JP5721485B2 - Communication system and control method thereof - Google Patents

Description

  The present invention relates to slot assignment information switching control in a TDMA communication system that can dynamically update slot assignment information.

  A TDMA (Time Division Multiplexing) communication system is known as an effective communication system for communication between a plurality of nodes connected by a single bus. This TDMA communication method is a communication method in which transmission time is allocated to each node in advance without duplication, and each node transmits data only at the time allocated to itself. The period in which the allocation is completed is called a frame, and the allocated time interval is called a slot.

  The above-described TDMA communication system can employ a bus topology in addition to guaranteeing the delay time, and therefore can reduce wiring compared to the conventional method of wiring in a star shape individually from the central controller. Therefore, it is suitable for a multi-view camera control system and the like. Here, the multi-viewpoint camera control system includes a plurality of cameras connected to a network, and a communication node is arranged in each camera. And it is a system which presents to a user by performing imaging control of each camera or composition of video data while communicating between the central control device and each communication node.

  By the way, in such a TDMA communication system, when the number of nodes connected to the network is increased or decreased, or data to be transmitted / received at a certain node is increased or decreased, it is necessary to change the slot allocation. At this time, it is desirable not to stop communication of other nodes. For example, in a multi-viewpoint camera control system, since precise control is performed by a certain camera, it is required that control and video of other cameras are not stopped even when data to be temporarily communicated increases. For this purpose, it is necessary to shift to new slot allocation information all at once at a certain timing without stopping communication from a state in which all nodes continue communication by conventional slot allocation.

  Therefore, a technique has been proposed in which all nodes change the slot assignment information at the same time at the beginning of the frame next to the frame in which the slot assignment information is transmitted from the parent node (see, for example, Patent Document 1). According to this technique, even if the time for completing the slot allocation information change process varies somewhat depending on each node, it is possible to shift to a new slot allocation all at once.

  In addition, a technique has been proposed in which slot allocation is changed all at once by transmitting the timing for enabling new slot allocation from a parent node (see, for example, Patent Document 2).

JP-A-8-251096 JP 2001-111588 A

  If a failure occurs due to noise, etc., in the communication of a bus that connects multiple nodes, one node can receive slot assignment information or an instruction to activate slot assignment, and another node cannot receive them. Will occur. At this time, the former node starts communication with a new slot assignment at a certain timing, and the latter node does not recognize that the slot assignment has been changed, and continues communication with the old slot assignment. Here, if there is an overlap between the new slot allocation information and the old slot allocation information, a plurality of nodes will transmit in the same slot. That is, in the conventional technology, even if the slot allocation information can be updated all at once, it is possible to solve the problem that communication is hindered by the node that has not received the slot allocation information when there is a node that has failed to update. Not. In addition to this, no consideration has been given to the automatic restoration of a node that failed to be updated to the network by a new slot assignment.

  For example, in a multi-view camera control system, if slot allocation information cannot be received at a communication node of a certain camera, it is impossible to control a camera that can be normally received. That is, even if only one node fails to update the slot assignment, there is a problem that the entire system does not function.

  It is an object of the present invention to provide a communication system and method for preventing a node that has not received information for validating slot allocation information from interfering with the communication of another node that has been received.

The present invention is a communication system that includes one parent node and a plurality of child nodes, and performs communication by assigning a frame to a plurality of communication slots based on slot assignment information generated by the parent node,
The parent node is
First generating means for generating the slot allocation information;
A response receiving means for receiving an acknowledgment from the plurality of child nodes after transmitting the slot allocation information;
Transmission means for transmitting slot allocation validation information for validating the slot allocation information to the plurality of child nodes upon receiving the confirmation response;
The plurality of child nodes are:
Upon receiving the slot allocation information transmitted from the parent node, a response transmission means for transmitting an acknowledgment to the parent node;
Receiving means for receiving the slot allocation validation information;
And limiting means for restricting communication when the slot allocation validation information cannot be received from the parent node before a predetermined time elapses.

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress that the node which could not receive slot allocation information inhibits communication of the other node which was able to receive slot allocation information correctly. Therefore, for example, in a multi-view camera control system, even when a communication failure occurs between a central control device and a certain camera, and slot assignment cannot be changed, the failure can be suppressed to only one camera. That is, it is possible to continue to present the synthesized video to the user by synthesizing the video of the remaining other cameras.

