Signal transmission apparatus

Abstract

To suppress increase in circuit scale and a device cost.SOLUTION: A signal transmission apparatus includes a pilot signal generation unit that generates pilot signals of different frequencies as monitoring pilot signals used to detect abnormal levels in specific frequency bands of an input signal and a control unit that generates pilot signals of different frequencies at a predetermined cycle for the pilot signal generation unit.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a signal transmitting device. [Background technology]

[0002] Conventionally, a signal transmission device is known that includes a pilot signal generating unit that generates a pilot signal used to detect an abnormality in a processing unit that performs internal processing of an input signal (see, for example, Non-Patent Documents 1 and 2). In such a signal transmission device, when the frequency band of the input signal spans a wide band, multiple pilot signal generating units are provided to generate multiple pilot signals with different bands.

[0003] Fig. 8 is a diagram showing a configuration example of a signal transmitting device 100 including a plurality of pilot signal generating units. Fig. 8 shows, as an example of a signal transmitting device, a signal transmitting device 100 included in a communication system to which an FM (Frequency Modulation) batch conversion method is applied. The signal transmitting device 100 includes an electric signal branching unit 110, a plurality of pilot signal generating units 120-1 to 120-4, a multiplexing unit 130, an electric signal abnormality detecting unit 140, an electric signal amplifying unit 150, an FM batch converted signal generating unit 160, an electric-optical converting unit 170, an optical signal amplifying unit 180, an optical signal branching unit 190, a demodulated signal abnormality detecting unit 200, a monitoring unit 210, and an alarm processing unit 220. Note that dotted lines extending from some of the functional units to the monitoring unit 210 represent control signals.

[0004] Signals of a plurality of frequency bands are input to the signal transmitting device 100 as input signals. For example, it is assumed that a signal with a frequency band of 70 to 770 MHz (47 to 864 MHz in Non-Patent Document 1) and a signal with a frequency band of 1000 to 2100 MHz (1000 to 2150 MHz in Non-Patent Document 1) are input to the signal transmitting device 100 as input signals. Note that the frequency bands of the input signals input to the signal transmitting device 100 are only examples. In the following, it is assumed that a signal with a frequency band of 70 to 770 MHz and a signal with a frequency band of 1000 to 2100 MHz are input to the signal transmitting device 100 as input signals. The electric signal branching unit 110 branches an input signal input from outside and outputs the branched signal to the multiplexing unit 130 and the electric signal abnormality detection unit 140. The pilot signal generating units 120-1 to 120-4 generate pilot signals with different frequencies. The pilot signal generating unit 120-1 generates a pilot signal having a frequency of, for example, about 70 MHz. The pilot signal generating unit 120-2 generates a pilot signal having a frequency of, for example, about 770 MHz. The pilot signal generating unit 120-3 generates a pilot signal having a frequency of, for example, about 1000 MHz. The pilot signal generating unit 120-4 generates a pilot signal having a frequency of, for example, about 2100 MHz.

[0005] The multiplexing unit 130 multiplexes the input signal branched by the electrical signal branching unit 110 with the pilot signals output from the pilot signal generating units 120-1 to 120-4 to generate a multiplexed signal. The multiplexing unit 130 outputs the generated multiplexed signal to the electrical signal amplifying unit 150. The electrical signal amplifying unit 150 amplifies the multiplexed signal output from the multiplexing unit 130 and outputs it to the FM batch converted signal generating unit 160.

[0006] The electrical signal abnormality detection unit 140 detects an abnormality in the power level of the input signal. The electrical signal abnormality detection unit 140 outputs a detection result indicating the presence or absence of an abnormality in the power level of the input signal to the monitoring unit 210. The FM batch converted signal generation unit 160 performs FM batch conversion on the multiplexed signal amplified by the electrical signal amplification unit 150 to generate an FM batch converted signal which is a wideband FM signal and outputs it to the electrical-optical conversion unit 170 and the monitoring unit 210. The electrical-optical conversion unit 170 converts the FM batch converted signal generated by the FM batch converted signal generation unit 160 into an optical signal and outputs it to the optical signal amplification unit 180 and the monitoring unit 210. The optical signal amplification unit 180 amplifies the optical signal output from the electrical-optical conversion unit 170 and outputs it to the optical signal branching unit 190 and the monitoring unit 210.

[0007] The optical signal branching unit 190 branches the optical signal amplified by the optical signal amplifying unit 180 and outputs the branched optical signal to the outside and to the demodulated signal abnormality detecting unit 200. The demodulated signal abnormality detecting unit 200 converts the optical signal branched by the optical signal branching unit 190 back into an electrical signal, performs FM demodulation, and then detects the state of the demodulated signal (FM batch converted signal). For example, the state detection performed by the demodulated signal abnormality detecting unit 200 is the detection of a level abnormality in a specific frequency band of the input demodulated signal. The demodulated signal abnormality detecting unit 200 outputs information on the measurement level to the monitoring unit 210.

[0008] The monitoring unit 210 detects an abnormality in each functional unit based on each signal output from the electrical signal abnormality detection unit 140, the FM batch converted signal generation unit 160, the electrical-optical conversion unit 170, the optical signal amplification unit 180, and the demodulated signal abnormality detection unit 200. For example, the monitoring unit 210 detects the following abnormalities. The monitoring unit 210 detects an abnormality in the power level of the input carrier signal based on the signal output from the electrical signal abnormality detection unit 140. Furthermore, the monitoring unit 210 detects an abnormality in the center frequency of the input FM batch converted signal based on the signal output from the FM batch converted signal generation unit 160. Furthermore, the monitoring unit 210 detects an abnormality in the optical conversion level in the electrical-optical conversion unit 170 based on the signal output from the electrical-optical conversion unit 170. Furthermore, the monitoring unit 210 detects an abnormality in the optical amplification output based on the signal output from the optical signal amplification unit 180. Furthermore, the monitoring unit 210 compares normal state signal level information stored in the memory with level information of the signal demodulated by the demodulated signal abnormality detection unit 200 to determine an abnormal state. When the monitoring unit 210 detects an abnormality, it causes the alarm processing unit 220 to output an alarm. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] “Transmission equipment for transferring multi-channel television signals over optical access networks by frequency modulation conversion” ITU-T Rec. J. 185, 2012. [Non-Patent Document 2] “Transmission equipment for multi-channel television signals over optical access networks by sub-carrier multiplexing (SCM)” ITU-T Rec. J. 186, 2008. Summary of the Invention [Problem to be solved by the invention]

[0010] As described above, in the configuration of the conventional signal transmission device, the number of pilot signal generating units increases according to the number of pilot signals. Therefore, there is a problem that the circuit scale increases according to the number of pilot signals, and the device cost also increases. Note that this problem is not limited to the signal transmission device that performs FM batch conversion shown in Figure 8, but is a problem common to all signal transmission devices that receive input signals with a wide frequency band.

