JP2012160806A - Train radio system, base station and mobile station - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a train radio system capable of normal signal reception by reducing the impact in a radio wave interference section, even in a train radio system where communication is performed using a multi-value modulation system of high transmission rate.SOLUTION: In the train radio system where zones Z1 and Z2 are set to correspond with the travel path of a train 109 mounting a mobile station 9, and radio communication is performed between base stations 1 and 2 included in respective zones and the mobile station 9 via leakage coaxial cables 4-7, when the mobile station 9 has reached the point "A" near the boundary 8 between base stations, the base station 1 performs communication with the mobile station 9 by switching a modulation system A, that has been applied so far, to a modulation system C of lower transmission rate.

Description

  The present invention relates to a train radio system that performs radio communication with a mobile station via a plurality of base stations and a leaky coaxial cable connected to the base station.

  A radio wave interference section exists between leaky coaxial cables (LCX) connected to two adjacent base stations, but if a mobile station antenna (aerial) exists in the radio wave interference section, normal radio waves There is a problem that cannot be received.

  In Patent Document 1, in order to solve such a problem, the mobile station selectively receives and demodulates the radio input signal from the antenna so as to block the radio input signal from the antenna in the radio wave interference section. A technique for reducing a communication error or the like in a radio wave interference section formed at the boundary between adjacent base stations by adopting the configuration is disclosed.

JP 2010-193336 A

  When high-speed communication is performed between a base station and a mobile station in a train radio system, for example, a multi-level modulation method with a high transmission speed such as 256QAM (Quadrature Amplitude Modulation) is often used. The radio wave interference section that can be made at the boundary between the base stations is long. On the other hand, because the antenna position of the mobile station is limited, if the radio interference section becomes long, all the antennas of the mobile station will enter the radio interference section at the same time, and the signal from the base station cannot be received correctly. there were.

  The present invention has been made to solve the above-described problems, and even in a train radio system that performs communication using a multi-value modulation method with a high transmission rate, the effect of the radio wave interference section is reduced and normal operation is performed. An object of the present invention is to provide a train radio system capable of receiving signals.

  In the train radio system according to the present invention, a plurality of zones that are radio areas are set corresponding to the travel path of a train equipped with a mobile station, and leakage occurs between the base station included in each zone and the mobile station. A train radio system that performs radio communication via a coaxial cable, wherein the base station, when the mobile station reaches a first point near a boundary between base stations, The communication is performed by switching to the second modulation method having a lower transmission speed than the first modulation method applied so far.

  According to the train radio system, the base station, and the mobile station according to the present invention, when the first point near the boundary between the base stations is reached, transmission is performed as compared with the first modulation scheme applied so far. By switching to the second modulation method having a low speed, the radio wave interference section is shortened, the time during which communication is interrupted is significantly reduced, and communication errors are reduced. Moreover, it can respond to the increase in the communication speed of the whole train radio system by this.

It is a figure which shows the structure of the train radio system of Embodiment 1 which concerns on this invention. It is a figure explaining the relationship between the modulation system of Embodiment 1 which concerns on this invention, and a radio wave interference area. It is a figure which shows the structure of one time slot which comprises a radio | wireless frame and a radio | wireless frame. It is a figure which shows the structure of the mobile station of Embodiment 1 which concerns on this invention. It is a figure which shows the structure of the base station of Embodiment 1 which concerns on this invention. It is a flowchart which shows the flow of the switching method of the modulation system of Embodiment 1 which concerns on this invention. It is a figure which shows the structure of the mobile station of Embodiment 2 which concerns on this invention. It is a figure which shows the structure of the base station of Embodiment 2 which concerns on this invention. It is a flowchart which shows the flow of the switching method of the modulation system of Embodiment 2 which concerns on this invention. It is a figure which shows the structure of the train radio system of Embodiment 3 which concerns on this invention. It is a figure explaining the relationship between the modulation system of Embodiment 3 which concerns on this invention, and a radio wave interference area. It is a flowchart which shows the flow of the switching process of the modulation system of Embodiment 3 which concerns on this invention. It is a flowchart which shows the flow of the switching method of the modulation system of Embodiment 4 which concerns on this invention.

<Embodiment 1>
<System configuration>
Hereinafter, Embodiment 1 of a train radio system according to the present invention will be described with reference to FIGS. FIG. 1 is a conceptual diagram showing a configuration of a train radio system according to the first embodiment.

  In a general train radio system, a plurality of radio areas are set corresponding to a train, that is, a traveling path of a mobile station, and each radio area is called a zone. One base station is provided in the zone.

  In the train radio system shown in FIG. 1, the radio area boundary between the zone Z1 and the zone Z2 is shown as an inter-base station boundary 8, and the base station 1 included in the zone Z1 and the base station 2 included in the zone Z2 are adjacent to each other. It is arranged as a base station. In addition, a central apparatus 3 is provided that aggregates signals from each base station and performs telephone calls, data communication, and monitoring with the mobile station.

  On both sides of a track (not shown) on which trains 109, 110, and 199 carrying mobile stations 9, 10 and 99 respectively travel, transmission radio waves of base stations 1 and 2 or transmission radio waves of mobile stations 9, 10, 99 Leaky coaxial cables (LCX) 4, 5, 6 and 7 are laid. Among these, LCX 4 and 5, LCX 6 and 7 make a pair, LCX 4 and 5 are connected to the base station 1, and LCX 6 and 7 are connected to the base station 2. The LCXs 4 to 7 may include devices that amplify radio waves, but are omitted here.