The figure which shows the outline | summary of the multiview camera control system in embodiment. The block diagram which shows an example of an internal structure of a parent node. The block diagram which shows an example of an internal structure of a child node. The figure showing an example of slot allocation update. The figure showing an example of the communication sequence which performs slot allocation. The flowchart which shows the process of the child node in 1st Embodiment. The flowchart which shows the process of the parent node in 1st Embodiment. The figure which shows an example of the mode of slot allocation at the time of returning the child node which stopped transmission to communication. The flowchart which shows the process of the parent node which returns communication. The figure which shows an example of the internal structure of the parent node in 2nd Embodiment. The figure which shows the structure of the slot allocation information to which ID was added. The flowchart showing the process of the child node in 2nd Embodiment. The figure which shows an example of the internal structure of the parent node in 3rd Embodiment. The figure which shows an example of the internal structure of the child node in 3rd Embodiment. The figure which shows the structural example of the slot allocation information in 3rd Embodiment. The figure which shows the sequence until the child node which stopped transmission returns to communication. The flowchart showing the process of the parent node in 3rd Embodiment. The flowchart showing the process of this node in 3rd Embodiment.

  Hereinafter, embodiments for carrying out the invention will be described in detail with reference to the drawings. In the embodiments described below, a multi-viewpoint camera control system will be described as an example of a communication system.

[First Embodiment]
FIG. 1 is a diagram showing an overview of a multi-viewpoint camera control system in the first embodiment. In this system, one parent node 100 and a plurality of child nodes 1 to 4 are configured by a network connected by a single bus. The child nodes 1 to 4 are connected to cameras 111 to 114 and pan head motors 121 to 124 (not shown), respectively. Here, the vision nodes 101 to 104 are video cameras that can be connected to the network, and are configured by child nodes connected to cameras 111 to 114 and pan head motors 121 to 124 (not shown).

  The cameras 111 to 114 capture the video of the subject 107 and output the video data to the parent node 100. The motors 121 to 124 are power for moving a head (not shown). In addition, cameras 111 to 114 are mounted on a platform (not shown), and the angles at which the cameras 111 to 114 are directed are changed by motors 121 to 124. The angle is detected by an angle sensor (not shown). Furthermore, the parent node 100 and the child nodes 1 to 4 are all interconnected by a bus 108.

  In the multi-viewpoint camera control system shown in FIG. 1, the parent node 100 synthesizes the images from the child nodes 1 to 4 and performs free-viewpoint image creation and synchronization operations such as panning, tilting, and zooming of the cameras 111 to 1144. Thus, automatic tracking of a specific subject 107 is realized. In addition, the free viewpoint video to be synthesized can be provided with a higher degree of freedom of viewpoint movement as the number of cameras increases. In addition, among the child nodes 1 to 4, a camera of a node far from the subject 107 performs shooting with higher resolution. As a result, it is possible to provide a certain level of image even when the free viewpoint moves with zooming of the synthesized video approaching the subject 107.

  Further, even if the subject 107 is a moving body, it is possible to cope with it by dynamically changing the resolution of the cameras 111 to 141 according to the distance of the subject 107. In addition, since communication is performed by one bus 108, time division multiplex communication (TDMA communication) is used as a communication method. The transmission / reception slot of each node is assigned by the parent node 100, and the child nodes 1 to 4 follow it. In addition, the child node farther away from the subject 107 is photographed at a higher resolution, so the amount of data increases, and the number of communication slots needs to be allocated more. The slot allocation information is updated each time the subject 107 moves and the resolution of the cameras 111 to 141 is changed, and is transmitted from the parent node 100 to the child nodes 1 to 4 and shared.

  In addition to the video data captured by the cameras 111 to 114, motor control information for controlling the motors 121 to 124 that move the camera platform (not shown) is communicated on the bus 108.

  The parent node 100 transmits motor control information to the child node 1. The motor control information includes a voltage value applied to the motor 121, for example. The parent node 100 synthesizes video data received from the cameras 111 to 114, creates a free viewpoint video, and presents it to the user. On the other hand, when the child node 1 receives the motor control information from the parent node 100, the motor 121 is operated based on the motor control information. Furthermore, a video is acquired from the camera 111 and transmitted to the parent node 100 as video data.

  The parent node 100 generates the next motor control information based on the video data received from the child node 1. Further, communication and control similar to those of the parent node 100 and the child node 1 described above are performed between the parent node 100 and the child nodes 2 to 4. As described above, the parent node 100 and the child nodes 1 to 4 repeat communication to perform an operation as a multi-viewpoint camera control system.

