Relay device, signal transmission system, and train radio communication system

Abstract

To reduce the likelihood of degradation in the quality of signals transmitted in signal transmission systems that utilize relay devices.SOLUTION: A relay device according to the present disclosure is a relay device that is provided between a first communication line and a second communication line and relays communication. The relay device includes: a first amplifier circuit that amplifies a first signal transmitted on the first communication line with a first gain that has an inverse correlation with a first frequency characteristic to obtain a second signal transmitted on the second communication line; and a first frequency characteristic detection circuit that detects the first frequency characteristic from the second signal.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a signal transmission system, a relay device used in the signal transmission system, and a train radio communication system using the signal transmission system. [Background technology]

[0002] BACKGROUND ART In the technology for monitoring wireless communications, for example, train radio communications, a technology using a leaky coaxial cable (hereinafter sometimes abbreviated as "LCX") is known.

[0003] In this wireless communication, a mobile station is mounted on a vehicle that constitutes a train. The wireless communication is performed between the mobile station and a base station. The vehicle moves by running on a vehicle track (hereinafter simply referred to as a "track"), for example, a railway track.

[0004] Signals transmitted from the base station to the LCX leak from the LCX as radio waves, and these radio waves are received by the mobile station. Radio waves transmitted from the mobile station are received by the LCX, and then transmitted from the LCX to the base station as signals.

[0005] The strength of the signal transmitted between the base station and the LCX is lost due to leakage from the LCX. To compensate for this loss, relay stations are installed between different LCXs to amplify the signal.

[0006] A technique for adjusting the amplification gain in a repeater in accordance with the power level of a signal output by the repeater to maintain the power of the signal is known (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-60504 Summary of the Invention [Problem to be solved by the invention]

[0008] Signals are transmitted between the base station and the relay station via the LCX, and these three can be said to be a signal transmission system that transmits the signals by wire using the LCX as the communication line (hereinafter simply referred to as "transmission").Wireless communication is performed between the mobile station mounted on the vehicle and the signal transmission system, and these two can be said to be a train wireless communication system in which the wireless communication is performed.

[0009] In a train radio communication system, signals may be transmitted within the signal transmission system via multiple communication channels (hereinafter simply referred to as "channels") that use different frequencies, and may also be wirelessly communicated between the signal transmission system and a mobile station.

[0010] Even if the amplification gain of the repeater is adjusted according to the power level of the signal output by the repeater when signal transmission and wireless communication are performed on one channel, the power of the signal output by the repeater when signal transmission and wireless communication are performed on another channel may not be maintained. This is because it is assumed that the loss in the LCX and the loss in the repeater each have frequency dependency, and a difference between the frequency used in one channel and the frequency used in another channel may cause a difference in these losses.

[0011] The wider the frequency band of the multiple channels allocated to signals in a train radio communication system, the more relay devices there are in the signal transmission system, and the longer the total length of the LCX in the signal transmission system, the more the differences in loss tend to accumulate or accumulate and become more noticeable.

[0012] The difference in loss increases the possibility that the power level of a signal will differ depending on the channel that the signal uses, thus degrading the quality of transmission and wireless communication.

[0013] The present disclosure aims to reduce the likelihood of signal quality degradation. [Means for solving the problem]

[0014] A first aspect of a relay device according to the present disclosure is a relay device that is provided between a first communication line and a second communication line and relays communications. The relay device includes a first amplifier circuit that amplifies a first signal transmitted through the first communication line by a first gain that has an inverse correlation with a first frequency characteristic to obtain a second signal transmitted through the second communication line, and a first frequency characteristic detection circuit that detects the first frequency characteristic from the second signal.

[0015] A second aspect of the relay device according to the present disclosure is the first aspect, further comprising a second amplifier circuit that amplifies a third signal transmitted on the second communication line with a second gain that has an inverse correlation with a second frequency characteristic to obtain a fourth signal transmitted on the first communication line, and a second frequency characteristic detection circuit that detects the second frequency characteristic from the fourth signal.

[0016] A signal transmission system according to the present disclosure includes the second aspect of the relay device according to the present disclosure, the first communication line, the second communication line, and a base station that transmits the first signal.

