Receiving device for estimating whether a communication device is in a non-communicable state

Abstract

Receiving device (3), comprising: a monitoring-side time determination unit (3c) configured to determine for each of a plurality of communication devices (2) a time to generate monitoring-side keep-alive signals at the same times as the times at which the corresponding communication device (2) transmits monitoring-side keep-alive signals; a monitoring-side keep-alive signal generation unit (3f) configured to generate a monitoring-side keep-alive signal at each of the times determined by the monitoring-side time determination unit (3c);and an estimation unit (3k) configured when the monitoring-side-keep-on-the-live-signals generation unit (3f) generates the plurality of monitoring-side-keep-on signals at one of the time points determined by the monitoring-side-time determination unit (3c), if a number of received monitoring-side-keep signals is less than a number of generated monitoring-side-keep signals, to estimate a communication device (2) that is in a non-communicable state, based on a comparison result of a number of monitoring-side-keep signals generated for each of one or more time points and a number of monitoring-side-keep signals received for each of the one or more time points.

Description

Area The present invention relates to a receiving device. State of the art JP 2003-067264A discloses a monitoring system. This monitoring system makes it possible to determine the communication status of a communication device. US 9,717,110 B1 relates to a system and method for efficient signaling between devices. US 9,141,489 B2 relates to a fail-safe procedure for a computer system. Summary Technical problem However, in the monitoring system described in JP 2003-067264A, a receiving device must send an acknowledgment signal to the communication device. Furthermore, the communication device must transmit an acknowledgment signal. Consequently, the amount of data exchanged when determining the communication status of the communication device increases. The present invention is based on the objective of solving the problem described above. One objective of the present invention is to provide a receiving device that can determine whether a communication device is in a non-communicable state without transmitting an acknowledgment signal. Solution to the task A receiving device according to the present invention comprises: a monitoring-side time determination unit configured to determine times for generating monitoring-side keep-alive signals at the same times as times at which a plurality of communication devices send monitoring-side keep-alive signals;a monitoring-side-live-signal generation unit configured to generate a plurality of monitoring-side-live signals at a plurality of time points determined by the monitoring-side-time determination unit, and an estimation unit configured to estimate, when the monitoring-side-live-signal generation unit simultaneously generates the multiple monitoring-side-live signals, if the number of received monitoring-side-live signals is less than the number of generated monitoring-side-live signals, a communication device in a non-communicable state based on a comparison of the number of subsequently generated monitoring-side-live signals and the number of subsequently received monitoring-side-live signals. Advantageous effects of the invention According to the present invention, if the number of received monitoring-side-keep-alive signals is less than the number of generated monitoring-side-keep-alive signals, the receiving device estimates that the communication device is in a non-communicable state, based on a comparison of the number of subsequently generated monitoring-side-keep-alive signals and the number of subsequently received monitoring-side-keep-alive signals. Accordingly, it is possible to indicate that the communication device is in the non-communicable state without transmitting an acknowledgment signal. Brief description of the drawings [Fig. 1] Fig. 1 is a configuration diagram of a monitoring system in a first embodiment. [Fig. 2] Fig. 2 is a diagram illustrating a method for determining the time required to transmit a monitored-side-keep-alive signal by a communication device of the monitoring system in the first embodiment. [Fig. 3] Fig. 3 is a flowchart illustrating an overview of the operation of the communication device of the monitoring system in the first embodiment. [Fig. 4] Fig. 4 is a flowchart illustrating an overview of the operation of a receiving device of the monitoring system in the first embodiment. [Fig. 5] Fig. 5 is a hardware configuration diagram of the communication device of the monitoring system in the first embodiment. [Fig. 6] Fig. 6 is a configuration diagram of a monitoring system of the first embodiment in a second embodiment. [Fig. 7] Fig.Figure 7 is a diagram illustrating an estimation method for a communication device in a non-communicable state by a receiving device of the monitoring system in the second embodiment. [Figure 8] Figure 8 is a diagram illustrating an estimation method for a communication device