  FIG. 2 is a block diagram illustrating an example of the internal configuration of the parent node 100. The motor control information generation unit 202 shown in FIG. 2 generates motor control information of the child nodes 1 to 4 based on the analysis result by the video data analysis unit 201, and outputs it to the communication unit 200 as transmission data. The video data analysis unit 201 performs analysis based on information on the subject 107 to be automatically tracked (subject shape, color, etc.) and video data received from the child nodes 1 to 4, and outputs the result to the motor control information generation unit 202. The analysis result includes information such as the moving direction, speed, and distance to the subject 107 of the object in the video. In addition, the video data analysis unit 201 calculates the distance between the subject 107 and the cameras 111 to 114, and controls the slot allocation information generation unit 204 so as to increase the used communication slots of the child node with the longest distance. For example, when the child node farthest from the subject 107 changes from the child node 4 to the child node 3, the slot allocation information generation unit 204 is caused to increase the number of communication slots used by the child node 3 and 4 is controlled so as to reduce the number of used communication slots.

  On the other hand, the slot allocation information generation unit 204 dynamically generates an appropriate slot allocation based on requests from the connected child nodes 1 to 4 and the analysis result in the video data analysis unit 201. In addition, the slot allocation information generation unit 204 adds an expiration date to the generated slot allocation information and broadcasts it to the child nodes 1 to 4.

  Although the validity period is added to the slot allocation information and transmitted, there is no problem even if a predetermined validity period is set in advance for the child nodes 1 to 4 or transmitted separately.

  Here, the parent node 100 broadcasts the slot assignment information to the child nodes 1 to 4 and starts communication with the broadcasted slot assignment validation information after the expiration time has elapsed. The timing control unit 203 stores the slot allocation information generated by the slot allocation information generation unit 204 and controls the communication unit 200 based on the information. For example, when the third slot from the head of the slot assignment information is a communication slot used by the parent node 100 for transmission, the communication unit 200 transmits data at the third slot from the head of the slot assignment information.

  When the slot allocation validation generation unit 205 receives an acknowledgment (ACK) for transmission of slot allocation information from all of the child nodes 1 to 4, it generates and transmits the validation deadline. When the transmission stop detection unit 206 detects a child node that does not transmit video data for a predetermined time or more from the child nodes 1 to 4, the slot allocation information generation unit 204 detects the slot allocation validation information. Control to send to child node.

  FIG. 3 is a block diagram illustrating an example of the internal configuration of the child node 1. The child nodes 2 to 4 have the same configuration. The video data generation unit 301 acquires video data from the camera 111 and outputs it to the communication unit 300 as transmission data to the parent node 100.

  The motor control unit 302 controls the motor 121 based on the motor control information received from the parent node 100. The communication control unit 303 stores the validity period set in the slot allocation information by the slot allocation information generation unit 204 of the parent node 100 when the slot allocation information is received. If the communication control unit 303 can receive the slot allocation activation information within the stored expiration date, the communication control unit 303 controls the communication unit 300 to start communication with the updated slot allocation information.

  On the other hand, if the slot allocation validation information cannot be received within this validation period, the communication unit 300 is controlled to stop transmission. The timing control unit 304 controls the communication unit 300 based on the slot allocation information set by the slot allocation information storage unit 305. For example, when the third slot from the top of the slot allocation information is a communication slot used by the child node 1 for transmission, the communication unit 300 transmits data at the third slot from the top of the slot allocation information.

  The slot allocation information storage unit 305 stores the slot allocation information generated and broadcast by the slot allocation information generation unit 204 of the parent node 100, and sets the information in the timing control unit 304. The communication unit 300 performs transmission / reception with other nodes based on the slot allocation information received from the parent node 100. All data transmission / reception between the parent node 100 and the child node 1 is performed via the communication unit 300.

  FIG. 4 is a diagram illustrating an example of slot allocation update. Communication is repeatedly performed with the slot assignment from the left end 403 to the right end 404 in FIG. 4 as one period, and this period is defined as a frame. One block represents one communication slot.

  4A and 4B show how slots are allocated. In the figure, it means that the parent node 100 performs transmission in the slot described as parent and the child node 1 performs transmission in the slot described as child 1.

