communication systems

Abstract

To automatically confirm soundness of a voice communication path for call of a communication system.SOLUTION: In a mechanism for confirming soundness of a voice communication path for call configured by connecting a command console 10 to a mobile station 70 via a central control apparatus 30 and a base station 50, the command console 10 includes a tone generation unit 15 which generates a tone signal to be transmitted toward the mobile station (downlink) and a tone detection unit 16 for detecting the tone signal, and the central control apparatus 30 includes a path diagnosis control unit 41 which controls forming and releasing a loop path for turning back the tone signal transmitted from the tone generation unit 15 toward the command console (uplink) in the middle of the voice communication path. On the basis of a result of the tone detection unit 16 detecting the tone signal turned back by the loop path, the soundness of the voice communication path can be confirmed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a communication system having a voice communication path for calls connecting a command console and a mobile station via a central control unit and a base station. [Background technology]

[0002] In the past, in communication systems with voice communication paths (voice lines) connecting a command console and mobile stations via a central control unit and base stations, the integrity of the voice lines was checked manually. Specifically, when a malfunction occurred in the communication system, a tone signal was input from any point on the voice line using a measuring instrument, and the tone signal loop position was manually changed to detect the tone signal, thereby narrowing down the malfunctioning area. In addition, when the communication system was installed or during periodic inspections, all paths of the voice lines were inspected, which required a great deal of work depending on the number of command consoles and base stations.

[0003] The following are examples of prior art related to the present invention: For example, Patent Document 1 discloses an invention in which a command is issued to a network control device to close a specified telephone line, and a test of a speech path through the telephone line is performed by determining whether or not a dial tone signal is received from the telephone line. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3037718 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above-mentioned conventional circumstances, and has as its object to automatically check the soundness of a voice communication path for calls that a communication system has. [Means for solving the problem]

[0006] In order to achieve the above object, a communication system according to one aspect of the present invention is configured as follows. That is, in a communication system having a voice communication path for calls connecting a command console and a mobile station via a central control device and a base station, the system is equipped with a tone generation unit that generates a tone signal and sends it to the command console side or the mobile station side, a tone detection unit that detects the tone signal, and a path control unit that controls the formation and release of a loop path that returns the tone signal sent from the tone generation unit midway through the voice communication path, and the soundness of the voice communication path is confirmed based on the detection result by the tone detection unit of the tone signal returned by the loop path.

[0007] Here, the route control unit may be capable of forming loop routes at a plurality of positions on the voice communication route, and may be configured to repeatedly send and detect tone signals while changing the position at which the loop route is formed. In this case, the route control unit may be configured to form the loop route in order of proximity to the command console.

[0008] The tone generating unit may generate and transmit tone signals while switching frequencies, and narrow down the fault conditions in the voice communication path based on the detection results of the tone signals of each frequency by the tone detecting unit.

[0009] In addition, the tone detection unit may be capable of detecting signals of frequencies different from the frequency of the tone signal, and the soundness of the voice communication path may be confirmed by further taking into consideration the detection results of the signals of different frequencies by the tone detection unit.

[0010] The central control device may also determine whether or not there is a period of no communication between the command console and the mobile station, and if it determines that there is a period of no communication, start checking the soundness of the voice communication path.

[0011] The tone generator and tone detector may be included in the command console or in the central control unit. [Effects of the Invention]

[0012] According to the present invention, it is possible to automatically check the soundness of a voice communication path for calls that a communication system has. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram illustrating an example of the configuration of a communication system according to an embodiment of the present invention. [Figure 2] 2 is a diagram illustrating an example of the configuration of a tone generation unit in the communication system of FIG. 1. [Figure 3] 2 is a diagram illustrating an example of the configuration of a tone detection unit in the communication system of FIG. 1. [Figure 4A] 1. FIG. 4 is a diagram showing an example of a voice health confirmation sequence in the communication system of FIG. [Figure 4B] 1. FIG. 4 is a diagram showing the continuation of the voice soundness confirmation sequence in the communication system of FIG. [Figure 5] FIG. 2 is a diagram illustrating an example of an extension of the communication system of FIG. [Figure 6] FIG. 10 is a diagram illustrating an example of the configuration of a communication system according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] A communication system according to an embodiment of the present invention will be described with reference to the drawings. 1 shows an example of the configuration of a communication system according to one embodiment of the present invention. The communication system of this example is generally composed of a command console 10, a central control unit 30, a base station 50, and a mobile station 70.

