Communication device, method for controlling the communication device, and program

Abstract

To suppress the degradation of time adjustment accuracy by time synchronization protocols in a more suitable manner. [Solution] The wireless communication interface 207 communicates wirelessly with one or more client devices. The time synchronization processing unit 206 determines whether the state of the wireless communication is good or not. If the time synchronization processing unit 206 determines that the state of wireless communication with a client device is poor, it restricts the execution of the communication sequence using the time synchronization protocol with that client device.

Description

Technical Field

[0001] The present disclosure relates to a communication device, a control method for a communication device, and a program.

Background Art

[0002] In recent years, technologies for operating a plurality of devices in synchronization as a system have been used in various fields. As an example, there is a technique called stadium vision or volumetric studio that creates a free viewpoint image by switching to an image at an arbitrary viewpoint using synchronized captured images of a plurality of imaging devices (for example, digital cameras, digital video cameras, etc.). When applying such a technique, in order to synchronize the imaging timings of each of the plurality of imaging devices, the imaging devices may perform time synchronization by communication via a network. As a technique for performing time synchronization between a plurality of devices by communication via a network, there is PTP (Precision Time Protocol) defined by the IEEE1588-2008 (also referred to as IEEE1588 version 2) standard. By generating imaging timings from the synchronized time, synchronized imaging between a plurality of imaging devices becomes possible. PTP is a communication protocol (also referred to as a time synchronization protocol) for time adjustment via communication. PTP enables the time of a client device to be continuously synchronized with high accuracy to the time of a server device by communicating between a time distribution server device called GMC (Grand Master Clock) and the client device.

[0003] When time synchronization via PTP is performed over a wireless LAN, packet loss due to radio wave reflection, attenuation, interference, etc., and the resulting retransmission process may occur due to the influence of the wireless environment and other wireless communication devices. Furthermore, it may be affected by collision avoidance mechanisms for communication data, such as CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance). In such situations, after the transmission timestamp of the necessary packets is stamped in PTP, a random delay in transmission may occur. These retransmission processes and long waiting periods can become delay jitter in wireless communication. Since PTP assumes that the communication delay time between the time distribution server device and the client device is constant in both directions, communication delay jitter can be a factor in the deterioration of the accuracy of time synchronization between the client device and the time distribution server device. Against this backdrop, in environments where jitter occurs, such as wireless communication, technologies are being considered to predict the occurrence of retransmission processes and long waiting processes that cause jitter, and to control the use of PTP packets that are predicted to have undergone these processes. Patent Document 1 discloses a technology that measures multiple communication delay times between a time distribution server device and a client device and adjusts the time based on the minimum value among them. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-225880 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] As mentioned above, in wireless communication, the surrounding wireless environment and other wireless communication devices can cause radio wave reflection, attenuation, and interference, which can lead to jitter in communication delays due to retransmission and long waiting times. When time synchronization using PTP is performed via wireless communication such as a wireless LAN, the jitter in the communication delay of PTP packets transmitted by the time distribution server device can be a factor in the deterioration of PTP time synchronization accuracy across multiple client devices. The technology disclosed in Patent Document 1 suppresses the deterioration of time synchronization accuracy by adjusting the time based on the minimum communication delay time in the client device. However, it may not be possible to obtain a uniform effect across multiple client devices.

[0006] In view of the above problems, the present invention aims to suppress the deterioration of the accuracy of time adjustment by a time synchronization protocol in a more suitable manner. [Means for solving the problem]

[0007] The communication device according to the present invention is characterized by comprising: communication means for performing wireless communication with one or more other wireless communication devices using a time synchronization protocol; determination means for determining whether the state of the wireless communication is good or not; and control means for restricting the execution of the communication sequence using the time synchronization protocol with the other wireless communication device when the determination means determines that the state of the wireless communication with the other wireless communication device is poor. [Effects of the Invention]

[0008] According to the present invention, it is possible to suppress the deterioration of the accuracy of time adjustment by the time synchronization protocol in a more suitable manner. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows an example of a schematic configuration of a synchronized imaging system. [Figure 2] This diagram shows an example of the hardware configuration of a communication device. [Figure 3] This figure shows an example of a PTP communication sequence. [Figure 4] This flowchart shows an example of the processing performed by a time distribution server device. [Figure 5] This flowchart shows an example of the processing performed by a time distribution server device. [Figure 6] This flowchart shows an example of the processing performed by a time distribution server device. [Figure 7] This figure shows an example of a schematic configuration of a synchronized imaging system. [Figure 8] This diagram shows an example of the hardware configuration of a communication device. [Figure 9] This is a flowchart illustrating an example of processing performed by a wireless access point (AP) device. [Figure 10] This is a flowchart illustrating an example of processing performed by a wireless access point (AP) device. [Modes for carrying out the invention]

[0010] Preferred embodiments of this disclosure will be described in detail below with reference to the attached drawings. In this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant descriptions will be omitted.

