Patent Publication Number: US-9889868-B2

Title: Dedicated channel establishment method and apparatus for high speed data transmission in railway wireless sensor network

Description:
Priority to Korean patent application number 2013-0052780 filed on May 9, 2013, the entire disclosure of which is incorporated by reference herein, is claimed. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a method of allocating a wireless channel between a wireless sensor and a router and a wireless channel between routers to enhance transmission efficiency of measuring information and a method thereof in a safety management technology of railway facilities where heat generation state of a bogie and operation state of parts included in a railway vehicle under operation are measured in real time for safety of the railway vehicle. 
     Discussion of the Related Art 
     Heating generation state and vibration state of axles of a railway vehicle need to be measured in real time in order to promptly repair the vehicle at the time of occurrence of an abnormal state for safety of the railway vehicle. 
     To this end, for example, Korean Patent Publication No. 10-2010-0067999 (published on Jun. 22, 2010) “automatic railway vehicle examination apparatus” discloses sensing and systematically managing an abnormal operation of the body of a railway vehicle as well as a wheel and a pantograph. 
     Currently, a scheme of installing a device for measuring generated heat of a railway vehicle in a non-contacting manner at a railroad, and transmitting measured temperature information to a maintenance center, is used. However, this scheme fails to play an appropriate role due to inaccuracy of measurement and limitation in the number of times measured, and thus accidents are not prevented in advance and trains have been derailed, thereby failing to maintain safe driving. 
     Hence, there is a need of a method for accurately measuring the state of a railway vehicle under operation and transmitting the measured result to a railway vehicle control center in real time. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a method of setting and operating a dedicated channel for high speed transmission of data in a railway wireless sensor network capable of accurately measuring the state of a railway vehicle and transmitting the measured result to a railway vehicle control center in real time. 
     Another object of the present invention is to provide a method of setting and operating a dedicated channel for high speed transmission of data in a railway wireless sensor network capable of transmitting information on the operation state of a railway vehicle, which is operated in a poor communication environment, at high speed. 
     In accordance with an aspect of the present invention, a railway wireless sensor network system includes a plurality of sensors which are included in a railway vehicle and measure an operation state of the railway vehicle in real time, a plurality of routers which receive information on the measured operation state through a dedicated channel with each sensor, and a gateway which receives information on the operation state through a dedicated channel between the routers, and periodically transmits information on the received operation state to a railway vehicle control center. 
     The router may set the dedicated channel with the sensor and the dedicated channel between the routers by utilizing a contention-free period of a medium access control (MAC) frame. 
     If a token issuing message is received from the gateway, the router may set the dedicated channel with the sensor and the dedicated channel between the routers. 
     The token issuing message may include a number of the router, numbers of sensors which are connected to the router, and information on a use period of the dedicated channel. 
     The gateway may set a dedicated channel with a router of a lowest hierarchy through the dedicated channel between the routers. 
     The gateway may integrate dedicated channels between the plurality of routers to control the integrated dedicated channels. 
     When setting the dedicated channel between the routers, the router may encapsulate a dedicated channel path between routers of a lower hierarchy of the router, and transmit the encapsulated path in a tunneling scheme. 
     The gateway may bind a dedicated channel path between routers of a lower hierarchy of the router to the dedicated channel between the routers. 
     If information on the operation state is not received from the router until a timer is terminated by operating the timer when issuing a token, the gateway may transmit a path canceling message to the router so as to cancel the dedicated channel with the router. 
     If the token issuing message is received from the gateway, the router may operate a timer, and if information on the operation state is not received until the timer is terminated, the router may cancel the dedicated channel between sensors, which are connected to the router, based on a token returning message which has been received from the gateway. 
     Information on the operation state may be information on temperatures and vibrations of bearings which are positioned at axles of the railway vehicle. 
     In accordance with another aspect of the present invention, a method of operating a gateway in a railway wireless sensor network includes transmitting a token issuing message to a router, receiving information on an operation state of a railway vehicle, which is measured in real time by a sensor included in the railway vehicle, from the router, through a dedicated channel which is set according to the token issuing message, and transmitting the received information on the operation state, periodically, to a railway vehicle control center. 