  In FIG. 4A, a slot group 405 is a slot group for the parent node 100 to transmit slot allocation information, slot allocation validation information, and motor control information. The slot group 406 is a slot group in which the child node 4 transmits video data. In this example, since the distance to the subject 107 is the farthest from the child node 4, many communication slots are assigned to the child node 4 for the other child nodes 1-3.

  On the other hand, in the example of FIG. 4B, after the subject 107 moves, the child node 3 has the longest distance to the subject 107 and is shooting at a high resolution. 4, many communication slots are allocated to the child node 3.

  FIG. 4C shows the contents of slot allocation information transmitted by the parent node 100 when slot allocation is performed as shown in FIG. In this example, the value of the 1-byte data string set in the communication slot shown in FIG. 4C represents a node that performs transmission. “0x03” represents data transmission of the child node 3, and “0x01” represents data transmission of the child node 1.

  The data transmission of the parent node 100 is expressed by “0x00”. Further, “0x11” represents a non-transmission period, and there is no node that transmits data on the bus 108. Further, when the slot allocation information is transmitted from the parent node 100 to the child nodes 1 to 4, the slot allocation information validity period 401 is added to the first byte.

  The slot allocation information generation unit 204 of the parent node 100 sets a predetermined value for the validity period 401. The value set as the predetermined value is sufficient for, for example, the slot allocation information storage unit 305, the timing control unit 304, and the communication control unit 303 of the child node to prepare for communication start with the updated slot allocation information. It's time.

  When the validity period 401 is set as shown in FIG. 4C, the parent node 100 starts communication with the slot assignment information when four frames have elapsed since the slot assignment information was transmitted. The child nodes 1 to 4 communicate with the slot allocation information if the slot allocation validation information can be received after 4 frames have elapsed since the slot allocation information was received.

  Although there is an overlap between the validity period 401 and the value of the slot group 402, the validity period 401 is always placed in the first 1 byte of the slot allocation information and can be discriminated. no problem.

  In the parent node 100, for example, when it is detected that the subject 107 has moved from the child node 3 to the front of the child node 4, (C) in FIG. 4 is transmitted to the child nodes 1 to 4, and the received child node Transmission is performed at a timing corresponding to the own node in the data string of 4 (C). The slot allocation information is generated by the slot allocation information generation unit 204 and is set in the timing control unit 203 in the parent node 100. The child nodes 1 to 4 are stored in the slot allocation information storage unit 305 and set in the timing control unit 304.

  Note that the slot allocation information for performing necessary communication in the initialization process is set in advance as an initial value in the timing control unit 203 of the parent node 100 and the timing control unit 304 of the child nodes 1 to 4. To do.

  Next, operations of the parent node 100 and the child nodes 1 to 4 will be described with reference to FIGS. 6 and 7 are flowcharts showing the processing of the child nodes 1 to 4 and the parent node 100 in the first embodiment. FIG. 5 is a diagram illustrating an example of a communication sequence when the parent node 100 and the child nodes 1 to 4 perform slot allocation based on the flowcharts illustrated in FIGS. 6 and 7.

  Hereinafter, operations of the parent node 100 and the child nodes 1 to 4 will be described in the order of the communication sequence of FIG. It is assumed that the parent node 100 and the child nodes 1 to 4 continue to communicate motor control information and video data even during the slot assignment communication sequence shown in FIG.

  First, the parent node 100 sends a broadcast by adding the validity period 401 to the slot allocation information 501 to the child nodes 1 to 4 and waits for the ACK 502 to be returned from all of the child nodes 1 to 4. In the sequence of FIG. 5, the ACK 502 is returned from all of the child nodes 1 to 4, but if not, the transmission of the slot allocation information 501 is repeated at a predetermined cycle until the ACK 502 is returned from all of the child nodes 1 to 4. Shall.

  Next, when the child nodes 1 to 4 receive the slot allocation information 501, they return an ACK 502 to the parent node 100 and wait for the slot allocation validation information 504 to be transmitted. On the other hand, when the ACK 502 is returned from all of the child nodes 1 to 4, the parent node 100 broadcasts the slot allocation validation information 504.

  Here, it is assumed that the child node 1 to 3 can correctly receive the slot allocation validation information 504, but the child node 4 cannot receive it. In this case, since the child nodes 1 to 3 have received the slot allocation validation information 504, when the time set as the validation deadline 503 elapses after receiving the slot allocation information 501, a new slot allocation information 501 is displayed. Based on the communication.