[0011] <First Embodiment> (System configuration for performing time synchronization) As an example of a communication device according to the first embodiment of this disclosure, a communication device having the function of a time distribution server will be described with reference to Figure 1. Figure 1 is a diagram showing an example of a schematic configuration of a synchronized imaging system using multiple time-synchronized cameras. Each of the communication devices 100 to 103 is a communication device equipped with an imaging function (in other words, an imaging device equipped with a communication function). That is, in the synchronized imaging system shown in Figure 1, still images and moving images (hereinafter collectively referred to as images) of a subject are captured (hereinafter also referred to as synchronized imaging) by synchronizing four imaging devices (communication devices 100 to 103 equipped with imaging functions) with high precision.

[0012] In synchronous imaging, in order to synchronize the imaging timings of a plurality of imaging devices with high precision, it is necessary to synchronize the system times of each imaging device (communication device) with high precision. In the example shown in FIG. 1, for the sake of convenience, among the four communication devices, the communication device 100 operates as a time distribution server that is the source of time synchronization, and the communication devices 101, 102, and 103 operate as clients that synchronize with the time of the communication device 100. Hereinafter, the communication device 100 that is the source of time synchronization will also be referred to as the time distribution server device 100. Further, the communication devices 101, 102, and 103 that synchronize with the time of the time distribution server device 100 will also be referred to as client devices 101, 102, and 103.

[0013] In the present embodiment, the time distribution server device 100 operates as a wireless LAN access point, and each of the client devices 101, 102, and 103 performs a wireless connection to the time distribution server device 100. Further, each of the client devices 101, 102, and 103 performs time synchronization with the time distribution server device 100 by PTP communication. The time distribution server device 100 has functions as a GMC (Grand Master Clock) and a BC (Boundary Clock) that play the role of the time synchronization source of PTP, and distributes its own time to the client devices 101, 102, and 103.

[0014] (Hardware Configuration of Communication Device) An example of the hardware configuration of a communication device having an imaging function in the present embodiment will be described with reference to FIG. 2. The communication device 200 shown in FIG. 2 is a device that can be applied as the time distribution server device 100 shown in FIG. 1. In the example shown in FIG. 2, a CPU (Central Processing Unit) 202, a RAM (Random Access Memory) 203, and a ROM (Read Only Memory) 204 are connected to a system bus 201. The CPU 202 controls the operation of the entire communication device 200 by expanding and executing the programs stored in the ROM 204. The RAM 203 is used as a temporary storage area that is expanded when system programs and application programs are executed. The ROM 204 is a storage area for storing various programs and data such as system programs and application programs, and can be realized by a non-volatile recording medium.

[0015] Also, a clock 205 and a time synchronization processing unit 206 are connected to the system bus 201. The clock 205 is a clock that measures the system time within the communication device 100. The clock 205 has a function of generating and outputting a pulse signal with a frequency such as 29.97 Hz or 25 Hz based on the time. The time synchronization processing unit 206 executes processing related to the control of the clock 205, such as PTP communication processing and time adjustment. The time synchronization processing unit 206 has the functions of the PTP GMC and BC as a time distribution server and the function of a client that performs time synchronization. The time synchronization processing unit 206 can be implemented as a microprocessor different from the CPU 202 and software executed thereon.

[0016] The wireless communication interface 207 includes a wireless communication controller implemented by an IC or the like, and an antenna for transmitting and receiving wireless communication signals. The wireless communication interface 207 is connected to the system bus 201 and controlled by software executed on the CPU 202. The time distribution server device 100 uses the wireless communication interface 207 to establish a wireless communication link with external client devices 101, 102, and 103 and transmit and receive packets. In this embodiment, the wireless communication interface 207 does not include a clock, and the time synchronization processing unit 206 adjusts the time of the clock 205, but the wireless communication interface 207 may also include a clock. Furthermore, in this embodiment, for convenience, various explanations are given focusing on the case where wireless LAN (Wi-Fi®) is applied as the wireless communication, but this does not limit the type of wireless communication to which it can be applied. As a specific example, mobile communication such as LTE (Long Term Evolution) or 5G may be applied.

