JP2023045229A - Information communication system and information communication device - Google Patents

Abstract

Kind Code: A1 An information communication system and apparatus capable of absorbing variation in propagation time of information communication and performing synchronization control with reduced error are provided.
Kind Code: A1 In an information communication system, a controller controls a set of first information communications, which are a plurality of information communications performed within a predetermined time period with respect to a first timing, between a master device and a slave device. , an interval for calculating the transmission interval time and the reception interval time in the set of the second information communication, which is a plurality of information communications performed within a predetermined time from the first timing to the second timing equal to or longer than the predetermined time. A time calculation unit 76, a selection unit 77 for selecting a set of information communications with the smallest difference between the reception interval time and the transmission interval time from the set of the first information communication and the set of the second information communication, and based on the set It has a frequency deviation calculator 78 for obtaining the clock frequency deviation between the master device and the slave device, and a synchronization controller 80 for synchronizing the clock frequencies or times of the master device and the slave device based on the deviation.
[Selection drawing] Fig. 4

Description

The present invention relates to an information communication system and an information communication device for synchronizing a plurality of information communication devices through communication.

IEEE1588 Precision Time Protocol (PTP) of Non-Patent Document 1, for example, is known as a general time synchronization method between a plurality of information communication devices. In Non-Patent Document 1, a master device that has a reference time and a slave device that time 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 transmission time of the master device and the reception time of the slave device of the packet transmitted from the master device to the slave device, and the transmission time of the slave device and the reception of the master device of the packet transmitted 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. JP 2016-225880 A

In the PTP system, when information is transmitted and received in both directions between the master device and the slave device, it is assumed that the propagation time from one to the other is the same as the propagation time from the other to the other. However, the propagation time depends on the buffering time of the devices forming the network, the number of nodes through which data is transmitted and received, and the like. Therefore, in reality, a difference occurs in the transmission and reception times, and symmetry cannot be maintained.

In order to deal with this, in the PTP system, the changing propagation time is canceled by using network relay devices such as boundary clocks (BC) and transparent clocks (TC), and the time synchronization precision derived from the fluctuations in the propagation time is improved. Reduces degradation problems. Based on the time received from the upper master device, the BC corrects the delay time and fluctuations and generates the time as the master for the lower slave. When relaying a packet, the TC adds the stay time within the relay device and transmits the packet to the lower slave.

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

For example, Patent Literature 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 obtained independently from moment to moment, the symmetry of the propagation time is not evaluated, resulting in deterioration of time synchronization accuracy.

In addition, since the main cause of time difference fluctuations is clock frequency deviation between devices, some implementations of PTP provide an option to obtain and cancel this frequency deviation. However, since the error factor due to the variation of the propagation time is not removed, the time synchronization accuracy is degraded.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides an information communication system and an information communication device capable of absorbing variations in propagation time of information communication and performing synchronous control with reduced errors. That's what it is.

The present invention is an information communication system in which a plurality of information communication devices perform information communication as a master device or a slave device, wherein the plurality of information communication is performed within a predetermined time period with respect to a first timing. In a first information communication set and a second information communication set that is a plurality of information communications performed within the predetermined time from the first timing to the second timing longer than the predetermined time , an interval time calculation unit for calculating a transmission interval time and a reception interval time, a selection unit for selecting a set of information communication in which a difference between the transmission interval time and the reception interval time is the smallest, and the selection unit. a frequency deviation calculator for obtaining a clock frequency deviation between the master device and the slave device based on the set of information communication obtained; a synchronization controller for synchronizing the clock or time of the device.

The present invention is an information communication device that communicates information with another information communication device, wherein a set of first information communication is a plurality of information communication performed within a predetermined time with respect to a first timing. and a set of a plurality of information communications performed within the predetermined time from the first timing to the second timing equal to or longer than the predetermined time, in the set of the transmission interval time and the reception interval an interval time calculation unit that calculates time; a selection unit that selects an information communication set in which the difference between the transmission interval time and the reception interval time is the minimum; a frequency deviation calculation unit for obtaining the deviation of the clock frequency between the master device and the slave device based on the frequency deviation calculation unit; and a synchronization control unit for synchronizing.

According to the present invention, it is possible to provide an information communication system and an information communication device capable of absorbing variation in propagation time of information communication and performing synchronization control with reduced error.

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. FIG. 2 is a diagram showing a mode of communication between information communication devices; 4 is a functional block diagram of a control unit according to the embodiment; FIG. FIG. 2 is a diagram illustrating aspects of communication with propagation time symmetry; FIG. 2 illustrates a mode of communication without propagation time symmetry; FIG. 10 is a diagram showing a synchronization state vector without error due to variations in propagation time and time difference; FIG. 4 is a diagram showing a synchronization state vector including errors due to variations in propagation time and time difference; 4 is a flowchart showing a procedure of synchronous control processing according to the embodiment; It is a figure which shows the collection|aggregation of the information communication of the information communication system which concerns on embodiment. FIG. 10 is a diagram showing the amount of shift of statistics of a set of information communication at different timings; FIG. 4 is a diagram plotting synchronization state vectors in a set of multiple information communications; FIG. 2 is a diagram showing a set of two-way information communication of the information communication system according to the embodiment; FIG. 4 is a plot of synchronization state vectors in an asymmetric two-way information communication ensemble;

Hereinafter, an information communication system and an information communication device according to embodiments will be described 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 configuring 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 section 70 of FIG.

The information communication system 100 according to the present embodiment is composed of a plurality of information communication devices 1, and each information communication device 1 is synchronized by information communication. The information communication device 1, which is a slave device, synchronizes with the information communication device 1, which is a master device. A master device is an information communication device 1 to be synchronized with another information communication device 1 in the information communication system 100 . A slave device is an information communication device 1 that synchronizes 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 through transmission and reception of synchronization information, which is information for achieving time synchronization from the master device to the slave 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. At least one slave device CLb may exist for the master device CLa, but as shown in FIG. 1, the system may include a plurality of slave devices CLb.

The master device CLa and the slave device CLb are connected via a wired network capable of communicating information. In this embodiment, an example will be described in which the information communication device 1 attempts synchronization by transmitting and receiving information by wire.

(Information communication device)
The information communication device 1 includes a computer, and performs necessary calculations by having a processor, such as 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 has a communication section 10, a clock 20, a clock 30, a storage section 50, an external interface 60, and a control section . For example, each unit 10 to 70 is configured as hardware. Each unit of the control unit 70 may be configured by software including programs and data. It is possible to appropriately change the design of which part of the control unit 70 is configured as software.