[0011] In view of the above circumstances, an object of the present invention is to provide a technique capable of suppressing an increase in circuit scale and device costs. [Means for solving the problem]

[0012] One aspect of the present invention is a signal transmission device that includes a pilot signal generation unit that generates pilot signals of different frequencies as monitoring pilot signals used to detect level abnormalities in a specific frequency band in an input signal, and a control unit that causes the pilot signal generation unit to generate pilot signals of different frequencies at a predetermined period. Effect of the Invention

[0013] The present invention makes it possible to suppress an increase in circuit scale and device costs. [Brief description of the drawings]

[0014] [Figure 1] 1 is a diagram illustrating an example of the configuration of a signal transmitting device according to a first embodiment. [Diagram 2] 5 is a diagram for explaining timing control of a pilot signal in a signal transmitting device in the first embodiment. FIG. [Diagram 3] FIG. 11 is a diagram illustrating an example of the configuration of a signal transmitting device according to a second embodiment. [Figure 4] FIG. 11 is a diagram illustrating an example of the configuration of a switching unit in the second embodiment. [Diagram 5] FIG. 13 is a diagram illustrating an example of the configuration of a signal transmitting device according to a third embodiment. [Figure 6] FIG. 11 is a diagram for explaining timing control of a pilot signal in a signal transmitting device in the third embodiment. [Figure 7] FIG. 13 is a diagram illustrating an example of the configuration of a signal transmitting device according to a fourth embodiment. [Figure 8] 1 is a diagram illustrating an example of the configuration of a signal transmitting device including a plurality of pilot signal generating units. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. (First embodiment) FIG. 1 is a diagram showing an example of the configuration of a signal transmission device 10 in the first embodiment. An input signal having a wide frequency band is input from the outside to the signal transmission device 10. The input signal input from the outside may be a carrier signal obtained from a video signal, for example. The signal transmission device 10 includes an electric signal branching unit 11, a plurality of pilot signal generating units 12-1 to 12-2, a multiplexing unit 13, an electric signal abnormality detecting unit 14, an electric signal amplifying unit 15, an FM batch converted signal generating unit 16, an electric-optical converting unit 17, an optical signal amplifying unit 18, an optical signal branching unit 19, a demodulated signal abnormality detecting unit 20, a monitoring unit 21, an alarm processing unit 22, and a control unit 23. Note that dotted lines extending from some of the functional units to the monitoring unit 21 represent control signals.

[0016] The electric signal branching unit 11, the electric signal abnormality detection unit 14, the electric signal amplification unit 15, the FM batch converted signal generation unit 16, the electrical-optical conversion unit 17, the optical signal amplification unit 18, the optical signal branching unit 19, the demodulated signal abnormality detection unit 20, the monitoring unit 21, and the alarm processing unit 22 basically perform the same processing as the functional units with the same names shown in Fig. 8 (the electric signal branching unit 110, the electric signal abnormality detection unit 14, the electric signal amplification unit 150, the FM batch converted signal generation unit 160, the electrical-optical conversion unit 170, the optical signal amplification unit 180, the optical signal branching unit 190, the demodulated signal abnormality detection unit 200, the monitoring unit 210, and the alarm processing unit 220). The following mainly describes the differences.

[0017] Pilot signal generating units 12-1 to 12-2 have a function of generating pilot signals of a plurality of frequencies. The pilot signals generated by pilot signal generating units 12-1 to 12-2 are monitoring signals used to detect abnormal levels of specific frequency bands in input signals. In the following description, it is assumed that the input signals include signals in the frequency bands of 70 to 770 MHz and 1000 to 2100 MHz.

[0018] Pilot signal generating unit 12-1 generates, for example, a pilot signal having a frequency near 70 MHz and a pilot signal having a frequency near 770 MHz for detecting level abnormalities in the frequency band of 70 to 770 MHz. Pilot signal generating unit 12-2 generates, for example, a pilot signal having a frequency near 1000 MHz and a pilot signal having a frequency near 2100 MHz for detecting level abnormalities in the frequency band of 1000 to 2100 MHz. Pilot signal generating units 12-1 to 12-2 generate pilot signals of different frequencies at different timings in accordance with the control of control unit 23. Pilot signal generating units 12-1 to 12-2 only need to generate pilot signals having frequencies near the frequency of the input signal, and the frequencies of the pilot signals are not limited to the above frequencies.

[0019] The control unit 23 changes the frequency of the pilot signal generated by each pilot signal generating unit 12 at a predetermined period. For example, the control unit 23 causes the pilot signal generating unit 12-1 to generate a pilot signal with a frequency of about 70 MHz at a certain time a, causes the pilot signal generating unit 12-1 to generate a pilot signal with a frequency of about 770 MHz at a certain time b, causes the pilot signal generating unit 12-2 to generate a pilot signal with a frequency of about 1000 MHz at a certain time c, and causes the pilot signal generating unit 12-2 to generate a pilot signal with a frequency of about 2100 MHz at a certain time d. In this way, the control unit 23 controls the timing at which the pilot signal generating unit 12 generates the pilot signal, thereby causing one pilot signal generating unit 12 to generate pilot signals with a plurality of frequencies. The control unit 23 is, for example, a microcomputer or the like.

[0020] The multiplexing unit 13 multiplexes the input signal branched by the electrical signal branching unit 11 and the pilot signals output from the pilot signal generating units 12-1 to 12-2 to generate a multiplexed signal. The multiplexing unit 13 outputs the generated multiplexed signal to the electrical signal amplifying unit 15.

[0021] Fig. 2 is a diagram for explaining the timing control of the pilot signal in the signal transmitting device 10 in the first embodiment. In Fig. 2, the horizontal axis represents time t, and the vertical axis represents the operation timing of each of the pilot signal generating units 12-1 to 12-2. As shown in Fig. 2, the control unit 23 instructs the pilot signal generating unit 12-1 to generate a pilot signal of a frequency near 70 MHz at time a. As a result, the pilot signal generating unit 12-1 is in an operating state (ON state) during the period of time a, generates a pilot signal of a frequency near 70 MHz, and outputs it to the multiplexing unit 13. As a result, the multiplexing unit 13 multiplexes the input signal and the pilot signal of a frequency near 70 MHz during the period of time a.

[0022] Next, at time b, control unit 23 instructs pilot signal generating unit 12-1 to generate a pilot signal with a frequency near 770 MHz. As a result, pilot signal generating unit 12-1 stops generating pilot signals with a frequency near 70 MHz during time b, and generates and outputs pilot signals with a frequency near 770 MHz to multiplexer 13. As a result, multiplexer 13 multiplexes the input signal and the pilot signal with a frequency near 770 MHz during time b.