     In accordance with yet another aspect of the present invention, a method of operating a router in a railway wireless sensor network includes receiving a token issuing message from a gateway, setting a dedicated channel with a sensor included in a railway vehicle and a dedicated channel with routers according to the token issuing message, receiving information on an operation state of the railway vehicle, which is measured by the sensor, from the sensor, through the dedicated channel with the sensor, and transmitting information on the received operation state to a gateway through the dedicated channel between the routers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a railway wireless sensor network system, according to an embodiment of the present invention; 
         FIG. 2  is a diagram illustrating an operation path of a railway wireless sensor network system according to the present invention; 
         FIG. 3  is a diagram illustrating a structure of a medium access control (MAC) frame of IEEE 802.15.4; 
         FIG. 4  is a diagram illustrating dedicated channel tunneling between routers, according to an embodiment of the present invention; 
         FIG. 5  is a diagram illustrating a dedicated channel path setting MAC message, according to an embodiment of the present invention; 
         FIG. 6  is a flowchart illustrating operation of a gateway, according to an embodiment of the present invention; and 
         FIG. 7  is a flowchart illustrating operation of a router, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that they can be readily implemented by those skilled in the art. 
     Hereinafter, some embodiments of the present invention are described in detail with reference to the accompanying drawings in order for a person having ordinary skill in the art to which the present invention pertains to be able to readily implement the invention. It is to be noted the present invention may be implemented in various ways and is not limited to the following embodiments. Furthermore, in the drawings, parts not related to the present invention are omitted in order to clarify the present invention and the same or similar reference numerals are used to denote the same or similar elements. 
     Terms such as “including,” “having,” “consist of” may be intended to indicate a plurality of components unless the terms are used with the term “only”. Terms such as “unit” refer to a unit for processing at least one function or operation, and may be implemented as hardware, software, or a combination of hardware and software. 
       FIG. 1  is a diagram illustrating a railway wireless sensor network system, according to an embodiment of the present invention. 
     Referring to  FIG. 1 , the railway wireless sensor network system according to the present invention may include a plurality of sensors  111 ,  112 ,  113 ,  121 ,  122 ,  123 ,  131 ,  132 ,  141 , and  142 , a plurality of routers  110 ,  120 ,  130 , and  140 , and at least one gateway  150 . 
     Respective sensors  111 ,  112 ,  113 ,  121 ,  122 ,  123 ,  131 ,  132 ,  141 , and  142  are included in a railway vehicle, and may be connected to routers  110 ,  120 ,  130 , and  140  having good electric wave receiving intensity. Referring to  FIG. 1 , for example, a first sensor  111 , a second sensor  112 , and a third sensor  113  are connected to a first router  110 , a fourth sensor  121 , a fifth sensor  122 , and a sixth sensor  123  are connected to a second router  120 , a seventh sensor  131  and a eighth sensor  132  are connected to a third router  130 , and a ninth sensor  141  and a tenth sensor  142  are connected to a fourth router  140 . 
     The respective sensors  111 ,  112 ,  113 ,  121 ,  122 ,  123 ,  131 ,  132 ,  141 , and  142  measure the operation status of the railway vehicle and transmit information on the measured operation status to the routers  110 ,  120 ,  130 , and  140  in real time. For example, the respective sensors  111 ,  112 ,  113 ,  121 ,  122 ,  123 ,  131 ,  132 ,  141 , and  142  periodically measure the temperature (T) and vibration (V) of the driving unit (e.g., bearings on axles) of the railway vehicle, and measured values to the connected router  110 ,  120 ,  130 , or  140 . 
     Each router  110 ,  120 ,  130 , and  140  may transmit information, which is received from respective sensors  111 ,  112 ,  113 ,  121 ,  122 ,  123 ,  131 ,  132 ,  141 , and  142 , to the gateway  150  via the routers which are positioned at another hierarchy. 
     The gateway  150  may transmit the information, which is received from the routers  110 ,  120 ,  130 , and  140 , to a railway vehicle control center  160  so that the railway vehicle control center  160  may manage safe driving of the railway vehicle based on the sensor measurement value. At this time, various wireless connection technologies (e.g., IEEE802.15.4/Zigbee) may be used in wireless transmission sections between a sensor and a router, between a router and a gateway, and between routers. 