[0017] The train wireless communication system of the present disclosure comprises a signal transmission system according to the present disclosure and a mobile station mounted on a vehicle moving on a vehicle track, receiving either or both of the first signal and the second signal from the signal transmission system, and transmitting either or both of the third signal and the fourth signal to the signal transmission system, and a leaky coaxial cable is used for both the first communication line and the second communication line. [Effects of the Invention]

[0018] A relay device according to the present disclosure contributes to reducing the possibility of deterioration in the quality of a signal transmitted in a signal transmission system that uses the relay device.

[0019] The signal transmission system according to the present disclosure contributes to reducing the possibility of deterioration in the quality of signals wirelessly transmitted in a train wireless communication system that uses the signal transmission system.

[0020] The train wireless communication system according to the present disclosure contributes to reducing the possibility of deterioration in the quality of signals wirelessly transmitted in the train wireless communication system. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a conceptual diagram illustrating a configuration of a train wireless communication system according to the present disclosure. [Figure 2] 1 is a block diagram illustrating a configuration of a relay device according to a first embodiment of the present disclosure. [Figure 3] FIG. 10 is a characteristic diagram showing frequency characteristics of the level of a signal transmitted to a relay device. [Figure 4] FIG. 10 is a block diagram illustrating a configuration of a relay device serving as a comparative example of the present disclosure. [Figure 5] 10 is a characteristic diagram illustrating an example of frequency characteristics of the level of a signal output from an amplifier. [Figure 6] 10 is a characteristic diagram illustrating the frequency dependency of the gain of a frequency characteristic correction circuit. [Figure 7] 10 is a characteristic diagram illustrating an example of frequency characteristics of the level of a signal output from an amplifier after correction. FIG. [Figure 8] FIG. 10 is a block diagram illustrating a configuration of a relay device according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0022] <1. Overview of the train wireless communication system 100> 1 is a conceptual diagram illustrating a configuration of a train radio communication system 100 according to the present disclosure. The train radio communication system 100 includes a signal transmission system 400 and mobile stations 51 and 52.

[0023] For example, mobile station 51 is mounted on vehicle 501, and mobile station 52 is mounted on vehicle 502. Vehicles 501 and 502 run on a railroad track 5. Vehicles 501 and 502 form a train either alone or together with a vehicle not shown.

[0024] Signal transmission system 400 includes relay device 201 or multiple relay devices 201-20k, LCX 301 or multiple LCXs 301-30k (k is an integer greater than or equal to 2 and less than or equal to n, n is an integer greater than or equal to 2), and base station 10. Fig. 1 illustrates an example where integer n is 5 or greater. Specifically, Fig. 1 shows relay devices 201, 202, 303, 204, and 20n, and LCXs 300, 301, 302, 303, 304, and 30n.

[0025] An LCX 301 is connected between the base station 10 and the relay device 201. One form of this connection is erection. In the LCX 301, signals are transmitted bidirectionally between the base station 10 and the relay device 201.

[0026] An LCX 30k is connected between the relay device 20j and the relay device 20k (j=k-1). One mode of this connection is erection. In the LCX 30k, signals are transmitted bidirectionally between the relay device 20j and the relay device 20k.

[0027] The signal transmission system 400 may further include a termination device 40. The following description will be given assuming that the signal transmission system 400 includes the termination device 40.

[0028] The LCX 300 is connected between the terminal device 40 and the repeater device 20n. One example of this connection is erection. In the LCX 300, signals are transmitted in both directions between the terminal device 40 and the repeater device 20n.

[0029] The LCXs 301 to 30n and 300 are connected in series between the base station 10 and the termination device 40. The termination device 40 has a function of terminating the LCXs 301 to 30n and 300.

[0030] Wireless communication is performed between the signal transmission system 400 and the mobile stations 51 and 52. The mobile stations 51 and 52 function as counterpart devices of the signal transmission system 400 for wireless communication in the train wireless communication system 100.

[0031] In this wireless communication, signals (hereinafter referred to as "downstream signals") provided from the signal transmission system 400 to the mobile stations 51 and 52 are transmitted as leaked radio waves T1 and T2 from the LCXs 301 to 30n and 300, and are received by the mobile stations 51 and 52, respectively.

[0032] In this wireless communication, signals (hereinafter referred to as "uplink signals") provided from the mobile stations 51 and 52 to the signal transmission system 400 are transmitted as radio waves R1 and R2 from the mobile stations 51 and 52, respectively, and received by the LCXs 301 to 30n and 300.