[0023] Next, at time c, the control unit 23 instructs the pilot signal generating unit 12-1 to stop generating the pilot signal, and instructs the pilot signal generating unit 12-2 to generate a pilot signal with a frequency near 1000 MHz. As a result, the pilot signal generating unit 12-1 is in a stopped state (OFF state) during the time c. In contrast, the pilot signal generating unit 12-2 is in an operating state (ON state) during the time c, generates a pilot signal with a frequency near 1000 MHz, and outputs it to the multiplexing unit 13. As a result, the multiplexing unit 13 multiplexes the input signal and the pilot signal with a frequency near 1000 MHz during the time c.

[0024] Next, at time d, control unit 23 instructs pilot signal generating unit 12-2 to generate a pilot signal with a frequency near 2100 MHz. As a result, pilot signal generating unit 12-2 stops generating pilot signals with a frequency near 1000 MHz during time d, generates pilot signals with a frequency near 2100 MHz, and outputs them to multiplexing unit 13. As a result, multiplexing unit 13 multiplexes the input signal and the pilot signal with a frequency near 2100 MHz during time d.

[0025] In FIG. 2, the timings of outputting the pilot signals of the four frequencies do not overlap. In contrast, the control unit 23 may cause the output timings of the pilot signals of the pilot signal generating unit 12-1 and the pilot signal generating unit 12-2 to overlap. For example, the control unit 23 instructs the pilot signal generating unit 12-1 to generate a pilot signal of a frequency near 70 MHz at time a, and instructs the pilot signal generating unit 12-2 to generate a pilot signal of a frequency near 1000 MHz. As a result, the pilot signal generating unit 12-1 becomes in an operating state (ON state) during the period of time a, generates a pilot signal of a frequency near 70 MHz, and outputs it to the multiplexing unit 13, and the pilot signal generating unit 12-2 becomes in an operating state (ON state) during the period of time a, generates a pilot signal of a frequency near 1000 MHz, and outputs it to the multiplexing unit 13. As a result, in the multiplexing section 13, during the period of time a, the input signal, the pilot signal having a frequency near 70 MHz, and the pilot signal having a frequency near 1000 MHz are multiplexed.

[0026] According to the signal transmission device 10 configured as above, the control unit 23 causes one pilot signal generating unit 12 to generate pilot signals of different frequencies at different timings, and shifts the timing of combining the pilot signals. As a result, in a specific time period, there will be a time period in which a pilot signal of a certain frequency does not exist, but if constant monitoring is not performed, the number of pilot signal generating units 12 can be reduced. In the video transmission system, the system is applied to a service with very strict monitoring conditions, but can be sufficiently applied by shortening the time interval. In this way, since one pilot signal generating unit 12 generates pilot signals of different frequencies at different timings, the increase in circuit scale corresponding to the increase in the number of pilot signals can be suppressed more than before. As a result, the device cost can also be suppressed.

[0027] Second embodiment In the second embodiment, a signal transmission device in the first embodiment will be described in which the input signal is input from a plurality of conductors. In some signal transmission devices, an electric signal amplifier is provided for each frequency band for reasons such as noise characteristics when amplifying an electric signal. This is to prevent the noise portion from being amplified by amplifying an electric signal of a wide frequency band in a single electric signal amplifier, which leads to deterioration of the video signal.

[0028] 3 is a diagram showing a configuration example of a signal transmission device 10a in the second embodiment. Input signals having a wide frequency band are input to the signal transmission device 10a from different paths. The signal transmission device 10a includes a plurality of electric signal branching units 11-1 to 11-2, a plurality of pilot signal generating units 12a-1 to 12a-2, a plurality of multiplexing units 13-1 to 13-2, an electric signal abnormality detecting unit 14, a plurality of electric signal amplifying units 15-1 to 15-2, an FM batch converted signal generating unit 16, an electric-to-optical converting unit 17, an optical signal amplifying unit 18, an optical signal branching unit 19, a demodulated signal abnormality detecting unit 20, a monitoring unit 21, an alarm processing unit 22, a plurality of control units 23a-1 to 23a-2, a switching unit 24, and a multiplexing unit 25. The dotted lines extending from some of the functional units to the monitoring unit 21 represent control signals.

[0029] The electrical signal abnormality detection unit 14, the FM batch converted signal generation unit 16, the electrical-optical conversion unit 17, the optical signal amplification unit 18, the optical signal branching unit 19, the demodulated signal abnormality detection unit 20, the monitoring unit 21, and the alarm processing unit 22 are basically the same as those in the first embodiment, and therefore their explanations are omitted. The following explanation will focus on the differences from the first embodiment.

[0030] It is assumed that a signal having a frequency band of 70 to 770 MHz is input to the electrical signal branching unit 11-1. The electrical signal branching unit 11-1 branches the input signal and outputs the branched signal to the multiplexing unit 13-1 and the electrical signal abnormality detection unit .

[0031] It is assumed that a signal having a frequency band of 1000 to 2100 MHz is input to the electrical signal branching unit 11-2. The electrical signal branching unit 11-2 branches the input signal and outputs the branched signal to the multiplexing unit 13-2 and the electrical signal abnormality detection unit .

[0032] The pilot signal generating units 12a-1 to 12a-2 have a function of generating pilot signals of multiple frequencies. The pilot signal generating unit 12a-1 generates a pilot signal of a frequency near 70 MHz, for example. The pilot signal generating unit 12a-2 generates a pilot signal of a frequency near 770 MHz, a pilot signal of a frequency near 1000 MHz, and a pilot signal of a frequency near 2100 MHz, for example. The pilot signal generating unit 12a-2 generates pilot signals of different frequencies at different timings according to the control from the control unit 23a-1 or 23a-2.

[0033] The control units 23a-1 to 23a-2 control the pilot signal generating unit 12a and the switching unit 24. For example, the control unit 23a-1 controls the pilot signal generating unit 12a, and the control unit 23a-2 controls the switching unit 24. Note that the control units 23a-1 to 23a-2 may control the pilot signal generating unit 12a and the switching unit 24 as a single control unit 23a. The control units 23a-1 to 23a-2 are, for example, microcomputers or the like.

[0034] The control unit 23a-1 changes the frequency of the pilot signal generated by the pilot signal generating unit 12a-2 at a predetermined period. For example, the control unit 23a-1 causes the pilot signal generating unit 12a-2 to generate a pilot signal with a frequency of about 770 MHz at a certain time b, causes the pilot signal generating unit 12a-2 to generate a pilot signal with a frequency of about 1000 MHz at a certain time c, and causes the pilot signal generating unit 12a-2 to generate a pilot signal with a frequency of about 2100 MHz at a certain time d. In this way, the control unit 23a-1 controls the timing at which the pilot signal generating unit 12a-2 generates the pilot signal, thereby causing one pilot signal generating unit 12a-2 to generate pilot signals with a plurality of frequencies. The control unit 23a-1 is one aspect of the first control unit. The certain times b, c, and d shown here are the times shown in FIG. 2.

