JP2024011842A - Information communication system and information communication device - Google Patents

Abstract

To provide an information communication system and an information communication device that can absorb a variation in propagation time of information communication and perform synchronization control reduced in error.SOLUTION: An information communication system 100 comprises: an interval time calculation unit 76 that calculates along a time-sequence a plurality of sets of reception interval time of sets of a pair of pieces of synchronization information received in less than a predetermined time in a set of reception timings in which a plurality of pieces of synchronization information transmitted from a slave device CLb are received by a master device CLa; a difference calculation unit 77 that calculates a difference in propagation time of synchronization information of the sets on the basis of the reception interval time of each set and a predetermined unit time determining the transmission interval time in which the slave device CLb transmits the synchronization information; an average value calculation unit 78 that calculates an average value of the differences of the propagation time; a correction value calculation unit 79 that calculates a correction value of the propagation time on the basis of the difference of the propagation time which is calculated for a set of subsequent synchronization information in a time-sequence subsequent in time sequence to a set of synchronization information in which the average value is calculated; and a correction value recording unit 80 that records the correction value on the synchronization information transmitted to the slave device CLb.SELECTED DRAWING: Figure 4

Description

TECHNICAL FIELD The present invention relates to an information communication system and information communication apparatus that synchronizes a plurality of information communication apparatuses through communication.

As a general time synchronization method between a plurality of information communication devices, for example, IEEE1588 Precision Time Protocol (PTP) of Non-Patent Document 1 is known. In Non-Patent Document 1, a master device that has a reference time and a slave device that synchronizes with the time of the master device are defined, and time synchronization packets are periodically exchanged between the master device and the slave device. Correct the time of the slave device.

Specifically, the master device's transmission time and the slave device's reception time of a packet sent from the master device to the slave device, as well as the slave device's transmission time and the master device's reception time of the packet sent from the slave device to the master device. Using the time, the slave device estimates and corrects the time offset, which is the time difference between the master device and the slave device.

“IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems.”IEEE Standard 1588-2008. JP2016-225880A

In the PTP system, when transmitting and receiving information bidirectionally between a master device and a slave device, it is assumed that the propagation time from one device to the other is the same as the propagation time from the other device to the other device. However, the propagation time depends on the buffering time of the devices that make up the network, the number of nodes passed through during transmission and reception, and the like. Therefore, in reality, there may be a difference between the transmission and reception times and symmetry cannot be maintained.

To deal with this, PTP systems use network relay devices such as boundary clocks (BCs) and transparent clocks (TCs) to cancel the varying propagation time, thereby improving the time synchronization accuracy derived from variations in propagation time. Decrease problems are reduced. The BC corrects delay time and fluctuations based on the time received from the higher-level master device, and generates a time as a master for the lower-level slaves. When relaying a packet, the TC adds the residence time within the relay device and transmits it to the lower slave.

However, BC and TC are generally expensive, leading to high costs for constructing a time synchronization system. Therefore, an alternative solution is expected that satisfies the system requirements for time synchronization accuracy without introducing BC and TC.

For example, Patent Document 1 proposes a method of absorbing variations in propagation time by using the minimum packet time. However, since the minimum packet time in each direction of information communication is determined independently and moment by moment, the symmetry of propagation time is not evaluated, leading to a decrease in time synchronization accuracy.

Furthermore, since the main cause of time difference fluctuations is the frequency deviation of clocks between devices, some implementations of PTP provide an option to find and cancel this frequency deviation. However, since error factors due to propagation time fluctuations are not removed, time synchronization accuracy deteriorates.

The present invention has been made to solve the above-mentioned problems, and provides an information communication system and an information communication device that can absorb fluctuations in the propagation time of information communication and perform synchronous control with reduced errors. There is a particular thing.

The present invention provides an information communication system in which a plurality of information communication devices communicate information as a master device or a slave device, wherein the master device transmits a plurality of synchronization information transmitted from the slave device to the master device. an interval time calculation unit that calculates a plurality of reception interval times of a pair of synchronization information sets received within a predetermined time in a set of reception timings received by the synchronous information set, and a reception interval time of each set; and a predetermined unit time that determines the transmission interval time at which the slave device transmits the synchronization information. an average value calculation unit that calculates an average value of the difference in the propagation time; and an average value calculation unit that calculates the average value of the difference in the propagation time; and a correction value calculation unit that calculates a correction value for the propagation time based on the time difference and the average value calculated by the average value calculation unit; and a correction value recording section for recording.

The present invention relates to an information communication device that communicates information with another information communication device, and in which a pair of synchronization information received within a predetermined time in a set of reception timings of a plurality of synchronization information from the other information communication device. an interval time calculation unit that calculates reception interval times of a plurality of sets of synchronization information along a time series; a reception interval time of each set; and a transmission interval time at which another information communication device transmits the synchronization information; a difference calculation unit that calculates a difference between the propagation times of each set of the synchronization information based on a predetermined unit time; and an average value calculation unit that calculates an average value of the differences in the propagation times calculated by the difference calculation unit; The difference in the propagation time obtained by the difference calculation section for the synchronization information set that is chronologically subsequent to the synchronization information set for which the average value was obtained, and the average value obtained by the average value calculation section. , and a correction value recording unit that records the correction value in the synchronization information to be transmitted to another information communication device.