  The mobile stations 9, 10 and 99 perform wireless communication with the base station and realize telephone calls and data transmission between the ground and the vehicle, but are not limited to three as shown in FIG. There may be more mobile stations in zones Z1 and Z2.

  The inter-base station boundary 8 is a radio area boundary between the base stations 1 and 2, and is an area of about 10 m between the end portions of the LCXs 4 and 5 and the end portions of the LCXs 6 and 7.

  In FIG. 1, when the mobile station 9 existing in the zone 1 moves in the direction of the zone 2, the modulation method A having a relatively high transmission rate is used until the mobile station 9 approaches the boundary 8 between the base stations. When the signal passes through the inter-base station boundary 8, the radio interference period becomes longer in the modulation scheme A, and therefore the time during which signals from any base station cannot be received correctly becomes longer.

  For example, when handling TCPIP (Transmission Control Protocol / Internet Protocol) data, even an ACK (Acknowledgment) signal does not pass due to temporary communication interruption, and the throughput is greatly reduced.

In the present embodiment, in order to prevent this, a configuration is adopted in which when the mobile station 9 reaches the vicinity of the boundary 8 between the base stations, a switching is made to the modulation scheme C having a relatively low transmission rate. As a result, the transmission speed is somewhat slow, but in modulation method C, the required C / N (Carrier to Noise ratio) is small, so the radio wave interference section is shortened, so the time for communication interruption is greatly reduced, and TCPIP data Even in this case, a decrease in throughput can be suppressed. After passing through the inter-base station boundary 8, the modulation scheme A is restored. This can be applied to other mobile stations 99, and can also be applied to the mobile station 10 traveling in the zone Z1 direction from the zone Z2. The required C / N is a level ratio between a carrier wave (desired wave) and noise necessary for correct reception. Here, the received correctly, but means that can be transmitted without an error in the wireless area, since it is operated as a system if the transmission to some extent correct, for example, BER (BIT ERROR RATE) is 1/1000000 following (1 × 10 ^-6 It may be defined by the value

  In FIG. 1, an area using modulation scheme A is shown as a modulation scheme A area, and an area using modulation scheme C is shown as a modulation scheme C area. The modulation scheme C area is set so as to include the inter-base station boundary 8 and its neighboring area.

  Next, the radio wave interference state near the boundary between base stations will be described with reference to FIG. FIG. 2 illustrates LCX4 included in the zone Z1 and LCX6 included in the zone Z2. The field strength characteristic of the radio wave of the LCX4 in the zone Z1 is shown as a characteristic E1, and the field intensity characteristic of the radio wave of the LCX6 in the zone Z2 is shown. Is shown as characteristic E2.

  The characteristics E1 and E2 indicate that the extending direction of the LCX is the X axis and the electric field strength is shown on the Y axis, both of which have a substantially constant electric field strength in their own zone and approach the boundary between base stations. Although the electric field strength begins to decrease, the electric field strength does not rapidly become zero even when entering an adjacent zone, but gradually decreases. For this reason, there are sections (radio wave interference sections) in which the radio waves from LCX 4 and LCX 6 interfere with the radio waves on the other side.

  As shown in FIG. 2, in the vicinity of the boundary between the base stations, which is the boundary between the zone Z1 and the zone Z2, the downlink signal from the base station 1 to the mobile station and the downlink signal from the base station 2 to the mobile station interfere, The downlink signal cannot be received correctly. The length of the radio wave interference section varies depending on the modulation method.

  For example, in the “modulation method A” corresponding to a high transmission rate, the required C / N for correctly receiving a signal needs to be larger than that of the modulation method C. For this reason, the radio wave interference section AR in the “modulation method A” is between the point “A” and the point “B”. On the other hand, in “modulation scheme C”, the required C / N is smaller than that in modulation scheme A. Therefore, the radio wave interference section CR in “modulation scheme C” changes from point “F” to point “G”. It can be seen that it is shorter than the radio wave interference section AR.

  Here, the point “A” and the point “F” are determined by the ratio of the desired wave (D wave) and the disturbing wave (U wave). That is, when the radio wave from the LCX 4 is a desired wave (D wave) in the zone Z1, the radio wave from the zone Z2 becomes an interference wave (U wave), that is, noise. Here, if the position where the electric field strengths of the zone Z1 and the zone Z2 are equal is the point “C”, D / U = 0 dB at the point “C”. When moving from the point “C” to the right in the drawing, that is, in a direction in which the electric field strength of the LCX4 radio wave increases, the electric field strength of the LCX4 radio wave becomes constant, while the electric field strength of the LCX6 radio wave gradually increases. For example, D / U = 10 dB, 20 dB, 30 dB... Gradually increases in D / U. In FIG. 2, the points where the D / U and the required C / N in each modulation scheme match are point “A” and point “F”.

  In FIG. 2, the electric field strength difference R1 at the points “A” and “B” is schematically shown as required C / N in the modulation scheme A. Further, the electric field intensity difference R3 at the points “F” and “G” is schematically shown as required C / N in the modulation scheme C.

