Abstract:
A method for selection of a received telegram in a train wireless communications system including a plurality of wireless base stations situated along the train tracks, for respectively communicating with a higher level device through a wired circuit, and at least one terminal having at least two or more antennas installed in cars of the train moving down the track, during a predetermined transmission interval of a downstream telegram received from a higher level device, the wireless base station twice transmits telegrams that include at least identical content; the terminal, using the plurality of antennas, receives the telegrams transmitted by the wireless base station, selects the received telegram having the best reception from among those received by the plurality of antennas as the received telegram, and transmits a response telegram to the wireless base station, in response to the telegram received from the wireless base station.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to train wireless communication systems, and in particular relates to the method of selection of a received telegram message in a train wireless communication system adapted for communication between a wireless base station and an on-board wireless terminal of a moving train. 
       BACKGROUND ART 
       [0002]    In recent years, the use of a wireless system that uses the radio frequency of 26 GHz band as a short distance wireless communication system has been expanding. 
         [0003]    The examples of a railway control system using a 2.4 GHz-band wireless communication system include a CBTC (Communication Based Train Control) system (e.g., see Patent Literature 1). 
       CITATION LIST 
     Patent Literature 
       [0004]    Patent Literature 1: JP-A-2009-225135 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    The purpose of the present invention is to provide a train wireless communication system adapted for communication between a plurality of wireless base stations and an on-board wireless terminal on a moving train, in which a telegram message having the best reception condition is selected from among telegram messages received by the on-board wireless terminal. 
       Solution to Problem 
       [0006]    According to an aspect of the present invention, there is provided a method for selection of a received telegram message in a train wireless communication system comprising: a plurality of wireless base stations arranged along the track of a train, each wireless base station communicating with a higher level device through a wired line; and at least one terminal having at least two or more antennas installed in a car of the train moving on the track, during a predetermined transmission interval, the wireless base station transmits at least twice a downstream telegram message, which is received from the higher level device, as a telegram message that includes an identical content; and the terminal receives, with the plurality of antennas, a telegram message transmitted from the wireless base station, selects the received telegram message having the best reception condition from among the telegram messages received with the plurality of antennas as a received telegram message, and transmits a response telegram message to the wireless base station in response to the telegram message received from the wireless base station. 
         [0007]    According to another aspect of the present invention, there is provided the above-described method, the base station receives the response telegram messages transmitted from the terminal in response to the telegram message that has been transmitted twice as the telegram message that includes at least an identical content, respectively, selects, as a received telegram message, a response telegram message having the best reception condition from among the response telegram messages, and transmits the same to the higher level device. 
         [0008]    According to yet another aspect of the present invention, there is provided a method for selection of a received telegram message in a train wireless communication system comprising: a plurality of wireless base stations arranged along the track of a train, each wireless base station communicating with a higher level device through a wired line; and at least one terminal installed in a car of the train moving on the track, during a predetermined transmission interval, the each wireless base station transmits at least twice a downstream telegram message, which is received from the higher level device, as a telegram message that includes an identical content; the terminal receives the telegram message transmitted from the wireless base station, and transmits a response telegram message to the base station in response to the received telegram message transmitted from the base station, and the base station receives the response telegram messages transmitted from the terminal in response to the telegram message that has been transmitted twice as the telegram message that includes at least an identical content, respectively, selects, as the received telegram message, a response telegram message having the best reception condition from among the response telegram messages, and transmits the same to the higher level device. 
       Advantageous Effects of Invention 
       [0009]    According to the present invention, a plurality of wireless base stations transmits an identical telegram message multiple times, and an on-board wireless terminal can select the telegram message having the best reception condition among the received telegram messages. Thanks to the time diversity of the present invention, it is possible to receive a telegram message with a reduced effect of electromagnetic interferences, such as fading. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a view illustrating the whole configuration of a CBTC wireless communication system to which the present invention is applied. 
           [0011]      FIG. 2  is a block diagram of an on-board wireless terminal that is an embodiment of the present invention. 
           [0012]      FIG. 3  is a view illustrating the configuration of software of the on-board wireless terminal that is an embodiment of the present invention. 
           [0013]      FIG. 4  is a view for explaining the control of the CBTC wireless subsystem that is an embodiment of the present invention. 
           [0014]      FIG. 5  is a memory table for explaining the radio wave condition of a telegram message to be stored into a RAM section of the on-board wireless terminal that is an embodiment of the present invention. 
           [0015]      FIG. 6  is a flow chart for explaining the time diversity processing performed by the on-board wireless terminal that is an embodiment of the present invention. 