The communication unit 10 transmits and receives information to and from another information communication device 1 . That is, the communication unit 10 transmits information to the outside of the information communication device 1, receives information from the outside of the information communication device 1, or both. The communication section 10 has 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 decomposes the information into the minimum components in time series and transmits the information to the outside. The information packet length (amount of communication information) is arbitrary and may differ 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 reconfigures information received from the outside of the information communication device 1 and is decomposed into minimum components in time series, and outputs the reconstructed information to other components within the information communication device 1 . For example, a reproducing 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 the audio signal to the reproducing unit. In this way, the information broken down into the minimum components to be transmitted and received in time series can specify the position of each element in time series, 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 contains time synchronization information between the master device CLa and the slave device CLb. synchronization information. The synchronization information of this embodiment includes at least time information corresponding to the transmission timing.

The information communication device 1 has one or both of a transmitter 11 and a receiver 12 . When both are provided, the transmitter 11 and the receiver 12 may be exclusively selected and operated, or both may be operated simultaneously.

The transmission timing detector 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 period of the clock 20 (in other words, the period of the pulse generated by the clock 20), which will be described later. That is, the transmission timing is expressed based on an integer multiple of the clock period.

Also, the transmission timing detection unit 13 outputs the detection result to other components in 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. For example, when the information is decomposed into eight minimum component bits in time series, the transmission timing detection unit 13 detects the timing at which the third information element position (bit position) is transmitted, The timing at which the information element position (bit position) was transmitted is output to the outside.

The reception timing detector 14 detects reception timing. The reception timing is the timing at which the predetermined information element position of the information received by the receiver 12 is received from the outside of the information communication device 1 . This reception timing is detected based on the clock period of the clock 20, which will be described later. That is, the reception timing is expressed as an integral multiple of the clock cycle.

Also, the reception timing detector 14 outputs the detection result to other components in the information communication device 1 . For example, when information is decomposed into eight minimum component bits in time series, the reception timing detection unit 14 detects the timing at which the third information element position (bit position) is received, and The timing at which the information element position (bit position) of is received is output to the outside.

In the above example of the transmission timing and the reception timing, the position of the same minimum component is detected. is detected, and the reception timing detection unit 14 of the information communication device 1 serving as a receiver detects the eighth element. )), it is not necessary to detect the same position, and the deviation of the detected element position can be ignored or corrected.

FIG. 3 is an example of wired communication, in packet transmission between information communication devices 1, a specific bit position in the packet is detected as transmission/reception timing, and transmission intervals and reception intervals are obtained from adjacent transmission timings and reception timings, respectively. showing configuration.

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

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

Even if the clock 20 has the same nominal frequency 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. The clock 20 may receive a frequency control signal from the outside and variably control the oscillation frequency corresponding to the signal.

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

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

The memory as the storage unit 50 inputs and outputs arbitrary information and stores the information in a designated storage area. Information is stored according to a storage request from the outside. At that time, information to be stored and a storage area are input. Information is referenced by a reference request from the outside. At that time, the storage area of the reference information is input, and the information in the storage area specified by the input is output. Information may be retained in memory only while the device is in operation, or may be permanent, including when the device is not in operation.

An external interface 60 (hereinafter also referred to as an external I/F 60) connects the inside and outside of the information communication device 1 and inputs/outputs arbitrary information. The information includes transmitted/received data and the time of the clock 30 . The external I/F 60 acquires information to be stored in the storage unit 50 from the outside, for example. In addition, the external I/F 60 may acquire the time from the reception timing detected by the reception timing detection unit 14 to the transmission timing detected by the transmission timing detection unit 13 from the outside, and use the obtained time in the scheduler 74 described later. .

Note that the master device CLa has an external I/F 60 that transmits at least synchronization information. Slave device CLb has an external I/F 60 that receives at least synchronization information. However, the master device CLa may have an external I/F 60 for receiving synchronization information, and the slave device CLb may have an external I/F 60 for transmitting synchronization information. Furthermore, the information communication device 1 may have a user interface such as a display device capable of controlling and displaying the internal state.

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

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

The communication control section 73 controls the operation of the communication section 10 . The communication control unit 73 inputs and outputs transmission/reception information between the communication unit 10 and the control unit 70 .

A scheduler 74 controls the schedule (time) for transmitting or receiving information. For example, in the case of one-way communication of information, the scheduler 74 on the transmitting side controls information transmission intervals and sets a schedule such that information transmission timing is detected at a predetermined time. The scheduler 74 may also control the time between receiving and transmitting information. When transmitting information, the communication control unit 73 can include the time corresponding to the transmission timing of the preset schedule or the detected transmission timing in the information. In this embodiment, the scheduler 74 controls a first timing, a second timing, and transmission timing of synchronization information according to the first timing and the second timing, which will be described later.

The time recording unit 75 associates the transmission timing of the predetermined information element position of the information transmitted by the transmission timing detection unit 13 with the time of the clock 30 at the transmission timing, and stores them in the memory of the storage unit 50 . For this association, for example, the time recording unit 75 receives a signal from the transmission timing detection unit 13 indicating that the transmission timing of the predetermined information element position of the transmitted information has been detected, and refers to the time of the clock 30. , to associate the time and the transmission timing.

The time recording unit 75 also serves as a time adding unit that adds the time corresponding to the transmission timing to the information to be transmitted. Similarly to transmission, the time recording unit 75 associates the reception timing of the predetermined element position of the information received by the reception timing detection unit 14 with the time of the clock 30 at the reception timing, and stores it in the memory. In addition, the time recording unit 75 causes the transmitter 11 to transmit the information including the time corresponding to the reception timing.

Thus, in this embodiment, "time" refers to the time of the clock 30 corresponding to the detected transmission timing or reception timing of the predetermined information element position of the information, and "time" refers to the difference between the times. .

The interval time calculator 76 calculates the transmission interval time and the reception interval time in the first information communication set and the second information communication set between the master device CLa and the slave device CLb. A set of first information communications is a plurality of information communications performed within a predetermined period of time with respect to the first timing. A set of second information communications is a plurality of information communications performed within a predetermined period of time from the first timing to a second timing longer than the predetermined period of time.

The predetermined time is an interval time during which the information propagation time between the master device CLa and the slave device CLb is not influenced by the clock frequency deviation between the master device CLa and the slave device CLb. Therefore, an interval time exceeding a predetermined time between the first timing and the second timing affects the propagation time due to the frequency deviation.

The transmission interval time is the difference between the transmission time of the first timing and the transmission time of the second timing. The transmission interval time is obtained from the time difference between two transmissions by referring to the transmission time included in the received information. The reception interval time is obtained from the time difference between two receptions by referring to the time corresponding to the reception timing from the clock 30 . The two transmission times and the two reception times may be read directly from the received information or may be read from the storage section 50 .

The selection unit 77 selects, from the first set of information communications and the second set of information communications, the set of information communications in which the difference between the reception interval time and the transmission interval time is the smallest. This set can be regarded as the one with minimal propagation time variation, as described below.