  Here, as an example of a modulation scheme, for example, modulation scheme A uses 256QAM with a required C / N of about 30 dB, and modulation scheme C uses QPSK (Quadrature Phase Shift Keying) with a required C / N of about 15 dB. It is possible. It is also conceivable to use BPSK (Binary Phase Shift Keying), which is slower than QPSK. Note that the value of the required C / N is an example, and varies depending on the performance on the receiving side.

  As shown in FIG. 2, the switching point of the modulation method shown in FIG. 1 is the point “A” or the point “B”. When the point “A” or the point “B” is reached, the “modulation method A” is changed to the “modulation method C”. To "".

  By setting the switching point in this way, it is possible to reliably eliminate the influence of the radio wave interference section, and it is possible to prevent the section that communicates at a low transmission rate from becoming too long.

  Since the modulation system switching process takes some time, it is efficient to enter the switching process earlier by the switching process time according to the traveling speed. By starting the switching process earlier by the switching process time, actual switching can be performed at a more appropriate timing.

  FIG. 3 shows the configuration of one radio frame and time slots constituting the radio frame. Since one base station communicates with a plurality of mobile stations, the frame format is time-divided and has a plurality of time slots SL as shown in part (a) of FIG. By adopting such a configuration, for example, one time slot communicates with the mobile station 9 (FIG. 1) on a one-to-one basis, and other time slots communicate with the mobile station 99 (FIG. 1) on a one-to-one basis. Can be done. Also, some time slots, for example, the first time slot may be used for transmission / reception of radio access control signals between the base station and the mobile station. Here, the synchronization word necessary for wireless communication is omitted.

  In FIG. 3, one time slot SL is divided into a header portion HP and a data portion DP, and the header portion HP uses a modulation scheme that is most easily received, that is, requires a small required C / N, for example, modulation scheme C. This includes a modulation method instruction signal for instructing the modulation method of the data portion DP. The receiving unit of the mobile station demodulates the data part according to the modulation method indicated by the header part HP of the time slot SL. By changing the instruction of the modulation method of the data portion DP, the modulation method can be changed in communication between the base station and the mobile station.

<Device configuration of mobile station>
Next, the device configuration of the mobile station 9 will be described with reference to FIG. The apparatus configuration is the same in the mobile stations 10 and 99.

  The mobile station 9 includes a transmission unit 91, a reception unit 92, and a control unit 93. The transmission unit 91 and the reception unit 92 include a high frequency unit (not shown) including a filter, a duplexer, a distributor, and a combiner.

  The receiving unit 92 performs demodulation processing on the data portion in the adaptive demodulating unit 921 in accordance with the modulation mode instruction signal included in the header portion of the time slot from the base station received via the antenna 204. The control unit 93 transmits the demodulated data from the receiving unit 92 to various terminals 201 such as a driver's cab and a control panel of the conductor's compartment in the vehicle, and transmits data of signals from various terminals to the transmitting unit 91 as modulation signals. Further, the control unit 93 obtains position information and speed information from the vehicle device 202 that manages the position and speed in real time, detects the switching timing of the modulation method, and in the data to be transmitted to the transmission unit 91, A modulation system switching request signal is included. For this reason, the control part 93 has memorize | stored the position which should switch the modulation system in the boundary between base stations as "position data" in this train radio system.

  In the case of railroads, for example, on the Shinkansen, the location of the equipment is managed by the distance of the track starting from Tokyo, and information such as “the boundary between base stations between XX station and YY station is 123.456 km point” The information of the switching point of the modulation method is stored as “position data”. Therefore, if information about where the vehicle is traveling on the route is acquired in real time using a distance meter, etc., the timing for switching the modulation method is calculated (detected) together with the speed information of the vehicle. Can do. The “position data” is not limited to distance information, and may be data such as latitude and longitude. In that case, the mobile station may be configured to acquire the latitude and longitude of the current position of the host vehicle by mounting a GPS (Global Positioning System).

  The transmitting unit 91 transmits a modulation method switching request signal together with various data to the base station via the antenna 203.

<Device configuration of base station>
Next, the apparatus configuration of the base station 1 will be described with reference to FIG. The apparatus configuration is the same in the base station 2.

  The base station 1 includes a transmission unit 11, a reception unit 12, a control unit 13, and a high frequency unit 14. The receiving unit 12 demodulates the signal from the mobile station received via the LCXs 4 and 5 and transmits the demodulated signal to the control unit 13. If there is a modulation method switching request signal, it is also demodulated and transmitted to the control unit 13.

  The control unit 13 transmits a signal to be transmitted to the mobile station as a modulation signal to the transmission unit 11, and when receiving a modulation method switching request signal, the control unit 13 instructs the transmission unit 11 to specify the modulation method. Transmit the signal.

  In accordance with the modulation method instruction from the control unit 13, the transmission unit 11 includes a modulation method instruction signal in the header portion of the time slot, and the data portion is modulated by the modulation method in the adaptive modulation unit 111. Transmit to the mobile station via LCX 4 and 5. The high frequency unit 14 includes a filter, a duplexer, a distributor, a combiner, and the like.

  Instead of instructing switching of the modulation method from the control unit 13 to the transmission unit 11, the control unit 13 may include a modulation method instruction signal directly in the header portion of the time slot.

  Since the base station 1 performs communication simultaneously with a plurality of mobile stations, the mobile station management unit 131 included in the control unit 13 associates each mobile station with each time slot as needed.

