or a passage of the vehicle. Further, it is possible to prevent unauthorized riding in the future by detecting and managing a habitual illegal rider.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a system for detecting an illegal passenger according to an embodiment of the present invention; FIG.
FIG. 2 is a flowchart illustrating a method of detecting an illegal passenger detecting server according to an embodiment of the present invention.
FIGS. 3A and 3B are views showing an example in which an RFID reader and a counter device according to an embodiment of the present invention are arranged in a predetermined area.
FIG. 4 is a diagram illustrating an example in which the illegitimate occupant detection system includes a riding heat forming partition according to an embodiment of the present invention.
FIG. 5 is a diagram illustrating an example in which an imaging apparatus is installed for each of the rowing heat generating partitions of FIG. 4 according to an embodiment of the present invention.
6 is a diagram illustrating a system for detecting an illegal passenger according to another embodiment of the present invention.
FIG. 7 is a block diagram illustrating a configuration of an illegal passenger detection server according to an embodiment of the present invention. Referring to FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. It should be understood, however, that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, the same reference numbers are used throughout the specification to refer to the same or like parts.

Throughout this specification, when a part is referred to as being "connected" to another part, it is not limited to a case where it is "directly connected" but also includes the case where it is "electrically connected" do.

Throughout this specification, when a member is " on " another member, it includes not only when the member is in contact with the other member, but also when there is another member between the two members.

Throughout this specification, when an element is referred to as "including " an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise. The terms "about "," substantially ", etc. used to the extent that they are used throughout the specification are intended to be taken to mean the approximation of the manufacturing and material tolerances inherent in the stated sense, Accurate or absolute numbers are used to help prevent unauthorized exploitation by unauthorized intruders of the referenced disclosure. The word " step (or step) "or" step "used to the extent that it is used throughout the specification does not mean" step for.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

1 is a schematic diagram illustrating a system 10 for detecting an illegal passenger according to an embodiment of the present invention. 1, an illegal passenger detection system 10 includes an RFID antenna 11a, 11b, 11c, an RFID reader 12, a counter device 13, 13a, 13b, And a detection server 14.

The RFID antenna 11 is installed within a predetermined area of the history (or bus) of the urban railway, and acquires the RFID tag signal after activating the RFID tag included in the RFID card or the portable device of users existing in the area. At this time, the RFID antenna 11 can activate the RFID tag using a preset frequency. For example, the RFID antenna 11 can transmit and receive signals to and from a plurality of RFID tags existing within about 3 to 8 meters using the frequency band of 860 to 960 MHz. However, the present invention is not limited thereto, and the RFID antenna 11 can communicate with the RFID tag using various frequency bands according to the area, the height, the installation interval with other RFID antennas, and the like.

The RFID reader 12 communicates with a plurality of RFID antennas 11 installed in the area and collects RFID tag signals obtained from the RFID antenna 11. [ The RFID tag signal includes at least one of identification information of the RFID tag, user identification information, and fare payment means information, for example. The RFID reader 12 decodes and encodes the RFID tag signal and provides it to the illegal passenger detection server 14 or another server (not shown) to calculate the riding information, transfer information, getting-off information, and fare fare information of the user, The calculated fare fare may be settled. Here, the boarding information is information calculated on the basis of the RFID reader in which the specific RFID tag signal is first collected. The boarding information is identification information of an urban railroad history (or bus station) where the RFID reader is located, time information, RFID tag identification information, (Or other station) of the RFID tag when the RFID tag signal is collected from the RFID reader of another history (or other station) after the RFID tag signal is collected for the first time, Time information, RFID tag identification information, and user identification information. Or if the RFID tag is of a type that is readable / writable, the RFID tag signal may further include riding information and transfer information.