[0035] The control unit 23a-2 outputs a switching instruction to the switching unit 24 to switch the output path of the pilot signal input to the switching unit 24. The switching instruction is an instruction for switching the output path of the switching unit 24, and includes, for example, information indicating the output path. For example, at a certain time b, the control unit 23a-2 switches the output path of the switching unit 24 to a path toward the multiplexer 13-1. This is because, since a pilot signal having a frequency near 770 MHz is generated in the pilot signal generating unit 12a-2 at the certain time b, the input signal (signal of 70 MHz to 770 MHz) input to the multiplexer 13-1 is multiplexed with the pilot signal having a frequency near 770 MHz generated by the pilot signal generating unit 12a-2, which is in the same frequency band as the input signal.

[0036] In response to this, the control unit 23a-2 switches the output path of the switching unit 24 to a path leading to the multiplexer 13-2 at certain times c and d. This is because, since the pilot signal generating unit 12a-2 generates a pilot signal having a frequency near 1000 MHz at certain time c and the pilot signal generating unit 12a-2 generates a pilot signal having a frequency near 2100 MHz at certain time d, the pilot signal generating unit 12a-2 generates a pilot signal having a frequency near 1000 MHz and a pilot signal having a frequency near 2100 MHz, which are in the same frequency band as the input signal (signal of 1000 MHz to 2100 MHz) input to the multiplexer 13-2, and the input signal.

[0037] When the control units 23a-1 and 23a-2 perform control in the cycle shown in Fig. 2, the control unit 23a-2 may switch the output path of the switching unit 24 to any path at a certain time a. This is because no signal is generated in the pilot signal generating unit 12a-2 at the certain time a. Note that the cycle described here is merely an example, and when the pilot signal generating unit 12a-2 generates a pilot signal at the certain time a, the control unit 23a-2 controls the switching unit 24 to switch the output path of the switching unit 24 to an appropriate path. The control unit 23a-2 is one aspect of the second control unit.

[0038] The switching unit 24 switches the path so that the input pilot signal is output from one of the paths under the control of the control unit 23a-2. For example, the switching unit 24 switches the path so that the pilot signal is output from the path instructed (instructed to switch) by the control unit 23a-2.

[0039] The multiplexing unit 13-1 generates a multiplexed signal by multiplexing the input signal (signal of 70 MHz to 770 MHz) branched by the electrical signal branching unit 11-1, the pilot signal output from the pilot signal generating unit 12a-1, and the pilot signal output from the switching unit 24. The multiplexing unit 13-1 outputs the generated multiplexed signal to the electrical signal amplifying unit 15-1.

[0040] The multiplexing unit 13-2 generates a multiplexed signal by multiplexing the input signal (signal of 1000 MHz to 2100 MHz) branched by the electrical signal branching unit 11-2, the pilot signal output from the pilot signal generating unit 12a-2, and the pilot signal output from the switching unit 24. The multiplexing unit 13-2 outputs the generated multiplexed signal to the electrical signal amplifying unit 15-2.

[0041] The electrical signal amplifier 15-1 amplifies the multiplexed signal output from the multiplexer 13-1 and outputs the signal to the multiplexer 25. The electrical signal amplifier 15-2 amplifies the multiplexed signal output from the multiplexer 13-2 and outputs the signal to the multiplexer 25. The multiplexer 25 multiplexes the amplified multiplexed signals output from the electrical signal amplifiers 15-1 to 15-2. The multiplexer 25 outputs the multiplexed signal to the FM batch converted signal generator 16.

[0042] Fig. 4 is a diagram showing an example of the configuration of the switching unit 24 in the second embodiment. As shown in Fig. 4, the switching unit 24 includes a switch unit 241. The switch unit 241 is composed of a first terminal 242, a second terminal 243, and a third terminal 244. The switch unit 241 connects the first terminal 242 and the second terminal 243, or connects the first terminal 242 and the third terminal 244, in response to a switching instruction from the control unit 23a-2. This switches the output path of the pilot signal output from the pilot signal generating unit 12a-2.

[0043] The signal transmitting device 10a configured as above includes a switching unit 24 that switches the output path of a pilot signal generated by the pilot signal generating unit 12a (for example, the pilot signal generating unit 12a-2). In this way, when input signals of different frequency bands are input to the signal transmitting device 10a from different paths and an electric signal amplifying unit 15 is provided on each path, the control unit 23a switches the output path of the pilot signal to be multiplexed with the input signal input to each path at a predetermined period. Therefore, pilot signals of different frequencies generated by one pilot signal generating unit 12 can be distributed to each path. This makes it possible to reduce the number of pilot signal generating units 12a, and to suppress an increase in circuit scale corresponding to an increase in the number of pilot signals more than in the past. As a result, the device cost can also be suppressed.

[0044] (Third embodiment) In the third embodiment, a signal transmitting device is described that generates a pilot signal of a frequency between two frequency bands used for a pilot signal when the interval between the two frequency bands is close. Here, when the interval between the two frequency bands is close, it means that the interval between the two frequency bands is less than a threshold value.

[0045] 5 is a diagram showing a configuration example of a signal transmitting device 10b in the third embodiment. An input signal having a wide frequency band is input from the outside to the signal transmitting device 10b. The signal transmitting device 10b includes an electric signal branching unit 11, a plurality of pilot signal generating units 12b-1 to 12b-2, a multiplexing unit 13, an electric signal abnormality detecting unit 14, an electric signal amplifying unit 15, an FM batch converted signal generating unit 16, an electric-optical converting unit 17, an optical signal amplifying unit 18, an optical signal branching unit 19, a demodulated signal abnormality detecting unit 20, a monitoring unit 21, an alarm processing unit 22, and a control unit 23b. Note that dotted lines extending from some of the functional units to the monitoring unit 21 represent control signals.

[0046] The electrical signal branching unit 11, the multiplexing unit 13, the electrical signal abnormality detection unit 14, the electrical signal amplification unit 15, the FM batch converted signal generation unit 16, the electrical-optical conversion unit 17, the optical signal amplification unit 18, the optical signal branching unit 19, the demodulated signal abnormality detection unit 20, the monitoring unit 21, and the alarm processing unit 22 are basically the same as those in the first embodiment, and therefore their explanations are omitted. The following explanation will focus on the differences from the first embodiment.