According to the present invention, it is possible to provide an information communication system and an information communication device that can absorb fluctuations in the propagation time of information communication and perform synchronous control with reduced errors.

1 is a schematic diagram of an information communication system according to an embodiment. FIG. 1 is a functional block diagram of an information communication device that constitutes an information communication system according to an embodiment. FIG. 2 is a diagram showing a mode of communication between information communication devices. It is a functional block diagram of a control part concerning an embodiment. FIG. 2 is a diagram illustrating an aspect of communication having propagation time symmetry. FIG. 2 is a diagram illustrating an aspect of communication without propagation time symmetry. FIG. 3 is a diagram showing a synchronization state vector without errors due to variations in propagation time and time difference. FIG. 3 is a diagram showing a synchronization state vector including errors due to fluctuations in propagation time and time difference. 1 is a diagram showing a collection of information communications in an information communications system according to an embodiment; FIG. It is a graph explaining a method of calculating a correction value from a time-series propagation time difference and an average value. It is a flowchart which shows the procedure of synchronous control processing of an embodiment.

An information communication system and an information communication device according to embodiments will be described below with reference to the drawings.

[composition]
FIG. 1 is a schematic diagram of an information communication system 100 according to an embodiment. FIG. 2 is a functional block diagram of the information communication device 1 that constitutes the information communication system 100 according to the embodiment. FIG. 3 is a diagram showing a mode of communication between the information communication devices 1, and FIG. 4 is a functional block diagram of the control unit 70 in FIG. 2.

The information communication system 100 according to this embodiment includes a plurality of information communication devices 1, and each information communication device 1 attempts to synchronize through information communication. The information communication device 1 that is a slave device is synchronized with the information communication device 1 that is a master device. A master device is an information communication device 1 that is a target to be synchronized with other information communication devices 1 in the information communication system 100. A slave device is an information communication device 1 that is synchronized with another information communication device 1 that is a master device in the information communication system 100. The slave device synchronizes with the master device by transmitting and receiving synchronization information, which is information for time synchronization, between the slave device and the master device.

The information communication device 1 serving as a master device is referred to as a master device CLa, and the information communication device 1 serving as a slave device is referred to as a slave device CLb. Although it is sufficient that at least one slave device CLb exists for the master device CLa, the system may include a plurality of slave devices CLb as shown in FIG.

The master device CLa and slave device CLb are connected via a network that allows them to communicate information. In this embodiment, an example will be described in which the information communication device 1 achieves synchronization by transmitting and receiving information by wire, but it may also be synchronized wirelessly.

(Information communication device)
The information communication device 1 includes a computer, and performs necessary calculations by having a processor including a CPU execute a program stored in advance in a storage unit such as an HDD or SSD.

Specifically, as shown in FIG. 2, the information communication device 1 includes a communication section 10, a clock 20, a timepiece 30, a storage section 50, an external interface 60, and a control section 70. For example, each section 10 to 70 is configured as hardware. Each part of the control unit 70 may be configured by software including programs and data. The design of which part of the control unit 70 is configured as software can be changed as appropriate.

The communication unit 10 transmits and receives information to and from other information communication devices 1 . That is, the communication unit 10 transmits information to the outside of the information communication device 1, receives information from outside the information communication device 1, or both. The communication section 10 includes a transmitter 11, a receiver 12, a transmission timing detection section 13, and a reception timing detection section 14.

The transmitter 11 is a device that transmits input information. Specifically, the transmitter 11 disassembles the information into minimum constituent elements in time series and transmits the information to the outside. The information packet length (communication information amount) is arbitrary and may be different for each communication. For example, an input unit that converts an audio signal input from a microphone into audio data is connected to the information communication device 1, and audio data as information is input to the information communication device 1 from the input unit.

The receiver 12 is a device that receives information from the outside. Specifically, the receiver 12 reconstructs information received from outside the information communication device 1 and decomposed in time series into the minimum constituent elements, and outputs the reconstructed information to other components in the information communication device 1. For example, a playback unit such as an ear receiver or a speaker that outputs audio is connected to the information communication device 1, and the receiver 12 converts audio data into an audio signal and outputs it to the playback unit. In this way, the information that is transmitted and received and decomposed in time series into the minimum constituent elements can specify the time series position of each element, that is, the information element position.

Here, the information communicated by the information communication device 1, that is, the information transmitted by the transmitter 11 and the information received by the receiver 12, includes information for synchronizing time between the master device CLa and the slave device CLb. Contains synchronization information.

The transmission timing detection unit 13 detects transmission timing. The transmission timing is the timing at which a predetermined information element position of the information transmitted by the transmitter 11 is transmitted to the outside of the information communication device 1. This transmission timing is detected based on the clock cycle of the clock 20 (in other words, the cycle of the pulses oscillated by the clock 20), which will be described later. That is, the transmission timing is expressed based on an integral multiple of the clock period.