       FIG. 2  is a diagram illustrating an operation path of a railway wireless sensor network system according to the present invention. Hereinafter, referring to  FIG. 2 , the first sensor  111 , the second sensor  112 , and the third sensor  113  are connected to the first router  110 , the fourth sensor  121 , the fifth sensor  122 , and the sixth sensor  123  are connected to the second router  120 , the seventh sensor  131  and the eighth sensor  132  are connected to the third router  130 , and the ninth sensor  141  and the tenth sensor  142  are connected to the fourth router  140 . 
     The gateway  150  issues a token for periodically transmitting measured information to sensors which are connected to a specific router. For example, the gateway  150  may transmit a first token to the first router  110  to receive information (measured values) of the first sensor  111 , the second sensor  121 , and the third sensor  131 . The first router  110 , which has received the first token, may form dedicated channels  211 ,  212 , and  213  respectively with the connected sensors, i.e., the first sensor  111 , the second sensor  112 , and the third sensor  113 , and may also set a dedicated channel  210  between the gate  140  and the first router  110  itself. Likewise, the information, which is measured in the sensor through the generated dedicated channel, may be transmitted at high speed without a transmission delay which is generated in the process of accessing a channel. 
     Further, if a second token is received from the gateway  150 , the second router  120  may form dedicated channels  221 ,  222 , and  223  with the sensors  121 ,  122 , and  123  which are connected to the second router  120  itself, and may also set the dedicated channel  220  between the second router  120  itself and the first router  110  and the dedicated channel  210  between the gateway  150  and the first router  110 . At this time, when the dedicated channel  210  between the gateway  150  and the first router  110  has been set, the setting is omitted. Likewise, the third router  130  and the fourth router  140  may also set dedicated channels with the connected sensors  131 ,  132 ,  141 , and  142 . 
     Further, when the gateway  150  does not want dedicated channel type communication with the sensors in a specific router or the wireless channel state is deteriorated, the procedure of returning the token may be performed. For example, when the gateway  150  returns the third token, the setting of the dedicated channel with the sensors  131  and  132 , which have been connected to the third router  130 , is cancelled, and the dedicated channel  230  between the second router  120  and the third router  130  may also be cancelled. At this time, when the fourth router  140  periodically communicates with the sensors  141  and  142  using a dedicated channel scheme, the dedicated channel  230  between the second router and the third router  130  and the dedicated channel between the third router  120  and the fourth router  130  may be maintained. To this end, the dedicated channels  210 ,  220 ,  230 , and  240  between routers may be used by tunneling information which is transmitted to respective routers. Hence, the gateway  150  may control sensors, which are connected to some specific routers, among a plurality of routers  110 ,  120 ,  130 , and  140 , independently from other routers. 
       FIG. 3  is a diagram illustrating a structure of a medium access control (MAC) frame of IEEE 802.15.4. 
     As illustrated in  FIG. 3 , the MAC frame structure of the low-power wireless sensor network is divided into a carrier sense multiple access-collision avoidance (CSMA-CA) section, which is a contention access period (CAP) for obtaining a channel based on contention for connection of a plurality of terminals, and a guaranteed time slot (GTS) section which is a contention free period (CFP) for obtaining a dedicated channel without contention. In the present invention, in order to transmit information measured in the sensor at high speed, dedicated channels between a sensor and a router, between a router and a gateway, and between routers may be configured by utilizing a GTS section. 
       FIG. 4  is a diagram illustrating dedicated channel tunneling between routers, according to an embodiment of the present invention. 
     As illustrated in  FIG. 4 , respective dedicated channels  210 ,  220 ,  230 , and  240  may include the path of a lower hierarchy. That is, the first dedicated channel  210  may bind and use paths of dedicated channels  210 ,  220 ,  230 , and  240  of all hierarchies within the network, and the second dedicated channel  220  may bind and use paths of the dedicated channels  220 ,  230 , and  240  of all hierarchies except the path of the dedicated channel  210  between the gateway  150  and the first router  110 . Here, the gateway  150  may randomly access and control the dedicated channel between respective routers. 
       FIG. 5  is a diagram illustrating a dedicated channel path setting MAC message, according to an embodiment of the present invention. 