  However, since the child node 4 has not received the slot allocation validation information 504, the transmission is stopped after the time set as the validation deadline 503 has elapsed since the slot allocation information 501 was received.

  Here, the processing of the child nodes 1 to 4 operating along the sequence processing described above will be described with reference to FIG. The processing in the child nodes 1 to 3 that can correctly receive the slot allocation validation information 504 will be described.

  First, in S601, new slot allocation information is received. In S602, since the new slot allocation information has been successfully received, the process proceeds to S603. In S603, the validity period set in the slot allocation information is set in the own node. In step S604, an ACK is transmitted to the parent node 100. Next, in S605, since slot allocation validation information has been received before the validation deadline set in S603 elapses, the process proceeds to S606. In S606, communication is performed based on the new slot allocation information received in S601.

  Next, processing in the child node 4 that has not received the slot allocation validation information 504 correctly will be described. Note that the processing in S601 to S603 is the same as that of the child nodes 1 to 3. In S605, since the slot allocation validation information has not been received before the validation deadline set in S603 elapses, the process proceeds to S607. In step S607, the transmission is stopped.

  Here, processing of the parent node 100 that operates in accordance with the above-described sequence processing will be described with reference to FIG. First, in S701, new slot allocation information is broadcast to all of the child nodes 1 to 4. In S702 and S703, since ACK has been received from all of the child nodes 1 to 4 until a predetermined time has elapsed, the process proceeds to S705. In this S705, the slot allocation validation information is broadcast to the child nodes 1 to 4. In S706, communication is performed using the new slot allocation information after the expiration time set in the slot allocation information transmitted in S701 has elapsed.

  It should be noted that even after the parent node 100 transmits the slot allocation information 501 and after the slot allocation information validation period 503 has passed and updated, the slot allocation information 501 is changed to the slot allocation information 501 and communication is performed. Communication is continued based on the slot allocation information.

  As described above, when the child node 4 that has not received the slot allocation validation information 504 stops transmission, communication between the parent node 100 and the child nodes 1 to 3 that have successfully received the slot allocation validation information 504 is performed. Inhibiting can be prevented.

  In particular, in the multi-viewpoint camera control system, the data to be lost is only the video data of the child node 4 that could not be received within the validity period 503 of the slot allocation information. Therefore, the data of the child nodes 1 to 3 that can be received within the validity period 503 can be communicated without loss, and the system operation can be continued without lowering the degree of freedom of viewpoint movement more than necessary.

  According to the first embodiment, in a communication system that changes slot assignment while continuing communication, a child node that has not received slot assignment validation information 504 can receive slot assignment validation information 504 correctly. Can be prevented from hindering communication.

  In the first embodiment, the validity period of the slot allocation information is included in the slot allocation information and transmitted. However, the same effect can be obtained if the validity period is transmitted separately from the slot allocation information. It goes without saying that can be obtained. If the validity period is transmitted separately from the slot allocation information, it is possible to flexibly cope with the transmission of the slot allocation information. For example, processing with a very high load is performed in the parent node 100, and even if the generation time of the activation time limit is not constant and it is not in time for the transmission slot of the slot allocation information, it can be transmitted later only with the activation time limit. .

  Next, a process for returning a child node that has stopped transmission to communication after the slot allocation information update validation process will be described with reference to FIGS. FIG. 8 is a diagram showing an example of slot assignment when returning a child node whose transmission has been stopped to communication. Here, the slot assignment information transmission slot 801 is assigned to a predetermined position of the slot assignment information by the slot assignment information generation unit 204. The slot allocation information transmission slot 801 does not change its position even when the slot allocation information is updated. By doing so, the slot assignment information transmission slot 801 is always in the same predetermined position even in the child node that does not hold the current slot assignment information, and therefore, it becomes possible to receive new slot assignment information.

  Next, the processing of the parent node 100 for returning the child node whose transmission is stopped based on the slot allocation information of FIG. 8 to communication will be described with reference to FIG. First, in step S901, the child node 4 that has stopped communication is detected because video data transmission that should have been continued has been stopped. In S902, the currently used slot allocation information is transmitted to the child node 4 that has stopped transmission. In S903, since the ACK has been received from the child node 4, the process proceeds to S906. In this S906, slot allocation validation information is transmitted to the child node 4.

  Here, the child node 4 can return to the communication by performing the same processing as in the flowchart of FIG. Accordingly, the video data of the child node 4 whose transmission has been stopped can be retransmitted, and the reduction in the degree of freedom of viewpoint movement in the free viewpoint video due to the decrease in the number of cameras that photograph the subject 107 while the system is operating is eliminated. It becomes possible.