Further, the transmission timing detection unit 13 can also output the detection result to other components within the information communication device 1. The information referred to here is, for example, a packet, and in this case, a predetermined information element position (hereinafter referred to as a predetermined information element position) is a bit position.

The reception timing detection section 14 detects reception timing. The reception timing is the timing at which the information received by the receiver 12 is received from outside the information communication device 1. This reception timing is detected based on the clock cycle of a clock 20, which will be described later. That is, the reception timing is expressed as an integral multiple of the clock period. Further, the reception timing detection unit 14 outputs the detection result to other components within the information communication device 1.

FIG. 3 takes wired communication as an example. In packet transmission between information communication devices 1, a specific bit position in the packet is detected as the transmission/reception timing, and the transmission interval and reception interval are determined from the adjacent transmission timing and reception timing, respectively. It shows the configuration.

Note that the transmission timing and reception timing may both detect the same position of the minimum component, but if a predetermined relationship is maintained in each timing detection between the information communication devices 1 that transmit and receive, it is not necessary to detect the same position. It is not necessary to do so, and the detected element position shift can be ignored or corrected.

Furthermore, the transmission timing may be detected a predetermined time later than the actual transmission timing. The reception timing may be detected a predetermined time later than the actual reception timing. These predetermined values may be fixed within the communication unit, or may be set statically or dynamically from the outside.

The clock 20 oscillates at a predetermined frequency and outputs a signal that provides operation timing to each part of the information communication device 1. As a result, each part within the information communication device 1 operates in synchronization with the clock 20. The entire information communication device 1 may be synchronized with a single clock 20 all at once, or each of a plurality of functional units may be independently synchronized with a plurality of clocks 20. This clock 20 has an inherent finite oscillation frequency tolerance. That is, the clock 20 has an error (for example, 20 ppm) with respect to a predetermined oscillation frequency (for example, 10 MHz). As the clock 20, for example, a fixed frequency oscillator such as a crystal resonator can be used.

Even if the nominal frequency of the clock 20 is the same between the master device CLa and the slave device CLb, there are actually individual differences. That is, there is a frequency deviation between the frequencies of the clocks 20 of the master device CLa and the slave device CLb. A frequency control signal may be inputted to the clock 20 from the outside, and the oscillation frequency may be variably controlled in response to the signal.

The clock 30 clocks using the output signal of the clock 20 as a source oscillation, and outputs the relative time from the start of the information communication device 1. The clock may be synchronized with the frequency-divided wave of the input clock signal. Further, the timing may be variable in advance width per clock, or the driving frequency of the clock may be intermittently controllable even if the clock frequency is fixed. Although the time is referred to in a specified unit, this specified value may be fixed within the clock, or may be set statically or dynamically from the outside. The relative time of the clock 30 is output, for example, in response to an external reference request.

The storage unit 50 is a recording medium such as an HDD, SSD, memory, or register. The storage unit 50 stores information necessary for the control unit 70 to perform calculations. It is preferable that the time of the clock 30 corresponding to the transmission timing or reception timing, which will be described later, be held in a recording medium that can be held by access only by hardware without using the CPU or software. This is because jitter caused by software can be eliminated. Note that it is important that the correspondence between the transmission/reception timing and the time is not affected by software jitter, and after the transmission/reception timing and the time are correlated, it may be stored in a low-speed access area.

The memory serving as the storage unit 50 inputs and outputs arbitrary information and stores the information in a designated storage area. Information is stored in response to an external storage request, and at that time the information to be stored and the storage area are input. Information is referenced by a reference request from the outside, and at that time, the storage area of the reference information is input, and the information of the storage area specified by the input is output. The storage of information may be maintained only while the device is in operation, or permanently, including when the device is stopped.

The external interface 60 (hereinafter also referred to as external I/F 60) connects the inside of the information communication device 1 and the outside, and inputs and outputs arbitrary information. The information includes transmitted and received data such as synchronization information, the time of the clock 30, and other information to be stored in the storage unit 50. Further, the information communication device 1 may have a user interface such as a display device that can control and display internal states.

The control section 70 controls the overall operation of each section of the information communication device 1. FIG. 4 is a functional block diagram of the control unit 70. As shown in FIG. 4, the control section 70 includes a main control section 71, a transmission/reception data I/F 72, a communication control section 73, a scheduler 74, a time recording section 75, an interval time calculation section 76, a difference calculation section 77, and an average value calculation section. section 78 , a correction value calculation section 79 , a correction value recording section 80 , and a synchronization control section 81 .

The main control section 71 is linked with each section within the control section 70 and controls the operation of each section within the control section 70 . The transmission/reception data I/F 72 converts the information in the storage unit 50 and the external I/F 60 into a format that can be transmitted to the outside of the device. Further, the transmission/reception data I/F 72 converts information received from outside the apparatus into a format suitable for the control section 70 and the storage section 50 .

The communication control unit 73 controls the operation of the communication unit 10. The communication control section 73 inputs and outputs information to be transmitted and received between the communication section 10 and the control section 70 .

Scheduler 74 controls the schedule (time) for transmitting or receiving information. For example, when communicating information in one direction, the scheduler 74 on the transmitting side controls the information transmission interval and sets a schedule in which the information transmission timing is detected at a predetermined time.