[0017] The camera unit 208 includes an image sensor that converts a subject image (optical image of the subject) into an electrical signal to generate image data, a lens group that forms an image of the subject on the image sensor, an image processing unit that performs image processing on the image data, and a storage media unit that stores the image data. The camera unit 208 receives a pulse signal output by the clock 205 mentioned above and generates imaging timings with frame rates such as 59.94 fps or 50 fps. In other words, the time distribution server device 100 and the client devices 101, 102, and 103 each generate imaging timings from the synchronized time, enabling synchronized imaging.

[0018] (Time-synchronized communication sequence) Next, the time synchronization communication sequence will be explained. Figure 3 shows an example of a PTP communication sequence between the time distribution server device 100 and the client device 101. Note that the example shown in Figure 3 shows only the minimum communication necessary for time synchronization of the client device.

[0019] The time distribution server device 100 periodically multicasts a Sync message 301 to the client device. This Sync message 301 is received by the client device 101. The time synchronization processing unit 206 of the time distribution server device 100 obtains the packet transmission timestamp measured by the clock 205 when the Sync message 301 is transmitted, and obtains the transmission time T1 as indicated by the code 305. The other client device 101 receives this Sync message 301 packet, obtains the reception timestamp, and obtains the reception time T2 as indicated by the code 306.

[0020] Next, the time distribution server device 100 multicasts a Follow-Up message 302. This Follow-Up message 302 contains the transmission time T1, indicated by the code 305. The client device 101 receives the Follow-Up message 302 and obtains the transmission time T1 indicated in the message.

[0021] Next, the client device 101 sends a Delay-Req message 303, and obtains a transmission time T3 at the time of packet transmission of this message, as indicated by the descriptive numeral 307. The time distribution server device 100 receives the packet of the Delay-Req message 303 sent by the client device 101. The time synchronization processing unit 206 of the time distribution server device 100 obtains a packet reception timestamp measured by the clock 205 at the time of reception of the Delay-Req message 303, and obtains a reception time T4 as indicated by the descriptive numeral 308.

[0022] The time distribution server device 100 then sends a Delay-Resp message 304. This Delay-Resp message contains the reception time T4, indicated by the code 308. The client device 101 obtains the reception time T4 by receiving the Delay-Resp message 304 from the time distribution server device 100.

[0023] Through the communication described above, the client device 101 can obtain four times, indicated as transmission time T1, reception time T2, transmission time T3, and reception time T4. The client device 101 obtains the packet transmission delay time D from the time distribution server device 100 to the client device 101 using the calculation formula shown below as (Equation 1). D = ((T4 - T1) - (T3 - T2)) / 2 …(Equation 1)

[0024] Furthermore, the time difference ΔT between the clock 105 of the time distribution server device 100 and the clock in the client device 101 can be obtained by the calculation formula shown below as (Equation 1). ΔT = ((T2 - T1) - (T4 - T3)) / 2 …(Equation 2)

[0025] The client device 101 corrects the time of its internal clock based on this time difference ΔT. The calculation formula described above is commonly used in PTP. In this embodiment, it is assumed that the communication delay time between the time distribution server device 100 and the client device 101 is constant in both directions.

[0026] The above describes an example of a PTP communication sequence between the time distribution server device 100 and the client device 101 for time synchronization. Note that other client devices, not just the client device 101, will also perform a similar communication sequence with the time distribution server device 100. Furthermore, the time distribution server device 100 not only periodically sends Sync messages, but also periodically multicasts a message called an Announce message, independently of the communication sequence shown in Figure 3. This Announce message is sent to inform other communication devices that the time distribution server device 100 is present on the network. Therefore, each of the client devices 101, 102, and 103 according to this embodiment will periodically receive Announce messages.

[0027] (Processing by time synchronization processor 206) In this embodiment, the technology relating to this disclosure is mainly embodied by the time synchronization processing unit 206. Therefore, an example of the PTP communication processing of the time synchronization processing unit 206 according to this embodiment will be described with reference to Figures 4, 5, and 6. Figure 4 is a flowchart showing an example of the transmission process of a Sync message in PTP. The time synchronization processing unit 206 periodically transmits PTP Sync messages, and therefore periodically executes the series of processes shown in Figure 4. The series of processes shown in Figure 4 starts from S401.

[0028] In S402, the time synchronization processing unit 206 determines whether the synchronized imaging system shown in Figure 1 is performing synchronized imaging. If the time synchronization processing unit 206 determines in S402 that the synchronized imaging system is performing synchronized imaging, it proceeds to S403. On the other hand, if the time synchronization processing unit 206 determines in S402 that the synchronized imaging system is not performing synchronized imaging, it proceeds to S406.