<Modulation switching process>
The flow of the modulation system switching process in the vicinity of the base station boundary when the train radio system described above is employed will be described using the flowchart shown in FIG. 6 with reference to FIGS.

  The mobile station 9 (simply described as “mobile station” in FIG. 6) periodically checks the position information from the vehicle device 202 (FIG. 4) (step S1), and the position where the own vehicle exists is between a predetermined base station. It is detected whether or not the vicinity of the boundary, that is, point A in FIG. 2 has been reached (step S2). Note that the detection cycle does not have to be a constant interval, and may be variable depending on travel speed and position information.

  The mobile station 9 has position data indicating where the boundary between the base stations is located in the control unit 93 (FIG. 4). The mobile station 9 receives the point “A” in FIG. When a point just before is reached, a modulation system switching request signal for requesting the base station 1 to switch to the modulation system C is transmitted (step S3).

  Receiving this, the base station 1 changes only the time slot used with the mobile station 9 to the modulation scheme C (step S4). Specifically, the header part HP (FIG. 3) of the time slot to be transmitted to the mobile station 9 includes a modulation method instruction signal for instructing the modulation method C, and the data portion DP (FIG. 3) is modulated by the modulation method C. To send. The header part HP is always modulated by the modulation method C. Thereby, the communication (downward direction) from the base station 1 to the mobile station 9 is performed by the modulation method C in the vicinity of the boundary between the base stations (step S5).

  Since the mobile station 9 transmits a modulation system switching request signal at a point before the position where the modulation system should be switched by the processing time, data of a time slot whose modulation system has been changed is transmitted from the base station 1. The timing coincides with the timing when the mobile station 9 reaches the position where the modulation method should be switched. Therefore, the operation of detecting a point before the position where the modulation method should be switched by the processing time can be said to be an operation of detecting the timing when the mobile station 9 (own vehicle) reaches a predetermined position near the boundary between base stations. .

  The mobile station 9 moves and moves from the zone Z1 to the zone Z2 at the point “C” (handover from the base station 1 to the base station 2), but communication from the base station 2 to the mobile station 9 (downward) Maintains the modulation scheme C (step S6).

  The mobile station 9 periodically checks the position information from the vehicle device 202 (FIG. 4) (step S7), and the position where the host vehicle exists is near a predetermined boundary between base stations, that is, at the point B in FIG. It is detected whether or not it has been reached (step S8).

  When the mobile station 9 reaches the point “B” (precisely, the point just before the processing time), the base station 2 transmits a modulation scheme switching request signal for requesting switching to the modulation scheme A (step S9).

  Receiving this, the base station 2 changes only the time slot used with the mobile station 9 to the modulation scheme A (step S10). Specifically, the header part HP (FIG. 3) of the time slot to be transmitted to the mobile station 9 includes a modulation method instruction signal for instructing the modulation method A, and the data portion DP (FIG. 3) is modulated by the modulation method A. To send.

  Thereby, the communication (downward direction) from the base station 2 to the mobile station 9 is performed by the modulation method A after passing through the point “B” (step S11). After passing through the boundary between the base stations, the communication speed of the entire train radio system is not hindered by returning to the communication with a high transmission speed.

  After changing to the modulation scheme A, the modulation scheme A is maintained until the vicinity of the next boundary between base stations is reached.

  In the above description, the mobile station 9 moving from the zone Z1 to the zone Z2 has been described as an example. However, in the case of the mobile station 10 traveling in the reverse direction, the points “A” and “B” The base station 2 is only described in the reverse order, and the processing procedure is the same.

  As described above, by adopting a mobile station-led train radio system that makes a request for switching the modulation method from the mobile station to the base station, the accuracy of detection of the timing when the mobile station reaches the vicinity of the boundary between base stations is improved. Can be increased.

<Embodiment 2>
The train radio system according to the first embodiment described above is a mobile station-led system that makes a request for switching the modulation method from the mobile station to the base station. However, in the train radio system according to the second embodiment, The base station takes the initiative to switch the modulation method.

<Device configuration of mobile station>
FIG. 7 is an apparatus configuration diagram of the mobile station 9 configuring the train radio system according to the second embodiment. The apparatus configuration is the same in the mobile stations 10 and 99.

  The configuration of the mobile station 9 is basically the same as that shown in FIG. 4, but the control unit 93 is not configured to store “position data”, does not output a modulation scheme switching request signal, and Data of a signal to be transmitted is provided to the transmission unit 91 as a modulation signal.

<Device configuration of base station>
FIG. 8 is an apparatus configuration diagram of the base station 1 configuring the train radio system according to the second embodiment. The apparatus configuration is the same in the base station 2.

  Although the configuration of the base station 1 is basically the same as that in FIG. 5, the control unit 13 stores, as “position data”, the position at which the modulation method at the boundary between base stations is switched in the train radio system.

  This “position data” is the same as the “position data” in the mobile station of FIG. 4 in that information on the distance from Tokyo and information on the switching point of the modulation method are stored.

  The control unit 13 grasps the existence position of the mobile station 9 almost in real time based on the position information periodically transmitted from the mobile station 9 and estimates the speed from the change in the position to switch the modulation method. Can be calculated.