The scheduler 74 in the slave device CLb of this embodiment controls the transmission timing of synchronization information. The synchronization information here corresponds to, for example, the IEEE1588 Delay_Req message. In IEEE1588, the slave device CLb repeatedly transmits a Delay_Req message, which is synchronization information, at random transmission intervals. Although the synchronization information transmission interval is a sufficiently large interval compared to the propagation time of the synchronization information, it includes discrete randomness. For example, it is a multiple of a predetermined unit time G, such as a time determined by a power of 2 such as 1/2 second or 1/4 second. Since the signals are transmitted from a large number of slave devices CLb, the intervals are random to prevent batting.

The time recording unit 75 associates the reception timing of the information received by the reception timing detection unit 14 with the time of the clock 30 at the reception timing, and stores them in the memory. For example, the time recording unit 75 receives a signal from the reception timing detection unit 14 indicating that the reception timing of the received information has been detected, refers to the time on the clock 30, and compares the time and the reception timing. Correlate with.

As described above, in the present embodiment, "time" refers to the time of the clock 30 corresponding to the detected reception timing or transmission timing of a predetermined information element position of information, and "time" refers to the difference between the times. .

The interval time calculation unit 76 chronologically calculates the reception interval times of a pair of synchronization information sets received within a predetermined time in a collection of reception timings of a plurality of synchronization information transmitted from other information communication devices 1. Calculate multiple sets along the same line. This reception timing is the timing at which the master device CLa receives a plurality of pieces of synchronization information transmitted from the slave device CLb. As will be described later, the predetermined time is the minimum interval time at which the influence of the frequency deviation between the master device CLa and the slave device CLb appears on the information propagation time between the master device CLa and the slave device CLb. The frequency deviation is the difference between the clock frequency of the master machine and the clock frequency of the slave machine.

The reception interval time is the difference between the reception timings of a pair of synchronization information. The reception interval time is determined from the time difference between two receptions by referring to the time corresponding to the reception timing from the clock 30.

The difference calculation unit 77 calculates the difference in the propagation time of each set of synchronization information based on the reception interval time of each set and a predetermined unit time G that determines the transmission interval time at which the slave device CLb transmits the synchronization information. . As described later, this unit time G is a value sufficiently larger than the propagation time, and can be a value specific to the information communication system 100.

The average value calculation unit 78 calculates the average value of the differences between the plurality of sets of propagation times determined by the difference calculation unit 77. Based on the average value and the difference in propagation time obtained by the difference calculation section 77, the correction value calculation section 79 calculates Find the propagation time correction value. The correction value recording unit 80 records the correction value in the synchronization information to be transmitted. That is, the correction value is included in the synchronization information packet transmitted to the slave device CLb.

The synchronization control unit 81 performs time synchronization based on the received synchronization information. That is, synchronization control is performed by assuming that the correction value included in the synchronization information received by the slave device CLb is a symmetrical propagation time between the master device CLa and the slave device CLb. For example, as will be described later, a time difference, that is, a time difference, with respect to the information communication device 1 serving as the synchronized device (master device CLa) is calculated, and the clock value of the clock 30 is corrected based on the time difference. For example, the correction may be performed by controlling the clock 30 itself to correct the clock time. Alternatively, when the clock 30 outputs the time, it may be corrected based on the time difference. That is, the clock 30 may not be corrected, but the clock 30 may be controlled to output a time with the deviation corrected when the clock 30 outputs the time.

[Measurement of time difference when there is symmetry in propagation time]
Next, measurement of propagation time and time difference when propagation time has symmetry will be described with reference to FIG. 5. Taking wired communication as an example, FIG. 5 shows the relationship between the time difference between the respective clocks, the information propagation time, and the transmission/reception timing observed through information communication between a pair of master device CLa and slave device CLb. .

Note that the synchronization information transmitted by the master device CLa and the other synchronization information transmitted by the slave device CLb are for the purpose of measuring timing for synchronization, and the synchronization information includes the synchronization information transmitted by the master device CLa. Although the transmission time and the like are listed, the contents of the synchronization information and the other synchronization information are arbitrary.

As shown in FIG. 5, the master device CLa transmits information at time t _a,T , and the slave device CLb receives it at time t _b,R after propagation time d. After Δt _b , the slave device CLb transmits another information at time t _b,T , and the master device CLa receives it at time t _a,R after the same propagation time d.

Here, the interval from transmission to reception in master device CLa is Δt _a , the interval from reception to transmission in slave device CLb is Δt _b , and the same timing as transmission timing t _a,T of master device CLa is It is assumed that the observation is made as t _{' a,T} in the device CLb. Therefore, the time difference g between the clock 20 and the slave device CLb based on the master device CLa at a certain moment can be determined as shown in equation (1). Furthermore, the time difference between the clocks of the master device CLa and the slave device CLb at the same instant can be expressed as -g.