[0029] In S403, the time synchronization processing unit 206 measures the communication delay time with each client device connected via wireless communication. The following communication delay time is measured as round-trip delay time. A simple measurement method that can be implemented is, for example, to measure the round-trip delay of sending and receiving ICMP Echo requests / replies to each client device with nanosecond resolution. In S404, the time synchronization processing unit 206 measures the wireless link status. In this process, data on parameters indicating wireless quality are acquired from the wireless communication interface 207 for each of the client devices 101, 102, and 103. Parameters indicating wireless quality include, for example, the received signal strength index (RSSI) of the wireless link, the signal-to-noise ratio (SNR) including noise in the wireless environment of the device itself, and the number of retransmissions.

[0030] In S405, the time synchronization processing unit 206 determines whether the wireless communication status is good or not. This determination is made based on the measurement results in the processing of S403 and S404. If the time synchronization processing unit 206 determines in S405 that the wireless communication status is good, it proceeds to S406. On the other hand, if the time synchronization processing unit 206 determines in S405 that the wireless communication status is not good, it proceeds to the end of the series of processes shown in Figure 4, indicated by S409. In this case, the time distribution server device 100 will not send a Sync message.

[0031] In determining whether the wireless communication status is good in S405, the determination conditions include checking at least one of the following: the value of the received signal strength in the wireless link with each client measured in S404, and the value of the noise ratio measured in S404. Specifically, at least one of the following checks is performed: whether the value of the received signal strength in the wireless link exceeds a predetermined threshold, and whether the value of the noise ratio exceeds a predetermined threshold. In addition, it may be checked whether the measured value of the communication delay time of each client device measured in S403 exceeds a predetermined threshold. If the communication status with each of the series of client devices is good based on these checks, S405 will be determined as Yes, and otherwise as No. Alternatively, instead of determining Yes when the communication status with each of the series of client devices is good, S405 may be determined as Yes when, for example, a predetermined number or more (e.g., more than half) of the client devices have a good communication status.

[0032] In S406, the time synchronization processing unit 206 sends a Sync message. In S407, the time synchronization processing unit 206 obtains the transmission timestamp T1 measured by the clock 205 when the Sync message packet is transmitted in S406. In S408, the time synchronization processing unit 206 records the Sync message sent in S406 and the timestamp T1 of the Sync message obtained in S407. Then, in S409, the time synchronization processing unit 206 completes the series of processes shown in Figure 4. In the S402 process, it is determined whether or not the synchronized imaging system is performing synchronized imaging. If it is performing synchronized imaging, the processes from S403 to S405 are executed, thus controlling the transmission of Sync messages based on the quality of the wireless communication.

[0033] Next, with reference to Figure 5, an example of the time synchronization processing unit 206's process for sending PTP Follow-Up messages will be described. Since the time synchronization processing unit 206 periodically sends Follow-Up messages in addition to PTP Sync messages, it periodically executes the series of processes shown in Figure 5. The series of processes shown in Figure 5 starts from S501.

[0034] In S502, the time synchronization processing unit 206 measures the wireless link status. The processing in S502 is substantially the same as the processing in S404 described above (see Figure 4), and data on parameters indicating wireless quality, such as the received signal strength of the wireless link, is acquired. In S503, the time synchronization processing unit 206 checks whether or not a Sync message has been sent based on whether or not there is a record of a Sync message being sent as shown in S408 in Figure 4. If the time synchronization processing unit 206 determines in S503 that it did not send a Sync message, it proceeds to S507 and terminates the series of processes shown in Figure 5 without sending a Follow-Up message. On the other hand, if the time synchronization processing unit 206 determines that it did not send a Sync message in S503, it proceeds to S504.

[0035] In S504, the time synchronization processing unit 206 determines whether the wireless communication status is good or not. The process in S504 is substantially the same as the process in S405 described above, with reference to Figure 4. If the time synchronization processing unit 206 determines in S504 that the wireless communication status is good, it proceeds to S505. On the other hand, if the time synchronization processing unit 206 determines in S504 that the wireless communication status is not good, it proceeds to S506.

[0036] In S505, the time synchronization processing unit 206 sends a Follow-Up message packet. In S505, the value of the transmission timestamp T1 recorded in the process of S418 shown in Figure 4 is written to the Follow-Up message and sent. In S506, the time synchronization processing unit 206 deletes the transmission record of the sent Sync message. Then, the time synchronization processing unit 206 proceeds to S507 and terminates the series of processes shown in Figure 5. If the process proceeds from S504 to S506, it means that although the Sync message has been sent, the Follow-Up message is not sent because the wireless communication status is poor. In other words, the sending of the Follow-Up message is controlled by the quality of the wireless communication status.

[0037] Next, with reference to Figure 6, an example of the PTP Delay-Resp message transmission process by the time synchronization processing unit 206 will be described. The series of processes shown in Figure 6 is initiated in S601 when Delay-Req messages are received from each client device.