The frequency deviation calculator 78 obtains the clock frequency deviation between the master device CLa and the slave device CLb based on the set of information communication selected by the selector 77 . That is, the frequency deviation calculator 78 calculates the deviation between the clock frequency of the information communication device 1 to be synchronized (master device CLa) and the clock frequency of the information communication device 1 to be synchronized (slave device CLb). The deviation of this clock frequency (hereinafter also simply referred to as "frequency") is a value expressed as a frequency ratio. That is, finding the frequency deviation is synonymous with finding the frequency ratio. The frequency deviation calculator 78 of the present embodiment obtains the frequency ratio by, for example, dividing the reception interval time in the set of information communication selected by the selector 77 by the transmission interval time.

In this embodiment, the frequency ratio is the ratio of the clock frequency of the slave device to the clock frequency of the master device (hereinafter also simply referred to as frequency ratio). In other words, the frequency deviation is the difference between the clock frequency of the master device and the clock frequency of the slave device.

The time difference calculator 79 obtains the time difference corresponding to the set with the largest number of sets with the smallest time difference errors in a set of a plurality of information communications between the master device CLa and the slave device CLb within a predetermined period of time. .

The synchronization control section 80 controls the clock 20 or the clock 30 based on the frequency ratio calculated by the frequency deviation calculation section 78 . That is, the synchronization control section 80 controls the oscillation frequency of the clock 20 so that the frequency ratio calculated by the frequency deviation calculation section 78 is set to one. For example, when the clock 20 is composed of a voltage-controlled crystal oscillator including a crystal oscillator, by controlling the voltage applied to the oscillator, the frequency ratio is set to 1, and information communication becomes a synchronized device (master device). Synchronize the device 1 with the clock frequency.

In addition, the synchronization control unit 80 calculates the time difference, that is, the time difference, with respect to the information communication device 1, which is the device to be synchronized (master device CLa), based on the frequency ratio obtained by the frequency deviation calculation unit 78, and calculates the time difference. The value ticked by the clock 30 is corrected based on. In this embodiment, the time difference calculator 79 can obtain the time difference, and the synchronization control unit 80 can correct the time based on the obtained time difference. For the correction, for example, the time may be corrected by controlling the clock 30 itself. Alternatively, the time may be corrected based on the time difference when the clock 30 outputs the time. That is, the time itself of the clock 30 may not be corrected, and the clock 30 may be controlled so as to output the time corrected for the deviation when the clock 30 outputs the time.

The timing information reference unit 81 refers to the timing information output from the synchronization control unit 80 and executes desired processing in synchronization therewith. The timing information is composed of a periodic timing signal and time information uniquely corresponding to the specified timing. The synchronization control section 80 can synchronize with another information communication device 1 based on the timing information.

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

Note that the synchronization information transmitted by the master device CLa and the separate synchronization information transmitted by the slave device CLb here are for the purpose of measuring timing for synchronization, and the synchronization information contains the master device CLa. However, the contents of the synchronization information and the other synchronization information are arbitrary.

As shown in FIG. 5, information is transmitted by the master device CLa at time _ta,T and received by the slave device CLb at time _tb,R after a propagation time d. After _Δtb , another piece of information is transmitted by slave device CLb at time _tb,T and received by master device CLa at time _ta,R, also after propagation time d.

Here, the interval from transmission to reception in the master device CLa is Δt _a , the interval from reception to transmission in the slave device CLb is Δt _b , and the same timing as the transmission timing t _a,T of the master device CLa is It is assumed to be observed as t'a _,T in the device CLb. Therefore, the time difference g between the master device CLa and the slave device CLb at a given moment between the clocks 20 can be obtained as shown in equation (1). Furthermore, the time difference between the clocks of the master device CLa relative to 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。

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, symmetrical in the direction of information communication. .

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

Therefore, the time difference g between the clocks 20 can be obtained from the equation (3) using the equation (2).

The synchronization control unit 80 of the slave device CLb can time-synchronize with the master device CLa by repeatedly adjusting the clock frequency and time so that the time difference g between the clocks 20 becomes zero.

If the clock frequencies of the master device CLa and the slave device CLb are the same, that is, if the clock domain is single, time synchronization can be achieved only by adjusting the time once. Due to deviations, clock frequency adjustment is essential for time synchronization. Even in a system in which the clock frequency cannot be directly adjusted, it is possible to control the driving frequency of the clock 30 and synchronize the time by repeatedly adjusting the time advance per 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.

Propagation time and internal delay between transmission and reception timings can be ignored or corrected depending on system requirements. Also, the synchronization information may be transmitted from the slave device CLb instead of starting the transmission of the synchronization information from the master device CLa. Furthermore, although one interface is sufficient for information communication, a configuration in which multiple interfaces are used at the same time, such as independent implementation of transmission and reception interfaces, is also possible.

[Influence of time difference and propagation time variation]
The above description assumes that the time difference is constant and that 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 moment to moment. For this reason, the time difference between the information communication devices 1 also fluctuates, and depending on the network system in which the master device CLa and the slave device CLb are connected, information propagation paths and communication arbitration are affected, and as shown in FIG. Propagation times are generally asymmetric.

In other words, the time difference _gb/a between the master device CLa and the slave device CLb at a certain moment is not the same as the time difference ga _/b between the same master device CLa and the slave device CLb after a certain period of time has passed. Further, 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 has the same sign as g _b/a and g a/b and g _{b/ a} · _ga/b ≧0 in order to match the expression with the time difference in FIG. 5 . Furthermore, as described above, the time difference and the propagation time fluctuate from moment to moment, and the time difference g _b/a [m] observed at one instant and the propagation time d _b/a [m] observed at a different instant The time difference g _b/a [n] and the propagation time d _b/a [n] are generally different.

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 converted into equations Organize as shown in (4) and (5).

In equation (2), the propagation time can be obtained on the premise of symmetry, but in equation (4), it can be seen that the average value of the propagation time includes the fluctuation component of the time difference. Similarly, in equation (3), the time difference could be obtained on the premise that the time difference is constant. I understand. If the time difference and propagation time fluctuation components are included in this way, the precision of time synchronization will be lowered.

[Errors due to variations in time difference and propagation time]
In the time synchronization system, the time synchronization error caused by the time difference and the variation of the propagation time will be explained. First, both equations (4) and (5) are synthesized and transformed into a matrix form as shown in equation (6).

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

Then, by focusing on the common factor of 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 represents the components of the time difference g _b/a and the propagation time db _/a when communication is performed from the master device CLa to the slave device CLb, and the vertical axis represents the components from the slave device CLb to the master device CLa. Consider a two-dimensional space with components of time difference g _a/b and propagation time d _a/b when communication is performed. Then, if (g _{b/a −} g _a/b ) ^T is the time difference vector g and (d _b/a d _a/b ) ^T is the propagation time vector d, then the time difference including the variation error in Equation (8) and the propagation time vector s=(g _d d _g ) ^T is the sum of the time difference vector g and the propagation time vector d, rotated +π/4 on the same space, and scaled in each dimension. can be interpreted as

In the operation of equation (8), there is no change in the elements g _b/a , g _a/b of the time difference vector g and no change in the elements d _b/a , d _a/b of the propagation time vector d, that is, g When _b/a = g _a/b and d _b/a = d _a/b , the synchronization state vector s can be orthogonally decomposed into d _g component and g _d component as shown in FIG. It can be seen that the time difference and the delay time can be obtained without including the time.