in a non-communicable state by a receiving device of a monitoring system in a third embodiment. Description of the embodiments Embodiments of the present invention are explained with reference to the accompanying drawings. It should be noted that identical or equivalent parts are designated by the same reference numerals and symbols in the illustrations. Recurring descriptions of the parts have been simplified or omitted where necessary. First embodiment. Fig. 1 is a configuration diagram of a monitoring system in a first embodiment. For example, a monitoring system is provided to be able to monitor a plurality of elevators 1. The monitoring system comprises a plurality of communication devices 2 and a receiving device 3. Each of the plurality of communication devices 2 is designed to correspond to each of the plurality of elevators 1. Each of the plurality of communication devices 2 comprises a supervised-side transmission unit 2a, a supervised-side receiving unit 2b, a supervised-side time determination unit 2c, a supervised-side random number generator 2d, a supervised-side comparison unit 2e, a supervised-side keep-alive signal generator 2f, and an acknowledgment signal generator 2g. The receiving device 3 is, for example, integrated into a cloud server. The receiving device 3 is, for instance, installed near the communication devices 2. The receiving device 3 comprises a monitoring-side receiving unit 3a, a monitoring-side transmitting unit 3b, a monitoring-side time determining unit 3c, a plurality of monitoring-side random number generating units 3d, a monitoring-side comparison unit 3e, a monitoring-side live signal generating unit 3f, a signal comparison unit 3g, a live determining unit 3h, a relevant device determining unit 3i, and an acknowledgment signal generating unit 3j. In each of the multiple communication devices 2, the monitored-side time determination unit 2c, the monitored-side random number generation unit 2d, and the monitored-side comparison unit 2e function as monitored-side time determination units and independently determine the time at which the monitored-side transmission unit 2a transmits a keep-alive signal to the receiving device 3. The monitored-side keep-alive signal generation unit 2f generates the monitored-side keep-alive signal such that the monitored-side transmission unit 2a transmits the monitored-side keep-alive signal to the receiving device 3 at the determined time. The monitored-side transmission unit 2a transmits the keep-alive signal to the receiving device 3. In the receiving device 3, the monitoring-side receiving unit 3a receives monitoring-side keep-alive signals from the plurality of communication devices 2. The monitoring-side timer 3c, the plurality of monitoring-side random number generators 3d, and the monitoring-side comparison unit 3e act as the monitoring-side timer and determine times for generating monitoring-side keep-alive signals at the same times as the plurality of communication devices 2 send the monitoring-side keep-alive signals. The monitoring-side keep-alive signal generator 3f generates a plurality of monitoring-side keep-alive signals at a specified plurality of times. The 3g signal comparison unit compares the number of generated monitoring-side-keep-alive signals and the number of received monitoring-side-keep-alive signals.The keep-alive determination unit 3h determines that the communication device 2 is in a non-communicable state based on a comparison result of the signal comparison unit 3g. For example, if the monitoring-side keep-alive signal generation unit 3f generates a monitoring-side keep-alive signal and no monitoring-side keep-alive signal is received, the keep-alive determination unit 3h determines that the communication device 2 corresponding to the monitoring-side keep-alive signal is in the non-communicable state.For example, if the monitoring-side-keep-alive-signal-generating unit 3f simultaneously generates a plurality of monitoring-side-keep-alive signals, the keep-alive-determining unit 3h determines, if the number of received monitoring-side-keep-alive signals is less than the number of generated monitoring-side-keep-alive signals, that one of the plurality of communication devices 2 corresponding to the plurality of monitoring-side-keep-alive signals is in the non-communicable state. At this point, the Relevant Device Acknowledge Unit 3i detects the plurality of communication devices 2 according to the plurality of monitoring-side keep-alive signals. The Acknowledge Signal Generation Unit 3j generates an acknowledgement signal, which is transmitted to the plurality of communication devices 2. The monitoring-side transmission Unit 3b transmits the acknowledgement signal generated by the Acknowledge Signal Generation Unit 3j to the plurality of communication devices 2. In each of the plurality of communication devices 2, the monitored-side receiving unit 2b receives the acknowledgment signal from the receiving device 3. The acknowledgment signal generating unit 2g generates an acknowledgment signal when the monitored-side receiving unit 2b receives the acknowledgment signal. Among the plurality