     For example, as illustrated in  FIG. 5 , a token issuing message  510  for issuing a fourth token may use a time for notifying the number (identifier) of the fourth router  140 , the number of sensors  141  and  142  related with the fourth router  140 , and the period of using the GTS mode, as the payload. If the MAC message is received, the fourth router  140  may set the dedicated channel with the sensors  141  and  142  and set the time value that uses the GTS mode. 
     Further, a path setting message  520  of the fourth token may include information for setting the dedicated path between routers. If the MAC message is received, the fourth router  140  sets the dedicated channel path between the third router  130  and the fourth router  140 . At the same time, the first router  110 , the second router  120 , and the third router  130 , which receive the path setting MAC message, set a dedicated channel between each corresponding routers and an adjacent router. 
     The token returning message  530 , which returns the third token, may include the number of the third router  130 , the number of the fourth router  140 , the number of the seventh sensor  131 , and the number of the eighth sensor  132 . The router  130 , which receives the MAC message, cancels the dedicated channel with the seventh sensor  131  and the eighth sensor  132 . 
     Further, the path canceling MAC message  540  of the third token includes the path of the third router dedicated channel  230 , and the router  130 , which receives the message, cancels the path. 
       FIG. 6  is a flowchart illustrating operation of a gateway, according to an embodiment of the present invention. 
     The gateway issues a token by first transmitting a token issuing message to the router in order to receive measured information of sensors, which belong to a specific router, at high speed ( 610 ), and operates a timer ( 620 ) so as to monitor whether there is a response within a given time ( 630 ). 
     The gateway waits for reception of measured values from sensors in a state where the time is not terminated ( 640 ), and repeats the process of receiving the measured values from the entire designated sensors ( 650 ). However, when the measured values are not received from all designated sensors even after the time is terminated, an abnormal following procedure is performed ( 660 ). 
     If the measured values are received from al designated sensors, the gateway continually issues the token ( 670 ), and may receive the measured values of the sensors, which have been connected all routers, by repeating the process. At this time, when setting the dedicated channel between routers, the gateway may encapsulate the dedicated channel path between routers of the lower hierarchy of the router and transmit the encapsulated path in a tunneling scheme. 
     Likewise, the gateway may integrate the dedicated channel between routers of the lower hierarchy as well as the dedicated channel with the first router  110  using the token issuing message to control the integrated channels. 
       FIG. 7  is a flowchart illustrating operation of a router, according to an embodiment of the present invention. 
     The router basically performs communication with sensors at the contention mode (CAP mode) ( 710 ). If the token issuing message is received from the gateway ( 720 ), the router monitors communication with sensors within a given time by setting the non-contention mode (GTS) and operating a timer ( 730 ) according to the information of the token issuing message. 
     If measured values are received from each sensor, the router transmits the received measured values to the router of the upper hierarchy ( 740 ). Such a process may be repeated until timer is terminated or the measured values are received from all sensors ( 750  and  760 ). If the timer has been terminated, but the measured values are not received from all sensors, the router may perform an abnormal following procedure ( 770 ). 
     Further, if a token returning message or a token canceling message is received from the gateway, the router may perform a procedure of canceling the dedicated channel with the sensors or the dedicated channel with the upper routers. 
     According to the present invention, information on the driving state of a railway vehicle may be obtained in real time through a sensor which is mounted on a driving unit of the railway vehicle, and thus the safe driving of the railway vehicle may be secured and the maintenance costs may be minimized. 
     Further, according to the present invention, the status information of the railway vehicle, which is driven in a poor communication environment, and thus the management of the railway vehicle may be automated. 
     A person having ordinary skill in the art to which the present invention pertains may change and modify the present invention in various ways without departing from the technical spirit of the present invention. Accordingly, the present invention is not limited to the above-described embodiments and the accompanying drawings. 
     In the above exemplary system, although the methods have been described based on the flowcharts in the form of a series of steps or blocks, the present invention is not limited to the sequence of the steps, and some of the steps may be performed in a different order from that of other steps or may be performed simultaneous to other steps. Furthermore, those skilled in the art will understand that the steps shown in the flowchart are not exclusive and the steps may include additional steps or that one or more steps in the flowchart may be deleted without affecting the scope of the present invention.