[0015] The command console 10 is a terminal device installed at a specific location (e.g., a monitoring room) within the communication system. The central control device 30 is a device that connects the command console 10 to the base stations 50 and performs line control and other operations to provide overall control of the entire communication system. The base stations 50 are wireless communication facilities installed on the ground as relay points for calls between the command console 10 and mobile stations 70. The mobile stations 70 are mobile wireless terminal devices that provide calls to the command console 10 via wireless communication with the base stations 50 at any location within the wireless communication area covered by the base stations 50.

[0016] This communication system has a voice communication path (voice line) for calls that connects the command console 10 and the mobile station 70 via the central control device 30 and the base station 50. Hereinafter, the voice communication path in the downlink direction from the command console 10 to the mobile station 70 will be referred to as the downlink path, and the voice communication path in the reverse uplink direction will be referred to as the uplink path. Also, for the sake of simplicity, FIG. 1 shows only one base station 50 and one mobile station 70, but generally there are multiple of these. Depending on the communication system, there may also be multiple command consoles 10.

[0017] The command console 10 has an A / D conversion unit 11, a buffer unit 12, a buffer unit 13, an A / D conversion unit 14, a tone generation unit 21, and a tone detection unit 22. The A / D conversion unit 11 converts the call voice input to the microphone of the command console 10 from an analog signal to a digital signal and sends it out on a downlink path to be transmitted to the mobile station 70. The A / D conversion unit 14 converts the call voice transmitted from the mobile station 70 via an uplink path from a digital signal to an analog signal and outputs it as a loudspeaker from the speaker of the command console 10. The buffer unit 12 is arranged near the interface with the central control device 30 on the downlink path. The buffer unit 13 is arranged near the interface with the central control device 30 on the uplink path. The tone generation unit 21 generates a tone signal and outputs it on the downlink path. The tone detection unit 22 detects the tone signal from the uplink path.

[0018] The central control device 30 includes a buffer unit 31, an encoder unit 32, a buffer unit 33, an IP unit 34, a buffer unit 35, a decoder unit 36, a buffer unit 37, and a route diagnosis control unit 41. The encoder unit 32 encodes downstream communication voice signals received from the command console 10 using a predetermined encoding method. The decoder unit 36 ​​decodes upstream communication voice signals received from the base station 50 using a decoding method corresponding to the encoding method. The IP unit 34 is a communication unit that performs IP communication with the base station 50. The buffer unit 31 is located near the interface with the command console 10 on the downstream path. The buffer unit 33 is located between the encoder unit 32 and the IP unit 34 on the downstream path. The buffer unit 35 is located between the IP unit 34 and the decoder unit 36 ​​on the upstream path. The buffer unit 37 is located near the interface with the command console 10 on the upstream path. The route diagnosis control unit 41 performs overall control of the voice health check sequence described below to check the health of the voice communication path.

[0019] The base station 50 has an IP unit 51, a buffer unit 52, an RF unit 53, and a buffer unit 54. The IP unit 51 is a communication unit that performs IP communication with the central control device 30. The RF unit 53 is a communication unit that performs wireless communication with the mobile station 70. The buffer unit 52 is disposed between the IP unit 51 and the RF unit 53 on the downlink path. The buffer unit 54 is disposed between the RF unit 53 and the IP unit 51 on the uplink path.

[0020] Between the buffer units 12 and 13 in the command console 10, there is a wiring switching circuit that connects or disconnects them. By connecting the buffer units 12 and 13 by wiring, it is possible to form a loop route R1 that turns back the tone signal traveling on the downstream route and takes a shortcut to the upstream route. In addition, by disconnecting the wiring connection between the buffer units 12 and 13, it is possible to release the loop route R1.

[0021] The same applies to the loop routes R2, R3, and R4 between buffer section 31 and buffer section 37 in central control device 30, between buffer section 33 and buffer section 35 in central control device 30, and between buffer section 52 and buffer section 54 in base station 50, and they can be formed or released at each of these positions. Note that the positions of the buffer sections described above, i.e., the positions at which loop routes are formed, are merely examples, and loop routes can be formed or released at any position within the voice communication route.