[0047] The pilot signal generating units 12b-1 to 12b-2 have a function of generating pilot signals of a plurality of frequencies. The pilot signal generating unit 12b-1 generates a pilot signal of a frequency near 70 MHz, for example. The pilot signal generating unit 12b-2 generates a pilot signal of a frequency near 885 MHz and a pilot signal of a frequency near 2100 MHz, for example. In this manner, the pilot signal generating unit 12b-2 generates a pilot signal of a frequency in a frequency band between two frequency bands (in FIG. 5, a frequency band of 70 MHz to 770 MHz and a frequency band of 1000 MHz to 2100 MHz) in response to an instruction from the control unit 23b. The pilot signal generating units 12b-1 to 12b-2 generate pilot signals of different frequencies at different timings in accordance with the control from the control unit 23b. The pilot signal generating units 12b-1 to 12b-2 only need to generate pilot signals having frequencies near the frequency of the input signal, and the frequencies of the pilot signals are not limited to the above frequencies.

[0048] The control unit 23b changes the frequency of the pilot signal generated by each pilot signal generating unit 12b at a predetermined period. For example, the control unit 23b causes the pilot signal generating unit 12b-1 to generate a pilot signal with a frequency of about 70 MHz at a certain time a, causes the pilot signal generating unit 12b-2 to generate a pilot signal with a frequency of about 885 MHz at a certain time b, and causes the pilot signal generating unit 12b-2 to generate a pilot signal with a frequency of about 2100 MHz at a certain time c. In this way, the control unit 23b controls the timing at which the pilot signal generating unit 12b generates the pilot signal, thereby causing one pilot signal generating unit 12b to generate pilot signals with multiple frequencies. The control unit 23b is, for example, a microcomputer or the like.

[0049] Fig. 6 is a diagram for explaining the timing control of the pilot signal in the signal transmitting device 10b in the third embodiment. In Fig. 6, the horizontal axis represents time t, and the vertical axis represents the operation timing of each of the pilot signal generating units 12b-1 to 12b-2. As shown in Fig. 6, the control unit 23b instructs the pilot signal generating unit 12b-1 to generate a pilot signal of a frequency near 70 MHz at time a. As a result, the pilot signal generating unit 12b-1 is in an operating state (ON state) during the period of time a, generates a pilot signal of a frequency near 70 MHz, and outputs it to the multiplexing unit 13. As a result, the multiplexing unit 13 multiplexes the input signal and the pilot signal of a frequency near 70 MHz during the period of time a.

[0050] Next, at time b, the control unit 23b instructs the pilot signal generating unit 12b-1 to stop generating the pilot signal and instructs the pilot signal generating unit 12b-2 to generate a pilot signal with a frequency near 885 MHz. As a result, the pilot signal generating unit 12b-1 is in a stopped state (OFF state) during time b. In contrast, the pilot signal generating unit 12b-2 is in an operating state (ON state) during time b, generates a pilot signal with a frequency near 885 MHz, and outputs it to the multiplexing unit 13. As a result, the multiplexing unit 13 multiplexes the input signal and the pilot signal with a frequency near 885 MHz during time b.

[0051] Next, at time c, the control unit 23b instructs the pilot signal generating unit 12b-2 to generate a pilot signal with a frequency near 2100 MHz. As a result, during time c, the pilot signal generating unit 12b-2 stops generating a pilot signal with a frequency near 885 MHz, generates a pilot signal with a frequency near 2100 MHz, and outputs it to the multiplexing unit 13. As a result, during time c, the multiplexing unit 13 multiplexes the input signal and the pilot signal with a frequency near 2100 MHz.

[0052] In FIG. 6, the timings of outputting the pilot signals of the three frequencies do not overlap. In contrast, the control unit 23b may cause the output timings of the pilot signals of the pilot signal generating unit 12b-1 and the pilot signal generating unit 12b-2 to overlap. For example, the control unit 23b instructs the pilot signal generating unit 12b-1 to generate a pilot signal of a frequency near 70 MHz at time a, and instructs the pilot signal generating unit 12b-2 to generate a pilot signal of a frequency near 885 MHz. As a result, the pilot signal generating unit 12b-1 becomes in an operating state (ON state) during the period of time a, generates a pilot signal of a frequency near 70 MHz, and outputs it to the multiplexing unit 13, and the pilot signal generating unit 12b-2 becomes in an operating state (ON state) during the period of time a, generates a pilot signal of a frequency near 885 MHz, and outputs it to the multiplexing unit 13. As a result, in the multiplexing section 13, during the period of time a, the input signal, the pilot signal having a frequency near 70 MHz, and the pilot signal having a frequency near 885 MHz are multiplexed.

[0053] 6, the control unit 23b has the pilot signal generating unit 12b-2 generate a pilot signal having a frequency of about 885 MHz, which is an intermediate frequency between two frequency bands included in the input signal, but the control unit 23b may generate a pilot signal having a frequency other than the intermediate frequency between two frequency bands included in the input signal. For example, since the 800 MHz band is already used for mobile phone transmission, if the transmission system is shared, it may be possible to generate a pilot signal having a frequency of about 950 MHz, which is an intermediate frequency between 900 MHz and 1000 MHz.

[0054] According to the signal transmitting device 10b configured as above, it is possible to obtain the same effect as the first embodiment. Furthermore, in the signal transmitting device 10b, when the interval between two frequency bands is close, a pilot signal of a frequency between the two frequency bands is generated. This allows one pilot signal generating unit 12b to generate multiple pilot signals. This allows the number of pilot signal generating units 12b to be reduced, and the increase in circuit scale in accordance with the increase in the number of pilot signals can be suppressed more than in the past. As a result, the device cost can also be suppressed.

[0055] (Fourth embodiment) In the fourth embodiment, a signal transmitting device in the third embodiment will be described in which the input signal is input from a plurality of conductors.

[0056] 7 is a diagram showing a configuration example of a signal transmission device 10c in the fourth embodiment. Input signals having a wide frequency band are input to the signal transmission device 10c from different paths. The signal transmission device 10c includes a plurality of electric signal branching units 11-1 to 11-2, a plurality of pilot signal generating units 12c-1 to 12c-2, a plurality of multiplexing units 13-1 to 13-2, an electric signal abnormality detecting unit 14, a plurality of electric signal amplifying units 15-1 to 15-2, an FM batch converted signal generating unit 16, an electric-optical converting unit 17, an optical signal amplifying unit 18, an optical signal branching unit 19, a demodulated signal abnormality detecting unit 20, a monitoring unit 21, an alarm processing unit 22, a plurality of control units 23c-1 to 23c-2, a switching unit 24, and a multiplexing unit 25. The dotted lines extending from some of the functional units to the monitoring unit 21 represent control signals.