[0038] In S602, the time synchronization processing unit 206 obtains the reception time T4 by acquiring the reception timestamp of the Delay-Req message packet from the clock 205. In S603, the time synchronization processing unit 206 sends a Delay-Resp message packet. In S603, the time synchronization processing unit 206 writes the value of the reception time T4 obtained in S602 into the Delay-Resp message and sends it. Then, the time synchronization processing unit 206 proceeds to S604 and completes the series of processes shown in Figure 5.

[0039] As illustrated in Figure 6, the time distribution server device 100 sends a Delay-Resp message when it receives a Delay-Req message from a client device, regardless of the wireless communication status.

[0040] As described above, in the first embodiment of this disclosure, the time synchronization processing unit 206 restricts the transmission of Sync messages and Follow-Up messages (for example, does not send these messages) when it determines that the wireless communication state is poor. When such control is applied, the execution of PTP time synchronization communication is restricted in the client devices 101, 102, and 103 (for example, communication during time synchronization is not performed). Therefore, for example, in situations where communication delay jitter is likely to occur due to wireless communication retransmission processing or long waiting processing, the execution of PTP time synchronization processing is restricted (for example, not performed), which is expected to have the effect of suppressing deterioration of the time synchronization accuracy of the imaging system. Furthermore, if the time synchronization processing unit 206 determines in S405 that the wireless communication status is poor, it may apply control to increase the interval between the periodically executed Sync message transmission process and delay the next Sync message transmission. Then, if the wireless communication status recovers to a good state, the time synchronization processing unit 206 may apply control to return the interval between the Sync message transmission process to its original state. Furthermore, the time distribution server device 100 also periodically transmits PTP Announce messages, regardless of the wireless communication status. Furthermore, although this embodiment describes a time distribution server device with a camera function as an example of an embodiment of the invention, this does not limit the scope of application of the technology disclosed herein. As a specific example, the technology disclosed herein may be applied to devices such as printers, smartphones, tablets, PCs (personal computers), and projectors.

[0041] <Second Embodiment> A second embodiment of this disclosure is described below. (System configuration for performing time synchronization) Referring to Figure 7, an example of a communication device according to one embodiment of this disclosure will be described, which functions as an access point for a wireless LAN (e.g., Wi-Fi®) (hereinafter also referred to as a wireless AP device). Figure 7 is a schematic diagram of a system for synchronized imaging using multiple time-synchronized cameras. The device denoted by reference numeral 700 corresponds to an example of a wireless AP device to which the technology of this disclosure is applied. The devices denoted by reference numerals 701, 702, and 703 are communication devices equipped with camera functions. That is, the example shown in Figure 7 illustrates a case in which synchronized imaging is performed using three cameras. The device denoted by reference numeral 704 corresponds to an example of a PTP time distribution server device.

[0042] The communication devices 701, 702, and 703 shown in Figure 7 can communicate with each other by wirelessly connecting to the wireless AP device 700. Furthermore, in order to synchronize the imaging timing of the three cameras with high precision during synchronous imaging, it is desirable to synchronize the system time of each device with high precision. For this reason, each of the communication devices 701, 702, and 703 performs time synchronization using PTP communication and synchronizes its system time with the time of the time distribution server device 704. In other words, each of the communication devices 701, 702, and 703 corresponds to a client device of the time distribution server device 704.

[0043] The time distribution server device 704 functions as a PTP GMC and BC, and distributes its own system time to client devices 701, 702, and 703, respectively. The time distribution server device 704 connects to the wireless AP device 700 via a wired LAN 705. PTP packets transmitted by the time distribution server device 704 are relayed by the wireless AP device 700 and transmitted wirelessly to client devices 701, 702, and 703, respectively.

[0044] The wireless AP device 700 relays wireless communication with each of the communication devices 701, 702, and 703, as well as communication with the wired LAN 705. Furthermore, the wireless AP device 700 functions as a PTP TC (Transparent Clock) that forwards PTP communication packets between these wireless communication devices (communication devices 701, 702, and 703) and the time distribution server device 704. In other words, the wireless AP device 700 determines whether the packets relayed between the wired LAN 705 and the wireless communication side are PTP packets and performs time synchronization processing according to the type of PTP message. For example, the wireless AP device 700 receives multicast PTP packets such as Sync messages and Follow-Up messages sent from the time distribution server device 704 and forwards them via wireless communication to the communication devices 701, 702, and 703, respectively. At this time, the wireless AP device 700 stores the time required to forward the Sync message packet (residence time), and after a delay when forwarding the Follow-Up message, it writes the residence time into the message before forwarding it.