  Note that the position information transmitted from the mobile station 9 is not limited to the distance information, and may be data such as latitude and longitude acquired by the GPS installed in the mobile station 9. In this case, it is assumed that “position data” includes information on a position where the modulation method represented by latitude and longitude is to be switched.

  By storing the position data in the base station, the position data can be easily updated via the central device (FIG. 1) or the like when the position data is changed.

<Modulation switching process>
The flow of the modulation system switching process in the vicinity of the base station boundary when the train radio system described above is adopted will be described using the flowchart shown in FIG. 9 with reference to FIG. 2, FIG. 3, FIG. 7, and FIG. To do.

  The mobile station 9 (described simply as a mobile station in FIG. 9) periodically acquires position information from the vehicle device 202 (FIG. 7) and transmits it to the base station 1. The base station 1 recognizes the location of the mobile station 9 in almost real time by checking the location information from the mobile station 9 (step S11). Then, it is detected whether the position where the mobile station 9 exists has reached the vicinity of a predetermined boundary between base stations, that is, the point A in FIG. 2 (step S12). That is, since the base station 1 has position data indicating where the boundary between the base stations is in the control unit 13 (FIG. 8), and the speed can be estimated from the change in the location of the mobile station 9, the mobile station 2 can detect the timing when it reaches the point “A” in FIG. 2 (precisely, the point before the processing time), and only the time slot used with the mobile station 9 in accordance with the timing. Is changed to the modulation scheme C (step S13). Specifically, the header part HP (FIG. 3) of the time slot to be transmitted to the mobile station 9 includes a modulation method instruction signal for instructing the modulation method C, and the data portion DP (FIG. 3) is modulated by the modulation method C. To send. The header part HP is always modulated by the modulation method C.

  As a result, communication (downward) from the base station 1 to the mobile station 9 is performed using the modulation scheme C in the vicinity of the boundary between the base stations (step S14).

  The mobile station 9 moves and moves from the zone Z1 to the zone Z2 at the point “C” (handover from the base station 1 to the base station 2), but communication from the base station 2 to the mobile station 9 (downward) Maintains the modulation scheme C (step S15).

  The base station 2 confirms the position information from the mobile station 9 (step S16), and the mobile station 9 is in the vicinity of the predetermined inter-base station boundary, that is, the point “B” in FIG. Is detected (step S17).

  Then, only the time slot used with the mobile station 9 is changed to the modulation scheme A in accordance with the timing of reaching the point B (step S18). Specifically, the header part HP (FIG. 3) of the time slot to be transmitted to the mobile station 9 includes a modulation method instruction signal for instructing the modulation method A, and the data portion DP (FIG. 3) is modulated by the modulation method A. To send. As a result, communication (downward) from the base station 2 to the mobile station 9 is performed using the modulation method A outside the boundary between the base stations (step S19).

  After passing through the boundary between the base stations, the communication speed of the entire train radio system is not hindered by returning to the communication with a high transmission speed.

  After changing to the modulation scheme A, the modulation scheme A is maintained until the vicinity of the next boundary between base stations is reached.

  In the above description, the mobile station 9 moving from the zone Z1 to the zone Z2 has been described as an example. However, in the case of the mobile station 10 traveling in the reverse direction, the points “A” and “B” The base station 2 is only described in the reverse order, and the processing procedure is the same.

<Embodiment 3>
<System configuration>
Hereinafter, Embodiment 3 of the train radio system according to the present invention will be described with reference to FIGS. FIG. 10 is a conceptual diagram showing the configuration of the train radio system according to the third embodiment, and is characterized by switching the modulation method more finely than the train radio system of the first embodiment described with reference to FIG. .

  In the train radio system shown in FIG. 10, the modulation scheme C is used at the inter-base station boundary 8, the transmission rate is faster than the modulation scheme C near the inter-base station boundary 8, and the transmission rate is slower than the modulation scheme A. By using method B, a configuration in which the modulation method is switched in stages is adopted. That is, when the mobile station 9 reaches the vicinity of the inter-base station boundary 8, the configuration is switched from the modulation scheme A to the modulation scheme B, and when the mobile station reaches the inter-base station boundary 8, the configuration is switched from the modulation scheme B to the modulation scheme C. .

  As a result, the transmission rate can be changed in stages, and problems caused by a sudden change in the transmission rate can be reduced.

  After passing through the inter-base station boundary 8, the modulation scheme B is returned to the modulation scheme A. This can be applied to other mobile stations 99, and can also be applied to the mobile station 10 traveling in the zone Z1 direction from the zone Z2.

  In FIG. 10, an area using modulation scheme A is shown as modulation scheme A area, an area using modulation scheme B is shown as modulation scheme B area, and an area using modulation scheme C is shown as modulation scheme C area. Yes. The modulation scheme C area is set in a substantially central area of the base station boundary 8.

  Note that the configurations of the mobile station and the base station are the same as those described with reference to FIGS. 4 and 5, respectively, and are a mobile station-led system in which a modulation switching request is sent from the mobile station to the base station. .

  Next, a radio wave interference state near the boundary between base stations will be described with reference to FIG. FIG. 1 exemplifies LCX4 included in zone Z1 and LCX6 included in zone Z2. The field strength characteristic of the radio wave of LCX4 in zone Z1 is shown as characteristic E1, and the field strength characteristic of the radio wave of LCX6 in zone Z2 is shown. Is shown as characteristic E2.