[0057] The electrical signal abnormality detection unit 14, the FM batch converted signal generation unit 16, the electrical-optical conversion unit 17, the optical signal amplification unit 18, the optical signal branching unit 19, the demodulated signal abnormality detection unit 20, the monitoring unit 21, and the alarm processing unit 22 are basically the same as those in the third embodiment, and therefore their explanations are omitted. The following explanation will focus on the differences from the third embodiment.

[0058] It is assumed that a signal having a frequency band of 70 to 770 MHz is input to the electrical signal branching unit 11-1. The electrical signal branching unit 11-1 branches the input signal and outputs the branched signal to the multiplexing unit 13-1 and the electrical signal abnormality detection unit .

[0059] It is assumed that a signal having a frequency band of 1000 to 2100 MHz is input to the electrical signal branching unit 11-2. The electrical signal branching unit 11-2 branches the input signal and outputs the branched signal to the multiplexing unit 13-2 and the electrical signal abnormality detection unit .

[0060] The pilot signal generating units 12c-1 to 12c-2 have a function of generating pilot signals of multiple frequencies. The pilot signal generating unit 12c-1 generates a pilot signal of a frequency near 70 MHz, for example. The pilot signal generating unit 12c-2 generates a pilot signal of a frequency near 885 MHz and a pilot signal of a frequency near 2100 MHz, for example. The pilot signal generating unit 12c-2 generates pilot signals of different frequencies at different timings according to the control from the control unit 23c-1 or 23c-2.

[0061] The control units 23c-1 to 23c-2 control the pilot signal generating unit 12c and the switching unit 24. For example, the control unit 23c-1 controls the pilot signal generating unit 12c, and the control unit 23c-2 controls the switching unit 24. Note that the control units 23c-1 to 23c-2 may control the pilot signal generating unit 12c and the switching unit 24 as one control unit 23c. The control units 23c-1 to 23c-2 are, for example, microcomputers or the like.

[0062] The control unit 23c-1 changes the frequency of the pilot signal generated by the pilot signal generating unit 12c-2 at a predetermined period. For example, the control unit 23c-1 causes the pilot signal generating unit 12c-2 to generate a pilot signal with a frequency of about 885 MHz at a certain time b, and causes the pilot signal generating unit 12c-2 to generate a pilot signal with a frequency of about 2100 MHz at a certain time c. In this manner, the control unit 23c-1 controls the timing at which the pilot signal generating unit 12c-2 generates the pilot signal, thereby causing one pilot signal generating unit 12c-2 to generate pilot signals with a plurality of frequencies. The control unit 23c-1 is, for example, a microcomputer. The certain times b and c shown here are times shown in FIG. 6. The control unit 23c-1 is one aspect of the first control unit.

[0063] The control unit 23c-2 outputs a switching instruction to the switching unit 24 to switch the output path of the pilot signal input to the switching unit 24. The control unit 23c-2 switches the output path of the switching unit 24 to a path toward the multiplexing unit 13-1 or the multiplexing unit 13-2 at a certain time b, for example. For example, the control unit 23c-2 switches the output path of the switching unit 24 to a path toward the output destination of the electric signal amplifier 15-1 or the electric signal amplifier 15-2 where a required gain can be obtained at a certain time b, for example. This is because, at a certain time b, the pilot signal generating unit 12c-2 generates a pilot signal with a frequency near 885 MHz, and 885 MHz is an intermediate frequency between the frequency band of the input signal (signal of 70 MHz to 770 MHz) input to the multiplexing unit 13-1 and the frequency band of the input signal (signal of 1000 MHz to 2100 MHz) input to the multiplexing unit 13-2, and there is no frequency band that is the same as 885 MHz. Therefore, it is more appropriate to select an output destination with a slightly higher gain as the output path.

[0064] In response to this, the control unit 23c-2 switches the output path of the switching unit 24 to a path leading to the multiplexer 13-2 at a certain time c. This is because, since a pilot signal with a frequency near 2100 MHz is generated in the pilot signal generating unit 12c-2 at the certain time c, the pilot signal with a frequency near 1000 MHz and the pilot signal with a frequency near 2100 MHz generated by the pilot signal generating unit 12c-2, which are in the same frequency band as the input signal (signal of 1000 MHz to 2100 MHz) input to the multiplexer 13-2, are multiplexed with the input signal.

[0065] When the control units 23c-1 and 23c-2 perform control in the cycle shown in Fig. 2, the control unit 23c-2 may switch the output path of the switching unit 24 to any path at a certain time a. This is because no signal is generated in the pilot signal generating unit 12c-2 at the certain time a. Note that the cycle described here is merely an example, and when the pilot signal generating unit 12c-2 generates a pilot signal at the certain time a, the control unit 23c-2 controls the switching unit 24 to switch the output path of the switching unit 24 to an appropriate path. The control unit 23c-2 is one aspect of the second control unit.

[0066] The switching unit 24 switches the path so that the input pilot signal is output from one of the paths under the control of the control unit 23c-2. The switching unit 24 switches the path so that the pilot signal is output from the path instructed (switching instruction) from the control unit 23c-2, for example. The internal configuration of the switching unit 24 is similar to the configuration described in the second embodiment (for example, see FIG. 4).

[0067] The multiplexing unit 13-1 generates a multiplexed signal by multiplexing the input signal (signal of 70 MHz to 770 MHz) branched by the electrical signal branching unit 11-1, the pilot signal output from the pilot signal generating unit 12a-1, and the pilot signal output from the switching unit 24. The multiplexing unit 13-1 outputs the generated multiplexed signal to the electrical signal amplifying unit 15-1.

[0068] The multiplexing unit 13-2 generates a multiplexed signal by multiplexing the input signal (signal of 1000 MHz to 2100 MHz) branched by the electrical signal branching unit 11-2, the pilot signal output from the pilot signal generating unit 12a-2, and the pilot signal output from the switching unit 24. The multiplexing unit 13-2 outputs the generated multiplexed signal to the electrical signal amplifying unit 15-2.

[0069] The electrical signal amplifier 15-1 amplifies the multiplexed signal output from the multiplexer 13-1 and outputs the signal to the multiplexer 25. The electrical signal amplifier 15-2 amplifies the multiplexed signal output from the multiplexer 13-2 and outputs the signal to the multiplexer 25. The multiplexer 25 multiplexes the amplified multiplexed signals output from the electrical signal amplifiers 15-1 to 15-2. The multiplexer 25 outputs the multiplexed signal to the FM batch converted signal generator 16.

[0070] According to the signal transmitting device 10c configured as above, it is possible to obtain the same effect as the second embodiment. Furthermore, in the signal transmitting device 10c, when the interval between two frequency bands is close, a pilot signal of a frequency between the two frequency bands is generated. This allows one pilot signal generating unit 12c to generate multiple pilot signals. This allows the number of pilot signal generating units 12c to be reduced, and the increase in circuit scale in accordance with the increase in the number of pilot signals can be suppressed more than in the past. As a result, the device cost can also be suppressed.