[0045] (Hardware configuration of wireless AP device) Next, an example of the hardware configuration of the wireless AP device 700 will be described with reference to Figure 8. The reference numeral 700 in Figure 8 indicates that the device in question corresponds to the wireless AP device 700 shown in Figure 7. The system bus 801, CPU 802, RAM 803, ROM 804, clock 805, and wireless communication interface 807 shown in Figure 8 are substantially the same as the components with similar names described with reference to Figures 1 and 2, so a detailed explanation will be omitted. On the other hand, the wireless AP device 700 shown in Figure 8 differs from the example shown in Figure 2 in that it includes a wired communication interface 808.

[0046] The wireless AP device 700 functions as an access point, for example, through a wireless communication interface 807 and software processing performed by the CPU 802. The wired communication interface 808 is connected to the wired LAN 705. The wired communication interface 808 can output transmission and reception timestamps based on the time measured by the clock 805 when transmitting and receiving packets via the wired LAN 705.

[0047] The time synchronization processing unit 806 can be implemented as a microprocessor different from the CPU 802, and as software executed on it, similar to the first embodiment described above. The TC (Transparent Clock) function described above is realized by this software processing.

[0048] (Processing by the time synchronization processing unit 806) In this embodiment, the technology relating to this disclosure is embodied by the time synchronization processing unit 806. An example of the PTP transfer process of the time synchronization processing unit 206 will be described with reference to Figures 9 and 10. Figure 9 is a flowchart showing an example of the PTP Sync message transfer process by the time synchronization processing unit 806. When the time distribution server device 704 periodically sends PTP Sync messages, the series of processes shown in Figure 9 are also executed by the time synchronization processing unit 806 in response to the periodic reception of Sync messages. The series of processes shown in Figure 9 begins when a Sync message packet is received at S901. Specifically, the time synchronization processing unit 806 receives the packet from the wired communication interface 808, analyzes the packet data to determine if it is a PTP packet, and then checks the message type of the PTP packet to determine if it is a Sync message. If it is not a PTP packet, or if the PTP packet is not a Sync message, the series of processes shown in Figure 9 are not applied.

[0049] In S902, the time synchronization processing unit 806 obtains the reception timestamp t1 of the Sync message packet received in S901. This timestamp is the timestamp output by the wired communication interface 808 and is information recorded along with the packet when it is received. In S903, the time synchronization processing unit 806 measures the wireless link status. The processing in S901 is substantially the same as the processing in S404 shown in Figure 4. That is, data of parameters indicating wireless quality are acquired from the wireless communication interface 807 for each of the client devices 701, 702, and 703. Examples of parameters indicating wireless quality include the received signal strength index (RSSI) of the wireless link, the signal-to-noise ratio (SNR) including noise in the wireless environment of the device itself, and the number of retransmissions.

[0050] In S904, the time synchronization processing unit 806 determines whether the wireless communication status is good or not based on the measurement results of the wireless link status in S903. If the time synchronization processing unit 806 determines in S904 that the wireless communication status is good, it proceeds to S905. On the other hand, if the time synchronization processing unit 806 determines in S904 that the wireless communication status is not good, it proceeds to S908. In determining whether the wireless communication status in S904 is good, at least one of the following is used as a determination criterion: the value of the received signal strength in the wireless link with each client measured in S903, and the value of the noise ratio. Specifically, at least one of the following checks is performed: whether the value of the received signal strength in the wireless link exceeds a predetermined threshold, and whether the value of the noise ratio exceeds a predetermined threshold. If the communication status with each of the client devices 701, 702, and 703 is good, S904 determines it as Yes; otherwise, it determines it as No.

[0051] If the time synchronization processing unit 806 proceeds from S904 to S908, it discards the Sync message packet at S908 and proceeds to S909, ending the series of processes shown in Figure 9. In other words, in this case, the wireless AP device 700 does not forward the Sync message.

[0052] On the other hand, if the time synchronization processing unit 806 proceeds from S904 to S905, it will transfer a Sync message. Specifically, in S905, the time synchronization processing unit 806 wirelessly transmits a packet of Sync messages. In S906, the time synchronization processing unit 806 obtains the transmission timestamp t2 of the Sync message packet transmitted wirelessly in S905. This timestamp is the time measured by the clock 805 when the Sync message is transmitted. In S907, the time synchronization processing unit 806 records that the Sync message has been transferred, along with the residence time (t2-t1), which is the time taken for the packet transfer of the Sync message. Then, the time synchronization processing unit 806 proceeds to S909 and completes the series of processes shown in Figure 9.