[Second Embodiment]
In the first embodiment, the slot allocation information transmission slot 801 is used, but in the second embodiment, transmission is stopped by adding an identifier (ID) that changes each time the slot allocation information is updated to the slot allocation information. The restored node is restored. The system configuration in the second embodiment is the same as that of the first embodiment shown in FIG.

  FIG. 11 is a diagram showing a configuration of slot allocation information to which ID 1101 is added. Here, the ID 1101 is added to a predetermined position of the slot allocation information, like the slot allocation information transmission slot of the first embodiment. Accordingly, the ID 1101 can be acquired even in a child node where the slot allocation information currently used cannot be identified.

  Next, the internal configuration of the parent node 100 and the child nodes 1 to 4 in the second embodiment will be described in order. FIG. 10 is a diagram illustrating an example of the internal configuration of the parent node 100. The first embodiment shown in FIG. 2 is that a slot allocation information ID generation unit 1001 is added, and the slot allocation information generation unit 204 generates the slot allocation information by adding the slot allocation information ID 1101 to a part of the slot allocation information. Different.

  When the child nodes 1 to 4 that have stopped transmission return, the slot allocation information ID generation unit 1001 communicates with the child nodes 1 to 4 without detecting the child nodes 1 to 4 that have stopped transmission. It was added for the purpose of returning to. The slot allocation information ID generation unit 1001 adds ID 1101 to the slot allocation information. The ID 1101 is changed when the slot allocation information is updated. For example, the initial slot assignment information ID 1101 is “0x01”, and the updated slot assignment information ID 1101 is “0x02”.

  Here, the internal configuration of the child nodes 1 to 4 is the same as that of the first embodiment shown in FIG. The difference from the first embodiment is that the communication control unit 303 compares the slot assignment information ID 1101 and the communication unit 400 can resume communication by the output. When the communication control unit 303 compares the ID 1101 of the slot assignment information, when the child nodes 1 to 4 that have stopped transmission are restored, the parent node 100 does not detect the child nodes 1 to 4 that have stopped transmission. The child nodes 1 to 4 can return to communication.

  That is, when the own node stops transmission, the communication control unit 303 acquires the ID 1101 of slot assignment information used in the current communication exchange from the bus 108 and receives it from the parent node 100 immediately before the communication is interrupted. The slot allocation information ID 1101 is compared. If the IDs 1101 are the same as a result of the comparison, it is determined that the own node holds the same slot allocation information used in the current communication, and transmission to the communication unit 400 of the own node is resumed. Control to do.

  In the following description, resuming transmission is described as returning to communication. For example, when the ID 1101 of the slot allocation information held by the own node is “0x03” and the ID 1101 of the slot allocation information used in the current communication is “0x05”, the ID 1101 is different and the communication is not restored.

  On the other hand, when the ID 1101 of the slot allocation information held by the own node is “0x03” and the ID 1101 of the slot allocation information used in the current communication is “0x03”, the ID 1101 matches and the communication is resumed. .

  FIG. 12 is a flowchart showing the processing of the child node in the second embodiment. First, in S1201, transmission is stopped if slot allocation validation cannot be received within a predetermined time. Here, it is recognized that the own node has not received the slot allocation validation information.

  Next, in S1202, the ID of the slot allocation information used in the current communication exchange is acquired from the bus 108. In step S1203, the ID 1101 of the slot assignment information used in the current communication acquired from the bus 108 is compared with the ID 1101 of the slot assignment information received from the parent node 100 immediately before the communication is interrupted. As a result of the comparison, if the IDs 1101 are the same, it is determined that the own node holds the same slot allocation information used in the current communication, and the process advances from S1204 to S1205. In S1205, the communication is restored. Note that the processing of the parent node 100 when the child node 4 that has stopped transmission returns to communication is not performed in the second embodiment.

  According to the second embodiment, the child nodes 1 to 4 can independently determine and return to communication. Therefore, in the parent node 100, there is no extra processing (overhead) such as detection of a child node that has stopped transmission and processing for returning communication, and communication can be restored by processing of only the child node 4. Therefore, the child node 4 that has stopped transmission resumes transmission without overhead, so that it is possible to quickly eliminate the decrease in the degree of freedom in moving the viewpoint of the free viewpoint video accompanying the decrease in the number of cameras that capture the subject 107. Become.