なお、上記のように、マスター装置ＣＬａからのスレーブ装置ＣＬｂへの伝搬時間ｄとスレーブ装置ＣＬｂからマスター装置ＣＬａへの伝搬時間ｄは同じ、つまり情報通信の方向において対称であることを前提としている。

Note that, as described above, it is assumed that the propagation time d from the master device CLa to the slave device CLb and the propagation time d from the slave device CLb to the master device CLa are the same, that is, they are symmetrical in the direction of information communication. .

From these conditions, the propagation time d can be determined as shown in equation (2).

Therefore, the time difference g between the clocks 20 can be determined as shown in equation (3) using equation (2).

The synchronization control unit 81 of the slave device CLb can synchronize the time with the master device CLa by repeatedly adjusting the clock frequency and time so that the time difference g between the clocks 20 becomes 0.

If the clock frequencies of the master device CLa and slave device CLb are the same, that is, if the clock domain is single, time synchronization is possible by simply adjusting the time once, but generally there is a frequency difference between the two clocks. Because of the deviation, clock frequency adjustment is essential for time synchronization. Even in systems where the clock frequency cannot be directly adjusted, the driving frequency of the clock 30 can be controlled and time synchronization can be achieved by repeatedly adjusting the advance width of each clock. In these frequency adjustments, closed-loop control is periodically performed in which the synchronization phase is input and the frequency adjustment value is output, and the output value is controlled so that the input synchronization phase becomes zero.

Note that the propagation time and internal delay between transmission and reception timings can be ignored or corrected depending on system requirements. Furthermore, instead of starting the transmission of synchronization information from the master device CLa, the synchronization information may be transmitted from the slave device CLb. Furthermore, although one interface is necessary and sufficient for information communication, a configuration may be adopted in which multiple interfaces are used simultaneously, for example, by implementing transmitting and receiving interfaces independently.

[Effects of time difference and propagation time fluctuations]
The above description assumes that the time difference is constant and the propagation times are symmetrical in the direction of information communication. However, the frequency deviation from the nominal frequency of the clock 20 between the actual information communication devices 1 is different and fluctuates from time to time. For this reason, the time difference between the information communication devices 1 also changes, and depending on the network system to which the master device CLa and slave device CLb are connected, the information propagation path and communication arbitration are affected, as shown in FIG. Generally, the propagation time is asymmetric.

That is, the time difference g _b/a between the master device CLa and slave device CLb at a certain moment and the time difference g _a/b between the same master device CLa and slave device CLb after a certain period of time are not the same. Furthermore, the propagation time d _b/a of information from the master device CLa to the slave device CLb is generally not the same as the propagation time d _a/b of information from the slave device CLb to the master device CLa. Note that the time difference in FIG. 6 is such that g _b/a and g _a/b have the same sign, and g _b/a ·ga _/b ≧0 in order to match the expression with the time difference in FIG. 5 . Furthermore, as mentioned above, the time difference and propagation time fluctuate from moment to moment, and the time difference g _b/a [m] observed at one moment and the propagation time d _b/a [m] observed at a different moment Generally, the time difference g _b/a [n] and the propagation time d _b/a [n] are different from each other.

Here, from the relationship of each time in FIG. 6, using the propagation times d _b/a and d _a/b and the time differences g _b/a and g _a/b , equations (2) and (3) are transformed into equations, respectively. Organize as shown in (4) and (5).

In Equation (2), the propagation time could be determined assuming symmetry, but in Equation (4), it can be seen that the average value of the propagation time includes a fluctuation component of the time difference. Similarly, in Equation (3), the time difference could be calculated on the assumption that the time difference is constant, but in Equation (5), the average value of the time difference includes the fluctuation component of the propagation time. I understand. If the time difference and propagation time fluctuation components are included in this way, the accuracy of time synchronization will be reduced.

[Error due to time difference and propagation time fluctuation]
In a time synchronization system, we will explain the time synchronization errors caused by variations in time difference and propagation time. First, both equations (4) and (5) are combined and transformed into matrix form as shown in equation (6).

Here, the two-dimensional rotation matrix R _θ is expressed as Equation (7).

Then, by focusing on the common factor in equation (6) and using R _θ in equation (7), equation (6) can be transformed into equation (8).

As shown in FIG. 7, the horizontal axis is the time difference g _b/a and propagation time d _b/a components when communicating from the master device CLa to the slave device CLb, and the vertical axis is the component from the slave device CLb to the master device CLa. Consider a two-dimensional space in which the time difference g _a/b and propagation time d _a/b are components when communication is performed. Then, if (g _{b/a -} g _a/b ) ^T is the time difference vector g and (d _{b/a da/b} ) ^T is the propagation time vector d, then the time difference including the fluctuation error in equation (8) Synchronous state vector ^s = (g _d d _g ) whose elements are propagation time and It can be interpreted as

In the operation of equation (8), there is no variation in the elements g _b/a and g _a/b of the time difference vector g, and there is no variation in the elements d _b/a and d _a/b of the propagation time vector d, that is, g When _b/a = g _a/b and d _b/a = da _/b , as shown in Fig. 7, the synchronization state vector s can be orthogonally decomposed into d _g components and g _d components to reduce the error. It can be seen that the time difference and delay time can be calculated without including the time difference and delay time.

