JP7431132B2 - wireless communication system - Google Patents

Description

The present invention relates to a wireless communication system provided with a plurality of base stations that communicate the same content.

2. Description of the Related Art In a wireless communication system including a moving object (mobile station) such as a train, it is required that communication between the mobile station and a base station is always possible when the mobile station moves. For this reason, communications with the same contents instructed by the central equipment are transmitted on the same frequency, multiple base stations are installed in different locations, and the mobile station selects the one base station with the best communication status when moving. Can communicate.

Each base station has a communication area set up in which it can communicate with mobile stations, and when a mobile station moves, it becomes the target of direct communication by moving between adjacent communication areas. The base station is switched. Here, by partially overlapping the communication areas of two adjacent base stations, it is possible to eliminate a period (area) in which communication to a mobile station is temporarily impossible during movement. On the other hand, although ideally the signals emitted from each base station are the same, in reality these signals are not completely the same due to errors in the transmission frequency of each base station. Therefore, in areas where communicable areas overlap in this way, two radio waves may interfere, making it difficult to reproduce received data.

For this reason, Patent Document 1 discloses that communication between a base station and a mobile station is performed using a space-time block coding (STBC) method or a differential space-time block coding (DSTBC) method. A technique is described in which the signals from two adjacent base stations are made orthogonal by using the Block Coding method to prevent interference from occurring.

Further, in order to perform communication when a train passes through a tunnel, a leaky coaxial cable as described in Patent Document 2, for example, is used. A leaky coaxial cable (LCX) is laid as a cable serving as a transmission path, and also functions as an antenna by leaking transmitted radio waves, and is easy to lay even in long tunnels. When using radio waves from two orthogonal base stations as described above, for example, two base stations are installed on both sides of the LCX, and the signals emitted by each base station transmit the signals from the common LCX in opposite directions. Flow in the direction. Even in such a case, if the signals are orthogonally related as described above, no interference will occur and no region will occur where the mobile station cannot communicate.

Japanese Patent Application Publication No. 2016-34147 Japanese Patent Application Publication No. 3-295323

When the LCX is used in this way, if the LCX is disconnected due to an accident or the like, communication from the base station on the opposite side will be impossible beyond the disconnection point. Such a situation can be recognized by inspection work on the LCX or by the occurrence of a period during which communication is unavailable while the mobile station is moving. However, the frequency with which the LCX is inspected is limited. In addition, during the period when communication is impossible while the mobile station is moving, this recognition is only possible when the mobile station actually moves along the route (when the train actually runs), and the mobile station It has been difficult for the base station alone to recognize this when the base station does not exist. For this reason, it has been difficult for the base station to quickly recognize the disconnection of the LCX.

The present invention was made in view of the above situation, and an object of the present invention is to solve the above problems.

The present invention provides a first base station and a second base station that respectively transmit a first signal and a second signal modulated with common transmission data, and a first base station and a second base station that respectively transmit a first signal and a second signal modulated with common transmission data. a leaky coaxial cable connected to the first base station and the second base station so as to flow simultaneously in opposite directions, and the first signal emitted from the leaky coaxial cable and the A wireless communication system in which a second signal is received by a mobile station, wherein the first base station is capable of receiving the second signal via the leaky coaxial cable, and the first base station is configured to receive the second signal via the leaky coaxial cable. If the leaky coaxial cable cannot be recognized, the second base station recognizes that there is a fault in the leaky coaxial cable, or the second base station is enabled to receive the first signal via the leaky coaxial cable, and the second base station If the signal cannot be recognized, it is recognized that there is a fault in the leaky coaxial cable.
The first base station determines whether the received signal is the second signal by performing a cross-correlation analysis between the received signal received via the leaky coaxial cable and the first signal. The second base station recognizes that the received signal is the first signal by performing a cross-correlation analysis between the received signal received via the leaky coaxial cable and the second signal. It may be recognized whether or not.
The first signal and the second signal may be generated using a space-time block coding (STBC) method or a differential space-time block coding (DSTBC) method.

According to the present invention, in a wireless communication system in which a leaky coaxial cable is used for communication between a plurality of base stations and a mobile station, a communication failure due to damage to a leaky coaxial cable can be quickly recognized from the base station side. be able to.