However, generally, as shown in FIG. 8, the time difference vector g and the propagation time vector d contain fluctuation errors in their respective elements. For this reason, the orthogonal components are combined with each other's errors, so that the error cannot be removed from the time difference and the propagation time only by the operation of Equation (8), resulting in deterioration of the time synchronization accuracy.

Since the equations (4) and (5) are linearly dependent, an analytical solution cannot be obtained unless another independent operation is introduced. It is not possible to find new independent operations that result in vectors. Therefore, another approach needs to be introduced to remove the variation error.

[motion]
Based on the above, the operation of the information communication system 100 of this embodiment will be described. First, the outline of the operation of this embodiment will be described with reference to the flowchart of FIG. The communication control unit 73 performs the first information communication and the second information communication according to the scheduler 74 (steps S101 and S102). This is because, as will be described later, the master device CLa transmits a plurality of pieces of synchronization information in bursts from the timing m, which is the first timing, and the first synchronization information is transmitted at a time interval of L _g [n] from the timing m. It corresponds to transmitting a plurality of pieces of synchronization information in bursts from the timing n, which is the timing of (see FIG. 10). Hereinafter, such continuous transmission of a large number of data in a relatively short period of time is also referred to as burst transmission.

Next, the interval time computing unit 76 computes the transmission interval time and the reception interval time in the set of the first information communication and the set of the second information communication (step S103). This is the transmission times _{ta, T} [n], ta _{, T} [m], the reception times t _{b, R} [n], t From _{b, R} [m], transmission interval time (t _{a, T} [n] - t _{a, T} [m], reception interval time (t _{b, R} [n] - t _{b, R} [m]) is equivalent to asking for

The selection unit 77 selects a set of information communication that minimizes the difference between the transmission interval time and the reception interval time (step S104), and the frequency deviation calculation unit 78, based on the selected set of information communication, The frequency ratio between the master device CLa and the slave device CLb, that is, the frequency deviation is found (step S105), and the time difference calculator 79 finds the time difference (step S106). Details of these will be described later.

By correcting the above frequency deviation and time difference, the synchronization control unit 80 performs clock frequency or time synchronization control between the master device CLa and the slave device CLb (step S107). Note that the synchronization control by the synchronization control unit 80 is repeatedly performed by feedback until the frequency deviation and the time difference converge to 0 (the frequency ratio is 1).

[Frequency deviation estimation under propagation time fluctuation]
Next, the selection of information communication pairs by the selector 77 (step S104) and the calculation of the frequency deviation by the frequency deviation calculator 78 (step S105) will be described in detail.

First, the transmission frequency f of the clock 20 of each information communication device 1 used for time synchronization includes a frequency deviation e with respect to the nominal frequency _fN . Furthermore, since the frequency deviation e fluctuates moment by moment according to the dynamic and electromagnetic operating environment of the clock 20, the relationship between the transmission frequency f[n] and the frequency deviation e[n] at the observation timing n is It can be expressed as the formula (9).

Note that the frequency deviation is sufficiently smaller than 1, and r[n] represents the frequency ratio. Each clock has a permissible frequency deviation from the nominal frequency, but as described above, the actual frequency deviation fluctuates from moment to moment, so it cannot be accurately grasped.

FIG. 10 shows the relationship between the transmission/reception timing, the time difference, and the propagation time when information is communicated from the master device CLa to the slave device CLb. Both devices have the same nominal frequency of the clock 20 used for time synchronization, but the frequency deviation is e _a [n] for the master device CLa and e _b [n] for the slave device CLb. When a large number of packets are transmitted from the master device CLa to the slave device CLb, a time difference gradually occurs due to the frequency deviation e as time elapses. Also, each propagation time has variations. The frequency deviation e is obtained from such a situation.

At this time, the frequency deviation of the slave device CLb seen from the master device CLa is represented by ( _eb [n] _-ea [n]). The frequency ratio rb _/a [n] at that time can be expressed as rb _/a [n]=1+( _eb [n]-ea[ _n ]). Similarly, the frequency deviation of the master device CLa seen from the slave device CLb is represented by (e _a [n]-e _b [n]). The frequency ratio ra _/b [n] at that time can be expressed as ra _/b [n]=1+( _ea [ _n ]-eb[n]). The frequency ratio is 1 when the frequency deviation is 0, and (e _b [n] - _ea [n]), ( _ea [n] - _eb [n]) is 1 with no frequency deviation. represents the amount of deviation from

Each clock 20 of the information communication device 1 is defined with an allowable deviation from the nominal frequency, and changes every moment within this range. If the clock frequency of each information communication device 1 is different, the advance width of clocking is also different, and a time difference occurs from moment _{to moment} . Time calculation between information communication devices 1 requires correction in consideration of frequency deviation. If the correction is not performed, an error will occur in the time calculation, resulting in deterioration of time synchronization accuracy.

In FIG. 10, if the average frequency ratio of the slave device CLb seen from the master device CLa from the first timing (timing m) to the second timing (timing n) is r _b/a [n, m], then The relationship of formula (10) is established.

From equation (10), g _b/a [n]=g _b/a [m]+(r _b/a [n, m]−1)(t _{a, T} [n]−t _{a, T} [m ]), and it can be seen that the time difference changes due to the influence of the frequency deviation.

In addition, in Equation (10), the frequency deviation is not applied to the propagation time, and no correction is required. That is, the case of multiplying and adding the frequency ratio r _b/a [n, m] to d _b/a [n] is substantially the same as the case of adding without multiplying. This is because the minimum time L _g [n] at which there is a time difference between the observation times of both devices between the information communication devices 1 with the clock 20 at the nominal frequency f _N and the apparent frequency deviation e [n] is given by equation (11) This is because the propagation time is generally smaller than this minimum time L _g [n]. Note that T _N =1/ _fN . In other words, since the propagation time is a very small value, even if the frequency deviation is applied to it, its effect does not appear. That is, the predetermined time period during which synchronization information is transmitted from timing m and the predetermined time period during which synchronization information is transmitted from timing n are times shorter than (less than) this minimum time L _g [n].

On the other hand, when the interval of the information communication group to be selected is less than L _g [n], even if it is calculated as in Equation 10, the effect of the frequency deviation does not appear, and the frequency deviation is 1, that is, there is no deviation. Become. Therefore, in order to observe the frequency deviation from the transmission/reception timing of information communication, it is necessary to select a set of information communication separated by a time of L _g [n] or more. That is, the time interval between the timing m and the timing n is a time longer than or equal to a predetermined time (a time after a predetermined time or longer), that is, a time longer than or equal to the minimum time L _g [n] at which the influence of the frequency deviation appears in the propagation time.