  The characteristics E1 and E2 indicate that the extending direction of the LCX is the X axis and the electric field strength is indicated on the Y axis, both of which have a constant electric field strength in their own zone, and the electric field as the base station boundary is approached. Although the intensity starts to decrease, the electric field intensity does not rapidly become zero even when entering an adjacent zone, but gradually decreases. For this reason, there are radio wave interference sections in which radio waves from LCX4 and LCX6 interfere with the radio waves on the other side.

  The length of the radio wave interference section differs depending on the modulation scheme. For example, in “Modulation scheme A” corresponding to a high transmission rate, the required C / N for correctly receiving a signal is smaller than that of modulation schemes B and C. Need to be big. For this reason, the radio wave interference section AR in the “modulation method A” is between the point “A” and the point “B”. On the other hand, in the “modulation method B”, the required C / N is smaller than that in the modulation method A. Therefore, the radio wave interference section BR in the “modulation method B” is changed from the point “D” to the point “E”. It can be seen that it is shorter than the radio wave interference section AR. Further, in “modulation method C”, the required C / N may be smaller than that in modulation method B. Therefore, the radio wave interference section CR in “modulation method C” is changed from the point “D” to the point “E”. It can be seen that it is shorter than the interference zone BR.

  In FIG. 11, the electric field strength difference R1 at the points “A” and “B” is schematically shown as required C / N in the modulation method A. Further, the electric field strength difference R2 at the points “D” and “E” is schematically shown as required C / N in the modulation method B, and the electric field strength difference R3 at the points “F” and “G” is modulated. This is schematically shown as the required C / N in method C.

  From FIG. 11, the first switching point of the modulation method shown in FIG. 10 is the point “A” or the point “B”, and when reaching the point “A” or the point “B”, the “modulation method A” to “ Switching to “modulation method B” is performed. Further, the second switching point of the modulation method is the point “D” or the point “E”, and when the point “D” or the point “B” is reached, the switching from the “modulation method B” to the “modulation method C” is performed. I do.

  Here, as an example of the modulation system, for example, modulation system A uses 256QAM with a required C / N of about 30 dB, and modulation system B uses 64QAM with a required C / N of about 25 dB or a required C / N of about 20 dB. It is conceivable that 16QAM is used, and modulation scheme C uses QPSK with a required C / N of about 15 dB. Note that the value of the required C / N is an example, and varies depending on the performance on the receiving side.

  When 256QAM is used as the modulation method A, the transmission speed is increased by using 256QAM outside the boundary between base stations, and the communication quality can be improved.

<Modulation switching process>
The flow of the modulation system switching process in the vicinity of the base station boundary when the train radio system described above is employed will be described using the flowchart shown in FIG. 12 with reference to FIGS.

  The mobile station 9 (simply described as “mobile station” in FIG. 12) periodically checks the position information from the vehicle device 202 (FIG. 4) (step S21), and the position where the host vehicle exists is between the predetermined base stations. It is detected whether or not the vicinity of the boundary, that is, the point A in FIG. 11 has been reached (step S22). Note that the detection cycle does not have to be a constant interval, and may be variable depending on travel speed and position information.

  When the mobile station 9 reaches the point “A” in FIG. 11 (precisely, the point before the processing time), the mobile station 9 sends a modulation scheme switching request signal for requesting the base station 1 to switch to the modulation scheme B. Transmit (step S23).

  Receiving this, the base station 1 changes only the time slot used with the mobile station 9 to the modulation scheme B (step S24). Specifically, the header part HP (FIG. 3) of the time slot to be transmitted to the mobile station 9 includes a modulation method instruction signal for instructing the modulation method B, and the data part DP (FIG. 3) is modulated by the modulation method B. To send. The header part HP is always modulated by the modulation method C. As a result, communication (downward) from the base station 1 to the mobile station 9 is performed using the modulation method B in the vicinity of the boundary between the base stations (step S25).

  The mobile station 9 periodically checks the position information from the vehicle device 202 (FIG. 4) (step S26), and the position where the own vehicle exists is within the boundary between the base stations, that is, at the point D in FIG. It is detected whether or not it has been reached (step S27).

  When the mobile station 9 reaches the point “D” in FIG. 11 (precisely, the point before the processing time), the mobile station 9 sends a modulation method switching request signal for requesting the base station 1 to switch to the modulation method C. Transmit (step S28).

  Receiving this, the base station 1 changes only the time slot used with the mobile station 9 to the modulation scheme C (step S29). Specifically, the header part HP (FIG. 3) of the time slot to be transmitted to the mobile station 9 includes a modulation method instruction signal for instructing the modulation method C, and the data portion DP (FIG. 3) is modulated by the modulation method C. To send. Thereby, the communication (downward direction) from the base station 1 to the mobile station 9 is performed by the modulation method C within the boundary between base stations (step S30).

  The mobile station 9 moves and moves from the zone Z1 to the zone Z2 at the point “C” (handover from the base station 1 to the base station 2), but communication from the base station 2 to the mobile station 9 (downward) Maintains the modulation scheme C (step S31).

  The mobile station 9 periodically confirms the position information from the vehicle device 202 (FIG. 4) (step S32), and the mobile station 9 further moves to the point “E” (precisely by the processing time). (Step S33), a modulation system switching request signal for requesting the base station 2 to switch to the modulation system B is transmitted (step S34).