1 is a diagram showing the configuration of a wireless communication system according to an embodiment. FIG. 3 is a diagram showing a signal flow when a leaky coaxial cable is normal in the wireless communication system according to the embodiment. FIG. 3 is a diagram showing a signal flow when a leaky coaxial cable is cut in the wireless communication system according to the embodiment.

Next, embodiments for carrying out the present invention will be specifically described with reference to the drawings. FIG. 1 is a diagram illustrating the configuration of a wireless communication system 1 according to an embodiment of the present invention. This wireless communication system 1 is used for train wireless communication, and is used to transmit transmission data from the central device 100 in FIG. 1 to a moving mobile station 200 (train). In this wireless communication 1, two adjacent base stations (first base station) 10A and base station (second base station) 10B are used. A central device 100 separated from the base stations 10A and 10B is connected to the base stations 10A and 10B, and the central device 100 transmits the same data (transmission data) to the base stations 10A and 10B.

This transmission data is finally transmitted to the mobile station 200 moving along the horizontal direction at the upper side of the figure. As transmitting antennas for this purpose, leaky coaxial cables (LCX) 50A and 50B are used. LCX50A and 50B are connected in series, LCX50A is connected to base station 10A, and LCX50B is connected to base station 10B. In reality, the communication area where base station 10A and mobile station 200 can communicate extends to the left side of FIG. 1, and the communication area where base station 10B and mobile station 200 can communicate extends to the right side of FIG. The area shown in FIG. 1 is an area where these communication areas are adjacent and partially overlap. Although shown in a simplified manner in FIG. 1, the LCXs 50A and 50B are actually long in the horizontal direction in the drawing, and the base stations 10A and 10B are sufficiently separated in the horizontal direction in the drawing. The LCXs 50A and 50B are installed along the traveling direction of the train (mobile station 200).

In a region where the communication areas overlap in this way, the base station 10A supplies the A-series signal (first signal) modulated with the above-mentioned transmission data to the LCX 50A, and the base station 10B supplies the B-series signal (first signal) modulated with the above-mentioned transmission data. A signal (second signal) is supplied to LCX50B. The frequencies of the carrier waves of the A-series signal and the B-series signal are set to be the same, but in reality, there is a slight difference in these frequencies due to errors in the oscillation frequency of each base station. Here, in the modulation of the A sequence signal and the B sequence signal, a space-time block coding (STBC) method or a differential space-time block coding (DSTBC) method is used. The A-series signal and the B-series signal are orthogonal to each other.

Therefore, although the A-series signals and B-series signals flow in opposite directions in the LCXs 50A and 50B in FIG. 1, no adverse effects occur due to interference between the A-series signals and the B-series signals. Therefore, regardless of whether the mobile station 200 in FIG. 1 receives an A-sequence signal or a B-series signal, it can recognize the transmission data by demodulating it. However, as described above, since the LCXs 50A and 50B are sufficiently long, the A-series signal is more dominant than the B-series signal in the LCX 50A, and the B-series signal is more dominant than the A-series signal in the LCX 50B.

Here, the base station 10A emits an A-series signal and also receives a B-series signal emitted by the base station 10B via the LCX 50A. Similarly, the base station 10B emits a B-series signal and also receives the A-series signal emitted by the base station 10A via the LCX 50B. The configuration of the base station 10A for performing such operations will be explained. The base station 10A is provided with a control unit 11A that includes a CPU that controls the entire base station 10A and performs signal cross-correlation processing calculations as will be described later. Furthermore, a transmitting section 12A that generates an A-sequence signal modulated with transmission data received by the control section 11A from the central device 100 in the STBC or DSTBC, and a receiving section 13A that receives a B-sequence signal are provided. Further, on the LCX 50A side, in order to pass the A-series signal and the B-series signal received from the base station 10B side, a filter 14A, which is a bandpass filter with a frequency F1 corresponding to these signals, is provided. The transmitter 12A, the receiver 13A, and the filter 14A are connected through a circulator 15A. The circulator 15A outputs the input from the transmitter 12A side (X) to the filter 14A side (Y), and outputs the B sequence signal input from the filter 14A side (Y) to the receiver 13A side (Z).

Furthermore, since the base station 10A receives the signal emitted by the mobile station 200, a receiving section 16A is provided to receive this signal, and a filter 17A which is a bandpass filter of frequency F2 corresponding to this signal is also provided on the LCX 50A side. . This frequency is different from the frequencies of the A-series signal and the B-series signal.

