JP7468679B2 - Communications system - Google Patents

Description

The present disclosure relates to a communication system.

In a communication system having a master device and a slave device, time synchronization is performed between the master device and the slave device, for example, for communication timing control. In this case, if there are two or more master devices that can be selected as the time synchronization source, one master device is selected as the synchronization source, for example, using the Best Master Clock Algorithm (BMCA) described in Non-Patent Document 1. As a communication method in such a communication system, for example, as exemplified in Non-Patent Document 2, a method is known in which the master device and the slave device send and receive main signals (C/U-Plane messages) and device setting signals (M-Plane messages) using a communication protocol that includes time synchronization information (S-Plane messages).

"IEEE Standard for a Precision Clock, Synchronization Protocol for Networked Measurement and Control Systems" "ORAN-WG4.CUS.0-v03.00 Technical Specification, O-RAN Fronthaul Working Group, Control, User and Synchronization Plane Specification"

In a communication system using the communication method as shown in Non-Patent Document 2, in order to establish communication between a master device and a slave device and transmit and receive a main signal, an exchange of synchronization information is necessary. When two or more master devices are connected to one slave device, using the technology as shown in Non-Patent Document 1, one master device will be selected as the synchronization source. In this case, synchronization information is exchanged between the master device selected as the synchronization source and the slave device, and communication is established. On the other hand, synchronization information is not exchanged between a master device not selected as a synchronization source and a slave device, and therefore communication cannot be established.

As shown in Non-Patent Document 1, messages exchanged between a master device and a slave device, which are synchronization information sources, to establish communication between the devices can be broadly divided into General messages and Event messages. The former General message includes an Announce message. In the Announce message, the master device notifies the slave device of master-specific information including information about the clock class (clock performance) of the master device. When two or more master devices are connected to one slave device, if multiple master devices notify the slave device of master-specific information indicating clocks of the same class, the optimal master clock cannot be selected and communication cannot be established.

The present disclosure has been made to solve such problems. Its purpose is to provide a communication system in which two or more master devices each transmit and receive a main signal to one slave device using a communication protocol including synchronization information, which is capable of selecting one master device as a time synchronization source for the slave device, while establishing communication between the master device not selected as the time synchronization source and the slave device, and which is capable of selecting an optimal time synchronization source from the two or more master devices.

The communication system according to the present disclosure comprises a master device group including two or more master devices, and one slave device connected to each of the master devices in the master device group, each of the master devices in the master device group and the slave device transmitting and receiving a main signal using a communication protocol including synchronization information, and the slave device comprises a timer that determines time information of the slave device, a synchronization information communication unit that transmits and receives the synchronization information with each of the master devices in the master device group, a correction value calculation unit that calculates synchronization difference information by comparing the synchronization information received by the synchronization information communication unit with the time information of the timer, a master information comparison unit that compares master unique information transmitted from each of the master devices in the master device group, and a master selection unit that selects one of the master devices from the master device group as a synchronization source based on the comparison result of the master unique information by the master information comparison unit and the synchronization difference information calculated by the correction value calculation unit, and the master unique information includes information regarding the performance of the clock possessed by the master device.

According to the communication system disclosed herein, in a communication system in which two or more master devices each transmit and receive a main signal to one slave device using a communication protocol including synchronization information, a communication system is provided in which one master device is selected as a time synchronization source for the slave device, while communication can be established between the master device not selected as the time synchronization source and the slave device, and the optimal time synchronization source can be selected from two or more master devices.

1 is a block diagram showing an overall configuration of a communication system according to a first embodiment; 2 is a block diagram showing a configuration of a main part, particularly related to synchronization signal processing, in a slave device of a communication system according to a first embodiment. FIG. 13 is a block diagram showing a configuration of a modified example of a main part related particularly to synchronization signal processing in a slave device of the communication system according to the first embodiment.

A description will be given of a form for implementing a communication system according to the present disclosure with reference to the attached drawings. In each drawing, the same or corresponding parts are given the same reference numerals, and duplicate descriptions are appropriately simplified or omitted. For convenience, in the following description, the positional relationship of each structure may be expressed based on the illustrated state. Note that the present disclosure is not limited to the following embodiments, and the embodiments may be freely combined, any component of each embodiment may be modified, or any component of each embodiment may be omitted, within the scope of the spirit of the present disclosure.

Embodiment 1.
A first embodiment of the present disclosure will be described with reference to Fig. 1 to Fig. 3. Fig. 1 is a block diagram showing an overall configuration of a communication system. Fig. 2 is a block diagram showing a configuration of a main part, particularly related to synchronous signal processing, in a slave device of the communication system. Fig. 3 is a block diagram showing a modified configuration of a main part, particularly related to synchronous signal processing in the slave device.