If the RFID tag signal is duplicated within a critical time (e.g., three minutes) by the RFID antenna 11 using different RFID tag identification information included in the RFID tag signal, The remaining signals other than the collected RFID tag signal can be removed. Also, the RFID reader 12 may selectively disable the RFID tag when the RFID tag signal is received from the same user using the user identification information. For example, if an RFID tag signal having the same user identification information is duplicated within a critical period (for example, one minute, etc.), the RFID reader 12 transmits the RFID tag signal corresponding to the remaining RFID tag signals other than the received RFID tag signal Lt; / RTI > Alternatively, the RFID reader 12 may deactivate the RFID tags other than the RFID tags corresponding to the riding information based on the riding information of the user. Meanwhile, according to the embodiment, the duplicate acknowledgment of the RFID tag identification information and / or the user identification information may be performed by the tampering detection server 14 or another server.

On the other hand, the RFID antenna 11 and the RFID reader 12 may be installed on a wall or an upper part (that is, a ceiling) surrounding a certain area.

The counter device 13 counts the number of users entering or advancing into a certain area. At this time, the counter device 13 is installed at an entrance or passage of a certain area. At this time, the counter device 13 counts the entry and advance of users by irradiating infrared rays to a predetermined area.

The illegal passenger detection server 14 communicates with the RFID reader 12 and the counter device 13 and may be located in a certain area or may be located outside (for example, a control room). The operation of the illegitimate occupant detection server 14 for detecting an illegitimate occupant will be described in detail below with reference to Fig.

Referring to FIG. 2, the illegal passenger detection server 14 receives the RFID tag signal obtained from the RFID antenna 11 disposed in a certain area through the RFID reader 12 (S110).

At the same time, the illegitimate occupant detection server 14 receives the entry and exit count information which is obtained by counting the number of users entering and leaving the predetermined area from the counter device 13 (S120). At this time, the unjust operator detection server 14 can receive the RFID tag signal and the entry and exit count information at a predetermined time interval (or in real time).

Then, the illegitimate occupant detection server 14 detects an unauthorized person based on the RFID tag signal and the entry and exit count information (S130). More specifically, the illegal passenger detection server 14 calculates the number of normal users (that is, the user who receives the RFID tag signal) in a certain area by using the RFID tag signal, and calculates the sum of the entry count information and the advance count information And compares the sum of the difference values with the number of normal users to detect an unauthorized person.

3A and 3B show an example in which the RFID reader 12 and the counter device 13 according to the embodiment of the present invention are arranged in a certain area. 3A shows the case where the counter device 13 is disposed at the entrance (entrance 1, entrance 2, exit 3) of the certain area 300a. FIG. 3B shows the case where the counter device 13 ) Are arranged in the same manner. The RFID reader 12 located in the fixed areas 300a and 300b is connected to a plurality of RFID antennas 11 to collect the RFID tag signals of the users. Also, the counter device (13) arranged at the entrance or passage of the certain areas (300a, 300b) counts entrants and entrants into the area.

, t는 시간, g는 출입구 번호)의 합과 진출 카운트 정보(

, t는 시간, g 는 출입구 번호)의 합간의 차이값(

)을 산출한다. 즉,

는 일정 구역(300a, 300b) 내에 존재하는 총 사용자 수를 나타낸다. 또한, 부정 승차자 검출 서버(14)는 RFID 리더기(12)로부터 제공받은 RFID 태그 신호를 기준으로 일정 구역(300a, 300b)의 정상 사용자 수(

)를 추출한다. 이때, 부정 승차자 검출 서버(14)는 RFID 태그 신호를 기준으로 동일한 RFID 식별 정보 및/또는 동일한 사용자 식별 정보를 검색하여 최종 정상 사용자 수(

)를 산출할 수 있다. The illegitimate occupant detection server 14 counts entry count information provided from each counter device 13

, t is the time, g is the entrance number) and advance count information (

, t is the time, and g is the entrance number)

). In other words,

Represents the total number of users residing within a given area 300a, 300b. In addition, the illegitimate vehicle occupant detection server 14 detects the number of normal users of the fixed areas 300a and 300b based on the RFID tag signal provided from the RFID reader 12

). At this time, the illegitimate vehicle detection server 14 searches for the same RFID identification information and / or the same user identification information on the basis of the RFID tag signal,

) Can be calculated.