[0022] The tone generation unit 21 and tone detection unit 22 in the command console 10 will be described with reference to FIGS. 2 and 3. As shown in FIG. 2, the tone generation unit 21 includes n frequency transmission circuits 23 (i.e., frequency 1 transmission circuit 23-1 to frequency n transmission circuit 23-n) and a frequency synthesis unit 24. Each frequency transmission circuit 23 is configured to generate a tone signal of a different frequency. These frequencies are set, for example, to cover the frequency band used during calls. Each frequency transmission circuit 23 includes a switch circuit that controls only one frequency transmission circuit to output a tone signal and the other frequency transmission circuits to stop outputting tone signals. The frequency synthesis unit 24 synthesizes the outputs of the frequency transmission circuits 23 and outputs the tone signal generated by the selected frequency transmission circuit 23 to the downstream path. This allows the tone generation unit 21 to arbitrarily switch the frequency of the tone signal to be output. In this example, the tone generation unit 21 generates a tone signal that loops between frequencies 1 to n.

[0023] As shown in FIG. 3, tone detection unit 22 has n frequency detection circuits 25 (i.e., frequency 1 detection circuit 25-1 to frequency n detection circuit 25-n). A signal propagating through the upstream path is branched and input to each frequency detection circuit 25. Each frequency detection circuit 25 has a band-pass filter (BPF) that selectively passes different frequencies corresponding to the output frequency of frequency transmission circuit 23 of tone generation unit 21. Each frequency detection circuit 25 extracts a desired frequency component using the BPF, full-wave rectifies the extracted frequency component, and then compares the signal level with a predetermined threshold. If the signal level is equal to or greater than the threshold, tone detection unit 22 outputs a tone detection signal DET indicating that a tone signal of that frequency has been detected. This enables tone detection unit 22 to individually detect the tone signals of each frequency output by tone generation unit 21.

[0024] The route diagnosis control unit 41 in the central control unit 30 controls the formation or release of the above-mentioned loop route. The route diagnosis control unit 41 also instructs the tone generation unit 21 to send a tone signal, receives the tone signal detection result from the tone detection unit 22, and checks the soundness of the voice communication route based on the tone signal detection result. If a fault is found in the voice communication route, it also narrows down the faulty location and the fault condition. The results of the check on the soundness of the voice communication route by the route diagnosis control unit 41 are output in a predetermined format. For example, they are displayed on a display terminal communicatively connected to the central control unit 30. The above-mentioned operations by the route diagnosis control unit 41 are performed using a communication route separate from the voice communication route.

[0025] The voice health check sequence in the communication system of FIG. 1 will be described with reference to FIGS. 4A and 4B. The voice health check sequence is assumed to be automatically started when there is no call or when maintenance is being performed. Whether there is no call or not can be determined, for example, by referring to call information managed by the central control device 30. Whether there is maintenance or not can be determined, for example, based on preset maintenance schedule information. The voice health check sequence may also be started by manual instruction from the user.

[0026] In this example, the route diagnosis control unit 41 in the central processing unit 30 checks the call status between the command console 10 and the mobile station 70 and determines whether or not it is a non-call period in which no call is being made (step S11). If it is determined that it is a non-call period, the audio health check sequence is started. The audio health check sequence is performed for each loop route while forming the loop routes in order of proximity to the command console 10 (i.e., loop routes R1, R2, R3, R4).

[0027] First, the path diagnosis control unit 41 starts checking the loop path R1 (step S12) and transmits a loop formation instruction and a tone transmission instruction to the command console 10. The command console 10 forms a loop path R1 within the command console 10 in accordance with the loop formation instruction and the tone transmission instruction (step S13), and causes the tone generation unit 21 to generate a tone signal and output it to the downstream path (step S14). This tone signal is returned from the downstream path to the upstream path by the loop path R1 within the command console 10 and is detected by the tone detection unit 22 (step S15).

[0028] The command console 10 transmits a detection result notification indicating that a tone signal has been detected to the route diagnosis control unit 41. The route diagnosis control unit 41 refers to the detection result notification from the command console 10 and determines that there is no problem with the voice communication route up to the loop route R1 (step S16). Note that the loop route R1 in the command console 10 is automatically released after a certain time has elapsed since its formation.

[0029] Next, the path diagnosis control unit 41 starts checking the loop path R2 (step S17), sends a tone sending instruction to the command console 10, and forms the loop path R2 within the central processing unit 30 (step S18). In accordance with the tone sending instruction, the command console 10 causes the tone generator 21 to generate a tone signal and outputs it to the downstream path (step S19). This tone signal is transmitted from the command console 10 to the central processing unit 30, returned from the downstream path to the upstream path by the loop path R2 within the central processing unit 30, transmitted from the central processing unit 30 to the command console 10, and detected by the tone detector 22 (step S20).