[0033] In the signal transmission system 400, the upstream and downstream signals are transmitted through the LCXs 301 to 30n and 300 while being relayed by the relay devices 201 to 20n.

[0034] An uplink signal input from the base station 10 to the relay device 201 via the LCX 301 is attenuated by the LCX 301. Depending on the level of the attenuation, the relay device 201 amplifies the uplink signal and outputs it to the LCX 302.

[0035] The upstream signal input to the repeater device 20j via the LCX 30j is attenuated by the LCX 30j. Depending on the level of attenuation, the repeater device 20j amplifies the upstream signal and outputs it to the LCX 30k.

[0036] An upstream signal input to the repeater device 20n via the LCX 30n is attenuated by the LCX 30n. Depending on the level of attenuation, the repeater device 20n amplifies the upstream signal and outputs it to the LCX 300. The termination device 40 terminates the upstream signal transmitted from the LCX 300.

[0037] Downlink signals input from the mobile stations 51 and 52 to the relay device 20j via the LCX 30k are attenuated by the LCX 30k. Depending on the level of attenuation, the relay device 20j amplifies the downlink signals and outputs them to the LCX 30j.

[0038] Downlink signals input from the mobile stations 51 and 52 to the relay device 20n via the LCX 300 are attenuated by the LCX 300. Depending on the level of attenuation, the relay device 20n amplifies the downlink signals and outputs them to the LCX 30n.

[0039] The wireless communication between the mobile stations 51, 52 and the signal transmission system 400, whether it is an uplink signal or a downlink signal, passes through more LCXs 301 to 30n and relay devices 201 to 20n in the signal transmission system 400 as the mobile stations 51, 52 are farther away from the base station 10.

[0040] Both the LCXs 301-30n and the repeaters 201-20n have frequency dependency. Therefore, the more LCXs 301-30n and repeaters 201-20n that an upstream signal or a downstream signal transmitted in the signal transmission system 400 passes through, the more the frequency dependency of those signals that pass through accumulates or accumulates. Therefore, reducing the frequency dependency in one or more of the repeaters 201-20n contributes to reducing the possibility of deterioration in the quality of signals transmitted in the signal transmission system 400.

[0041] <2. First Embodiment> <2-1. Relay Device According to the Present Disclosure> 2 is a block diagram illustrating a configuration of a relay device 27j according to the first embodiment of the present disclosure. The relay device 27j can be used for any of the relay devices 20j. As described above, the integer j is an integer smaller than the integer k by 1, the integer k is an integer greater than or equal to 2 and less than or equal to n, and the integer n is an integer greater than or equal to 2.

[0042] The relay device 27j can also be used as the relay device 20n in FIG. 1, and in that case, the LCX 30k in FIG.

[0043] The relay device 27j does not need to be employed in all of the relay devices 201 to 20n. This is because, even if the relay device 27j is employed in any of the relay devices 201 to 20n, the reduced frequency dependency in the relay device 27j contributes to reducing the possibility of deterioration in the quality of signals transmitted in the signal transmission system 400.

[0044] The relay device 27j is connected between the LCX 30j and the LCX 30k. In the following description, when the relay device 27j is used as the relay device 20n, the LCX 30k is replaced with the LCX 300.

[0045] The repeater 27j includes duplexers 22a and 22b, frequency characteristic detection circuits 23a and 23b, and amplifier circuits 2a and 2b. The amplifier circuit 2a includes an amplifier 21a and a frequency characteristic correction circuit 24a. The amplifier circuit 2b includes an amplifier 21b and a frequency characteristic correction circuit 24b.

[0046] In LCX 30j, a downstream signal Sj is transmitted from base station 10 to relay device 27j. The downstream signal Sj is input from LCX 30j to splitter 22a. Splitter 22a outputs the downstream signal Sj to amplifier circuit 2a. Amplifier circuit 2a amplifies the downstream signal Sj with a gain described below and outputs the resulting downstream signal Gj. Splitter 22b outputs the input downstream signal Gj to LCX 30k. The downstream signal Sj is transmitted in LCX 30k.

[0047] In LCX 30k, the upstream signal Sk is transmitted from the termination device 40 to the repeater device 27j. The upstream signal Sk is input from LCX 30k to the splitter 22b. The splitter 22b outputs the upstream signal Sk to the amplifier circuit 2b. The amplifier circuit 2b amplifies the upstream signal Sk with a gain to be described later and outputs the resulting upstream signal Gj. The splitter 22a outputs the input upstream signal Gk to LCX 30j. The upstream signal Sk is transmitted in LCX 30j.