However, as shown in FIG. 8, the time difference vector g and the propagation time vector d generally include fluctuation errors in their respective elements. Therefore, since mutual errors are combined into each orthogonal component, the errors cannot be removed from the time difference and propagation time only by the operation of equation (8), resulting in a decrease in time synchronization accuracy.

Since Equations (4) and (5) are linearly dependent, solutions cannot be obtained analytically without introducing other independent operations. It is not possible to find new independent operations that become vectors. Therefore, it is necessary to introduce another approach to remove the fluctuation error.

[Improvement of synchronization accuracy using master device]
According to conventional time synchronization principles such as IEEE1588, it is the slave device CLb that performs time synchronization calculations, and the master device CLa only performs transmission and reception of synchronization information. Therefore, in order to update the existing information communication system 100 and perform time synchronization based on a new principle, it is necessary to incorporate new applications into each of the many slave devices CLb, or replace the existing slave device CLb with a new slave device CLb. It is necessary to replace it with a new one, which incurs a great deal of effort and cost. Therefore, in the information communication system 100, it is preferable to improve time synchronization accuracy by replacing the master devices CLa, which are smaller in number than the slave devices CLb.

FIG. 9 shows the relationship between the time difference in transmission and reception timing and the propagation time when synchronization information is communicated from the slave device CLb to the master device CLa in this embodiment.

Master device CLa receives the synchronization information transmitted from slave device CLb as described above. The master device CLa does not need to know the transmission timing of the synchronization information, and it is generally not included in the Delay_Req message. Therefore, the master device CLa can only know the timing of receiving this synchronization information. In this embodiment, the master device CLa uses only the reception timing of the synchronization information in the direction from the slave device CLb to the master device CLa.

The interval between t _a,R [j] and t _a,R [i] shown in FIG. 9 is set to Δt _a,R [i,j]=t _a,R [j]-t _a,R [i] can be expressed as in equation (9).

In equation (9), the first term t _b,T [j]−t _b,T [i] on the right side is the transmission interval of the slave device CLb. The second term g _a/b [j] - _{g a/b} [i] on the right side is the time difference between the master device CLa and the slave device CLb, and the same master device CLa and slave device CLb after the transmission interval. This is the difference between the time difference between The third term d _a/b [j] - d _a/b [i] on the right side is the propagation time from the master device CLa to the slave device CLb, and the propagation time from the same master device CLa to the slave device CLb after a transmission interval. This is the difference between the propagation time and the propagation time.

What the master device CLa can recognize is only Δt _a,R [i,j] on the left side. The first, second, and third terms on the right side are information that the master device CLa cannot recognize. Each item will be considered below.

First, the second term is the difference in time difference, as described above. Therefore, if the period from timing n to timing n+N is less than the minimum time Lg[n] in which the time difference occurs, the second term can be regarded as 0. This is because the propagation time is generally smaller than this minimum time L _g [n]. Since the propagation time is a very small value, even if a frequency deviation is applied to it, its effect will not be apparent.

Here, between the information communication devices 1 where the clock 20 has a nominal frequency f _N and an apparent frequency deviation e [n], the minimum time L _g [n] at which there is a time difference between the observation times of both devices is given by equation (10). It can be expressed as follows. Note that T _N =1/f _N.

Therefore, by selecting communication at timing n+N, which is less than the minimum time Lg[n] from timing n, the second term can be canceled. In other words, less than the predetermined time required for a pair of reception timings for which the reception interval time is to be calculated is a time smaller than (less than) this minimum time L _g [n]. Note that the time may be set to be longer than L _g [n] as long as the time synchronization accuracy required for the information communication system 100 can be satisfied. That is, the predetermined time is not limited to the minimum time L _g [n], and may be a larger value depending on the required accuracy of the information communication system 100. Here, for example, the upper limit of the predetermined time corresponds to the allowable time difference G _T in observation time occurring between the master device CLa and the slave device CLb, and if k = G _T f _N , then kL _g [n ].

Next, the first term is the synchronization information transmission interval, and this transmission interval is a value that is sufficiently larger than the propagation time, that is, from each propagation time d _a/b [n] to d _a/b [n+N]. is also a sufficiently large multiple of unit time G. Therefore, w[i,j]G corresponding to Δt _a,R [i,j] can be obtained. Note that w[i,j] is a coefficient corresponding to Δt _a,R [i,j].

Since the unit time G is a set value of IEEE1588, it can be specified by setting it as a value unique to the information communication system 100. However, as described above, different values can be set for each slave device CLb in order to avoid conflict between the slave devices CLb. In this case, G may be specified by finding and comparing Δt _a,R [i, j] for various combinations of [i, j]. Since G is a constant and w[i,j] is a random integer, G can be specified. For example, the ratio of w[i,j]G and w[i,k]G is w[i,j]/w[i,k], but if this is 2, then w[i,j ]Gw[i,k]G=(2-1)G=G.

By satisfying the above conditions, equations (9) to (11) can be expressed. In other words, Δd _a/b [i, j], which is the difference in propagation time, can be obtained.

Then, with timing n as a reference, the average value μΔd _{a /b [} n , N] can be determined according to equation (12). FIG. 10 shows a graph in which the differences in each propagation time are schematically arranged in chronological order.