[0030] The command console 10 transmits a detection result notification indicating that a tone signal has been detected to the route diagnosis control unit 41. The route diagnosis control unit 41 refers to the detection result notification from the command console 10 and determines that there is no problem with the voice communication route up to the loop route R2 (step S21). Note that the loop route R2 in the central processing unit 30 is automatically released after a certain time has elapsed since its formation.

[0031] Next, the path diagnosis control unit 41 starts checking the loop path R3 (step S22), sends a tone sending instruction to the command console 10, and forms the loop path R3 within the central processing unit 30 (step S23). In accordance with the tone sending instruction, the command console 10 causes the tone generator 21 to generate a tone signal and outputs it to the downstream path (step S24). This tone signal is transmitted from the command console 10 to the central processing unit 30, returned from the downstream path to the upstream path by the loop path R3 within the central processing unit 30, transmitted from the central processing unit 30 to the command console 10, and detected by the tone detector 22 (step S25).

[0032] The command console 10 transmits a detection result notification indicating that a tone signal has been detected to the route diagnosis control unit 41. The route diagnosis control unit 41 refers to the detection result notification from the command console 10 and determines that there is no problem with the voice communication route up to the loop route R3 (step S26). Note that the loop route R3 in the central processing unit 30 is automatically released after a certain time has elapsed since its formation.

[0033] Next, the route diagnosis control unit 41 starts checking the loop route R4 (step S27) and transmits a tone sending instruction to the base station 50. The base station 50 forms a loop route R4 within the base station 50 in accordance with the loop formation instruction (step S28), and transmits a loop formation notification indicating that the loop formation has been completed to the central control device 30. After receiving the loop formation notification from the base station 50, the route diagnosis control unit 41 transmits a tone sending instruction to the command console 10. In accordance with the tone sending instruction, the command console 10 generates a tone signal using the tone generation unit 21 and outputs it to the downlink route (step S29).

[0034] This tone signal is normally transmitted from the command console 10 via the central control device 30 to the base station 50, then looped back from the downlink path to the uplink path via loop path R4 within the base station 50, and then transmitted from the base station 50 to the command console 10 via the central control device 30, and detected by the tone detection unit 22. However, if there is a fault in the voice communication path within the base station 50, the tone detection unit 22 will not be able to detect the tone signal even after a certain time has passed since the tone generation unit 21 sent out the tone signal. In other words, the tone detection unit 22 will fail to detect the tone signal (step S30).

[0035] In this case, the command console 10 transmits a detection result notification indicating that the detection of the tone signal has failed to the route diagnosis control unit 41. Based on the detection result notification from the command console 10, the route diagnosis control unit 41 determines that there is a fault in the voice communication path between loop route R3 and loop route R4 (step S31). Note that the loop route R4 within the base station 50 is automatically released after a certain time has elapsed since its formation.

[0036] In the above description, each device automatically releases the loop path, but the path diagnosis control unit 41 may transmit a loop release instruction specifying a loop path, and when each device receives this instruction, the specified loop path may be released. The waiting time for tone detection unit 22 to detect a tone signal may be the same for each loop path, or may be longer the longer the distance from tone generation unit 21 or tone detection unit 22 to the loop path, as long as the time required for the tone signal to return is secured. The above description does not take into account the number of command consoles 10 and base stations 50, but it goes without saying that the required steps of the voice health confirmation sequence are repeated depending on the number of command consoles 10 and base stations 50.

[0037] As described above, the communication system of this example is a mechanism for checking the soundness of the voice communication path for calls connecting the command console 10 and the mobile station 70 via the central control device 30 and the base station 50. The command console 10 includes a tone generator 21 that generates a tone signal and sends it to the mobile station (downstream) and a tone detector 22 that detects the tone signal. The central control device 30 includes a path diagnosis controller 41 that controls the formation and release of a loop path that loops back the tone signal sent from the tone generator 21 to the command console (upstream) midway along the voice communication path. The system is configured to check the soundness of the voice communication path based on the detection result by the tone detector 22 of the tone signal looped back by the loop path. This configuration makes it possible to automatically check the soundness of the voice communication path for calls that the communication system has.