Similarly to the base station 10A, the base station 10B also includes a control unit 11B, a transmitting unit 12B that generates a B-series signal, a receiving unit 13B that receives an A-series signal, a filter 14B corresponding to these, a circulator 15B, and a mobile station 200. A receiving section 16B that receives signals from the receiving section 16B and a corresponding filter 17B are provided.

FIG. 2 shows the flow of A-series signals, B-series signals, etc. in the configuration of FIG. 1, and the description of the mobile station 200 is omitted here. Here, first, as shown by arrows C1 and C2, the same transmission data is transmitted from the central device 100 to the control units 11A and 11B. The controllers 11A and 11B cause the transmitters 12A and 12B to generate and transmit A-series signals and B-series signals based on the transmission data, respectively.

The A-series signal sequentially passes through the transmitter 12A, circulator 15A, and filter 14A, and then passes through the LCX 50A and LCX 50B, as indicated by the dashed arrow A in FIG. This allows mobile station 200 to receive the A-series signal. Similarly, the B-series signal sequentially passes through the transmitter 12B, circulator 15B, and filter 14B, and then passes through the LCX 50B and LCX 50A, as indicated by the dotted arrow B in FIG. This allows mobile station 200 to receive the B sequence signal. Therefore, mobile station 200 can receive both A-series signals and B-series signals within the range shown in FIG.

On the other hand, as shown by the broken line arrow A in FIG. ). As a result, the A-series signal is received by the receiving section 13B, and the control section 11B recognizes that the A-series signal has flowed through the LCXs 50A and 50B. However, as mentioned above, the LCXs 50A and 50B are sufficiently long in the horizontal direction in the figure, and the base stations 10A and 10B are sufficiently far apart, so the strength of the A-series signal after passing through the LCX 50B is the B-series signal at the same location. lower than the signal strength. Similarly, as shown by the dotted arrow B in FIG. 2, the B-series signal passes through the LCX 50A and then flows to the base station 10A, and the control unit 11A of the base station 10A receives the B-series signal via the LCXs 50B and 50A. Recognize that it has flowed. At this time, the intensity of the B-series signal after passing through the LCX 50A is lower than the intensity of the A-series signal at the same location.

On the other hand, in the base station 10A, the A-series signal emitted from the transmitter 12A has an intensity that is output from the transmitter 12A side (X) to the filter 14A side (Y), as shown by the broken line arrow DA in FIG. Although the intensity is as low as about 10 ^-6 , it also flows to the receiving section 13A side (Z) via the circulator 15A. Therefore, the receiving unit 13A receives both the A-series signal and the B-series signal, but as described above, these are in an orthogonal relationship, so the control unit 11A recognizes the A-series signal and the B-series signal individually. can do. Since the transmission data transmitted by the A-series signal and the B-series signal are the same, the control unit 11A calculates, for example, the cross-correlation coefficient of the two received signals, and if the value increases, the two signals are correlated. If it is determined that there is a signal, it can be estimated that the two signals received by the receiving unit 13A are an A-series signal and a B-series signal. That is, in this case, the base station 10A can be estimated to have received the B sequence signal. Similarly, in the base station 10B, if the control unit 11B determines that there is a correlation between the two received signals, it can be estimated that the base station 10B has received the A sequence signal.

On the other hand, FIG. 3 shows a case where the LCX50A is cut at a point P, similar to FIG. 2. The same applies when a failure that obstructs signal propagation occurs at point P due to a cause other than disconnection. In this case, since the A-series signal does not flow to the right of the point P, and the B-series signal does not flow to the left of the point P, the A-series signal is transmitted on the base station 10B side, the B-series signal is transmitted on the base station 10A side, and so on. Unable to receive either. When the control unit 11A is unable to significantly recognize a signal other than the A-series signal, or when a signal is received in addition to the A-series signal, but no correlation is found between this received signal and the A-series signal. In this case, it can be estimated that this received signal is not a B-sequence signal but a signal other than the B-series signal having the same frequency. Similarly, if no correlation is found between the two signals on the base station 10B side, it can be estimated that the A sequence signal was not received.