  Receiving this, the base station 2 changes only the time slot used with the mobile station 9 to the modulation method B (step S35). Specifically, the header part HP (FIG. 3) of the time slot to be transmitted to the mobile station 9 includes a modulation method instruction signal for instructing the modulation method B, and the data part DP (FIG. 3) is modulated by the modulation method B. To send.

  Thereby, the communication (downward direction) from the base station 2 to the mobile station 9 is performed by the modulation method B after passing through the point “E” (step S36).

  The mobile station 9 periodically confirms the position information from the vehicle device 202 (FIG. 4) (step S37), and the mobile station 9 further moves to the point “B” (precisely by the processing time). (Step S38), a modulation scheme switching request signal for requesting the base station 2 to switch to the modulation scheme A is transmitted (step S39).

  Receiving this, the base station 2 changes only the time slot used with the mobile station 9 to the modulation method A (step S40). Specifically, the header part HP (FIG. 3) of the time slot to be transmitted to the mobile station 9 includes a modulation method instruction signal for instructing the modulation method A, and the data portion DP (FIG. 3) is modulated by the modulation method A. To send.

  Thereby, the communication (downward direction) from the base station 2 to the mobile station 9 is performed by the modulation method A after passing through the point “B” (step S41).

  After passing through the boundary between the base stations, the communication speed of the entire train radio system is not hindered by returning to the communication with a high transmission speed.

  After changing to the modulation scheme A, the modulation scheme A is maintained until the vicinity of the next boundary between base stations is reached.

  In the above, an example in which three modulation schemes are switched is shown. However, when a modulation scheme having a smaller required C / N than modulation scheme C can be used, the section from “F” to “G” in FIG. It is assumed that communication is performed by a method, a new point other than the point “D” is set between the points “A” and “F”, and a point other than the point “E” is set between the points “B” and “G”. By setting a new point, it may be configured to switch between four modulation schemes, and if there are further modulation schemes, switching in five or more stages may be performed.

<Embodiment 4>
Although the train radio system according to the third embodiment described above is a system led by a mobile station that makes a request for switching the modulation method from the mobile station to the base station, it is led by the base station as in the second embodiment. The modulation scheme may be switched with

  The configurations of the mobile station and the base station are the same as those described with reference to FIGS. 7 and 8, respectively, and the modulation scheme is switched by the base station.

<Modulation switching process>
FIG. 3, FIG. 7, FIG. 8 and FIG. 11 show the flow of processing for switching modulation schemes in multiple stages when a train radio system that switches modulation schemes led by a base station is adopted. This will be described with reference to the flowchart shown in FIG.

  The mobile station 9 (described simply as a mobile station in FIG. 13) periodically acquires position information from the vehicle device 202 (FIG. 7) and transmits it to the base station 1. The base station 1 recognizes the position of the mobile station 9 in almost real time by confirming the position information from the mobile station 9 (step S51).

  Then, it is detected whether the position where the mobile station 9 exists has reached the vicinity of a predetermined boundary between base stations, that is, the point A in FIG. 11 (step S52). That is, since the base station 1 has position data indicating where the boundary between the base stations is in the control unit 13 (FIG. 8), and the speed can be estimated from the change in the location of the mobile station 9, the mobile station 9 can detect the timing when it reaches the point “A” in FIG. 11 (precisely, the point before the processing time), and only the time slot used with the mobile station 9 according to the timing. Is changed to modulation method B (step S53). Specifically, the header part HP (FIG. 3) of the time slot to be transmitted to the mobile station 9 includes a modulation method instruction signal for instructing the modulation method B, and the data part DP (FIG. 3) is modulated by the modulation method B. To send. The header part HP is always modulated by the modulation method C. As a result, communication (downward) from the base station 1 to the mobile station 9 is performed using the modulation method B between ADs and EBs in FIG. 11 (step S54).

  The base station 1 periodically confirms the position information from the mobile station 9 (step S55), and the mobile station 9 moves and the position where the vehicle exists is within the boundary between the base stations, that is, FIG. It is detected whether or not the point D has been reached (step S56).

  Then, only the time slot used with the mobile station 9 is changed to the modulation scheme C in accordance with the timing of reaching the point “D” in FIG. 11 (precisely the point before the processing time). (Step S57). Specifically, the header part HP (FIG. 3) of the time slot to be transmitted to the mobile station 9 includes a modulation method instruction signal for instructing the modulation method C, and the data portion DP (FIG. 3) is modulated by the modulation method C. To send. As a result, communication (downward) from the base station 1 to the mobile station 9 is performed using the modulation scheme C within the boundary between base stations (step S58).

  The mobile station 9 moves and moves from the zone Z1 to the zone Z2 at the point “C” (handover from the base station 1 to the base station 2), but communication from the base station 2 to the mobile station 9 (downward) Maintains the modulation scheme C (step S59).

  The base station 2 periodically confirms the position information from the mobile station 9 (step S60), and the mobile station 9 further moves to a point “E” (precisely, the point before the processing time) Is detected (step S61).

  Then, only the time slot used with the mobile station 9 is changed to the modulation method B in accordance with the timing of reaching the point E (step S62). Specifically, the header part HP (FIG. 3) of the time slot to be transmitted to the mobile station 9 includes a modulation method instruction signal for instructing the modulation method B, and the data part DP (FIG. 3) is modulated by the modulation method B. To send. As a result, communication (downward) from the base station 1 to the mobile station 9 is performed using the modulation method B between ADs and EBs in FIG. 11 (step S63).