[Third Embodiment]
In the third embodiment, when the child node detects the stop of transmission, the notification is sent to the parent node 100, and the parent node 100 performs processing for receiving and returning from the notification from the child node. The system configuration in the third embodiment is the same as that of the first embodiment shown in FIG.

  First, the internal configurations of the parent node 100 and the child nodes 1 to 4 in the second embodiment will be described in order. FIG. 15 is a diagram illustrating a configuration example of slot allocation information according to the third embodiment. A shared slot 1501 that can be used in common by the parent node 100 and the child nodes 1 to 4 is provided at a specific position of the slot allocation information. Further, it is assumed that the position of the shared slot 1501 does not change even when the slot allocation information is updated. Therefore, even a node that cannot determine slot allocation information that is currently used can transmit and receive using the shared slot 1501.

  Next, the internal configuration of the parent node 100 in the third embodiment will be described with reference to FIG. In FIG. 13, the difference from the first embodiment is that a shared slot insertion unit 1301 and a slot allocation validation request determination unit 1302 are added and the transmission stop detection unit is deleted.

  That is, the shared slot insertion unit 1301 and the slot allocation validation are made so that the child nodes 1 to 4 that have stopped transmission request the return of communication, and the parent node 100 allows the request to return to the communication. A request determination unit 1302 is added.

  The shared slot insertion unit 1301 controls the slot allocation information generation unit 204 to provide a shared slot 1501 that allows the parent node 100 and the child nodes 1 to 4 to transmit and receive in common at a predetermined position of the slot allocation information. The slot allocation validation request determination unit 1302 determines the data received in the shared slot 1501, and notifies the slot allocation validation generation unit 205 when it is a slot allocation validation request. Then, the slot allocation validation generating unit 205 receives the notification from the slot allocation validation request determining unit 1302, generates slot allocation validation information, and transmits it to the child nodes 1 to 4.

  Next, an example of the internal configuration of the child node 1 will be described with reference to FIG. The child nodes 2 to 4 have the same configuration. In FIG. 14, the difference from the first embodiment is that a slot allocation validation request unit 1401 is added.

  The slot allocation validation request unit 1401 transmits a slot allocation validation request to the parent node 100 using the shared slot 1501 when the child nodes 1 to 4 stop transmission. Further, the slot allocation validation requesting unit 1401 allows the child nodes 1 to 4 that have stopped transmission to request communication return, and allows the child nodes 1 to 4 to return to communication when the parent node 100 permits it. It was added for the purpose.

  The slot allocation validation request unit 1401 transmits a slot allocation validation transmission request to the parent node 100 using the shared slot 1501 provided in the slot allocation information when the own node stops transmission. Further, after receiving the slot allocation validation request, when receiving slot allocation validation information from the parent node 100, the communication control unit 303 controls the communication unit 400 so that the own node returns to communication.

  Here, the flow until the child node that has stopped transmission returns to communication will be described with reference to FIG. FIG. 16 is a diagram illustrating a sequence until the child node 4 that has stopped transmission returns to communication. The sequence until the child node 4 stops communication is the same as that in FIG. 5 of the first embodiment.

  The child node 4 that has stopped transmission transmits a slot allocation validation request 1601 to the parent node 100 after recognizing that its own node has stopped transmission. When the parent node 100 receives the request, it transmits the slot allocation validation information 1602 to the child node 4, and the child node 4 returns to communication when triggered by receiving the information.

  Here, the processing of the parent node 100 in the third embodiment will be described with reference to FIG. First, in S1701, when the slot assignment validation request 1601 is received from the child node 4, the process proceeds to S1702, where the slot assignment validation information 1602 is transmitted to the child node 4 and it is determined whether or not the return to communication is permitted. . If it is determined in S1703 that return to communication is permitted, the process advances to S1704, and slot assignment validation information 1602 is transmitted to the child node 4. On the other hand, if it is determined that the return to communication is not permitted, the process proceeds to S1705, and the slot allocation validation information 1602 is not transmitted.

  Next, processing of the child node 4 in the third embodiment will be described with reference to FIG. First, in S1801, it is recognized that the own node has stopped transmission. In step S1802, a slot allocation validation request 1601 is transmitted to the parent node 100. In step S1803, the process waits for reception of slot allocation validation information 1602, and proceeds to step S1804 if received. In S1804, it is determined that the parent node 100 is permitted to return to communication, and the communication returns to communication. On the other hand, if the slot allocation validation information 1602 is not received from the parent node 100, it is determined that the return to the communication is not permitted, the process proceeds to S1805, and the communication interruption is continued.