of communication devices 2, in the communication device 2 when it is capable of communication, the monitored-side transmission unit 2a sends the acknowledgment signal to the receiving device 3. In the communication device 2 when it is not capable of communication, the monitored-side transmission unit 2a does not send the acknowledgment signal to the receiving device 3. In the receiving device 3, the monitoring-side receiving unit 3a receives confirmation signals from the multitude of communication devices 2. According to the received state of the confirmation signal, the receiving device 3 detects the communication device 2 that is no longer communicable. The following describes a method for determining the time required to transmit a monitored-side-keep-alive signal with reference to Fig. 2. Fig. 2 is a diagram illustrating a method for determining the time for the transmission of a monitored-page-keep-alive signal by the communication device of the monitoring system in the first embodiment. The horizontal axis of Fig. 2 represents time. The vertical axis of Fig. 2 represents an output value of the monitored-page time determination unit 2c and the monitored-page random number generation unit 2d. In Fig. 2, an alternating long and short dashed line represents an output value of the monitored-page-time-determination unit 2c at the current time only. Dots represent output values ​​of the monitored-page-random-number-generation unit 2d. The supervised page random number generator 2d outputs signals at fixed time intervals. If an output value at that time is equal to the output value at the current time, the supervised page comparison unit 2e sends a message that a supervised page keep-alive signal is being transmitted. The output values ​​of the monitored-page random number generator 2d are set such that they show no correlation across the multitude of communication devices 2. In this case, no two communication devices 2 ever send monitored-page keep-alive signals simultaneously. As a result, the receiving device 3 can detect the communication device 2 in a non-communicating state. The simplest method for using a supervised random number generator (SRN) in any of the multiple communication devices is to employ a uniform random number generator to which an independent seed value is fed. For example, a pseudo-random number generator implemented with software such as a linear congruent algorithm, X-OS-Shift, or similar can be used as the SRN. Alternatively, a hardware random number generator utilizing thermal noise or similar techniques can be used. Finally, a cryptographically secure pseudo-random number generator based on a hash function such as SHA can be used as the SRN. It should be noted that a time generator based on an operating state of elevator 1 can be used as the supervised random number generator 2d. For example, a time generator based on the current floor of an elevator car in elevator 1 can be used as the supervised random number generator 2d. For example, a time generator based on the current acceleration of the elevator car in elevator 1 can be used as the supervised random number generator 2d. For example, a time generator based on the cumulative number of starts of the elevator car in elevator 1 can be used as the supervised random number generator 2d. For example, a time generator based on the value of an electrical current flowing to a lifting mechanism of elevator 1 can be used as the supervised random number generator 2d. At this point, the adjacent elevators 1 have similar output values. In this case, a pseudo-random number generator can be used as the supervised random number generation unit 2d, which uses data about the operating state of elevator 1 as a seed value. A time generator based on attributes of elevator 1 can be used as the supervised page random number generator 2d. For example, a time generator based on a floor of elevator 1 and elevator 1 specifications such as speed can be used as the supervised page random number generator 2d. Alternatively, a time generator based on how elevator 1 is used in a station, office, or similar location can be used as the supervised page random number generator 2d. The characteristics of elevator 1 result in a difference in the required frequency of life-keeping monitoring. For example, more frequent life-keeping monitoring is required in a train station building than in a condominium. In the supervised-page random number generator 2d, S(x) is output according to a Gaussian distribution with mean µ and distribution σ², based on a specific distribution corresponding to the properties of elevator 1. Specifically, S(x) is represented by the following expression (1). [Math. 1] For a specific object group, such as condominiums, a parameter is given representing a mean value of 20 from the Gaussian distribution. For another object group, such as station buildings, a parameter is given representing a mean value of 40 from the Gaussian distribution. This makes it possible to place the generation times of the "monitored page live" signals for a large number of object groups within any desired time range. It should be noted that the "monitored page live" signals can be transmitted at a high frequency by changing the interval of their generation times. An overview of the functionality of the communication device 2 is explained with reference to Fig. 3. Fig. 3 is a flowchart to illustrate an overview of the operation of the communication device of the monitoring system in the first embodiment. In step S1, the communication device 2 refers to the current time. Then, in step S2, the communication device 2 performs an operation. In step S2, the communication device 2 determines whether the current time is the time for generating random numbers. If the current time in step S2 is not the random number generation time, communication device 2 performs the operation in step S1. If the current time in step S2 is the random number generation time, communication device 2 performs the operation in step S3. In step S3, the communication device 2 generates a random number. Then, in step S4, the communication device 2 performs an operation. In step S4, the communication device 2 determines whether the random number corresponds to the current time. If the random number in step S4 does not match the current time, the communication device 2 terminates the process. If the random number in step S4 equals the current time, communication device 2 executes the operation in step S5. In step S5, communication device 2 sends a "keep monitored page alive" signal. Afterward, communication device 2 terminates the operation. An overview of the operation of the receiving device 3 is explained with reference to Fig. 4. Fig. 4 is a flowchart to illustrate an overview of the operation of the receiving device of the monitoring system in the first embodiment. In step S11, receiver 3 refers to the current time. Then, in step S12, receiver 3 performs an operation. In step S12, receiver 3 determines whether the current time is the time for generating random numbers. If the current time in step S12 is not the time of random number generation, receiver 3 performs the operation in step S11. If the current time in step S12 is the time of random number generation, receiver 3 performs the operation in step S13. In step S13, the receiving device 3 generates random numbers corresponding to all communication devices 2. The receiving device 3 then performs the operation in step S14. In step S14, the receiving device 3 can determine whether a random number equal to the current time is present. If a random number equal to the current time is missing in step S14, the receiving device 3 terminates the process. If a random number equal to the current time is present in step S14, receiver 3 executes the operation in step S15. In step S15, receiver 3 compares the number of generated monitoring-side-keep signals with the number of received monitoring-side-keep signals. Then, receiver 3 executes the operation in step S16. In step S16, receiver 3 determines whether the number of generated monitoring-side-keep signals and the number of received monitoring-side-keep signals are equal. If the number of generated monitoring-side-keep-alive signals and the number of received monitoring-side-keep-alive signals are equal in step S16, the receiving device 3 terminates the operation. If the number of generated monitoring-side-keep-alive signals and the number of received monitoring-side-keep-alive signals in step S16 are not equal, the receiving device 3 performs the operation in step S17. In step S17, the receiving device 3 performs a keep-alive acknowledgment operation. Afterward, the receiving device 3 terminates the operation. According to the first embodiment described above, the communication device 2 itself determines the time for transmitting a monitored-page-keep-alive signal to the receiving device 3. At this time, the receiving device 3 determines a communication state of the communication device 2 based on the presence or absence of the monitored-page-keep-alive signal at that time. Accordingly, it is possible to reduce the amount of data exchanged by determining the communication state of the communication device 2. Consequently, it is possible to reduce the load on a network. The "Keep the monitored page alive" signal is generated at a specific time. This prevents the unnecessary generation of the "Keep the monitored page alive" signal and thus avoids mistransmissions. The time is determined based on a uniform random number. Therefore, it is possible to determine the time with a simple configuration. The timing is determined based on an operating state of elevator 1 corresponding to that time. Accordingly, it is possible to transmit the monitored-side-keep-alive signal at a suitable time for elevator 1, according to that time. The timing is determined based on attributes of elevator 1 according to the time. The timing of the transmission of the monitored-side-keep-alive signal is suitable for elevator 1 according to the time. It should be noted that if a random number output by the random number generator corresponds to a uniform distribution and the timing is controlled in one-minute increments, the collision probability Pc of the collision occurring because n communication