[0048] The demultiplexer 22a performs demultiplexing by outputting the downstream signal Sj input from the LCX 30j to the amplifier circuit 2a and outputting the upstream signal Gk input from the amplifier circuit 2b to the LCX 30j.

[0049] The demultiplexer 22b performs demultiplexing by outputting the upstream signal Sk input from the LCX 30k to the amplifier circuit 2b and outputting the downstream signal Gj input from the amplifier circuit 2a to the LCX 30k.

[0050] The frequency characteristic detection circuit 23a detects the frequency characteristic of the upstream signal Gj. The frequency characteristic detection circuit 23b detects the frequency characteristic of the downstream signal Gk. For example, by employing the technology disclosed in Patent Document 1, the power level is detected as the signal level of the upstream signal Gj. Similarly, the power level is detected as the signal level of the downstream signal Gk.

[0051] The frequency characteristic detection circuit 23a does not detect the signal level of only one channel, but detects the signal level of the downstream signal Gj for each of a plurality of channels with different frequencies, thereby detecting the frequency characteristics of the downstream signal Gj.

[0052] Similarly, the frequency characteristic detection circuit 23b detects the signal level of the upstream signal Gk for each of a plurality of channels with different frequencies, thereby detecting the frequency characteristic of the upstream signal Gk.

[0053] 3 is a characteristics diagram illustrating the frequency characteristics of the downstream signal Sj when it is input from the LCX 30j to the relay device 27j. The horizontal axis represents frequency, and the vertical axis represents the signal level of the downstream signal Sj (simply labeled "signal level" in the diagram).

[0054] 3 illustrates a case where the downstream signal Sj has a signal level L0 in a channel employing frequency f0, and a signal level L1 in both channels employing frequency f1 and frequency f1. These signal levels L0 and L1, as well as the signal levels of the downstream signal Sj in channels employing other frequencies, appear as a curve C1 in FIG. 3. Curve C1 can be said to represent the frequency characteristics of the downstream signal Sj.

[0055] Frequency f1 is smaller than frequency f0, and frequency f2 is larger than frequency f0. Curve C1 exhibits a single peak with respect to frequency, with signal level L0 as the maximum value. The signal level of the downstream signal Sj increases sharply around frequency f1. The signal level of the downstream signal Sj decreases sharply around frequency f2.

[0056] <2-2. Relay device according to comparative example> 4 is a block diagram illustrating a configuration of a relay device 29j serving as a comparative example of the present disclosure. The relay device 29j has a configuration in which the frequency characteristic detection circuits 23a and 23b and the frequency characteristic correction circuits 24a and 24b are removed from the relay device 27j described in the first embodiment. The downstream signal Gj is obtained by amplifying the downstream signal Sj by the amplifier 21a. The upstream signal Gk is obtained by amplifying the downstream signal Sk by the amplifier 21b. The functions of the branching filters 22a and 22b are common to both the relay devices 27j and 29j.

[0057] The gain of amplifier 21a has inherent frequency dependency, similar to the gain of a general amplifier. The loss of LCX 30j has inherent frequency dependency, similar to the loss of a general transmission line. Due to this frequency dependency, the signal level of downstream signal Gj output from amplifier 21a differs depending on the frequency adopted for the channel of downstream signal Sj input to repeater device 29j.

[0058] For example, it is assumed that the gain of the amplifier 21a is set to a gain B0 with the frequency f0 as a reference, and the frequency dependence of the gain exhibits a single peak with the gain B0 as a maximum value.

[0059] If the gain of amplifier 21a is introduced at a frequency distant from the reference frequency f0, for example, at frequency f1, the downstream signal Gj will have signal levels L0·B0 and L1·B1 at frequencies f0 and f1, respectively. The ratio of the two holds true: (L1·B1) / (L0·B0)=(L1 / L0)·(B1 / B0)<(L1 / L0).

[0060] 5 is a characteristic diagram illustrating the frequency characteristics of the downstream signal Gj in the relay device 29j. In FIG. 5, the horizontal axis represents frequency, and the vertical axis represents the signal level of the downstream signal Gj (simply labeled "signal level" in the diagram).