As shown in FIG. 1, the communication system according to this embodiment includes a master device group 10 and one slave device 100. The master device group 10 includes two or more master devices. In the illustrated example, the master device group 10 includes N master devices, where N is an integer equal to or greater than two. To distinguish between the master devices, a serial number is assigned to each master device for convenience, and the master devices are represented as master device #1, master device #2, ..., master device #N. Note that the master devices in the master device group 10 may each be individual devices or may be integrated devices.

The slave device 100 is connected to each of the master devices in the master device group 10. The master devices in the master device group 10 are built into, for example, a parent station device. The slave device 100 is built into, for example, a child station device. When the communication system is applied to the mobile fronthaul of an O-RAN (Open Radio Access Network), the parent station device is the CU (Central Unit) and/or DU (Distributed Unit) of the base station. In this case, the child station device corresponds to the RU (Radio Unit).

The slave device 100 transmits and receives a main signal to each of the master devices in the master device group 10 over the same medium using a communication protocol that includes synchronization information. That is, each of the master devices in the master device group 10 and the slave device 100 are connected using a communication method that requires not only the main signal but also time synchronization information. A specific example of such a communication method is eCPRI (Common Public Radio Interface (CPRI is a registered trademark)).

For example, suppose that an interface defined by ORAN-WG4 (O-RAN Alliance Working Group 4) is used for communication between the master device group 10 and the slave device 100. In this case, the configuration information of the slave device 100 is obtained from the master device using the M-plane protocol. Furthermore, C-plane messages correspond to the control information of the main signal, and U-plane messages correspond to the user information of the main signal. Furthermore, time synchronization information is included in the S-plane messages.

The slave device 100 has two or more slave functions 101. The slave functions 101 correspond to each of the master devices in the master device group 10 with which the slave device 100 communicates. The same number of slave functions 101 are provided as there are master devices. That is, in the illustrated configuration example, the slave device 100 has N slave functions 101. Thus, in the communication system of this embodiment, multiple slave functions 101 corresponding to multiple master devices share one slave device 100.

Next, the configuration of the slave device 100 shared by multiple slave functions 101 will be described with reference to Figure 2. As shown in the figure, the slave device 100 includes an interface unit 111, a switch unit 112, an oscillator 121, a timer 122, a correction value calculation unit 123, a correction value comparison unit 124, a master selection unit 131, a master information comparison unit 132, and a synchronization information communication unit 140.

The slave device 100 may be configured as hardware, such as a computer equipped with a processor and memory. The processor is also called a CPU (Central Processing Unit), central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, or DSP. The memory may be, for example, a non-volatile or volatile semiconductor memory such as RAM, ROM, flash memory, EPROM, and EEPROM, or a magnetic disk, flexible disk, optical disk, compact disk, mini disk, and DVD.

A program as software is stored in the memory of the slave device 100. The slave device 100 then performs pre-set processing by having a processor execute the program stored in the memory, and as a result of the hardware and software working together, it realizes the functions of each of the switch unit 112, timer 122, correction value calculation unit 123, correction value comparison unit 124, master selection unit 131, master information comparison unit 132, and synchronization information communication unit 140, as well as the slave function 101.

The interface unit 111 is a communication interface for transmitting and receiving synchronization information and main signals with each of the master devices in the master device group 10. The interface unit 111 corresponds to each of the master devices in the master device group 10 with which the slave device 100 communicates. The same number of interface units 111 are provided as there are master devices. That is, the slave device 100 has two or more interface units 111. In the illustrated configuration example, the slave device 100 has N interface units 111. The switch unit 112 switches between the two or more interface units 111. The switch unit 112 switches the interface units 111, thereby switching the master device that communicates synchronization information with the slave device 100.

The oscillator 121 outputs a timing signal that the timer 122 uses to keep time. For example, the oscillator 121 has a quartz crystal oscillator and outputs a periodic sine wave signal, a square wave signal, a pulse signal, or the like as a timing signal. The timer 122 keeps time based on the timing signal output from the oscillator 121. The timer 122 determines time information used for various processes in the slave function 101 of the slave device 100.

The synchronization information communication unit 140 transmits and receives synchronization information to and from each of the master devices in the master device group 10. The synchronization information communication unit 140 corresponds to each of the master devices in the master device group 10 with which the slave device 100 communicates. There are the same number of synchronization information communication units 140 as there are master devices. In other words, the slave device 100 has two or more synchronization information communication units 140.