과

가 동일하면, 일정 구역(300a, 300b) 내에 부정 승차자가 존재하지 않는 것으로 판단하며,

과

가 동일하지 않은 경우, 부정 승차자가 존재하는 것으로 판단한다. 만약, 부정 승차자가 존재하는 것으로 판단되면, 부정 승차자 검출 서버(14)는 알림음 또는 알림 메시지를 출력할 수 있다. 이를 통해, 도심 철도 역사의 관리자 등은 부정 승차자의 존재를 인지할 수 있다. The illegal passenger detection server 14

and

It is determined that there are no illegal passengers in the certain zones 300a and 300b,

and

Is not the same, it is judged that there is an unjust passenger. If it is determined that an unauthorized person exists, the unauthorized person detecting server 14 may output a notification sound or a notification message. In this way, managers of downtown railroad history can recognize the presence of unjust people.

는 RFID 안테나(11)의 식별 번호)를 산출하며, 카운터 장치(13)의 식별 정보를 기준으로 총 사용자 수인

는 카운터 장치(13)의 식별 번호)를 산출한다. 이후, 부정 승차자 검출 서버(14)는 동일 칸막이에 설치된 RFID 안테나와 카운터 장치의 식별 정보를 이용하여

와

(

은 각각 동일한 칸막이에 설치된 RF안테나와 카운터 장치의 식별 번호)를 비교한다. 만약,

와

이 동일하지 않은 경우, 부정 승차자 검출 서버(14)는 알림음 또는 알림 메시지를 출력한다. 이때, 알림음을 출력할 수 있는 알림음 출력 장치(15)는 도 4에 도시된 바와 같이, 각 칸막이에 부착되어 있을 수 있다. 따라서, 부정 승차자 검출 서버(14)는 일정시간 간격 (또는 실시간)으로

와

을 비교한 후, 알림음을 출력하여 부정 승차자에게 경고하거나, 역사의 관리자에게 부정 승차의 존재 사실을 알릴 수 있다. Meanwhile, as shown in FIG. 4, the illegitimate occupant detection system 10 may include a riding heat forming partition 400 that allows users to enter or advance a certain area sequentially. At this time, the RFID antenna 11 and the counter device 13 may be installed for each partition. In this case, the illegitimate occupant detection server 14 detects the illegitimate passenger for each partition based on the identification information of the RFID antenna 11 and the counter device 13 provided for each partition. Specifically, the illegitimate vehicle occupant detection server 14 detects the number of normal users based on the identification information of the RFID antenna 11

(Identification number of the RFID antenna 11), and based on the identification information of the counter device 13,

The identification number of the counter device 13). Thereafter, the illegal passenger detection server 14 uses the identification information of the RFID antenna and the counter device installed in the same partition

Wow

(

Compares the identification numbers of the RF antenna and the counter device installed in the same partition, respectively). if,

Wow

The irregular-passenger detection server 14 outputs a notification sound or a notification message. At this time, a notification sound output device 15 capable of outputting a notification sound may be attached to each partition as shown in FIG. Therefore, the illegitimate occupant detection server 14 can detect the illegal passenger detection server 14 at a predetermined time interval (or in real time)

Wow

A warning sound may be output to warn the unjust passenger, or the history manager may be informed of the existence of the unauthorized riding.

와

을 비교한 결과, 특정 칸막이에서 부정 승차자가 검출되면, 부정 승차자가 검출된 시점에 대응하는 이미지 프레임을 기초로 부정 승차자의 특징점을 산출할 수 있다. 또한, 부정 승차자 검출 서버(14)는 산출된 특징점을 상습 부정 승차자 DB(17)에 저장할 수 있다. Also, according to an embodiment, the illegal passenger detection system 10 may further include a video device 16 installed in each of the riding heat generating partitions 400. FIG. 5 is a diagram showing an example in which the imaging device 16 is installed for each of the riding heat generating partitions 400 of FIG. 4 according to an embodiment of the present invention. The illegitimate occupant detection server 14 can receive image frames from the video device 16 in real time. At this time, the unjust passenger detection server 14

Wow

It is possible to calculate the minutiae point of the unjust passenger based on the image frame corresponding to the time point at which the illegal passenger is detected when the illegal passenger is detected in the specific partition. Furthermore, the illegitimate occupant detection server 14 can store the calculated minutiae in the irregular-ridden passenger DB 17.