[0061] The signal level of the downstream signal Gj output from the amplifier 21a appears as curve C2 in Figure 5. Curve C2 can be said to represent the frequency characteristics of the downstream signal Gj. The signal level Q0 at frequency f0 corresponds to the above-mentioned signal levels L0·B0. The signal level Q1 at frequencies f1 and f2 corresponds to the above-mentioned signal levels L1·B1.

[0062] When downstream signal Sj is amplified by amplifier 21a having the above-described frequency dependency to obtain downstream signal Gj, the frequency characteristics of the signal level are less flat than the frequency characteristics shown in Fig. 3. The fact that gain B1 is smaller than gain B0 can be seen as meaning that channels using other frequencies experience greater loss in repeater device 29j compared to channels using reference frequency f0.

[0063] Similarly, with respect to the upstream signals Sk and Gk and the amplifier 21b, the frequency dependency of the gain of the amplifier 21a reduces the flatness of the frequency characteristics of the signal level.

[0064] The same is true for the frequency dependence of loss in LCX30j and 30X, reducing the flatness of the frequency characteristics of the signal level.

[0065] As can be seen from the explanation of the comparative example, differences in loss cause the power level of a signal to differ depending on the channel used by the signal, thereby increasing the likelihood of degrading the quality of transmission and wireless communication.

[0066] 2-3. Description with Reference to Comparative Examples of Relay Devices According to the Present Disclosure In the relay device 27j according to the present disclosure, the frequency characteristic detection circuit 23a detects the frequency characteristic of the downstream signal Gj as described above. For example, the frequency characteristic detection circuit 23a detects the frequency characteristic of the signal level illustrated in FIG. 5. The detected frequency characteristic is input to the frequency characteristic correction circuit 24a. The frequency characteristic correction circuit 24a corrects the frequency characteristic of the downstream signal Sj based on the frequency characteristic input from the frequency characteristic detection circuit 23a (which initially appears as the curve C2 illustrated in FIG. 5, for example).

[0067] Specifically, for example, the frequency characteristic correction circuit 24a amplifies the downstream signal Sj with a gain having frequency dependency before inputting it to the amplifier 21a. Here, amplification includes not only the case where the gain exceeds 1, but also the case where the downstream signal Sj is substantially attenuated when the gain is less than 1, and the case where the downstream signal Sj is substantially neither amplified nor attenuated when the gain is 1. A technique for controlling the gain by comparing the power level of a signal with a reference gain is known, for example, from Patent Document 1.

[0068] The frequency characteristic correction circuit 24a does not correct the signal level of only one channel, but corrects the gain of the downstream signal Sj for each of a plurality of channels having different frequencies, thereby correcting the frequency characteristics.

[0069] 6 is a characteristic diagram illustrating the frequency dependency of the gain of the frequency characteristic correction circuit 24a. In FIG. 6, the horizontal axis represents frequency and the vertical axis represents gain. The frequency dependency appears as curve C3 in FIG. 6.

[0070] This example shows a case where curve C3 exhibits a bimodal relationship with frequency. Specifically, the gain of the frequency characteristic correction circuit 24a is set to gain B2 with frequency f0 as the reference, and gain B2 is the minimum value of the gain. At both frequencies f3, which is lower than frequency f0, and f4, which is higher than frequency f0, gain B3 (>B2) is the maximum value.

[0071] 5, it is assumed that frequency f3 is set to frequency f1 or its vicinity, and frequency f4 is set to frequency f2 or its vicinity. In this case, the frequency characteristics of the signal level of the downstream signal Gj shown by curve C2 and the frequency dependence of the gain of the frequency characteristic correction circuit 24a shown by curve C3 have an inverse correlation with frequency.

[0072] 7 is a characteristic diagram illustrating the frequency characteristics of the signal level of the downstream signal Gj output from the amplifier 21a after correction to obtain the above-mentioned inverse correlation. The horizontal axis represents frequency, and the vertical axis represents the signal level (simply labeled "signal level" in the diagram). The frequency characteristics appear as curve C4.

[0073] In the above example, the signal level H0 at frequency f0 corresponds to signal levels Q0·B0·B2, and the signal level H1 at frequencies f1 and f2 corresponds to signal levels Q1·B1·B3.