           [0016]      FIG. 7  is a memory table for explaining the radio wave condition of a telegram message to be stored into the RAM section of an on-board wireless terminal that is another embodiment of the present invention. 
           [0017]      FIG. 8  is a flow chart for explaining the first-time time diversity processing performed by the on-board wireless terminal that is another embodiment of the present invention. 
           [0018]      FIG. 9  is a flow chart for explaining the second-time time diversity processing performed by the on-board wireless terminal that is another embodiment of the present invention. 
           [0019]      FIG. 10  is a flow chart for explaining the final determination process performed by a wireless base station that is another embodiment of the present invention performs. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0020]    Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 
         [0021]      FIG. 1  is a view illustrating the whole configuration of a CBTC (Communication Based Train Control) wireless communication system to which the present invention is applied. 
         [0022]    In  FIG. 1 , a monitoring device  101  and management devices  103  and  104  are connected to a LAN (Local Area Network)  102 . 
         [0023]    The monitoring device  101  monitors the operation of a train via the LAN  102 . 
         [0024]    The management devices  103  and  104  secure the safety operation of a train  120  by managing the operation information about the train in a predetermined zone, and are connected to a Base Station Master (hereinafter, referred to as BSC)  111  installed in the zone of a CBTC wireless subsystem  110 . 
         [0025]    The BSC  111  is connected to a plurality of wireless base stations (hereinafter, each is referred to as a Base Master: BS)  112  to  115  installed along a track  130  of the train, and serves as a relay device that relays uplink/downlink telegram messages (communication messages) between these BSs and the management device  103 . Each of the BS  112  to BS  115  wirelessly transmits a downlink telegram message received from the BSC  111 , and transfers to the BSC  111  an uplink telegram message that is wirelessly received from the train  120 . 
         [0026]    In each train  120  moving on the track  130 , on-board wireless terminals (hereinafter, each is referred to as a Mobile Station: MS)  121  and  122  are installed in a front car and a rear car. The front car may be the first car or may be the second car, and the rear car may be the last car or may be the car proceeding to the last car. These MS  121  and MS  122  are connected to an on-board controller: ATP/ATO (Automatic Train Protection/Automatic Train Operation)  123  installed in the front car, via a communication line  124  in the train. The ATP/ATO  123  includes a display device for displaying a command given from the management device  103 , and further includes, for example, an alarm-output device for notifying an operating staff of an alarm and a GPS (Global Positioning System) for measuring the current location of the train, in addition to the display device. 
         [0027]    The MS  121  and MS  122  installed in the train  120  wirelessly communicate with the BS  112  to BS  115  positioned within a communication area, receive via the BS  112  to BS  115  a downlink telegram message transmitted from the management device  103 , transfer the same to the ATP/ATO  123 , and wirelessly transmit to the BS  112  to BS  115  an uplink telegram message generated by the ATP/ATO  123 . 
         [0028]    The ATP/ATO  123  extracts a message transmitted by the management device  103  from the downlink telegram message received by the MS  121  and MS  122 , displays a received message, and performs a control action in response to a control instruction indicated by the received message. The .  ATP/ATO  123  generates an uplink telegram message including the status information, such as the location of the train detected by the GPS, and the identifier of the train, and transmits the generated uplink telegram message from the MS  121  and MS  122  at a predetermined timing as described later. In the embodiment, a case is described where one MS is installed in the front car of the train  120  and one MS is installed in the rear car, but three or more MSs may be installed in one and the same train in order to improve the diversity effect. 
         [0029]      FIG. 2  is a block diagram of the on-board wireless terminal that is an embodiment of the present invention. 
         [0030]    In  FIG. 2 , the MS  121  and  122  each include an antenna RX 0  system  206 , an antenna RX 1  system  207 , an FPGA/DSP (Field Programmable Gate Array/Digital Signal Processor) section  205  configured to transmit and receive radio data, a PLD (Programmable Logic Device) section  204  having an interface function to connect to the outside and the like, a CPU (Central Processing Unit) section  201  configured to control the terminal, a ROM (Read Only Memory) section  203  having stored therein the software for operating the CPU section  201  and the like, and a RAM (Random Access Memory) section  202  configured to temporarily store a memory table of a radio status and the like. 
         [0031]      FIG. 3  is a view illustrating the configuration of software of the on-board wireless terminal that is an embodiment of the present invention. 
         [0032]    The software of  FIG. 3  comprises application  301 , middleware  302 , an OS (Operation System)  304 , and hardware/CPU/FPGA 305  for operating the PLD section  204 , CPU section  201 , and FPGA/DSP section  205 . 