L _g [n] also changes from moment to moment and cannot be obtained directly. It never exceeds |2e|. Therefore, L _g [n]=T _N /|2e| is used as a selection criterion for information communication sets. Two equations (10) are obtained from the communication of timing m and timing n selected according to this criterion, and from these two equations, the frequency ratio r _b/a [n, m] is obtained as equation (12). can be asked for.

Two equations are obtained based on equation (10) from information communication of timing m and timing n selected according to this criterion. One formula is a formula for timing n, which is t _b,R [n] shown in formula (10) above. Another equation (10)′ is an equation for timing m, where t _b,R [m]=t _a,r [m]+g _b/a [ m]+d _b/a [m]. Therefore, subtracting equation (10)′ from equation (10), that is, t _b,R [n]−t _b,R [m] yields the frequency ratio r _b/a [n , m].

However, the propagation time variation (d _b/a [n] - _{d b/a} [m]), which is the latter term of the numerator of Equation (12), cannot be directly observed, and is expressed as the frequency deviation error be included. Therefore, if (d _b/a [n]-d _b/a [m]) becomes zero and is canceled, an ideal frequency deviation can be obtained.

Here, in order to minimize this error, the formula (13) is obtained from the two formulas (10) and (10)' from which the formula (12) was obtained.

As shown in FIG. 10, information communication is performed m'+1 times by timing m+m', which is within the time _kLg (predetermined time above) in which the influence of the frequency deviation does not appear with respect to timing m. In other words, communication is performed in bursts in a short period of time. Here, k is a positive coefficient that can be set according to the required accuracy of the time synchronization system. Similarly, information communication is performed n'+1 times by timing n+n' which is within the time _kLg in which the influence of the frequency deviation does not appear with respect to the timing n. In other words, communication is performed in bursts in a short period of time.

Let m ^* be the timing of one information communication extracted from the set of information communications related to timing m, and let n ^* be the timing of one information communication extracted from the set of information communications related to timing n. When Equation (13) is obtained using these information communications, the variation in the time difference (g _b/a [n ^* ] - _{g b/a} [m ^* ]) is assumed to take the same value. Let That is, the latter term (g _b/a [n ^* ]− _{g b/a} [m ^* ]) on the left side of equation (13) is a constant value and can be regarded as not fluctuating. Therefore, if the right side of equation (13) can be minimized, the first half term (d _b/a [n]−d _b/a [m]) of the left side can be minimized. Here, the right side of Equation (13) is the difference between the reception interval time and the transmission interval time.

Hereinafter, the first half term of the left side of Equation (13) will be referred to as d difference (difference due to variation in propagation time), and the second half term will be referred to as g difference (difference due to variation in time difference). Here, the d-difference and the g-difference cannot be observed separately only by an operation using transmission/reception timing of information communication. Here, in general, the g difference exceeds the d difference in an asynchronous state, the g difference and the d difference become equal in the middle of synchronization, and when the synchronization stabilizes, the g difference transitions to be lower than the d difference. Therefore, the magnitude relationship between the d-difference and the g-difference is virtually classified, and the error of the equation (12) due to the d-difference is organized.

If the absolute value of the g-difference is more dominant than the absolute value of the d-difference, e.g., if their ratio is 10 or more, then any choice of m ^* and n ^* will lead to an error of the order of d-difference. Accordingly, equation (13) takes a constant value, and the frequency ratio can be obtained from equation (12). That is, coarse adjustment of the frequency deviation is possible.

On the other hand, if the absolute value of the d-difference is greater and dominant than the absolute value of the g-difference, e.g., if their ratio is 10 or greater, then all m ^* and n ^* combinations are (m′+1) If (n′+1) pairs of equation (13) are obtained and a combination that minimizes the right side is selected from the set, |d _b/a [n ^* ]−d _b/a [m ^* ]| can also be considered minimal. That is, the frequency ratio r _b/a [n ^* , m ^* ] can be obtained with the minimum error from equation (12). In other words, the frequency ratio can be obtained based on the combination that minimizes the propagation time error.

However, when the absolute value of the d-difference and the absolute value of the g-difference are about the same size, the operation to minimize the right side of the equation (13) is performed by changing the equation (12) to 1, regardless of the actual frequency ratio. , and it is erroneously assumed that there is no frequency deviation of the clock 20 between the information communication devices 1 .

Here, with m' and n' being about the same, information communication is performed near timing m and timing n, respectively. At this time, the statistics such as the probability density distribution of the set {S _b/a [m+k]|0≦k≦m′} of Equation (14) obtained near timing m and Equation (14) obtained near timing n The set of {S _b/a [n+k]|0≤k≤m'} is a statistical quantity such as the probability density distribution, unless the characteristics of the communication path or the network devices on the communication path switch discontinuously, the correlation is I can say there is. Note that the statistical quantity referred to here includes, for example, an average value, a median value, a minimum value, a maximum value, an amount related to cross-correlation, etc., in addition to the probability density distribution. Further, the vicinity of the timings m and n referred to here is, for example, the time within the predetermined time from the timing m or the timing n, that is, the time less than the minimum time Lg[n].

すなわち、図１１に示すように、タイミングｍ近傍のＳ_ｂ／ａ［ｍ＋ｋ］の集合による確率密度分布と、タイミングｎ近傍のＳ_ｂ／ａ［ｎ＋ｋ］の集合による確率密度分布とは、相関はあるが、情報通信装置１間のクロック周波数偏差の影響で、ｇ_ｂ／ａ［ｎ］－ｇ_ｂ／ａ［ｍ］のシフトを生じる。このシフトの影響で、式（１３）の最小な右辺を求めても、｜ｄ_ｂ／ａ［ｎ^＊］－ｄ_ｂ／ａ［ｍ^＊］｜を最小化することができない。

That is, as shown in FIG. 11, the correlation between the probability density distribution by the set of S _b/a [m+k] near the timing m and the probability density distribution by the set of S _b/a [n+k] near the timing n is However, a shift of g _b/a [n]−g _b/a [m] occurs due to the clock frequency deviation between the information communication devices 1 . Due to the effect of this shift, |d _b/a [n ^* ]−d _b/a [m ^* ]| cannot be minimized even if the minimum right-hand side of equation (13) is found.

To cancel this shift, the statistic f _s [*] of the set of S _b/a [*] is obtained as x to solve the optimization problem (15) in the neighborhood of timing m and timing n. Here, U is a parameter according to the time synchronization system.

The difference between the obtained statistics f _s [n] and f _s [m] (f _s [n] - _{f s} [m]) is the variation of the time difference (g _b/a [n] - g _b/a [ m]), the combination of n ^* and m ^* that minimizes the right-hand side can be selected by transforming equation (13) as shown in equation (16) so as to cancel the variation in the time difference. , |d _b/a [n ^* ]−d _b/a [m ^* ]| can also be considered a minimum. That is, the frequency ratio r _b/a [n ^* , m ^* ] in Equation (12) can be obtained with the minimum error.