[0074] The flatness of the downstream signal Gj with respect to frequency in the frequency band equal to or greater than frequency f1 and equal to or less than frequency f2 is higher for curve C4 than for curve C2 shown in Fig. 5. This is because there is an inverse correlation between the frequency characteristic of the signal level of the downstream signal Gj shown by curve C2 and the frequency dependency of the gain of the frequency characteristic correction circuit 24a shown by curve C3.

[0075] From the above, compared to the relay device 29j shown in the comparative example, the relay device 27j reduces the differences depending on the channel adopted by the downlink signal Gj in at least the frequency band, thereby reducing the possibility of degrading the quality of transmission and wireless communication.

[0076] Similarly, the frequency characteristic detection circuit 23b detects the frequency characteristic of the upstream signal Gk. The detected frequency characteristic is input to the frequency characteristic correction circuit 24b. The frequency characteristic correction circuit 24b corrects the frequency characteristic of the upstream signal Sk based on the frequency characteristic input from the frequency characteristic detection circuit 23b.

[0077] For example, the frequency characteristic correction circuit 24b amplifies the upstream signal Sk with a gain that has frequency dependency (this includes the above-mentioned cases of attenuation and cases where neither attenuation nor amplification is performed) and then inputs the signal to the amplifier 21b. The frequency characteristic of the signal level of the upstream signal Gk and the frequency dependency of the gain of the frequency characteristic correction circuit 24b have an inverse correlation with frequency.

[0078] The frequency characteristic correction circuit 24b does not correct the signal level of only one channel, but corrects the gain of the upstream signal Sk for each of a plurality of channels having different frequencies, thereby correcting the frequency characteristics.

[0079] Compared to the relay device 29j shown in the comparative example, the relay device 27j reduces the differences depending on the channel adopted by the uplink signal Gk at least in the set frequency band, thereby reducing the possibility of degrading the quality of transmission and wireless communication.

[0080] <2-4. General Description of Relay Device According to First Embodiment> From the above-described configuration, the relay device 27j can be described as follows. The relay device 27j is provided between a first communication line and a second communication line and relays communications. A first signal is transmitted through the first communication line, and a second signal is transmitted through the second communication line. LCX 30j is an example of the first communication line, LCX 30k is an example of the second communication line, downstream signal Sj is an example of the first signal, and downstream signal Sk is an example of the second signal.

[0081] The relay device 27j has an amplification circuit 2a. The amplification circuit 2a amplifies the downstream signal Sj with a first gain to obtain a downstream signal Gj. Either or both of the products B0·B2 of the gain B0 and the gain B2 and the product B1·B3 of the gain B1 and the gain B3 described above are examples of the first gain.

[0082] The relay device 27j has a frequency characteristic detection circuit 23a. The frequency characteristic detection circuit 23a detects a first frequency characteristic from the downstream signal Sk (see curve C2 in FIG. 5).

[0083] The first gain has an inverse correlation with the first frequency characteristic. In the above example, B1 < B0, and the gain exemplified by the curve C3 shows a frequency-dependent line having an inverse correlation with the frequency characteristic of the signal level exemplified by the curve C2.

[0084] In the relay device 27j, either or both of the frequency dependence of LCX30j and the frequency dependence of the relay device 27j are reduced.

[0085] The relay device 27j has an amplification circuit 2b. The amplification circuit 2b amplifies the upstream signal Sk with a second gain to obtain an upstream signal Gj. The upstream signal Sk can be regarded as a third signal transmitted on a second communication line exemplified by LCX30k. The upstream signal Gk can be regarded as a fourth signal transmitted on a first communication line exemplified by LCX30j.

[0086] The relay device 27j has a frequency characteristic detection circuit 23b. The frequency characteristic detection circuit 23b detects a second frequency characteristic from the upstream signal Gk. Similar to the first gain and the first frequency characteristic described above, the second gain has an inverse correlation with the second frequency characteristic.

[0087] In the relay device 27j, either or both of the frequency dependence of LCX30k and the frequency dependence of the relay device 27j are reduced.

[0088] The signal transmission system 400 includes a relay device 27j, a first communication line exemplified by LCX30j, a second communication line exemplified by LCX30k, and a base station 10 that transmits a first signal exemplified by a downstream signal Sj. The adoption of the relay device 27j having the above-described configuration in the signal transmission system 400 contributes to reducing the possibility of deterioration in the quality of signals transmitted in the signal transmission system 400.