devices 2 of N communication devices 2 simultaneously generate monitored-side-keep-alive signals is represented by the following expression (2) using a binomial distribution. [Math. 2] If only the identification information is used, a maximum of 256 communication devices 2 can be monitored with one byte. However, according to this method, if the output random number of the random number generation unit corresponds to the uniform distribution, it is possible to increase the number of communication devices 2 to be monitored by allowing a collision probability Pc of 0.37. A probability Pnt that a particular communication device 2 will not send a monitored-side-keep-alive signal for m minutes is represented by the following expression (3) [Math. 3] In this case, monitored-page-keep-alive signals are transmitted with a probability of approximately 0.64 every sixty minutes. To reduce the interval for transmitting monitored-page-keep signals, only the interval for generating random numbers needs to be reduced. An embodiment of the communication device 2 is explained with reference to Fig. 5. Fig. 5 is a hardware configuration diagram of the communication device of the monitoring system in the first embodiment. The functions of the communication device 2 can be implemented by a processing circuit arrangement. For example, the processing circuit arrangement includes at least one processor 4a and at least one memory 4b. For example, the processing circuit arrangement includes at least one dedicated hardware 5. If the processing circuit comprises at least one processor 4a and at least one memory 4b, the functions of the communication device 2 are implemented by software, firmware, or a combination of both. At least one of the software and firmware is described as a program. At least one of the software and firmware is stored in the at least one memory 4b. The at least one processor 4a reads the program stored in the at least one memory 4b and executes it to implement the functions of the communication device 2. The at least one processor 4a is also referred to as a central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, or DSP.The at least one memory 4b is, for example, a non-volatile or volatile semiconductor memory such as a RAM, a ROM, a flash memory, an EPROM or an EEPROM, a magnetic disk, a flexible disk, an optical disk, a compact disk, a minidisk, a DVD or the like. If the processing circuit includes at least one dedicated hardware component 5, the processing circuit is implemented, for example, by a single circuit, a composite circuit, a programmed processor, a parallel-programmed processor, an ASIC, an FPGA, or a combination of the single circuit, the composite circuit, the programmed processor, the parallel-programmed processor, the ASIC, and the FPGA. For example, the respective functions of the communication device 2 are each implemented by processing circuits. For example, the functions of the communication device 2 are implemented jointly by processing circuits. Some of the functions of the communication device 2 can be implemented by the dedicated hardware 5, and other functions can be implemented by software or firmware. For example, the function of the supervised page random number generator 2d can be implemented by a processing circuit acting as the dedicated hardware 5. The functions other than the supervised page random number generator 2d can be implemented by the at least one processor 4a, which reads and executes a program stored in the at least one memory 4b. In this way, the processing circuit implements the functions of the communication device 2 with the hardware 5, the software, the firmware or a combination of the hardware 5, the software and the firmware. Although not shown, the functions of the receiving device 3 are also realized by a processing circuit that corresponds to the processing circuit that realizes the functions of the communication device 2. Second embodiment. Fig. 6 is a configuration diagram of a monitoring system of the first embodiment in a second embodiment. It should be noted that parts that are identical or equivalent to the parts in the first embodiment are designated with the same reference numerals and symbols. An explanation of the parts is omitted. In the second embodiment, the receiving device 3 does not include the monitoring-side transmission unit 3b, the relevant device acknowledgment unit 3i, and the acknowledgment signal generation unit 3j. The receiving device 3 includes an estimation unit 3k. If the monitoring-side-keep-signal-generating unit 3f simultaneously generates a multitude of monitoring-side-keep signals, the estimating unit 3k estimates, if the number of received monitoring-side-keep signals is less than the number of generated monitoring-side-keep signals, the communication device 2 in a non-communicable state based on a comparison of the number of subsequently generated monitoring-side-keep signals and the number of subsequently received monitoring-side-keep signals. For example, the estimating unit 3k estimates the communication device 2 in the non-communicable state based on graph theory. An estimation method for