Note that the frequency deviation e _b/a [n,m] may be estimated directly from (f _s [n]−f _s [m]) using Equation (17).

Also, the continuity of the correlation may be verified prior to obtaining these statistics. That is, it may be determined whether or not the cross-correlation function between the probability density distributions of the sets of S _b/a [*] in the vicinity of timing m and timing n changed discontinuously. If there is a discontinuous change, it is considered that the characteristics of the communication path or the network equipment on the communication path have changed discontinuously, or that the traffic on the communication path has changed. suppress control over

The synchronization control unit 80 can feedback-control the clock oscillation frequency of the slave device CLb or the driving frequency of the clock 30 so that the frequency deviation obtained from the equation (12) or the equation (17) becomes zero. This enables frequency synchronization of the slave device CLb with respect to the master device CLa, and reduces errors in time calculation in time synchronization.

[Estimation of time difference under propagation time fluctuation]
Next, calculation of the time difference by the time difference calculation unit 79 will be described (step S106). As described above, the operation of minimizing |d _b/a [n ^* ]− _{d b/a} [m ^* ]| and the expression (12) enabled estimation of the frequency deviation between the information communication devices 1. Therefore, the frequency By synchronizing, the time difference of the clocks 20 between the information communication devices 1 can be kept constant. In other words, the absolute values of both elements of the time difference vector g in equation (8) are equal (g _b/a =g _a/b ), and the propagation time component error can be kept to a minimum. In the vector diagram of FIG. 8, this is almost the same as the state in which there is no error as shown in FIG. 7 for the time difference vector g.

Note that if the transmission of synchronization information from timings m and n is performed within a predetermined period of time (a short period of time less than L _g [n]), the effect on the frequency deviation is negligible. can be said to have a small error. Therefore, the estimation of the frequency deviation and the synchronization processing based thereon are not essential. In other words, even if the estimation of the frequency deviation and the synchronization process described above are not performed, the estimation of the time difference described below is possible. Therefore, for example, a configuration in which the frequency deviation calculator 78 of the present embodiment is omitted is also possible. In addition, when transmission of synchronization information from timings m and n is performed for a predetermined time or longer, it is conceivable to estimate the frequency deviation by another method.

From the above, when obtaining the synchronization state vector s by the equation (8), it is sufficient to consider only the variation of the propagation time. Here, the packet communication volume of other communication on the network can be mentioned as a variable factor of the propagation time of information communication. Since the packet communication time is discrete, the variation of the propagation time is also discrete, and when the group of information communication is changed and the iterative expression (8) is obtained, the synchronization state vector s is g _d −d _g plane Above, as shown in FIG. 12, they are arranged in a +π/4 rotated lattice.

In other words, with respect to the time difference vector g, assuming that the error is minimal, only the synchronous state vector s can be observed in a set of multiple information communications, and plotted points thereof are shown in FIG. Note that the observation of the synchronization state vector s corresponds to measuring the four transmission/reception timings as described above and obtaining the left side of Equation (6), that is, the left side of Equation (8). Two-way communication such that the synchronous state vector s can be obtained by equation (8) is performed within a short period of time, that is, within a predetermined period of time during which interruptions due to other communications can be eliminated and frequency deviation does not appear. This time is, for example, less than the minimum time Lg[n]. This is because information communication is continuously performed in bursts in a short period of time to create many situations in which communication for synchronization is continued without being interrupted by other communication.

When such information communication used for time synchronization is continuously performed in a short period of time, a synchronization state vector with a constant propagation time that eliminates waiting for a turn due to multiple communications and is not affected by fluctuations in propagation time due to other communications There is a timing to find s. These timings are the points on the dashed line perpendicular to the _gd axis shown in FIG.

Such a set of synchronous state vectors s can be regarded as having minimal error in the time difference components and symmetrical propagation times, with the elements _gd of each vector approaching a constant value g. This value g is the estimated value of the time difference.

However, in obtaining the estimated value g of the time difference, if the average of the elements _gd of the synchronization state vector s is simply obtained, the arrangement of the synchronization state vector s is biased as shown in FIG. .

Therefore, for example, with the element g _d [k] of the synchronization state vector s [k] obtained from a set of information communications continuously performed in a short period of time and the variable x of the g _d component on the g _d −d _g plane, When focusing on the distance (g _d [k]-x) of , the estimated value g of the time difference is solved by solving the optimization problem of finding x that minimizes the evaluation function Σk (g _d [k]-x) ⁴ can ask. Instead of finding the average, by summing the distances (g _d [k]−x) to the power of four, penalizing longer distances and lessening the penalties for shorter distances, the synchronization state vector s becomes the most It is possible to obtain a straight line that has a large number of clusters. In the example of FIG. 12, the value corresponding to the vertical dotted line (straight line) is the time difference estimated value g. The equation for solving the optimization problem may be of the form of equation (15).

The synchronization control unit 80 of the slave device CLb synchronizes time with the master device CLa by repeatedly adjusting the clock frequency or the time so that the obtained time difference g becomes zero.

[Estimation of time difference in asymmetric communication path]
As shown in FIG. 6 above, depending on the network system in which the master device CLa and the slave device CLb are connected, the propagation times may be constantly asymmetrical. This is caused, for example, by the difference in the amount of traffic between upstream (slave→master) and downstream (master→slave) communications.

Stationary asymmetry of the propagation time in the two-way communication path always adds the error of the time difference component to the propagation time vector d in the above equation (8), and the offset of the time difference component of the obtained synchronization state vector s ( deviation due to error). That is, the asymmetry causes a steady shift in synchronization phase.

Regarding the asymmetry of the time difference, within a predetermined time period in which the frequency deviation of the clock 20 between the master device CLa and the slave device CLb does not appear, that is, less than the minimum time L _g [n] shown in the above equation (11). If the synchronous state vector s is obtained in terms of time, the time difference between upstream and downstream communication will be the same and can be regarded as symmetrical. Furthermore, by performing frequency synchronization of the clocks 30 between devices through a series of operations to solve the optimization problem shown in the above equation (15), it is possible to control the denominator of the equation (11) to be very small. Therefore, the period during which the time difference is symmetrical can be increased.

Since the time difference calculator 79 calculates the time difference corresponding to such an asymmetric communication path, information is transmitted in bursts from both the master device CLa and the slave device CLb, as shown in FIG. Burst transmission of information is assumed to occur within a predetermined time period, ie less than Lg[n], in order to ensure time difference symmetry. In FIG. 13, burst transmission is sequentially performed in each direction, but burst transmission can be performed in both directions at the same time (for example, within a common predetermined time). Also, in FIG. 13, the number of times of burst transmission in each direction is the same (n'+1) from timing n to timing n+n', but the number of times may not be the same in each direction. That is, the number of times of transmission may differ between the master device CLa and the slave device CLb.