In the illustrated configuration example, the slave device 100 has N synchronization information communication units 140. In order to distinguish between the synchronization information communication units 140, a serial number is assigned to each synchronization information communication unit 140 for convenience, and the synchronization information communication units 140 are denoted as synchronization information communication unit 140#1, synchronization information communication unit 140#2, ..., synchronization information communication unit 140#N. The synchronization information communication unit 140#1 transmits and receives synchronization information with the master device #1. Similarly, the synchronization information communication unit 140#2 transmits and receives synchronization information with the master device #2. The synchronization information communication unit 140#N transmits and receives synchronization information with the master device #N. The master device that communicates synchronization information with the slave device 100 is switched by the switch unit 112 switching the interface unit 111 used by two or more synchronization information communication units 140 for communication.

The master information comparison unit 132 compares the master unique information transmitted from each of the master devices in the master device group 10. Each of the master devices in the master device group 10 transmits master unique information. The master unique information transmitted from a master device includes information regarding the performance of the clock possessed by the master device. When PTP (Precision Time Protocol) is used for time synchronization between the master device and the slave device 100, the master unique information is, for example, information such as GrandMasterIdentity, Priority, and ClockQuality included in the Announce message in the General message.

The master information comparison unit 132 compares the master unique information transmitted from each of the master devices in the master device group 10, and notifies the master selection unit 131 of the master selection information as the comparison result. In comparing the master unique information, the master information comparison unit 132 compares, for example, any of the values of GrandMasterIdentity, Priority, ClockQuality, etc. contained in the Announce message. The master selection information is information on the master device that has the highest performance as a clock (oscillator) among the master device group 10. If there are multiple master devices with the highest performance, the information on all of the corresponding master devices is notified. The master information comparison unit 132 holds the master unique information of each master device. The held master unique information is stored, for example, in the memory of the slave device 100 described above.

The correction value calculation unit 123 calculates synchronization difference information, which is the difference between the synchronization information of the master device received by each synchronization information communication unit 140 and the time measured by the timer 122. That is, the correction value calculation unit 123 calculates synchronization difference information for each master device. The synchronization difference information calculated by the correction value calculation unit 123 is notified to the correction value comparison unit 124. The correction value calculation unit 123 can recalculate and update the synchronization difference information for each time synchronization sequence between each master device and the synchronization information communication unit 140.

The correction value comparison unit 124 compares the synchronization difference information calculated by the correction value calculation unit 123 for each of the master devices in the master device group 10, and notifies the master selection unit 131 of the master selection information as the comparison result. The correction value comparison unit 124 holds the calculated synchronization difference information for each master device. The held synchronization difference information is stored, for example, in the memory of the slave device 100 described above. Note that the correction value calculation unit 123 and the correction value comparison unit 124 may be provided as a single functional block rather than as separate functional blocks. In other words, the correction value calculation unit 123 may have the function of the correction value comparison unit 124.

The master selection unit 131 selects one master device from the master device group 10 as a synchronization source for the slave device 100 based on the master selection information notified by the correction value comparison unit 124 and the master selection information notified by the master information comparison unit 132. In other words, the master selection unit 131 selects one master device from the master device group 10 as a synchronization source based on the comparison result of the master specific information by the master information comparison unit 132 and the synchronization difference information calculated by the correction value calculation unit 123. The master device selected as the synchronization source will function as a so-called grand master or boundary clock.

The master selection unit 131 first extracts master devices that are candidates for the synchronization source from the master device group 10 based on the comparison result of the master unique information by the master information comparison unit 132. Then, the master selection unit 131 selects one master device from the extracted candidate group as the synchronization source based on the synchronization difference information calculated by the correction value calculation unit 123 for each of the master devices in the extracted candidate group.

A specific example will be given of a method for the master selection unit 131 to select a master device to be a synchronization source. For example, assume that there are four master devices in the master device group 10: master device #1, master device #2, master device #3, and master device #4. First, the master unique information of master devices #1 to #4 is notified to the master information comparison unit 132 via the interface unit 111 and the switch unit 112.

Here, there are four types of master unique information: A, B, C, and D, with A having the highest performance, D having the lowest performance, and B and C having intermediate performance. In this example, the master unique information of master device #1, master device #2, and master device #3 is A, and the master unique information of master device #4 is B. In this case, the master information comparison unit 132 compares these master unique information, selects master device #1, master device #2, and master device #3 that show the highest performance A, and notifies the master selection unit 131. Then, the master selection unit 131 extracts three master devices, master device #1, master device #2, and master device #3, as a group of candidates for the synchronization source.