[0089] The train wireless communication system 100 includes a signal transmission system 400 and mobile stations 51 and 52. The mobile station 51 is mounted on a vehicle 501. The mobile station 52 is mounted on a vehicle 502. The vehicles 501 and 502 move on a railroad 5.

[0090] The mobile station 51 receives a downlink signal Sj (or a signal Gj, or both) from the signal transmission system 400 as a radio wave T1, and transmits an uplink signal Sk (or a signal Gk, or both) to the signal transmission system 400 as a radio wave R1.

[0091] The mobile station 52 receives a downlink signal Sj (or a signal Gj, or both) from the signal transmission system 400 as a radio wave T2, and transmits an uplink signal Sk (or a signal Gk, or both) to the signal transmission system 400 as a radio wave R2.

[0092] LCX 30j is used for the first communication line, and LCX 30k is used for the second communication line. Radio wave T1 leaks from either or both of LCX 30j and 30k and is transmitted to mobile station 51. Radio wave T1 leaks from either or both of LCX 30j and 30k and is transmitted to mobile station 51. Radio wave R1 is received by either or both of LCX 30j and 30k. Radio wave R2 is received by either or both of LCX 30j and 30k.

[0093] The adoption of the signal transmission system 400 in the train wireless communication system 100 contributes to reducing the possibility that the quality of signals wirelessly communicated in the train wireless communication system 100 will deteriorate.

[0094] <3. Second Embodiment> 8 is a block diagram illustrating a configuration of a relay device 28j according to the second embodiment of the present disclosure. The relay device 28j can be used for any of the relay devices 20j. The relay device 28j is connected between the LCX 30j and the LCX 30k.

[0095] 1, in which case the LCX 30k in FIG. 8 is replaced with the termination device 40. In the following description, when the relay device 28j is used as the relay device 20n, the LCX 30k is replaced with the LCX 300.

[0096] The relay device 28j does not need to be employed in all of the relay devices 201 to 20n. This is because, even if the relay device 28j is employed in any of the relay devices 201 to 20n, the reduced frequency dependency in the relay device 28j contributes to reducing the possibility of deterioration in the quality of signals transmitted in the signal transmission system 400.

[0097] The repeater device 28j has a configuration in which a test signal generator 25 is added to the repeater device 27j according to the first embodiment.

[0098] The test signal generator 25 inputs a test signal St to the amplifier circuit 2b. The test signal St includes a plurality of frequencies that are different from one another. Here, "including a plurality of frequencies" means that the test signal St may be a plurality of types of signals that each include a different frequency, or may be a single signal that has a frequency band that spans a plurality of different frequencies.

[0099] These multiple frequencies include any multiple of the frequencies of the channels used by the upstream signal Sk. For example, when the frequencies f0, f1, and f2 are used for the three channels used by the upstream signal Sk, the test signal St includes any two or three of a signal having a frequency f0, a signal having a frequency f1, and a signal having a frequency f2. For example, when the frequencies f0, f1, and f2 are used for the three channels used by the upstream signal Sk, the frequency band of the test signal St includes any two or three of the frequencies f0, f1, and f2.

[0100] In repeater 28j, amplifier circuit 2b amplifies test signal St with a second gain to obtain upstream signal Gj. Similar to the function in repeater 20j, frequency characteristic detection circuit 23b detects a second frequency characteristic from upstream signal Gj. In repeater 28j, similar to repeater 27j, either or both of the frequency dependence of LCX 30k and the frequency dependence of repeater 28j are reduced.

[0101] The adoption of test signal St does not mean the non-adoption of upstream signal Sk. Upstream signal Gk is generated when upstream signal Sk is received by LCX 30k. For example, when upstream signal Sk is not received by LCX 30k, test signal St is input to amplifier circuit 2b. Test signal St may be selectively output from test signal generator 25 and input to amplifier circuit 2b when, for example, the signal level indicated by the frequency characteristic detected by frequency characteristic detection circuit 23b falls below a preset threshold. In FIG. 8, such a trigger is conceptually indicated by a dashed arrow pointing from frequency characteristic detection circuit 23b to test signal generator 25.

[0102] In the train wireless communication system 100, downlink signals from the base station 10 to the mobile stations 51 and 52 are constantly transmitted, and the first gain when the amplifier circuit 2a amplifies the signals is likely to be improved. On the other hand, uplink signals from the mobile stations 51 and 52 to the base station 10 are transmitted only on the channels used by those signals, and it is assumed that the second gain when the amplifier circuit 2b amplifies the signals is not improved.