[0053] Next, with reference to Figure 10, an example of the PTP Follow-Up message forwarding process by the time synchronization processing unit 806 will be described. The series of processes shown in Figure 10 begins in S1001 when a PTP Follow-Up message packet sent from the time distribution server device 704 is received. Specifically, the time synchronization processing unit 806 analyzes the packet data received from the wired communication interface 808 and determines whether or not it is a PTP Follow-Up message. Note that if it is not a PTP packet, or if the PTP packet is not a Follow-Up message, the series of processes shown in Figure 10 are not applied.

[0054] In S1002, the time synchronization processing unit 806 measures the wireless link status. The process in S1002 is substantially the same as the process in S903 shown in Figure 9, so a detailed explanation is omitted. In S1003, the time synchronization processing unit 806 checks whether there is a record of a Sync message with the same sequence ID as the Follow-Up message received in S1001. If the time synchronization processing unit 806 determines in S1003 that a corresponding transfer record exists, it proceeds to S1004. On the other hand, if the time synchronization processing unit 806 determines in S1003 that no corresponding transfer record exists, it proceeds to S1009. In this case, it means that a Follow-Up message for a Sync message that has not been transferred has been received. Therefore, in S1009, the time synchronization processing unit 806 discards the packet of the Follow-Up message and proceeds to S1010, terminating the series of processes shown in Figure 10.

[0055] In S1004, the time synchronization processing unit 806 determines whether the wireless communication status is good or not based on the measurement results of the wireless link status in S1002. The determination process in S1004 is substantially the same as the determination process in S904 shown in Figure 9, so a detailed explanation is omitted. If the time synchronization processing unit 806 determines in S1004 that the wireless communication status is good, it proceeds to S1005. On the other hand, if the time synchronization processing unit 806 determines in S1004 that the wireless communication status is not good, it proceeds to S1008.

[0056] In S1005, the time synchronization processing unit 806 writes the residence time (t2-t1) to the CorrectionField of the Follow-Up message. More specifically, the time synchronization processing unit 806 updates the value of the field to the value obtained by adding the residence time. In S1006, the time synchronization processing unit 806 wirelessly transmits a Follow-Up message. Then, in S1007, the time synchronization processing unit 806 deletes the transfer record of the Sync message corresponding to the transferred Follow-Up message, proceeds to S1010, and terminates the series of processes shown in Figure 10.

[0057] On the other hand, if the process proceeds from S1004 to S1008, it corresponds to a case where the wireless communication status is determined to be poor. In S1008, the time synchronization processing unit 806 discards the Follow-Up message without forwarding it. Then, in S1007, the time synchronization processing unit 806 deletes the transfer record of the corresponding Sync message and proceeds to S1010, ending the series of processes shown in Figure 10.

[0058] As described above, in the second embodiment of this disclosure, if the time synchronization processing unit 806 determines that the wireless communication state is poor, the transmission of Sync messages and Follow-Up messages from the wireless AP device 700 is restricted (for example, they are not transmitted). As a result, PTP time synchronization communication is not performed in each of the client devices 701, 702, and 703. Therefore, for example, in situations where communication delay jitter is likely to occur due to wireless communication retransmission processing or long waiting processing, the execution of PTP time synchronization processing is restricted, which is expected to have the effect of suppressing deterioration of the time synchronization accuracy of the imaging system.

[0059] <Other Embodiments> The present invention can also be realized by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions.