Next, assume that the synchronization difference values of the master devices are master device #1: 20, master device #2: 28, master device #3: 32, and master device #4: 120. In a first example of comparison by the correction value comparison unit 124, these synchronization difference values are simply compared. Then, based on the comparison result by the correction value comparison unit 124, the master selection unit 131 selects the master device with the smallest synchronization difference value as the synchronization source. In the above example, master device #1, which has the smallest synchronization difference value of 20 among the candidate group of master devices #1, #2, and #3, is selected as the synchronization source.

In addition, in a second example of comparison by the correction value comparison unit 124, the difference between the synchronization difference value of each master device and the average synchronization difference value of all master devices is compared. For example, in the example of the synchronization difference value described above, the average synchronization difference value of all master devices is (20 + 28 + 32 + 120) / 4 = 50. Therefore, the difference between the synchronization difference value of each master device and the average synchronization difference value is 50-20 = 30 for master device #1, 50-28 = 22 for master device #2, 50-32 = 18 for master device #3, and 50-120 = -70 for master device #4. Then, based on the comparison result by the correction value comparison unit 124, the master selection unit 131 selects the master device with the smallest difference value as the synchronization source. In the example described here, master device #3, which has the smallest difference value of 18 among the candidate group of master devices #1, #2, and #3, is selected as the synchronization source. By using the comparison method according to the second example, it is possible to deal with network fluctuations in which the packet transmission time (latency) is not constant.

As described above, the correction value calculation unit 123 can update the synchronization difference information for each time synchronization sequence between each master device and the synchronization information communication unit 140. Therefore, the correction value comparison unit 124 may compare the synchronization difference values based on the synchronization difference information updated by recalculation for each time synchronization sequence. In this way, it is possible to further respond to network fluctuations.

Note that, as a result of the master information comparison unit 132 comparing the master unique information, the master selection information notified from the master information comparison unit 132 may include all the master devices of the master device group 10. In this case, the master selection unit 131 will set all the master devices of the master device group 10 as a candidate group for the synchronization source. Therefore, after going through the judgment based on the master unique information, the master selection unit 131 will ultimately select a master device to be the synchronization source based on the respective synchronization difference information of all the master devices of the master device group 10. In addition, as a result of the correction value comparison unit 124 comparing the synchronization difference information of each master device, it is also possible that the master selection information notified from the correction value comparison unit 124 indicates that the synchronization difference information is equivalent for all the master devices of the master device group 10. In this case, the master selection unit 131 will ultimately select a master device to be the synchronization source based on the comparison result of the master unique information by the master information comparison unit 132. In other words, depending on the situation, the master selection unit 131 may be able to select a synchronization source based on the comparison result of the master unique information or the comparison result of the synchronization difference information.

The synchronization difference information calculated from the synchronization information of the master device selected by the master selection unit 131 as the synchronization source is used as a correction value for the time measured by the timer 122. In other words, the timer 122 determines the time information using the synchronization difference information calculated from the synchronization information of the master device selected by the master selection unit 131 as the synchronization source. In this way, time synchronization is performed between the master device selected as the synchronization source and the slave device 100. Then, this timer 122 can measure the transmission delay time required to synchronize the slave device 100 and the master device.

In the communication system configured as described above, the synchronization information communication unit 140 transmits and receives synchronization information to and from all of the master devices in the master device group 10. Therefore, synchronization information is exchanged not only with the master device selected as the synchronization source for the slave device 100, but also with master devices that were not selected as the synchronization source. Therefore, communication can be established between the slave device 100 and a master device that was not selected as the synchronization source.

Therefore, in a communication system in which two or more master devices each transmit and receive a main signal to one slave device 100 using a communication protocol including synchronization information, one master device can be selected as a time synchronization source for the slave device 100, while communication can be established between the master device not selected as the time synchronization source and the slave device 100, and main signals can also be transmitted and received between the master device not selected as the time synchronization source and the slave device 100.

In addition, in the communication system configured as described above, one master device from the master device group 10 is selected as the synchronization source for the slave device 100 using master specific information including information on the performance of the clock possessed by the master device and synchronization difference information calculated by the correction value calculation unit 123 of the slave device 100. Therefore, even if multiple master devices notify the slave device of master specific information indicating clocks of the same class, it is possible to select the optimal master clock and establish communication.