The first term μd _a/b [n+1, n+N] on the right-most side of equation (12) is the average value of the propagation time d _a/b [ ] from timing n+1 to timing n+N, and the second term d _a/b [n] means the propagation time of timing n. That is, the average value of the propagation time difference includes the average value of the propagation time. Therefore, if it is possible to continuously obtain μd _a/b [n+1, n+N] by shifting the timing n in time series, the propagation will be more stable and smooth than the propagation time d _a/b [ ] at each timing. You get time.

Therefore, at timing n+N+1 as well, the propagation time difference Δd _a/b [n+1, n+N+1] is calculated, and as shown in equation (13), μd _a/b [n+1, n+N] of equation (12) is used. , a propagation time correction value c _a/b [n+N+1] at timing n+N+1 is determined. d _a/b [n] included in the first and second terms on the right side of equation (24) are canceled out by subtraction.

For time synchronization calculation in the slave device CLb, the master device CLa records the reception timing t _a,R [ ] of the synchronization information from the slave device CLb in new synchronization information and sends it back to the slave device CLb. There is a need. At this time, the correction value c _a/b [n+N+1] obtained by equation (13) is recorded in the synchronization information.

More specifically, the synchronization information returned by the master device CLa corresponds to a Delay_Resp message in IEEE1588. The correction value c _a/b [n+N+1] corresponds to the value inserted into the CorrectionField in the Delay_Resp message. In IEEE1588, the CorrectionField includes the sum total of residence time due to synchronization information passing through a relay device between the master device CLa and the slave device CLb.

The slave device CLb compliant with IEEE1588 corrects fluctuations in the propagation time of information communication by subtracting the value of CorrectionField from the reception timing of the Delay_Resp message. Similarly, in this embodiment, the slave device CLb subtracts the correction value c _a/b [n+N+1] recorded in the CorrectionField from the timing of receiving the returned synchronization information, as shown in equation (14). The average value μd _a/b [n+1, n+N] of the stable synchronization information propagation time is determined (see FIG. 10).

As a result, the slave device CLb can perform time synchronization calculations using the average value μd _a/b [n+1, n+N] of the propagation time of synchronization information as the propagation time, so that the time synchronization accuracy can be improved. can. In order to improve synchronization accuracy, the closer the uplink and downlink propagation times are to symmetrical, the better. As mentioned above, even if the propagation time is manipulated to a value different from the actual time in one direction, the value is smoothed by the average value μd _a/b [n+1, n+N], so that the propagation time in both directions is The difference in time fluctuation becomes smaller than before smoothing. This makes it possible to approximate the two-way propagation time to a symmetrical state and determine the time difference.

[motion]
Based on the above, the operation of the information communication system 100 of this embodiment will be explained with reference to the flowchart of FIG. 12. Note that an information communication method, an information communication program, and a recording medium on which the information communication program is recorded are also one aspect of the present invention. First, the communication control unit 73 of the slave device CLb transmits a plurality of pieces of synchronization information to the master device CLa according to the scheduler 74. This is done at a transmission interval based on the unit time G, as described above.

Master device CLa receives synchronization information from slave device CLb (step S101). The interval time calculation unit 76 of the master device CLa selects a set of reception timings from timing n to timing n+N less than the minimum time L _g [n], and calculates the reception interval time of each set (step S102).

The difference calculation unit 77 calculates the difference in propagation time of each set of synchronization information (step S103). This is done by subtracting the transmission interval set based on a predetermined unit time G from the reception interval. The average value calculation unit 78 calculates the average value of the differences in the propagation times of the plurality of sets (step S104). The correction value calculation unit 79 calculates a correction value by subtracting the average value calculated by the average value calculation unit 78 from the difference in propagation time calculated by the difference calculation unit 77 for the subsequent synchronization information set (step S105). ). The correction value recording unit 80 records the correction value in the synchronization information (step S106). That is, the correction value is written in the CorrectionField of the Delay_Resp message.

The communication control unit 73 of the master device CLa transmits the synchronization information in which the correction value is recorded to the slave device CLb (step S107). The synchronization control unit 81 of the slave device CLb performs synchronization control based on the received synchronization information.

[effect]
(1) The present embodiment is an information communication system 100 in which a plurality of information communication devices 1 communicate information as a master device CLa or a slave device CLb, and in which a plurality of synchronization information transmitted from a slave device CLb is transmitted. In the set of reception timings received by the master device CLa, an interval time calculation unit 76 calculates a plurality of reception interval times of a pair of synchronization information sets received within a predetermined time in a chronological order; a difference calculation unit 77 that calculates the difference between the propagation times of each set of synchronization information based on the reception interval time and a predetermined unit time G that determines the transmission interval time at which the slave device CLb transmits the synchronization information; The average value calculation unit 78 calculates the average value of the differences in the propagation times calculated by the difference calculation unit 77, and the propagation time calculated by the difference calculation unit 77 for a set of synchronization information that is subsequent in time series to the set of synchronization information for which the average value was calculated. and a correction value calculation unit 79 that calculates a correction value for the propagation time based on the difference between the values and the average value calculated by the average value calculation unit 78. It has a recording section 80.