[0071] (Modification 1 common to the first to fourth embodiments) The signal transmission devices 10, 10a, 10b, and 10c in the above-described embodiments are configured to perform FM batch conversion and conversion to optical signals, but the signal transmission devices 10, 10a, 10b, and 10c may be signal transmission devices that transmit electric signals. When configured in this way, the signal transmission device 10 in the first embodiment may be configured as a signal transmission device including an electric signal branching unit 11, pilot signal generating units 12-1 to 12-2, a multiplexing unit 13, an electric signal abnormality detection unit 14, an electric signal amplifying unit 15, a demodulated signal abnormality detection unit 20, a monitoring unit 21, and an alarm processing unit 22. The electric signal amplifying unit 15 amplifies the multiplexed signal output from the multiplexing unit 13 and outputs it to the demodulated signal abnormality detection unit 20.

[0072] In addition, when the multiplexed signal output from the electrical signal amplifier 15 is output to the outside, the signal transmitter 10 may include an electrical signal branching unit instead of the optical signal branching unit 19. The electrical signal branching unit branches the input multiplexed signal and outputs it to the outside and to the demodulated signal abnormality detection unit 20. The demodulated signal abnormality detection unit 20 inputs the multiplexed signal directly from the electrical signal amplifier 15 or branched by the electrical signal branching unit. The demodulated signal abnormality detection unit 20 performs state detection using the input multiplexed signal. In this case, the demodulated signal abnormality detection unit 20 does not need to convert the optical signal to an electrical signal or perform FM demodulation.

[0073] The signal transmission device 10a in the second embodiment may be configured as a signal transmission device including a plurality of electric signal branching units 11-1 to 11-2, a plurality of pilot signal generating units 12a-1 to 12a-2, a plurality of multiplexing units 13-1 to 13-2, an electric signal abnormality detecting unit 14, a plurality of electric signal amplifying units 15-1 to 15-2, a demodulated signal abnormality detecting unit 20, a monitoring unit 21, an alarm processing unit 22, a plurality of control units 23a-1 to 23a-2, a switching unit 24, and a multiplexing unit 25. The multiplexing unit 25 outputs the multiplexed signal to the demodulated signal abnormality detecting unit 20.

[0074] In addition, when the multiplexed signal output from the multiplexing unit 25 is output to the outside, the signal transmitting device 10a may include an electric signal branching unit instead of the optical signal branching unit 19. The electric signal branching unit branches the input multiplexed signal and outputs it to the outside and the demodulated signal abnormality detection unit 20. The demodulated signal abnormality detection unit 20 inputs the multiplexed signal directly from the multiplexing unit 25 or branched by the electric signal branching unit. The demodulated signal abnormality detection unit 20 performs state detection using the input multiplexed signal. In this case, the demodulated signal abnormality detection unit 20 does not need to convert the optical signal to an electric signal and does not need to perform FM demodulation.

[0075] The signal transmission device 10b in the third embodiment may be configured as a signal transmission device including an electric signal branching unit 11, a plurality of pilot signal generating units 12b-1 to 12b-2, a multiplexing unit 13, an electric signal abnormality detecting unit 14, an electric signal amplifying unit 15, a demodulated signal abnormality detecting unit 20, a monitoring unit 21, an alarm processing unit 22, and a control unit 23b. The electric signal amplifying unit 15 amplifies the multiplexed signal output from the multiplexing unit 13 and outputs the amplified signal to the demodulated signal abnormality detecting unit 20.

[0076] In addition, when the multiplexed signal output from the multiplexing unit 13 is output to the outside, the signal transmitting device 10b may include an electrical signal branching unit instead of the optical signal branching unit 19. The electrical signal branching unit branches the input multiplexed signal and outputs it to the outside and to the demodulated signal abnormality detection unit 20. The demodulated signal abnormality detection unit 20 inputs the multiplexed signal directly from the multiplexing unit 13 or branched by the electrical signal branching unit. The demodulated signal abnormality detection unit 20 performs state detection using the input multiplexed signal. In this case, the demodulated signal abnormality detection unit 20 does not need to convert the optical signal to an electrical signal or perform FM demodulation.

[0077] The signal transmission device 10c in the fourth embodiment may be configured as a signal transmission device including a plurality of electric signal branching units 11-1 to 11-2, a plurality of pilot signal generating units 12c-1 to 12c-2, a plurality of multiplexing units 13-1 to 13-2, an electric signal abnormality detecting unit 14, a plurality of electric signal amplifying units 15-1 to 15-2, a demodulated signal abnormality detecting unit 20, a monitoring unit 21, an alarm processing unit 22, a plurality of control units 23c-1 to 23c-2, a switching unit 24, and a multiplexing unit 25. The multiplexing unit 25 outputs the multiplexed signal to the demodulated signal abnormality detecting unit 20.

[0078] In addition, when the multiplexed signal output from the multiplexing unit 25 is output to the outside, the signal transmitting device 10c may include an electric signal branching unit instead of the optical signal branching unit 19. The electric signal branching unit branches the input multiplexed signal and outputs it to the outside and the demodulated signal abnormality detection unit 20. The demodulated signal abnormality detection unit 20 inputs the multiplexed signal directly from the multiplexing unit 25 or branched by the electric signal branching unit. The demodulated signal abnormality detection unit 20 performs state detection using the input multiplexed signal. In this case, the demodulated signal abnormality detection unit 20 does not need to convert the optical signal to an electric signal and does not need to perform FM demodulation.

[0079] (Modification 2 common to the first to fourth embodiments) The signal transmission devices 10, 10a, 10b, and 10c in the above-described embodiments are configured to perform FM batch conversion, but the signal transmission devices 10, 10a, 10b, and 10c may be signal transmission devices that do not perform FM batch conversion. When configured in this way, the signal transmission device 10 in the first embodiment may be configured as a signal transmission device including an electric signal branching unit 11, a plurality of pilot signal generating units 12-1 to 12-2, a multiplexing unit 13, an electric signal abnormality detecting unit 14, an electric signal amplifying unit 15, an electric-to-optical converting unit 17, an optical signal amplifying unit 18, an optical signal branching unit 19, a demodulated signal abnormality detecting unit 20, a monitoring unit 21, an alarm processing unit 22, and a control unit 23. The electric signal amplifying unit 15 amplifies the multiplexed signal output from the multiplexing unit 13 and outputs it to the electric-to-optical converting unit 17. The electrical-optical converter 17 converts the multiplexed signal amplified by the electrical signal amplifier 15 into an optical signal and outputs it to the optical signal amplifier 18 and the monitor 21. When the signal transmitter 10 does not perform FM batch conversion, the demodulated signal abnormality detector 20 does not need to perform FM demodulation.