[0038] The route diagnosis control unit 41 is also configured to form loop routes at multiple positions on the voice communication route, and to repeatedly send and detect tone signals while changing the position at which the loop route is formed. This not only makes it possible to determine whether or not there is a fault in the voice communication route, but also to narrow down the location of the fault in the voice communication route. The route diagnosis control unit 41 is also configured to form loop routes in order of proximity to the command console 10. This makes it possible to efficiently narrow down the location of the fault in the voice communication route.

[0039] Furthermore, tone generator 21 generates and transmits tone signals while switching frequencies, and tone detector 22 is configured to be able to detect tone signals of each frequency. This makes it possible to identify which frequency has a problem when there is a problem with part of the frequency band used during a call.

[0040] Next, an extension example of the communication system shown in Fig. 1 will be described. In this example, it is assumed that an LPF (Low-Pass Filter) is implemented in the audio communication path. Furthermore, frequency 1 to frequency n are set as the output frequency of tone generation unit 21 and the detection frequency of tone detection unit 22. The smaller the frequency number, the lower the frequency, and the higher the frequency number, the higher the frequency. Note that frequency n is assumed to be a high frequency that is filtered by the LPF.

[0041] In this extended example, Fig. 5 shows in table form an example of the tone transmission conditions of tone generation unit 21 and the detection states of tone detection unit 22 in various fault states. In the table of Fig. 5, for the fault states "normal," "path disconnection," and "LPF characteristic degradation," the tone transmission condition for tone generation unit 21 is to transmit all of frequencies 1 to n. Furthermore, for the fault state "abnormal noise," the tone transmission condition for tone generation unit 21 is to not transmit any of frequencies 1 to n.

[0042] If the fault condition is "normal," looped tone signals from frequency 1 to frequency n-1 can be detected, but only frequency n, which is filtered by the LPF, cannot be detected. In other words, when tone signals from frequency 1 to frequency n-1 are sent, frequencies 1 to n-1 can be detected, but only frequency n, which is removed by the LPF, cannot be detected, and the system is determined to be "normal."

[0043] If the fault condition is "path broken," the looped tone signals from frequency 1 to frequency n cannot be detected. In other words, if the tone signals sent from frequency 1 to frequency n-1 cannot be detected at any of frequencies 1 to n, it is determined to be "path broken."

[0044] If the fault condition is "LPF characteristic degradation," it will be possible to detect looped tone signals from frequency 1 to frequency n-1, and it will also be possible to detect frequency n, which is normally filtered out by the LPF. In other words, if not only frequencies 1 to n-1 but also frequency n, which should be removed by the LPF, are detected when tone signals from frequency 1 to frequency n-1 are sent, it will be determined to be "LPF characteristic degradation."

[0045] When the fault condition is "abnormal noise," no tone signal is sent from tone generation unit 21, and therefore tone detection unit 22 would not normally be able to detect any frequencies, but in the table of Fig. 5, frequency 3 and frequency n are detected. The table of Fig. 5 is just an example, and if any frequency is detected even when the tone signal is stopped, it is determined to be "abnormal noise."

[0046] As described above, according to the above-described extended example, it is possible to narrow down not only the location of the fault in the voice communication path but also the fault state of the voice communication path. In the explanation so far, the output frequency of tone generation unit 21 and the detection frequency of tone detection unit 22 are made to match, but the detection frequency of tone detection unit 22 may be wider than the output frequency of tone generation unit 21. As a result, in a system configuration that does not include an LPF, if a frequency other than the output frequency of tone generation unit 21 (i.e., a frequency that should not normally be detected) is detected, it is possible to determine that there is an abnormality in the voice communication path.

[0047] Next, a modification of the communication system shown in Fig. 1 will be described with reference to Fig. 6. In the modification shown in Fig. 6, tone generators 42 and 44 and tone detectors 43 and 45 are provided in central control device 30 instead of tone generator 21 and tone detector 22 in command console 10 of Fig. 1.

[0048] The tone generator 42 and the tone detector 43 are used to check the soundness of the voice communication path upstream of their respective positions. The tone generator 42 generates a tone signal and outputs it to the upstream path. The tone detector 43 detects, from the downstream path, the tone signal that has been returned via the loop path R1 or loop path R2.