         [0033]    The time diversity is controlled by a TRX Control  303  inside the middleware  302 . The TRX Control  303  is controlled by the CPU section  201  and receives radio data (a telegram message) from the FPGA/DSP section  205 . 
       First Embodiment 
       [0034]    Next, the operation of the time diversity that is an embodiment of the present invention is described using  FIG. 1  to  FIG. 6 . 
         [0035]    In the embodiment, the operation is described by limiting to the management device  103 , BSC  111 , BS  113 , MS  122 , and ATP/ATO  123 . Assume that the MS  121  will not involve in the operation of the embodiment. Further assume that the antenna RX 1  system  207  of the MS  122  will not involve in the operation of the embodiment, either. 
         [0036]      FIG. 4  is a view for explaining the control of the CBTC wireless subsystem  110  that is an embodiment of the present invention. 
         [0037]    In  FIG. 4 , the management device  103  transmits a telegram message that is train control information to the BS  113  via the BSC  111 . 
         [0038]    In an embodiment of the present invention, the management device  103  transmits the train control information at every 500 msec that is a predetermined cycle. 
         [0039]    The BS  113  transmits a telegram message that includes an identical content to the MS  122  at least twice at a predetermined interval specified by a system parameter. Note that, the system parameter is a variable parameter, and in the embodiment the predetermined interval specified by the system parameter is an interval of 160 msec as an example, but not limited thereto. 
         [0040]    The MS  122  obtains train location information and the like from the ATP/ATO  123 . 
         [0041]    The MS  122  receives a first-time telegram message transmitted from the BS  113 , and transmits a response telegram message that includes the location information and the like about the train to the BS  113 . 
         [0042]    Furthermore, the MS  122  receives a second-time telegram message transmitted from the BS  113 , and transmits a response telegram message that includes the location information and the like about the train to the BS  113 . Note that the MS  122  may transmit a telegram message having a better reception condition to the ATP/ATO  123 . 
         [0043]    The BS  113  selects a response telegram message having a better reception condition from among the response telegram messages including two times of train location information and the like transmitted from the MS  122 , and transmits the same to the management device  103  via the BSC  111 . 
         [0044]      FIG. 5  is a memory table for explaining the radio wave condition of a telegram message to be stored into a RAM section  202  of the on-board wireless terminal that is an embodiment of the present invention. 
         [0045]    The BS  113  transmits a telegram message that includes an identical content at least twice within an interval of 500 ms. 
         [0046]    The MS  122  receives the telegram message transmitted from the BS  113 , with the antenna RX 0  system  206 . 
         [0047]    The memory table obtains a BLER (BLock Error Rate) and a RSSI (Received Signal Strength Indication) from the telegram message received through the first-time time diversity and the second-time time diversity and stores the obtained data. 
         [0048]    “XX” in BLER=XX indicates whether or not an error exists, where the non-error existing corresponds to “0” and an error existing corresponds to “1”. 
         [0049]    “YY” in RSSI=YY indicates the value of reception sensitivity, where the higher the value, the better the reception sensitivity. 
         [0050]      FIG. 6  is a flow chart for explaining the time diversity processing performed by the on-board wireless terminal that is an embodiment of the present invention. 
         [0051]    The CPU section  201  of the MS  122  reads and obtains the first-time and second-time BLER information from the memory table stored in the RAM section  202 , in step S 601 . After obtaining the first-time and second-time BLER information, the flow proceeds to step S 602 . 
         [0052]    In step S 602 , the first-time and second-time RSSI information are read and obtained from the memory table stored in the RAM section  202 . After obtaining the first-time and second-time RSSI information, the flow proceeds to step S 603 . 
         [0053]    In step S 603 , it is determined whether both the first-time BLER and second-time BLER have no error: indicated by “0”, and when the both have no error: indicated by “0” (YES), the flow proceeds to step S 604 , while when either of or both the first-time BLER and second-time BLER has or have an error: indicated by “1” (NO), the flow proceeds to step S 606 . 
         [0054]    In step S 606 , it is determined whether the first-time BLER has no error, and when it has no error: indicated by “0” (YES), the flow proceeds to step S 607  while when it has an error: indicated by “1” (NO), the flow proceeds to step S 604 . 
         [0055]    In step S 604 , data (telegram message) having a higher reception sensitivity is selected based on the first-time and second-time RSSI information, and then the flow proceeds to step S 605 . 
         [0056]    In step S 607 , data (a telegram message) when the first-time BLER and second-time BLER have no error: indicated by “0”, is selected, and then the flow proceeds to step S 605 . 
         [0057]    In step S 605 , the selected data (telegram message) and the train location information are transmitted to the BS  113  and the time diversity processing is completed. 