the communication device 2 in the non-communicable state is explained with reference to Fig. 7. Fig. 7 is a diagram illustrating an estimation method for the communication device in the non-communicable state by the receiving device of the monitoring system in the second embodiment. In Fig. 7, the circles on the bottom are nodes representing the communication devices 2. Solid lines represent the communication devices 2 in a communication-capable state. Dashed lines represent the communication devices 2 in a non-communicable state. Squares are function nodes for calculating the total number of monitored-page-keep-alive signals received at a relevant time. Triangles are nodes representing the receive states of the monitored-page-keep-alive signals. White represents a state in which all monitored-page-keep-alive signals that should have been received are received. Black represents a state in which not all monitored-page-keep-alive signals that should have been received are received. For example, if time t is "1", communication device 2 of "1" and communication device 2 of "3" send monitored-side-keep-alive signals. These monitored-side-keep signals are received correctly. At this time, the number of received packets and the number of graph connections match. It is determined that communication device 2 of "1" and communication device 2 of "3" are in a communicating state. For example, if time t is "2", while communication device 2 of "2", communication device 2 of "3", and communication device 2 of "6" should be sending monitored-side-keep-alive signals, communication device 2 of "2" does not send a monitored-side-keep-alive signal. In this case, an abnormality is detected. At this time, communication device 2 of "2", communication device 2 of "3", and communication device 2 of "6" cannot be assessed as being in a non-communicable state. For example, if time t is "3" while communication device 2 of "8" should be sending a monitored-side-keep-alive signal, communication device 2 of "8" does not send a monitored-side-keep-alive signal. In this case, an abnormality is detected. At this time, it is determined that communication device 2 of "8" is in a non-communicable state. As time t progresses to “5”, it is estimated, based on the communication devices 2 that should be sending monitored-side-keep-alive signals up to that time and the number of packets received, that communication device 2 is in the non-communicable state when time t is “2”, communication device 2 is of “2”. According to the second embodiment described above, if the number of received monitoring-side-keep-alive signals is less than the number of generated monitoring-side-keep-alive signals, the receiving device 3 estimates the communication device 2 in the non-communicable state based on a comparison of the number of subsequently generated monitoring-side-keep-alive signals and the number of subsequently received monitoring-side-keep-alive signals. Specifically, the receiving device 3 estimates the communication device 2 in the non-communicable state based on graph theory. Accordingly, it is possible to put the communication device 2 into the non-communicable state without sending an acknowledgment signal. Third embodiment. Fig. 8 is a diagram illustrating an estimation method for a communication device in a non-communicable state by a receiving device of a monitoring system in a third embodiment. It should be noted that parts identical or equivalent to those in the second embodiment are designated with the same reference numbers and symbols. A further explanation of the parts is omitted. In the receiving device 3 in the third embodiment, the estimating unit 3k estimates the communication device 2 in a non-communicable state based on compressed sensing, which is a method for estimating a high-dimensional vector (sparse vector) with a large number of zero elements in the number of observations smaller than the number of dimensions of the vector. An estimated sparse target vector x is represented by the following expression (4). [Math. 4] An observation vector y is represented by the following expression (5).[Math. 5]where M is smaller than n. At this point, an MxN matrix A, used for estimating the sparse vector x, is represented by the following expression (6).[Math. 6] A relationship between the sparse vector x, the observation vector y, and the MxN matrix A is represented by the following expression (7). [Math. 7] At this point, the estimation unit 3k solves the following expression (8) to estimate the vector x. [Math. 8] The following expression (9) represents a norm. [Math. 9] If p is greater than 0, the following expression (10) holds.