[0080] The signal transmission device 10a in the second embodiment may be configured as a signal transmission device including a plurality of electric signal branching units 11-1 to 11-2, a plurality of pilot signal generating units 12a-1 to 12a-2, a plurality of multiplexing units 13-1 to 13-2, an electric signal abnormality detection unit 14, a plurality of electric signal amplifying units 15-1 to 15-2, an electric-to-optical conversion unit 17, an optical signal amplifying unit 18, an optical signal branching unit 19, a demodulated signal abnormality detection unit 20, a monitoring unit 21, an alarm processing unit 22, a plurality of control units 23a-1 to 23a-2, a switching unit 24, and a multiplexing unit 25. The multiplexing unit 25 outputs the multiplexed signal to the electric-to-optical conversion unit 17. The electric-to-optical conversion unit 17 converts the multiplexed signal output from the multiplexing unit 25 into an optical signal and outputs it to the optical signal amplifying unit 18 and the monitoring unit 21. If the signal transmitting device 10a does not perform FM batch conversion, the demodulated signal abnormality detecting unit 20 does not need to perform FM demodulation.

[0081] The signal transmission device 10b in the third embodiment may be configured as a signal transmission device including an electric signal branching unit 11, a plurality of pilot signal generating units 12b-1 to 12b-2, a multiplexing unit 13, an electric signal abnormality detecting unit 14, an electric signal amplifying unit 15, an electric-to-optical converting unit 17, an optical signal amplifying unit 18, an optical signal branching unit 19, a demodulated signal abnormality detecting unit 20, a monitoring unit 21, an alarm processing unit 22, and a control unit 23b. The electric signal amplifying unit 15 amplifies the multiplexed signal output from the multiplexing unit 13 and outputs it to the electric-to-optical converting unit 17. The electric-to-optical converting unit 17 converts the multiplexed signal amplified by the electric signal amplifying unit 15 into an optical signal and outputs it to the optical signal amplifying unit 18 and the monitoring unit 21. If the signal transmission device 10b does not perform FM batch conversion, the demodulated signal abnormality detecting unit 20 does not need to perform FM demodulation.

[0082] The signal transmission device 10c in the fourth embodiment may be configured as a signal transmission device including a plurality of electric signal branching units 11-1 to 11-2, a plurality of pilot signal generating units 12c-1 to 12c-2, a plurality of multiplexing units 13-1 to 13-2, an electric signal abnormality detection unit 14, a plurality of electric signal amplifying units 15-1 to 15-2, an electric-to-optical conversion unit 17, an optical signal amplifying unit 18, an optical signal branching unit 19, a demodulated signal abnormality detection unit 20, a monitoring unit 21, an alarm processing unit 22, a plurality of control units 23c-1 to 23c-2, a switching unit 24, and a multiplexing unit 25. The multiplexing unit 25 outputs the multiplexed signal to the electric-to-optical conversion unit 17. The electric-to-optical conversion unit 17 converts the multiplexed signal output from the multiplexing unit 25 into an optical signal and outputs it to the optical signal amplifying unit 18 and the monitoring unit 21. If the signal transmitting device 10c does not perform FM batch conversion, the demodulated signal abnormality detecting unit 20 does not need to perform FM demodulation.

[0083] The signal transmitting devices 10, 10a, 10b, and 10c in the above-described embodiments may be realized by a computer. In this case, a program for realizing the functions may be recorded in a computer-readable recording medium, and the program recorded in the recording medium may be read into a computer system and executed to realize the functions. Note that the term "computer system" here includes hardware such as an OS (Operating System) and peripheral devices. Also, the term "computer-readable recording medium" refers to portable media such as a flexible disk, a magneto-optical disk, a ROM (Read Only Memory), and a CD-ROM, and a storage device such as a hard disk built into a computer system.

[0084] Furthermore, the term "computer-readable recording medium" may include a medium that dynamically holds a program for a short period of time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, and a medium that holds a program for a certain period of time, such as a volatile memory inside a computer system that serves as a server or client in such a case. The above program may be one for implementing part of the above-mentioned functions, or may be one that can realize the above-mentioned functions in combination with a program already recorded in the computer system, or may be one that is realized using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0085] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and designs that do not deviate from the gist of the present invention are also included. [Explanation of symbols]

[0086] 10, 10a, 10b, 10c...signal transmission device, 11, 11-1 to 11-2...electrical signal branching section, 12, 12a-1 to 12a-2, 12b-1 to 12b-2, 12c-1 to 12c-2...pilot signal generating section, 13, 13-1 to 13-2...combining section, 14...electrical signal abnormality detecting section, 15, 15-1 to 15-2...electrical signal amplifying section, 16...FM batch converted signal generating section, 17...electrical-optical converting section, 18...optical signal amplifying section, 19...optical signal branching section, 20...demodulated signal abnormality detecting section, 21...monitoring section, 22...alarm processing section, 23, 23a-1 to 23a-2, 23b, 23c-1 to 23c-2...control section, 24...switching section, 25...combining section, 241...switch section, 242...first terminal, 243...second terminal, 244...third terminal

Claims

1. a pilot signal generating unit that generates pilot signals of different frequencies as monitoring pilot signals used for detecting a level abnormality in a specific frequency band of an input signal; a control unit that causes the pilot signal generating unit to generate pilot signals of different frequencies at a predetermined cycle; A signal transmitting device comprising:

2. A switching unit that switches an output path of the pilot signal generated by the pilot signal generating unit, When a plurality of input signals having different frequency bands are input as the input signal through different paths, the control unit controls the switching unit to switch an output path of the pilot signal generated by the pilot signal generating unit at a predetermined period.

2. A signal transmitting device according to claim 1.

3. a multiplexing unit that multiplexes the input signal and a pilot signal generated by the pilot signal generating unit; A conversion unit further includes a conversion unit that converts the signal multiplexed by the multiplexing unit into an optical signal by optical modulation.

3. A signal transmitting device according to claim 1 or 2.

4. a multiplexing unit that multiplexes the input signal and a pilot signal generated by the pilot signal generating unit; and an FM batch conversion unit that performs FM (Frequency Modulation) batch conversion on the signal multiplexed by the multiplexing unit to generate an FM batch converted signal.

3. A signal transmitting device according to claim 1 or 2.

5. the input signal includes a signal in a first frequency band and a signal in a second frequency band; When an interval between the first frequency band and the second frequency band is less than a threshold, the control unit causes the pilot signal generation unit to generate a pilot signal of a frequency between the first frequency band and the second frequency band.

3. A signal transmitting device according to claim 1 or 2.

6. The control unit includes a first control unit that controls the pilot signal generation unit and a second control unit that controls the switching unit.

3. A signal transmitting device according to claim 2.

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