Next, a modified example of the communication system of this embodiment will be described with reference to FIG. 3. In this modified example, the slave device 100 further includes a monitoring unit 150 in comparison with the configuration example of FIG. 2. As described above, the correction value calculation unit 123 recalculates and updates the synchronization difference information for each time synchronization sequence between the master device and the synchronization information communication unit 140. The monitoring unit 150 monitors the value of the synchronization difference information calculated and updated by the correction value calculation unit 123 for the master device selected as the synchronization source by the master selection unit 131. When the value of the synchronization difference information of the master device that is the synchronization source becomes equal to or greater than the threshold value α, an alert signal is output. The threshold value α of the monitoring unit 150 is set, for example, by a setting signal input from outside the slave device 100. Alternatively, the threshold value α of the monitoring unit 150 may be set in advance in the memory of the slave device 100. When an alert signal is output from the monitoring unit 150, the master selection unit 131 reselects the master device that is the synchronization source.

A concrete example will be given of an alert by the monitoring unit 150 and the reselection of a master device to be a synchronization source by the master selection unit 131. For example, assume that there are four master devices 10: master device #1, master device #2, master device #3, and master device #4. Consider a situation in which master device #1 is selected as a synchronization source. In this situation, assume that the synchronization difference value of master device #1 has changed from 5 to 30 due to recalculation of synchronization difference information for each time synchronization sequence. In this example, assume that the monitoring threshold α by the monitoring unit 150 is set to 20. Therefore, since the synchronization difference value of master device #1 selected as a synchronization source has become equal to or greater than the threshold α, the master selection unit 131 reselects a master device to be a synchronization source.

At the time of this reselection, the synchronization difference values of the master devices are: master device #1 is 30, master device #2 is 5, master device #3 is 10, and master device #4 is 50. For example, the correction value comparison unit 124 simply compares these synchronization difference values. Then, based on the comparison result by the correction value comparison unit 124, the master selection unit 131 selects the master device with the smallest synchronization difference value as the synchronization source. Therefore, in this example, master device #2, which has the smallest synchronization difference value of 5, is selected as the new synchronization source.

In the modified example configured as above, if the synchronization difference information of the master device currently selected as the synchronization source deteriorates, a new synchronization source can be reselected and the synchronization source can be switched to the new master device. Therefore, even in a situation where the packet transmission time (latency) is not constant, time synchronization with the master device can be stably established and communication can be continued.

The present disclosure can be used in a communication system that includes a master device group including two or more master devices and one slave device connected to each of the master devices in the master device group, and in which each master device and slave device transmits and receives a main signal using a communication protocol that includes time synchronization information.

10 Master device group 100 Slave device 101 Slave function 111 Interface section 112 Switch section 121 Oscillator 122 Timer 123 Correction value calculation section 124 Correction value comparison section 131 Master selection section 132 Master information comparison section 140 Synchronization information communication section 150 Monitoring section

Claims (5)

a master device group including two or more master devices;
a slave device connected to each of the master devices of the master device group;
Each of the master devices in the master device group and the slave device transmit and receive a main signal using a communication protocol including synchronization information;
The slave device is
a timer for determining time information of the slave device;
a synchronization information communication unit that transmits and receives the synchronization information to and from each of the master devices of the master device group;
a correction value calculation unit that calculates synchronization difference information by comparing the synchronization information received by the synchronization information communication unit with time information of the timer;
a master information comparison unit that compares master unique information transmitted from each of the master devices of the master device group;
a master selection unit that selects one of the master devices as a synchronization source from the master device group based on a comparison result of the master unique information by the master information comparison unit and the synchronization difference information calculated by the correction value calculation unit,
the master specific information includes information regarding the performance of a clock possessed by the master device ;
A communication system in which the master selection unit selects the master device to be a synchronization source based on the difference between the average value of the synchronization difference information of all the master devices included in the master device group and the value of the synchronization difference information of each of the master devices . a monitoring unit that outputs an alert signal when the synchronization difference information calculated by the correction value calculation unit for the master device selected as a synchronization source by the master selection unit becomes equal to or exceeds a threshold value;
The communication system according to claim 1 , wherein the master selection unit selects the master device that serves as a synchronization source when the alert signal is output from the monitoring unit. The master selection unit is
extracting the master devices that are candidates for a synchronization source from the master device group based on a comparison result of the master unique information by the master information comparison unit;
3. The communication system according to claim 1, further comprising: selecting one of the master devices from the group of candidates based on the synchronization difference information calculated by the correction value calculation unit for each of the master devices in the group of candidates. The communication system according to claim 1 , wherein the correction value calculation unit is capable of updating the synchronization difference information for each time synchronization sequence between the master device and the synchronization information communication unit. The slave device is
two or more of the synchronization information communication units provided corresponding to each of the master devices of the master device group;
two or more interface units for communicating with each of the master devices of the master device group;
The communication system according to claim 1 , further comprising a switch unit that switches the interface unit used by two or more of the synchronous information communication units for communication.

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