In this case, on the base station 10A and base station 10B sides, it can be estimated that the LCX 50A or LCX 50B has been disconnected. That is, without using the reception status of the mobile station 200, it is possible to recognize a failure in the LCX 50A or LCX 50B at the base stations 10A and 10B. Generally, when an A-series signal is emitted from base station 10A, a B-series signal is also emitted from base station 10B at the same time, so the above determination can be made if transmission data is emitted from central device 100. Therefore, when a failure occurs in the LCXs 50A, 50B, the base stations 10A, 10B can quickly recognize this failure.

Note that in the above example, the cross-correlation coefficient of the two signals recognized by the control unit 11A (11B) was calculated, but other methods may be used to determine whether there is a correlation between the two signals. can.

In the above example, in order for the control unit 11A (control unit 11B) to recognize the A sequence signal (B sequence signal) and the B sequence signal (A sequence signal) emitted by the transmission unit 12A (transmission unit 12B), , circulator 15A (circulator 15B) was used. However, other configurations may be used, as long as each base station is able to receive both signals originating from its own side and signals originating from the other base station.

In addition, in the above example, even if the A-series signal (first signal) and B-series signal (second signal) coexist, they are processed using the STBC method or the DSTBC method to prevent any adverse effects due to interference. Although it is assumed that the A-series signals and B-series signals are generated, it is also possible to generate and use the A-series signals and B-series signals using other methods that do not cause interference in these signals.

Furthermore, in the configuration shown in the figure, the base stations 10A and 10B each have the same configuration, and each can detect a failure in the LCXs 50A and 50B as described above. However, each base station may transmit a signal similar to the above, and only one of the base stations may be able to make the above determination.

Further, as mentioned above, in FIG. 1, the area where the communication area of base station 10A and the communication area of base station 10B overlap is the area where LCXs 50A and 50B are installed, but in actual train radio communication In this case, more base stations are installed. Even in such a case, it is possible to implement a configuration similar to that in FIG. 1 between two adjacent base stations. In other words, if you have two or more base stations, you can apply the above configuration between two adjacent base stations, and quickly troubleshoot leaky coaxial cables used between them from the base station side. can be recognized.

Furthermore, in the above example, transmission data to be transmitted from the central device 100 to the mobile station 200 is transmitted to the base stations 10A and 10B, resulting in an A sequence signal (first signal) and a B sequence signal (first signal). 2) is generated and transmitted, and this is used to detect a failure in the LCXs 50A and 50B. However, for example, regardless of the transmission data received from the central device 100, each base station may emit A-series signals and B-series signals similar to those described above only for the purpose of inspecting leaky coaxial cables. Cables may be inspected. In this case, if the A-series signal and B-series signal modulated with common data are set to be transmitted simultaneously, the above operation can be performed in the same way.

The present invention has been described above based on the embodiments. It will be understood by those skilled in the art that this embodiment is merely an example, and that various modifications can be made to the combinations of these components, and that such modifications are also within the scope of the present invention.

1 Wireless communication system 10A base station (first base station)
10B base station (second base station)
11A, 11B Control section 12A, 12B Transmission section 13A, 13B, 16A, 16B Receiving section 14A, 14B, 17A, 17B Filter 15A, 15B Circulator 50A, 50B Leakage coaxial cable (LCX)
100 central device 200 mobile station

Claims (3)

A first base station and a second base station each transmitting a first signal and a second signal modulated with common transmission data, and the first signal and the second signal are respectively directed in opposite directions. a leaky coaxial cable connected to the first base station and the second base station such that the first signal and the second signal emitted from the leaky coaxial cable are streamed simultaneously; is received by a mobile station, the wireless communication system comprising:
The first base station is capable of receiving the second signal via the leaky coaxial cable, and recognizes that there is a fault in the leaky coaxial cable if the first base station cannot recognize the second signal. ,
Or
The second base station is capable of receiving the first signal via the leaky coaxial cable, and recognizes that there is a fault in the leaky coaxial cable if the second base station cannot recognize the first signal. ,
A wireless communication system characterized by: The first base station determines whether the received signal is the second signal by performing a cross-correlation analysis between the received signal received via the leaky coaxial cable and the first signal. recognize,
or The second base station determines whether the received signal is the first signal by performing a cross-correlation analysis between the received signal received via the leaky coaxial cable and the second signal. recognize,
The wireless communication system according to claim 1, characterized in that: The radio according to claim 1 or 2, wherein the first signal and the second signal are emitted by a space-time block coding (STBC) method or a differential space-time block coding (DSTBC) method. Communications system.

Images