Here, the difference in transmission/reception timing in the uplink direction is represented by equation (18) as in equation (14). At this time, the set of S _b/a [k] obtained by downlink burst transmission is set to S _b/a (n, n′)={S _b/a [n+k]|0≦k≦n′}. , the set of S _a/b [k] obtained by burst transmission in the uplink is S _a/b (n, n′)={S _a/b [n+k]|0≦k≦n′}.

The time difference can be estimated with high accuracy by obtaining the variance of these sets and selecting the estimated direction of the time difference according to the magnitude of the variance. That is, the variance VAR[Sb _{/ a} (n,n')] of Sb _{/a(n,n') is equal to or less than Tb /a} , and the variance VAR[S _a/b (n,n')] is equal to or less than Ta _/b , time difference estimation method 1 is selected as follows, and in other cases, time difference estimation method 2, which will be described later, is selected. Note that T _b/a and T _a/b are values determined according to the traffic of the communication path and the quality of time synchronization. That is, if the variance VAR[S _b/a (n,n′)] exceeds T _b/a and the variance VAR[S _a/b (n,n′)] exceeds T _a/b , then the propagation It can be said that the degree of time asymmetry exceeds a predetermined criterion.

In an environment where time difference estimation method 1 is selected, S _b/a (n, n′) and S _a/b (n, n′) have small variations, and it can be said that the traffic on the communication path is stable. In such an environment, the synchronization state vector s with the smallest propagation time component is selected, and its time difference component is used as the time difference for estimation.

That is, the operation of extracting elements one by one from S _b/a (n, n′) and S _a/b (n, n′) and obtaining the synchronization state vector from equation (8) is performed by This is done for combinations, and a set S of synchronization state vectors s in the following equation (19) is obtained. Then, from the set S, the synchronization state vector s with the minimum propagation time component is selected.

In an environment where time difference estimation method 2 is selected, S _b/a (n, n′) and S _a/b (n, n′) vary greatly. In other words, the traffic on the communication path is unstable and the propagation time can be asymmetrical. In such an environment, it is necessary to estimate the propagation time asymmetry and remove the offset of the time difference component from the synchronization state vector s.

For this purpose, first, as shown in FIG. 14, similarly to the time difference estimation method 1, a set S of synchronization state vectors is obtained by the equation (19), and its center of gravity c is obtained. Here, a straight line l _d =a+t(ca) passing through the center of gravity c and the point a when a=(g, 0) ^T is referred to as a propagation time base line. The _gd component g of a is a variable.

なお、図１４は単純な集合Ｓに簡素化して表現しているが、Ｓ_ｂ／ａ（ｎ，ｎ´）とＳ_ａ／ｂ（ｎ，ｎ´）の確率密度分布は、時差推定方法２を選択した環境では異なることが一般的であると言える。このため、たとえ集合Ｓの分布形状が長方形であったとしても、求まる重心ｃは長方形の中心と一致するとは限らない。集合Ｓの分布形状によらず、その重心が式（２０）の制約条件に示した演算によりｃとして求まる。 In order to obtain the propagation time baseline _ld that minimizes the sum of the Euclidean distances between each element _sk of the set S and the propagation time baseline _ld , the optimization problem of the following equation (20) is solved.

Although FIG. 14 is simplified and expressed as a simple set S, the probability density distributions of S _b/a (n, n′) and S _a/b (n, n′) are obtained by time difference estimation method 2 It can be said that it is common to be different in environments where For this reason, even if the distribution shape of the set S is rectangular, the obtained center of gravity c does not necessarily coincide with the center of the rectangle. Regardless of the distribution shape of the set S, its center of gravity can be obtained as c by the operation shown in the constraint condition of Equation (20).

The propagation time base line _ld obtained by solving the optimization problem of equation (20) corresponds to a straight line on the propagation time vector d, which is an element forming the synchronization state vector s. However, since the time difference vector g is added, it is shifted from the propagation time vector d.

That is, the _gd component of a, _which is an element of the propagation time baseline ld obtained from Equation (20), can be estimated as the time difference. In the case where a plurality of propagation time baselines _ld are obtained, the propagation time baseline _ld that minimizes ||a|| should be selected.

By feedback-controlling the clock oscillation frequency of the slave device CLb or the drive frequency of the clock so that the time difference obtained by these time difference estimation methods 1 and 2 becomes 0, the time synchronization of the slave device CLb with respect to the master device CLa is achieved. This makes it possible to reduce errors due to asymmetry of propagation time.

[effect]
(1) This embodiment is an information communication system 100 in which a plurality of information communication devices 1 perform information communication as a master device CLa or a slave device CLb, and between the master device CLa and the slave device CLb, A set of first information communications, which is a plurality of information communications performed within a predetermined period of time with respect to the first timing, and a second timing of at least a predetermined period of time from the first timing, within a predetermined period of time an interval time calculator 76 for calculating a transmission interval time and a reception interval time in a set of second information communications, which is a plurality of information communications performed in the same period; A selection unit 77 that selects from the set an information communication pair in which the difference between the reception interval time and the transmission interval time is the smallest; Synchronization for synchronizing the clock frequencies or times of the master device CLa and the slave device CLb based on the frequency deviation calculation unit 78 that obtains the clock frequency deviation from the device CLb and the clock frequency deviation obtained by the frequency deviation calculation unit 78 and a control unit 80 .

Further, the present embodiment is an information communication device 1 that communicates information with another information communication device 1, and is a plurality of information communications performed within a predetermined time with respect to a first timing. and a second set of information communications, which is a plurality of information communications performed within a predetermined time period from the first timing to a second timing that is equal to or longer than the predetermined time period, in which the transmission interval time is and an interval time calculation unit 76 for calculating the reception interval time, and from the set of the first information communication and the set of the second information communication, the set of information communication in which the difference between the transmission interval time and the reception interval time is the minimum a frequency deviation calculator 78 that obtains the clock frequency deviation between the master device CLa and the slave device CLb based on the set of information communication selected by the selector 77, and a frequency deviation calculator 78 and a synchronization control unit 80 for synchronizing the clock frequencies or times of the master device CLa and the slave device CLb based on the deviation of the clock frequencies obtained by the above.

In this way, based on the transmission interval time and the reception interval time that can be calculated from the observable transmission time and reception time at different timings, the error is minimized by selecting a set of information notifications with the smallest difference. Since the frequency deviation can be obtained, even in an environment where the propagation time fluctuates from moment to moment due to frequency fluctuations, synchronization control that absorbs the fluctuation of the propagation time and evaluates the symmetry of the propagation time to reduce the error. becomes possible. As a result, accurate time synchronization can be performed without using a specific network relay device compatible with time synchronization such as BC or TC in the PTP time synchronization system. In other words, while using the PTP time synchronization system and eliminating the need for BC and TC, it is possible to achieve time synchronization with the desired precision required by the system.