Thereafter, the illegitimate occupant detection server 14 calculates the characteristic points of the user on the basis of the image frames received in real time from the video apparatuses installed at arbitrary locations, and then outputs the calculated characteristic points to the minutiae points . If the comparison result is the same, the illegitimate vehicle detection server 14 outputs a notification sound or a notification message to the manager or informs the manager's personal portable terminal of a notification message (for example, " ). ≪ / RTI > Thus, the illegitimate occupant detection system 10 allows an administrator to easily identify an unauthorized rider, and at the same time, it is possible to separately manage users who are likely to ride illegally, thereby preventing unauthorized riding in the future.

FIG. 6 is a diagram illustrating a false passenger detection system 10 according to another embodiment of the present invention. 6, the illegal passenger detection system 10 includes an RFID antenna 11, an RFID reader 12, an illegal passenger detection server 14 and an area identical to the recognition range of the RFID reader 12, field of view of the object. The recognition range of the RFID reader 12 may be determined according to the number of the RFID antennas 11 communicating with the RFID reader 12, the structure in which the RFID antenna 11 is arranged, In addition, the object identification imaging device 18 may be a device that embeds a program that identifies an entity within a frame, and identifies the number of entities present in the image frame captured in the object identification imaging device 18. [

Thus, the illegal passenger detection server 14 can be provided with the number of users identified in the object identification video device 18 and the RFID tag signal collected from the RFID reader 12. Thereafter, the illegitimate occupant detection server 14 can detect an unauthorized person based on a result of comparing the number of normal users calculated based on the RFID tag signal with the total number of users identified in the object identification video device 18. [

6, the counter device 13 may be omitted, or an unauthorized person may be detected using both the counter device 13 and the object identification video device 18. [

As described above, the embodiments of the present disclosure can provide a system capable of collecting freight charges and detecting unauthorized persons by recognizing RFID tags held by users in the history (or bus) of the urban railroad. Further, some embodiments in accordance with the present disclosure can prevent future unauthorized riding by detecting and managing habitual improper riders.

FIG. 7 is a block diagram showing the configuration of the illegal passenger detection server 14 according to the embodiment of the present invention. The configurations of the illegal passenger detection server 14 shown in Fig. 7 relate to the embodiments described in Figs. 1 to 6 described above. Therefore, the contents described above in Figs. 1 to 6 can be applied to the configuration of the illegal passenger detection server 14 in Fig.

As shown in Fig. 7, the illegal passenger detection server 14 includes a communication circuit 710, a memory 720, and a processor 730.

The communication circuit 710 is a communication circuit 710 for controlling the illegal passenger detection server 14 to communicate with the RFID reader 12, the counter device 13, the video device 16, the object identification video device 18, And includes the above components. For example, the communication circuit 710 may include at least one of a mobile communication chip (not shown), a wired communication chip (not shown), a Wi-Fi chip (not shown), and a wireless communication chip (not shown).

The memory 720 stores a program for the processor 730 to control the improper rider detection server 14 and detect an unauthorized person. At this time, the memory 720 collectively refers to a non-volatile storage device that keeps stored information even when power is not supplied, and a volatile storage device that requires power to maintain stored information.

The processor 730 controls the overall operation of the illegal passenger detection server 14. For example, the processor 730 may include at least one component for controlling the operation of the memory 720 and the communication circuitry 710. For example, the processor 730 may include a random access memory (RAM) (not shown), a read only memory (ROM) (not shown), a CPU (not shown), a GPU (Graphic Processing Unit) (Not shown). At this time, the RAM, the ROM, the CPU and the GPU can be connected to each other via the bus.

In addition, the processor 730 can detect an unauthorized person by executing programs stored in the memory 720. [ Specifically, the processor 730 receives the RFID tag signal collected in a certain area from the RFID reader 12 through the communication circuit 710, and receives the RFID tag signal from the counter device 13 installed in the entrance door or the passage of the predetermined area, As well as entry and exit count information. Thereafter, the processor 730 compares the difference between the entry and advance count information with the normal number of users calculated on the basis of the RFID tag signal, thereby detecting an unauthorized person. That is, if the difference value between the entry and advance count information is equal to the normal user number, the processor 730 determines that there is no illegal passenger. If the difference value does not equal the normal number of users, . At this time, the processor 730 may output a notification sound when the indefinite-passenger detection server 14 further includes a speaker (not shown), and may transmit a message indicating that an illegal passenger is detected to the manager's portable terminal .