  The base station 2 periodically confirms the position information from the mobile station 9 (step S64), and the mobile station 9 further moves to a predetermined boundary between base stations, that is, the point “B” in FIG. It is detected whether or not it has reached the point (precisely by the processing time) (step S65).

  Then, only the time slot used with the mobile station 9 is changed to the modulation scheme A in accordance with the timing of reaching the point B (step S66). Specifically, the header part HP (FIG. 3) of the time slot to be transmitted to the mobile station 9 includes a modulation method instruction signal for instructing the modulation method A, and the data portion DP (FIG. 3) is modulated by the modulation method A. To send. As a result, communication (downward) from the base station 1 to the mobile station 9 is performed using the modulation method A outside the boundary between base stations (step S67).

  After passing through the boundary between the base stations, the communication speed of the entire train radio system is not hindered by returning to the communication with a high transmission speed.

  After changing to the modulation scheme A, the modulation scheme A is maintained until the vicinity of the next boundary between base stations is reached.

  In the above description, the mobile station 9 moving from the zone Z1 to the zone Z2 has been described as an example. However, in the case of the mobile station 10 traveling in the reverse direction, the points “A” and “B” The base station 2 is only described in the reverse order, and the processing procedure is the same.

  Further, in the above, an example in which three modulation schemes are switched is shown. However, when a modulation scheme having a smaller required C / N than modulation scheme C can be used, a section from “F” to “G” in FIG. It is assumed that communication is performed using the modulation method, a new point other than the point “D” is set between the points “A” and “F”, and the point “E” is set between the points “B” and “G”. By setting a new point other than “”, the four modulation schemes may be switched, and if there are further modulation schemes, switching may be performed in five steps or more.

  1, 2 Base station, 4-7 LCX, 8 Inter-base station boundary, 9, 10, 99 Mobile station.

Claims (9)

A train radio in which a plurality of zones, which are radio areas, are set corresponding to the traveling path of a train equipped with a mobile station, and wireless communication is performed between the base station included in each zone and the mobile station via a leaky coaxial cable A system,
The base station
When the mobile station reaches a first point near the boundary between base stations, the transmission rate from the base station to the mobile station is slower than the first modulation method applied so far. A train radio system characterized by switching to the second modulation method. The mobile station
Based on the position information and speed information of the train acquired from the train, and the position data of the boundary between the base stations held by itself, the timing at which the train reaches the first point is detected, and the timing is In addition, modulation scheme switching that requests the base station to switch to the second modulation scheme so that the base station performs transmission by switching communication from the first modulation scheme to the second modulation scheme. Send a request signal,
The base station
In response to the modulation scheme switching request signal from the mobile station, the header portion of the transmission signal transmitted to the mobile station is instructed that the modulation scheme of the data portion of the transmission signal is the second modulation scheme. 2. The train radio system according to claim 1, further comprising: a modulation scheme instruction signal, wherein the data portion is modulated by the second modulation scheme and transmitted to the mobile station. The mobile station
Sends the train location information periodically acquired from the train to the base station,
The base station
Based on the position information from the mobile station and position data of the boundary between the base stations held by itself, the timing at which the train reaches the first point is detected, and the movement is performed in accordance with the timing. A header part of a transmission signal to be transmitted to a station includes a modulation method instruction signal that indicates that the modulation method of the data part of the transmission signal is the second modulation method, and the data part is included in the second part. The train radio system according to claim 1, wherein the train radio system is modulated by a modulation method and transmitted to the mobile station. The base station
After the communication to the mobile station is switched from the first modulation method to the second modulation method, and after reaching a second point relative to the first point, the mobile station The train radio system according to claim 1, wherein communication to a station is performed by switching to the first modulation method. The base station
Communication to the mobile station is transmitted more than the second modulation scheme at least once after switching from the first modulation scheme to the second modulation scheme and before reaching the second point. The train radio system according to claim 4, wherein the train radio system is switched to a low-speed modulation system.   The train radio system according to claim 1, wherein the first modulation scheme is selected from among 256QAM (Quadrature Amplitude Modulation), 64QAM, 16QAM, and QPSK. The first and second points are:
The train radio system according to claim 4, wherein when the first modulation method is applied to communication from the base station, the train radio system corresponds to both end positions of a radio wave interference section in which electric fields in adjacent zones interfere with each other. A plurality of zones that are wireless areas corresponding to the travel route of a train equipped with a mobile station are set, and base stations included in each zone,
The base station performs radio communication with the mobile station via a leaky coaxial cable, and has been applied so far when the mobile station reaches a first point near the boundary between base stations. A base station, wherein the base station performs communication from the base station to the mobile station by switching to a second modulation method having a transmission rate slower than that of the first modulation method. A mobile station mounted on a train,
The mobile station
A plurality of zones that are wireless areas are set corresponding to the travel route of the train equipped with the mobile station, the mobile station performs wireless communication with a base station included in each zone via a leaky coaxial cable,
When the mobile station reaches a first point near the boundary between base stations, communication from the base station to the mobile station is slower in transmission speed than the first modulation scheme applied so far. A mobile station characterized in that, when switched to the second modulation scheme, the modulation scheme is changed accordingly.

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