[0049] The tone generator 44 and the tone detector 45 are used to check the soundness of the voice communication path downstream of their respective positions. The tone generator 44 generates a tone signal and outputs it to the downstream path. The tone detector 45 detects, from the upstream path, the loop path R3 or the tone signal returned via the loop path R3.

[0050] As described above, the communication system of the modified example is a mechanism for checking the soundness of the voice communication path for calls connecting the command console 10 and the mobile station 70 via the central control device 30 and the base station 50. The central control device 30 includes tone generators 42, 44 that generate tone signals and send them to the command console side (uplink direction) or the mobile station side (downlink direction), and tone detectors 43, 45 that detect the tone signals. The central control device 30 also includes a path diagnosis control unit 41 that controls the formation and release of a loop path that loops back the tone signals sent from the tone generators 42, 44 to the command console side (uplink direction) or the mobile station side (downlink direction) along the voice communication path. The soundness of the voice communication path is checked based on the detection results of the tone detectors 43, 45 for the tone signals looped back by the loop path. This configuration also makes it possible to automatically check the soundness of the voice communication path for calls that the communication system has.

[0051] In the above explanation, the command console 10 and the central control device 30 are provided with a tone generating unit and a tone detecting unit, but the base station 50 may also be provided with a tone generating unit and a tone detecting unit. Also, another device may be interposed in the voice communication path, and this other device may be provided with a tone generating unit and a tone detecting unit.

[0052] Although the embodiments of the present invention have been described above, the above embodiments are merely illustrative and do not limit the technical scope of the present invention. The present invention can take various other embodiments, and various modifications such as omissions and substitutions can be made without departing from the spirit of the present invention. These embodiments and modifications are included in the scope and spirit of the invention described in this specification, etc., and are included in the invention described in the claims and their equivalents.

[0053] Furthermore, the present invention can be provided not only as devices such as those described above or as systems composed of these devices, but also as methods executed by these devices, programs for realizing the functions of these devices using a processor, and storage media for storing such programs in a computer-readable manner. [Industrial Applicability]

[0054] The present invention can be used in a communication system having a voice communication path connecting between a command console and a mobile station via a central control unit and a base station. [Explanation of symbols]

[0055] 10: command console, 11, 14: A / D conversion unit, 12, 13: buffer unit, 21: tone generation unit, 22: tone detection unit, 23-1 to 23-n: frequency transmission circuit, 24: frequency synthesis unit, 25-1 to 25-n: frequency detection circuit, 30: central control unit, 31, 33, 35, 37: buffer unit, 32: encoder unit, 34: IP unit, 36: decoder unit, 41: route diagnosis control unit, 42, 44: tone generation unit, 43, 45: tone detection unit, 50: base station, 51: IP unit, 52, 54: buffer unit, 53: RF unit, 70: mobile station

Claims

1. In a communication system having a voice communication path for calls connecting a command console and a mobile station via a central control unit and a base station, a tone generating unit that generates a tone signal and transmits it to the command console side or the mobile station side; a tone detection unit that detects the tone signal; a route control unit that controls the formation and release of a loop route in which the tone signal sent from the tone generating unit is looped back midway along the voice communication route; the route control unit is capable of forming the loop route at a plurality of positions on the voice communication route, repeating transmission and detection of the tone signal while changing the position where the loop path is formed; A communication system characterized in that the soundness of the voice communication path is confirmed based on the detection result of the tone signal returned by the loop path by the tone detection unit.

2. 2. The communication system according to claim 1, A communication system characterized in that the route control unit forms the loop route in order of proximity to the command console.

3. 2. The communication system according to claim 1, the tone generating unit generates and transmits tone signals while switching frequencies; A communication system comprising: a step of narrowing down a fault condition in the voice communication path based on the result of detection of the tone signal of each frequency by the tone detection unit;

4. 2. The communication system according to claim 1, the tone detection unit is capable of detecting a signal having a frequency different from the frequency of the tone signal; A communication system characterized in that the soundness of the voice communication path is confirmed by further taking into consideration the detection result of the signals of the different frequencies by the tone detection unit.

5. 2. The communication system according to claim 1, The central control device determines whether or not a period of no communication is taking place between the command console and the mobile station, and when it is determined that a period of no communication is taking place, starts checking the soundness of the voice communication path.

6. 2. The communication system according to claim 1, A communication system characterized in that the command console has the tone generation unit and the tone detection unit.

7. 2. The communication system according to claim 1, A communication system characterized in that the central control unit has the tone generation unit and the tone detection unit.

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