In addition, one embodiment of the present invention may be embodied in the form of a recording medium including instructions executable by a computer, such as program modules, being executed by a computer. Computer readable media can be any available media that can be accessed by a computer and includes both volatile and nonvolatile media, removable and non-removable media. The computer-readable medium may also include computer storage media. Computer storage media includes both volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data.

It will be understood by those of ordinary skill in the art that the foregoing description of the embodiments is for illustrative purposes and that those skilled in the art can easily modify the invention without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention.

10: illegal passenger detection system
11: RFID antenna
12: RFID reader
13: Counter device
14: illegal passenger detection server
15: Sound output device
16: Imaging device
17: Repeated DB
18: Object Identification Imaging Device

Claims (11)

A plurality of RFID antennas disposed in a predetermined area to acquire RFID tag signals;
An RFID reader communicating with the plurality of RFID antennas to collect the RFID tag signals;
A plurality of counter devices installed at an entrance or a passage of the predetermined area to count a user's entry and exit; And
And a server communicating with the RFID reader and the plurality of counter devices and detecting an unauthorized person based on the RFID tag signal and the entry and exit count information,
The RFID reader
Extracts identification information of the user from the RFID tag signal and deactivates the RFID tag corresponding to the RFID tag signal received later when the same user identification information is duplicated within a threshold period. The method according to claim 1,
The server
Calculating a number of normal users in the predetermined area by using the RFID tag signal provided from the RFID reader,
And a difference between the sum of the entry count information and the advance count information provided from each of the counter devices disposed in the entrance or passage of the predetermined area is compared with the normal number of users to detect an unauthorized passenger, . 3. The method of claim 2,
The server
And outputs a notification sound when the difference between the sum of the entry count information and the advance count information is different from the normal number of users. The method according to claim 1,
Wherein the plurality of RFID antennas and the plurality of counter devices
A plurality of partition members installed to form a row of users in an entrance or a passage of the predetermined area,
The server
Wherein the unauthorized passenger detection unit detects an unauthorized passenger for each partition by using the number of normal users of each partition and the entry and exit count information of the partition based on the RFID antenna and the counter device installed in each partition. 5. The method of claim 4,
The illegal passenger detection system
And an image device provided for each partition to provide a photographed image frame to the server,
The server
And calculates the minutiae points of the unjust passenger based on the image frame corresponding to the time point at which the unjust passenger is detected, and stores the calculated minutiae points in the irregular passenger database. 6. The method of claim 5,
The server
Wherein the feature point of the user is calculated on the basis of an image frame received from another image device in real time and the calculated feature point is compared with previously stored feature points of the routine. The method according to claim 1,
The illegal passenger detection system
Further comprising an imaging device having a field of view the same as the recognition range of the RFID reader,
The server
And detects an unauthorized passenger by comparing the number of users identified in the video apparatus with the number of normal users calculated using the RFID tag signal. delete The method according to claim 1,
Wherein the RFID reader is installed above the fixed area. A method of operating a server for controlling an illegitimate occupant detection system,
Receiving the RFID tag signal from an RFID reader collecting RFID tag signals acquired from a plurality of RFID antennas installed in a predetermined area;
Receiving a user's entry and exit count information from a plurality of counter devices installed in an access door or passage of the predetermined area; And
Comparing the difference between the entry and exit count information and the number of normal users calculated based on the RFID tag signal to detect an illegal passenger,
Wherein the step of receiving the RFID tag signal comprises:
Extracting identification information of the user from the RFID tag signal by the RFID reader and deactivating the RFID tag corresponding to the RFID tag signal received later when the same user identification information is duplicated within a threshold period. A computer-readable recording medium on which a computer program for performing the method of claim 10 is recorded.

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