         [0058]    This processing allows the MS  122  to select data (a telegram message) having a better radio quality from among the data (telegram messages) transmitted from the BS  113 . 
       Second Embodiment 
       [0059]    Next, the operation of a combination of time diversity and antenna diversity that is another embodiment of the present invention is described using  FIG. 1  to  FIG. 4  and  FIG. 7  to  FIG. 10 . 
         [0060]    In the embodiment, the operation is described by limiting to the management device  103 , BSC  111 , BS  113 , MS  122 , and ATP/ATO  123 . Assume that the MS  121  will not involve in the operation of the embodiment. 
         [0061]    Next, the control of the CBTC wireless subsystem  110  that is another embodiment of the present invention is described using  FIG. 4 . 
         [0062]      FIG. 4  is a view for explaining the control of the CBTC wireless subsystem  110  that is an embodiment of the present invention. 
         [0063]    In  FIG. 4 , the management device  103  transmits a telegram message that is train control information to the BS  113  via the BSC  111 . 
         [0064]    In another embodiment of the present invention, the management device  103  transmits train control information at every 500 msec that is a predetermined cycle. 
         [0065]    The BS  113  transmits a telegram message that includes an identical content to the MS  122  at least twice at a predetermined interval specified by a system parameter. Note that, the system parameter is a variable parameter, and in the embodiment the predetermined interval specified by the system parameter is an interval of 160 msec as an example, but not limited thereto. 
         [0066]    The MS  122  obtains train location information and the like from the ATP/ATO  123 . 
         [0067]    The MS  122  receives a first-time telegram message transmitted from the BS  113 , and transmits a response telegram message that includes the location information and the like about the train to the BS  113 . 
         [0068]    Furthermore, the MS  122  receives a second-time telegram message transmitted from the BS  113 , and transmits a response telegram message that includes the location information and the like about the train to the BS  113 . Note that the MS  122  may transmit a telegram message having a better reception condition to the ATP/ATO  123 . 
         [0069]    The control in  FIG. 4  is performed on both a telegram message received with the antenna RX 0  system  206  of the MS  122  and on a telegram message received with the antenna RX 1  system  207 . 
         [0070]    The BS  113  selects a response telegram message having the best reception condition from among the response telegram messages including four times of train location information transmitted from the MS  122 , and transmits the same to the management device  103  via the BSC  111 . 
         [0071]      FIG. 7  is a memory table for explaining the radio wave condition of a telegram message to be stored into the RAM section  202  of the on-board wireless terminal that is another embodiment of the present invention. 
         [0072]    The BS  113  transmits a telegram message that includes an identical content at least twice within an interval of 500 ms 
         [0073]    The MS  122  receives the two telegram messages transmitted from the BS  113 , with the antenna RX 0  system  206 . 
         [0074]    The memory table obtains BLER and RSSI from the telegram message of the first-time time diversity and the telegram message of the second-time time diversity that are received with the antenna RX 0  system  206 , and stores the obtained data. 
         [0075]    Next, the MS  122  receives the two telegram messages transmitted from the BS  113 , with the antenna RX 1  system  207 . 
         [0076]    The memory table obtains BLER and RSSI from the telegram message of the first-time time diversity and the telegram message of the second-time time diversity that are received with the antenna RX 1  system  207 , and stores the obtained data. 
         [0077]    “XX” in BLER=XX indicates whether or not an error exists, where the non-error existing corresponds to “0” and the error existing corresponds to “1”. 
         [0078]    “YY” in RSSI=YY indicates the value of reception sensitivity, where the higher the value, the better the reception sensitivity. 
         [0079]      FIG. 8  is a flow chart for explaining the first-time time diversity processing performed by the on-board wireless terminal that is another embodiment of the present invention. 
         [0080]    The CPU section  201  of the MS  122  reads and obtains the BLER information of the antenna RX 0  system  206  and the BLER information of the antenna RX 1  system  207  from the memory table stored in the RAM section  202 , in step S 801 . After obtaining these BLER information, the flow proceeds to step S 802 . 
         [0081]    In step S 802 , the RSSI information of the antenna RX 0  system  206  and the RSSI information of the antenna RX 1  system  207  are read and obtained from the memory table stored in the RAM section  202 . After obtaining these RSSI information, the flow proceeds to step S 803 . 
         [0082]    In step S 803 , it is determined whether BLER is the same between the antenna RX 0  system  206  and the antenna RX 1  system  207 , and when it is the same (YES), the floe proceeds to step S 804 , while when it is different (NO), the flow proceeds to step S 805 . 