[0060] Furthermore, the disclosure of this embodiment includes the following configurations, methods, and programs. (Configuration 1) A communication device comprising: communication means for performing wireless communication with one or more other wireless communication devices using a time synchronization protocol; determination means for determining whether the state of the wireless communication is good or not; and control means for restricting the execution of the communication sequence using the time synchronization protocol with the other wireless communication device when the determination means determines that the state of the wireless communication with the other wireless communication device is poor. (Configuration 2) The communication device according to Configuration 1, characterized in that the communication device is a server device that distributes the time of its own device to the one or more other wireless communication devices by performing wireless communication with them using a time synchronization protocol. (Configuration 3) The communication device according to Configuration 1, characterized in that the communication device is a server device that communicates with one or more other wireless communication devices and distributes the time of the device to the other wireless communication devices, and a device that functions as an access point that relays the communication between the one or more other wireless communication devices. (Configuration 4) The communication device according to any one of Configurations 1 to 3, wherein the determination means determines whether the state of the wireless communication is good or not by comparing at least one of the radio wave intensity, retransmission count, and noise ratio of the wireless communication with a predetermined threshold. (Configuration 5) The communication device according to any one of Configurations 1 to 4, wherein the determination means determines whether the state of the wireless communication is good or not by comparing the measurement result of the communication delay time in wireless communication with one or more other wireless communication devices with a predetermined threshold. (Configuration 6) The communication device according to any one of Configurations 1 to 5, wherein the control means restricts the execution of a communication sequence by the time synchronization protocol by restricting the transmission of Sync messages in the time synchronization protocol. (Configuration 7) The communication device according to any one of Configurations 1 to 6, wherein the control means restricts the execution of a communication sequence by the time synchronization protocol by restricting the transmission of Follow-Up messages corresponding to Sync messages that have already been transmitted in the time synchronization protocol. (Configuration 8) The communication device according to any one of Configurations 1 to 7, wherein the control means restricts the execution of the communication sequence by the time synchronization protocol by widening the time interval for transmitting Sync messages in the time synchronization protocol. (Configuration 9) The communication device according to any one of Configurations 1 to 8, characterized in that the control means controls the transmission of an Announce message in the time synchronization protocol even when the determination means determines that the state of the wireless communication with the other wireless communication device is poor. (Method 1) A method for controlling a communication device, comprising: a communication step of performing wireless communication with one or more other wireless communication devices using a time synchronization protocol; a determination step of determining whether the state of the wireless communication is good or not; and a control step of restricting the execution of a communication sequence using the time synchronization protocol with the other wireless communication device if the determination step determines that the state of the wireless communication with the other wireless communication device is poor. (Program 1) A program for causing a computer to function as a communication device, comprising: communication means for performing wireless communication with one or more other wireless communication devices using a time synchronization protocol; determination means for determining whether the state of the wireless communication is good or not; and control means for restricting the execution of the communication sequence using the time synchronization protocol with the other wireless communication device when the determination means determines that the state of the wireless communication with the other wireless communication device is poor. [Explanation of symbols]

[0061] 100 Time Distribution Server Device 101 Client device 206 Time Synchronization Processing Unit 207 Wireless Communication Interface

Claims

1. A communication means that performs wireless communication with one or more other wireless communication devices using a time synchronization protocol, A determination means for determining whether the wireless communication status is good or not, If the determination means determines that the state of the wireless communication with the other wireless communication device is poor, the control means restricts the execution of the communication sequence using the time synchronization protocol with the other wireless communication device. A communication device characterized by having the following.

2. The communication device according to claim 1, characterized in that the communication device is a server device that distributes the time of the device to the other wireless communication devices by wirelessly communicating with the one or more other wireless communication devices using a time synchronization protocol.

3. The communication device according to claim 1, characterized in that the communication device is a server device that communicates with one or more other wireless communication devices and distributes the time of the device to the other wireless communication devices, and a device that functions as an access point that relays the communication between the one or more other wireless communication devices.

4. The communication device according to claim 1, characterized in that the determination means determines whether the state of the wireless communication is good or not by comparing at least one of the radio wave intensity, retransmission count, and noise ratio of the wireless communication with a predetermined threshold.

5. The communication device according to claim 1, characterized in that the determination means determines whether the state of the wireless communication is good or not by comparing the measurement result of the communication delay time in wireless communication with one or more other wireless communication devices with a predetermined threshold.

6. The communication device according to claim 1, characterized in that the control means restricts the execution of a communication sequence by the time synchronization protocol by restricting the transmission of Sync messages in the time synchronization protocol.

7. The communication device according to claim 1, characterized in that the control means restricts the execution of a communication sequence by the time synchronization protocol by restricting the transmission of Follow-Up messages corresponding to transmitted Sync messages in the time synchronization protocol.

8. The communication device according to claim 1, characterized in that the control means restricts the execution of a communication sequence by a time synchronization protocol by widening the time interval for transmitting Sync messages in the time synchronization protocol.

9. The communication device according to claim 1, characterized in that the control means controls the transmission of an Announce message in the time synchronization protocol even when the determination means determines that the state of the wireless communication with the other wireless communication device is poor.

10. A method for controlling a communication device, A communication step that uses a time synchronization protocol to communicate wirelessly with one or more other wireless communication devices, A determination step to determine whether the wireless communication status is good or not, If the determination step determines that the state of the wireless communication with the other wireless communication device is poor, a control step restricts the execution of the communication sequence using the time synchronization protocol with the other wireless communication device. A method for controlling a communication device, characterized by including the following:

11. Computers, A communication means that performs wireless communication with one or more other wireless communication devices using a time synchronization protocol, A determination means for determining whether the wireless communication status is good or not, If the determination means determines that the state of the wireless communication with the other wireless communication device is poor, the control means restricts the execution of the communication sequence using the time synchronization protocol with the other wireless communication device. A program for causing a communication device to function, characterized by having the following features.

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