[Math. 10] If p is 0, the norm is represented by the following expression (11). [Math. 11] In expression (11) the norm represents the number of non-zero elements of the vector b. In the receiving device 3, a signal to be received y represents the number of monitored-side-keep-alive signals received in a specific time period, and x represents an operating state of the communication device 2. If the communication device 2 is, for example, in a communicative state, x is not equal to zero. If the communication device 2 is in a non-communicative state, x is equal to zero. In Fig. 8, the live states of eight communication devices 2 are estimated from five observation states. At this point, the signal input and output are represented in this case by the following expression (12). [Math. 12] In expression (12), however, most elements of a vector to be estimated are non-zero elements. Accordingly, expression (12) does not pose a problem for the compressed sampling solution. In an actual system, a situation in which the communication devices 2 occupy a majority in the non-communicable state is less likely to occur. The majority of the communication devices 2 are in the communicable state. To make the estimation vector sparse, zero is therefore used for simplicity to represent the communicable state and non-zero the non-communicable state. However, a true vector is unknown to an observer. This is inconsistent with the number of observation signals. Therefore, the number of signals to be received at time t is represented as rt. An element of a new observation vector is defined by the following expression (13). [Math. 13] As a result, the signal input and output are converted into the following expression (14). [Math. 14] The estimation unit 3k determines the number of signals that are actually expected to be received. Accordingly, the estimation unit 3k calculates the left-hand side from the number of signals actually received. A conversion matrix is ​​also known, as a random number generator is used. Therefore, the estimation unit 3k sparsifies an operating state vector of the right-hand side and then treats this operating state vector as a compressed sensing estimation problem. According to the third embodiment described above, the receiving device 3 estimates the communication device 2 in the non-communicable state based on the compressed sample. In this case as well, it is possible to indicate the communication device 2 in the non-communicable state without transmitting an acknowledgment signal. It should be noted that communication device 2 in the non-communicable state can be estimated based on a pseudo-inverse matrix. Even in this case, it is possible to specify communication device 2 in the non-communicable state without transmitting an acknowledgment signal. Industrial applicability As explained above, the receiving device according to the present invention can be used in an elevator system. Reference symbol list 1 Elevator 2 Communication device 2a Monitored-side transmission unit 2b Monitored-side receiving unit 2c Monitored-side time determination unit 2d Monitored-side random number generation unit 2e Monitored-side comparison unit 2f Monitored-side live signal generation unit 2g Acknowledgement signal generation unit 3 Receiving device 3a Monitored-side receiving unit 3b Monitored-side transmission unit 3c Monitored-side time determination unit 3d Monitored-side random number generation unit 3e Monitored-side comparison unit 3f Monitored-side live signal generation unit 3g Signal comparison unit 3h Live determination unit 3i Relevant device confirmation unit 3j Confirmation signal generation unit 3k Estimation unit 4a Processor 4b Memory 5 Hardware

Claims

Receiving device (3), comprising: a monitoring-side time determination unit (3c) configured to determine for each of a plurality of communication devices (2) a time to generate monitoring-side keep-alive signals at the same times as the times at which the corresponding communication device (2) transmits monitoring-side keep-alive signals; a monitoring-side keep-alive signal generation unit (3f) configured to generate a monitoring-side keep-alive signal at each of the times determined by the monitoring-side time determination unit (3c);and an estimation unit (3k) configured when the monitoring-side-keep-on-the-live-signals generation unit (3f) generates the plurality of monitoring-side-keep-on signals at one of the time points determined by the monitoring-side-time determination unit (3c), if a number of received monitoring-side-keep signals is less than a number of generated monitoring-side-keep signals, to estimate a communication device (2) that is in a non-communicable state, based on a comparison result of a number of monitoring-side-keep signals generated for each of one or more time points and a number of monitoring-side-keep signals received for each of the one or more time points. Receiving device (3) according to claim 1, wherein the estimating unit (3k) estimates the communication device (2) which is in the non-communicable state, based on graph theory, using the comparison result of the number of monitoring-side-keep-alive signals and the number of monitoring-side-keep-alive signals. Receiving device (3) according to claim 1, wherein the estimating unit (3k) estimates the communication device (2) which is in the non-communicable state, based on a compressed sampling using a conversion matrix comprising the comparison result of the number of monitoring-side-keep-alive signals and the number of monitored-side-keep-alive signals and time generation information.

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