The slave device CLb includes a synchronization control unit 81 that performs synchronization control based on synchronization information in which correction values are recorded.

Further, the present embodiment is an information communication device 1 that communicates information with another information communication device 1, and in a set of reception timings of a plurality of synchronization information from the other information communication devices 1, within a predetermined time. An interval time calculation unit 76 calculates the reception interval time of a plurality of sets of received synchronization information in chronological order, the reception interval time of each set, and another information communication device 1 transmits the synchronization information. a difference calculation unit 77 that calculates the difference in propagation time of each set of synchronization information based on a predetermined unit time G that determines the transmission interval time; and an average value calculation unit 78 that calculates the average value of the difference in propagation time; Based on the difference in propagation time obtained by the difference calculation unit 77 for a set of synchronization information subsequent to the set of synchronization information for which the average value was calculated, and the average value calculated by the average value calculation unit 78, It has a correction value calculation unit 79 that calculates a time correction value, and a correction value recording unit 80 that records the correction value in synchronization information that is transmitted to another information communication device 1.

In this way, in order to smooth the propagation time between the information communication devices 1, that is, the propagation time from the slave device CLb to the master device CLa, using the correction value, the slave device CLb adjusts the time based on the smoothed propagation time. Synchronization is possible. Therefore, variations in propagation time can be absorbed, errors can be reduced, and time synchronization accuracy can be improved. In addition, by including the correction value in the synchronization information, time synchronization can be achieved at low cost using an existing time synchronization mechanism. In other words, time synchronization with the desired accuracy required for the information communication system 100 is possible while utilizing the existing PTP system without using BC or TC. The slave device CLb can also be compliant with the existing protocol and can be used as is, so that high costs can be suppressed.

(2) The predetermined time is the minimum interval time at which the influence of frequency deviation between the master device and the slave device appears. Therefore, time difference errors can be eliminated by observing within the minimum time period in which the influence of frequency deviations is not apparent.

[Other embodiments]
The present invention is not limited to the above-mentioned embodiments as they are, and in the implementation stage, the constituent elements can be modified and embodied without departing from the spirit of the invention. Moreover, various inventions can be formed by appropriately combining the plurality of components disclosed in the above embodiments.

1 Information communication device 10 Communication unit 11 Transmitter 12 Receiver 13 Transmission timing detection unit 14 Reception timing detection unit 20 Clock 30 Clock 50 Storage unit 60 External interface 70 Control unit 71 Main control unit 72 Transmission/reception data I/F
73 Communication control section 74 Scheduler 75 Time recording section 76 Interval time calculation section 77 Difference calculation section 78 Average value calculation section 79 Correction value calculation section 80 Correction value recording section 81 Synchronization control section 100 Information communication system

Claims (5)

An information communication system in which a plurality of information communication devices communicate information as a master device or a slave device,
The master device receives a plurality of synchronization information transmitted from the slave device, in a set of reception timings at which the master device receives, the reception interval time of a pair of synchronization information sets received less than a predetermined time, an interval time calculation unit that performs multiple sets of calculations along the time series;
a difference calculation unit that calculates a difference between the propagation times of the synchronization information of each set based on the reception interval time of each set and a predetermined unit time that determines the transmission interval time at which the slave device transmits the synchronization information;
an average value calculation unit that calculates an average value of the difference in the propagation time calculated by the difference calculation unit;
The difference in the propagation time obtained by the difference calculation section for the synchronization information set that is chronologically subsequent to the synchronization information set for which the average value was obtained, and the average value obtained by the average value calculation section. a correction value calculation unit that calculates a correction value for the propagation time based on;
a correction value recording unit that records the correction value in the synchronization information transmitted to the slave device;
An information communication system characterized by having. 2. The information communication system according to claim 1, wherein the predetermined time is a minimum interval time at which the influence of frequency deviation between the master device and the slave device appears. 3. The information communication system according to claim 1, wherein the slave device includes a synchronization control section that performs synchronization control based on the synchronization information in which the correction value is recorded. An information communication device that communicates information with another information communication device,
Interval time calculation that calculates the reception interval times of a pair of synchronization information sets received less than a predetermined time in a time series in a set of reception timings of multiple synchronization information from other information communication devices. Department and
A difference calculation unit that calculates the difference in the propagation time of each set of synchronization information based on the reception interval time of each set and a predetermined unit time that determines the transmission interval time at which another information communication device transmits the synchronization information. and,
an average value calculation unit that calculates an average value of the difference in the propagation time calculated by the difference calculation unit;
The difference in the propagation time obtained by the difference calculation section for the synchronization information set that is chronologically subsequent to the synchronization information set for which the average value was obtained, and the average value obtained by the average value calculation section. a correction value calculation unit that calculates a correction value for the propagation time based on;
a correction value recording unit that records the correction value in the synchronization information transmitted to another information communication device;
An information communication device comprising: 5. The information communication device according to claim 4, wherein the predetermined time is a minimum interval time at which the influence of frequency deviation with other information communication devices appears.

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