[0103] The adoption of the test signal St improves the second gain even when no uplink signal is transmitted from the mobile stations 51, 52 to the base station 10, thereby contributing to reducing the possibility of deterioration in the quality of the signal transmitted in the signal transmission system 400. The adoption of the signal transmission system 400 including the repeater device 28j in the train wireless communication system 100 contributes to reducing the possibility of deterioration in the quality of the wirelessly communicated signal.

[0104] It should be noted that the embodiments can be freely combined, and each embodiment can be modified or omitted as appropriate.

[0105] Various aspects of the present disclosure are summarized below as appendices.

[0106] (Appendix 1) A relay device that is provided between a first communication line and a second communication line and relays communication, a first amplifier circuit that amplifies a first signal transmitted through the first communication line by a first gain that has an inverse correlation with a first frequency characteristic to obtain a second signal transmitted through the second communication line; a first frequency characteristic detection circuit that detects the first frequency characteristic from the second signal; A relay device comprising:

[0107] (Appendix 2) a second amplifier circuit that amplifies the third signal transmitted through the second communication line by a second gain that has an inverse correlation with a second frequency characteristic to obtain a fourth signal transmitted through the first communication line; a second frequency characteristic detection circuit that detects the second frequency characteristic from the fourth signal; 2. The relay device according to claim 1, further comprising:

[0108] (Appendix 3) a test signal generator that inputs a test signal including a plurality of frequencies to the second amplifier circuit; Further provided with 3. The relay device according to claim 2, wherein the second amplifier circuit amplifies the test signal with the second gain to obtain the fourth signal.

[0109] (Appendix 4) A relay device according to Supplementary Note 2 or 3; the first communication line and the second communication line; a base station that transmits the first signal; A signal transmission system comprising:

[0110] (Appendix 5) a signal transmission system according to Supplementary Note 4; a mobile station that is mounted on a vehicle that moves on a vehicle track, and that receives either or both of the first signal and the second signal from the signal transmission system, and transmits either or both of the third signal and the fourth signal to the signal transmission system; Equipped with A train wireless communication system, wherein leaky coaxial cables are used for both the first communication line and the second communication line. [Explanation of symbols]

[0111] 10 base station, 2a, 2b amplifier circuits, 23a, 23b frequency characteristic detection circuits, 25 test signal generator, 51, 52 mobile stations, 100 train radio communication system, 201-204, 20j, 20k, 20n, 27j, 28j repeaters, 300-304, 30j, 30k, 30n LCX, 400 signal transmission system, 501, 502 vehicles, B0-B3 gain, C1-C4 curves, f0-f4 frequency, Gj, Sj downstream signals, Gk, Sk upstream signals, H0, H1, L0, L1, Q0, Q1 signal levels, St test signal, T1, T2, R1, R2 radio waves.

Claims

1. A relay device that is provided between a first communication line and a second communication line and relays communication, a first amplifier circuit that amplifies a first signal transmitted through the first communication line by a first gain that has an inverse correlation with a first frequency characteristic to obtain a second signal transmitted through the second communication line; a first frequency characteristic detection circuit that detects the first frequency characteristic from the second signal; A relay device comprising:

2. a second amplifier circuit that amplifies the third signal transmitted through the second communication line by a second gain that has an inverse correlation with a second frequency characteristic to obtain a fourth signal transmitted through the first communication line; a second frequency characteristic detection circuit that detects the second frequency characteristic from the fourth signal; The relay device according to claim 1 , further comprising:

3. a test signal generator that inputs a test signal including a plurality of frequencies to the second amplifier circuit; Further provided with The relay device according to claim 2 , wherein the second amplifier circuit amplifies the test signal with the second gain to obtain the fourth signal.

4. The relay device according to claim 2 or 3; the first communication line and the second communication line; a base station that transmits the first signal; A signal transmission system comprising:

5. A signal transmission system according to claim 4; a mobile station that is mounted on a vehicle that moves on a vehicle track, and that receives either or both of the first signal and the second signal from the signal transmission system, and transmits either or both of the third signal and the fourth signal to the signal transmission system; Equipped with A train wireless communication system, wherein leaky coaxial cables are employed for both the first communication line and the second communication line.

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