         [0083]    In step S 804 , data (a telegram message) having a higher reception sensitivity is selected based on the RSSI information, and then the flow proceeds to step S 806 . 
         [0084]    In step S 805 , the data (telegram message) with BLER=0 is selected from among the data of the antenna RX 0  system  206  and of the antenna RX 1  system  207 , and then the flow proceeds to step S 806 . 
         [0085]    In step S 806 , the selected data (telegram message) and the train location information are transmitted to the BS  113 , and then the first-time time diversity processing is completed. 
         [0086]      FIG. 9  is a flow chart for explaining the second-time time diversity processing performed by the on-board wireless terminal that is another embodiment of the present invention. 
         [0087]    The CPU section  201  of the MS  122  reads and obtains the BLER information of the antenna RX 0  system  206  and the BLER information of the antenna RX 1  system  207  from the memory table stored in the RAM section  202 , in step S 901 . After obtaining these BLER information, the flow proceeds to step S 902 . 
         [0088]    In step S 902 , the RSSI information of the antenna RX 0  system  206  and the RSSI information of antenna RX 1  system  207  are read and obtained from the memory table stored in the RAM section  202 . After obtaining these RSSI information, the flow proceeds to step S 903 . 
         [0089]    In Step S 903 , it is determined whether BLER is the same between the antenna RX 0  system  206  and the antenna RX 1  system  207 , and when it is the same (YES), the floe proceeds to step S 904 , while when it is different (NO), the flow proceeds to step S 905 . 
         [0090]    In Step S 904 , data (a telegram message) having a higher reception sensitivity is selected based on the RSSI information, and then the flow proceeds to step S 906 . 
         [0091]    In step S 905 , the data (telegram message) with BLER=0 is selected from among the data of the antenna RX 0  system  206  and of the antenna RX 1  system  207 , and then the flow proceeds to step S 906 . 
         [0092]    In Step S 906 , the selected data (telegram message) and the train location information are transmitted to the BS  113 , and then the second-time time diversity processing is completed. 
         [0093]      FIG. 10  is a flow chart for explaining the final determination process performed by the wireless base station that is another one embodiment of the present invention performs. 
         [0094]    The BS  113  obtains the resulting data of the first-time and second-time time diversity processing transmitted from the MS  122 , in step S 1001 , and then the flow proceeds to step S 1002 . 
         [0095]    In step S 1002 , it is determined whether both the first-time BLER and the second-time BLER have the same data, i.e., the both have no error: indicated by “0”, or the both have an error: indicated by “1”, and when both the first-time BLER and the second-time BLER have the same data: indicated by “YES”, the flow proceed to step S 1003 , while when both the first-time BLER and the second-time BLER have different data: indicated by “NO”, the flow proceed to step S 1004 . 
         [0096]    In step S 1003 , data (a telegram message) having a higher reception sensitivity is selected based on the first-time and second-time RSSI information, and the final determination process is completed. 
         [0097]    In step S 1004 , the data (telegram message) with BLER=0 is selected and the final determination process is completed. 
         [0098]    This determination process allows the BS  113  to select data having a better radio quality from among the data transmitted from the MS  112 . 
         [0099]    In the above-described embodiments, MS and ATP/ATO are described as separate devices, but MS may include the function of ATP/ATO. 
         [0100]    In the above-described embodiments, assume that MS has two antennas and antenna diversity is implemented using signals received with these two antennas, but the antenna diversity may be implemented using one antenna of the front terminal and one antenna of the rear terminal of a train. In this case, data selection is performed in ATP/ATO. 
         [0101]    According to the present invention, a plurality of wireless base stations transmit an identical telegram message multiple times, and an on-board wireless terminal can select the telegram message having the best reception condition among the received telegram messages. 
         [0102]    Thanks to the time diversity of the present invention, it is possible to receive a telegram message with a reduced effect of electromagnetic interferences, such as fading. 
         [0103]    Although the present invention has been described above in detail, it should be readily apparent that the present invention is not limited to the train wireless communication system described herein and can be widely applied to wireless communication systems other than the above-described one. 
       INDUSTRIAL APPLICABILITY 
       [0104]    The present invention is suitable for a train wireless communication system comprising a plurality of wireless base stations and an on-board wireless terminal of a moving train, each wireless base station communicating with the on-board wireless terminal, in which electromagnetic interferences, such as fading, may be generated. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           101 : monitoring device, 
           102 : LAN, 
           103 ,  104 : management device, 
           110 : CBTC wireless subsystem, 
           111 : BSC, 
           112  to  115 : BS, 
           120 : train, 
           121 , 122 : MS, 
           123 : ATP/ATO, 
           130 : track