  According to the third embodiment, since the child nodes 1 to 4 detect the node that has stopped transmission, it is possible to quickly detect the node that has stopped transmission. Furthermore, since the parent node 100 permits the return of communication, communication management can be concentrated on the parent node 100.

  Therefore, the child node 4 that has stopped transmitting can quickly detect the node that has stopped transmitting, so that it is possible to quickly eliminate the decrease in the degree of freedom of viewpoint movement in the free viewpoint video that accompanies a decrease in the number of cameras that photograph the subject 107. It becomes possible. At the same time, communication management can be performed centrally at the parent node, which facilitates system setting and management. For example, regarding a child node whose transmission has been stopped twice, ignore the second and subsequent slot allocation activation requests to the parent node 100 without changing the child nodes 1 to 4 when managing to not return to communication. It can be set and realized.

[Other Embodiments]
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (8)

A communication system that includes one parent node and a plurality of child nodes, and performs communication by assigning a frame to a plurality of communication slots based on slot assignment information generated by the parent node,
The parent node is
First generating means for generating the slot allocation information;
A response receiving means for receiving an acknowledgment from the plurality of child nodes after transmitting the slot allocation information;
Transmission means for transmitting slot allocation validation information for validating the slot allocation information to the plurality of child nodes upon receiving the confirmation response;
The plurality of child nodes are:
Upon receiving the slot allocation information transmitted from the parent node, a response transmission means for transmitting an acknowledgment to the parent node;
Receiving means for receiving the slot allocation validation information;
And a restricting means for restricting communication when the slot allocation validation information cannot be received from the parent node before a predetermined time elapses.   The communication system according to claim 1, wherein the predetermined time is preset in the plurality of child nodes or included in the slot allocation information transmitted from the parent node. The parent node further includes second generation means for generating an expiration date for validating the slot allocation information,
The second generation unit generates an expiration date of the slot allocation information every time the slot allocation information is updated,
The transmitting means transmits the activation deadline;
The communication system according to claim 1, wherein the plurality of child nodes set the predetermined time based on the transmitted expiration date. The parent node further includes detection means for detecting a child node whose communication is restricted by the restriction means,
When detecting a child node that restricts communication, the transmission means transmits the slot allocation validation information to the child node,
The plurality of child nodes further include resuming means for resuming the restricted communication,
The communication system according to claim 1, wherein the reproduction unit of the child node that restricts the communication resumes the communication when receiving the slot allocation validation information from the parent node. The child node further includes slot allocation validation request means for requesting retransmission of the slot allocation validation information,
The slot allocation validation request means transmits a slot allocation validation request to the parent node after the local node restricts communication,
The communication system according to claim 1, wherein the transmission unit of the parent node transmits the slot allocation validation information in response to the slot allocation validation request from the child node. The parent node further includes third generation means for generating an identifier of the slot allocation information,
The third generation unit generates an identifier of the different slot allocation information every time the slot allocation information is updated, and adds the generated identifier to the slot allocation information.
The plurality of child nodes further include resuming means for resuming the restricted communication,
The restarting means transmits the child node when the identifier of the slot assignment information received before the node restricts communication matches the identifier of the slot assignment information received after restricting the communication. The communication system according to claim 1, wherein the communication system is resumed. The first means generates the slot allocation information in which a slot for retransmission is allocated at a predetermined position,
The communication system according to any one of claims 1 to 6, wherein the parent node and the plurality of child nodes perform communication using a slot for the retransmission. A control method for a communication system that includes one parent node and a plurality of child nodes, and performs communication by assigning a frame to a plurality of communication slots based on slot assignment information generated by the parent node,
The parent node is
Generating step for generating the slot allocation information;
A response receiving step of receiving confirmation responses from the plurality of child nodes after transmitting the slot allocation information;
A step of transmitting slot assignment validation information for validating the slot assignment information upon reception of the confirmation response to the plurality of child nodes;
The plurality of child nodes are:
When receiving the slot allocation information transmitted from the parent node, a response transmission step of transmitting an acknowledgment to the parent node;
Receiving the slot allocation validation information; and
And a restriction step of restricting communication when the slot allocation validation information cannot be received from the parent node before a predetermined time elapses.

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