(2) The predetermined time is the minimum interval time at which the influence of the frequency deviation appears in the information propagation time between the master device CLa and the slave device CLb. As a result, although the effect of frequency deviation does not appear on each of the set of first information communication and the set of second information communication, the effect of frequency deviation appears on the set of first information communication and second information communication. is included, the frequency deviation that minimizes the error can be obtained by selecting the set of information communication that minimizes the difference between the transmission interval time and the reception interval time.

(3) The frequency deviation calculation unit 78 calculates a statistic based on a set of information communication within a predetermined time with respect to the first timing and a statistic based on a set of information communication within a predetermined time with respect to the second timing. Then, the deviation of the clock frequency is obtained by canceling the variation of the time difference. Therefore, even if the difference due to the time difference variation is as large as the difference due to the propagation time variation, highly accurate synchronization control is possible.

(4) The frequency deviation calculation unit 78 calculates a statistic based on a set of information communications within a predetermined time with respect to the first timing and a statistic based on a set of information communications within a predetermined time with respect to the second timing. The deviation of the clock frequency is obtained based on the difference between . Therefore, the frequency deviation can be obtained directly from the statistical difference.

(5) A time difference calculation unit that calculates the time difference corresponding to the largest set among the sets with the smallest time difference errors in a plurality of information communication sets between the master device CLa and the slave device CLb within a predetermined period of time. 79. More specifically, the time difference calculator 79 obtains the time difference corresponding to the straight line with the largest number of synchronization state vectors whose elements are time differences and propagation times in a set of a plurality of information communications. As a result, even in an environment where the propagation time fluctuates from moment to moment, the time difference with the symmetry of the propagation time and the minimum error can be obtained to enable highly accurate synchronization control.

(6) The time difference calculator 79 calculates a synchronization state vector whose elements are the time difference and the propagation time in a set of a plurality of information communications when the degree of non-symmetry of the propagation time in two-way communication exceeds a predetermined standard. It is also possible to find the time difference corresponding to a straight line passing through the set's centroid. As a result, even in an asymmetrical communication path, the time difference with the minimum error can be obtained, and highly accurate synchronization control can be performed.

[Other embodiments]
The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying constituent elements without departing from the scope of the present invention at the implementation stage. Further, various inventions can be formed by appropriate combinations of the plurality of constituent elements 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 unit 74 scheduler 75 time recording unit 76 interval time calculation unit 77 selection unit 78 frequency deviation calculation unit 79 time difference calculation unit 80 synchronization control unit 81 timing information reference unit 100 information communication system

Claims (14)

An information communication system in which a plurality of information communication devices communicate information as a master device or a slave device,
A set of first information communications, which is a plurality of information communications performed within a predetermined time period with respect to a first timing, between the master device and the slave device; an interval time calculation unit for calculating a transmission interval time and a reception interval time in a second information communication set, which is a plurality of information communications performed within the predetermined time, with respect to a second timing equal to or longer than the time;
a selection unit that selects, from the set of the first information communication and the set of the second information communication, a set of information communication in which the difference between the reception interval time and the transmission interval time is the smallest;
a frequency deviation calculation unit that obtains a clock frequency deviation between the master device and the slave device based on the set of information communication selected by the selection unit;
a synchronization control unit that synchronizes the clock frequencies or times of the master device and the slave device based on the clock frequency deviation obtained by the frequency deviation calculation unit;
An information communication system characterized by comprising: 2. The information communication system according to claim 1, wherein said predetermined time is the minimum interval time at which the influence of frequency deviation appears in the information propagation time between said master device and said slave device. The frequency deviation calculation unit calculates a statistic based on a set of information communication within the predetermined time with respect to the first timing and a statistic based on a set of information communication within the predetermined time with respect to the second timing 3. An information communication system according to claim 1, wherein the deviation of the clock frequency is obtained by canceling the variation of the time difference based on the difference from the amount. The frequency deviation calculation unit calculates a statistic based on a set of information communication within the predetermined time with respect to the first timing and a statistic based on a set of information communication within the predetermined time with respect to the second timing 3. The information communication system according to claim 1, wherein the deviation of the clock frequency is obtained based on the difference from the quantity. A time difference calculation unit that calculates the time difference corresponding to the set with the smallest time difference error and the largest number in a set of a plurality of information communications between the master device and the slave device within a predetermined time. 5. The information communication system according to any one of claims 1 to 4. 6. The time difference calculator calculates the time difference corresponding to a straight line having the largest number of synchronization state vectors whose elements are the time difference and the propagation time in the set of the plurality of information communications. Information communication system as described. The time difference calculation unit calculates a set of synchronization state vectors whose elements are the time difference and the propagation time in the set of the plurality of information communications when the degree of non-symmetry of the propagation time in the two-way communication exceeds a predetermined criterion. 7. The information communication system according to claim 5, wherein the time difference corresponding to a straight line passing through the center of gravity is obtained. An information communication device that communicates information with another information communication device,
A set of first information communications, which is a plurality of information communications performed within a predetermined period of time with respect to a first timing, and a second timing of at least the predetermined period of time from the first timing, an interval time calculation unit for calculating a transmission interval time and a reception interval time in a second set of information communications, which is a plurality of information communications performed within a predetermined time;
a selection unit that selects, from the set of the first information communication and the set of the second information communication, a set of information communication in which the difference between the transmission interval time and the reception interval time is the smallest;
a frequency deviation calculation unit that obtains a clock frequency deviation between another information communication device based on the set of information communication selected by the selection unit;
a synchronization control unit for synchronizing the clock frequency or time based on the clock frequency deviation obtained by the frequency deviation calculation unit;
An information communication device characterized by comprising: 9. The information communication device according to claim 8, wherein said predetermined time is a minimum interval time at which the influence of frequency deviation appears in information propagation time between other information communication devices. The frequency deviation calculator calculates a statistic based on a set of information communications within the predetermined time for a first timing and a statistic based on a set of information communications for a second timing. 10. The information communication device according to claim 8, wherein the deviation of the clock frequency is obtained by canceling the variation of the time difference based on the difference between the two. The frequency deviation calculator calculates a difference between a statistic of a set of information communication within the predetermined time with respect to a first timing and a statistic of a set of information communication within the predetermined time with respect to a second timing. 10. The information communication device according to claim 8, wherein the deviation of the clock frequency is obtained based on . 12. The method according to any one of claims 8 to 11, further comprising a time difference calculator that calculates the time difference corresponding to a set with the smallest time difference error and the largest number of sets of information communication within a predetermined time. The information communication device described in . 12. The time difference calculator determines the time difference corresponding to a straight line having the largest number of synchronization state vectors whose elements are the time difference and the propagation time in the set of the plurality of information communications. The information communication device described. The time difference calculation unit calculates a set of synchronization state vectors whose elements are the time difference and the propagation time in the set of the plurality of information communications when the degree of non-symmetry of the propagation time in the two-way communication exceeds a predetermined standard. 14. The information communication device according to claim 12, wherein the time difference corresponding to a straight line passing through the center of gravity is obtained.

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