JP6160389B2 - COMMUNICATION SYSTEM, COMMUNICATION METHOD, AND COMMUNICATION DEVICE - Google Patents

Description

  The present invention relates to a communication system, a communication device, and a communication method.

  In a communication system having a plurality of communication devices, a system for notifying other communication devices of the power state of one communication device is known. Patent Documents 1 to 3 describe a technique for notifying other communication devices that a certain communication device is turned off and terminating the communication safely.

JP 2007-293776 A JP 2007-293775 A JP 2005-174117 A

In the techniques described in Patent Documents 1 to 3, it is not assumed that a predetermined parameter is transmitted along with the notification of the state of the power supply. Therefore, even when a certain communication device receives a power supply state notification, if a parameter is not received, the communication device continues to wait for reception of the parameter and cannot accept an operation by the user.
An object of the present invention is to reduce a time during which a communication device does not accept an operation when a parameter transmitted along with a request for disconnecting communication is not received by the communication device.

  In order to solve the above-described problem, the present invention includes a first communication device and a second communication device, and the first communication device communicates with the second communication device. And a first communication control means for establishing a communication connection with the second communication device via the first communication device, and the second communication device is connected to the first communication device. A second communication unit that communicates; a second communication control unit that controls communication via the second communication unit; and a processing unit that performs a predetermined process, wherein the second communication unit includes: A first request is transmitted via the communication connection, and the first communication means transmits a response to the first request via the communication connection, and the first request is transmitted. If the response is not received before the first time elapses, the processing means performs a predetermined process, and the first The communication means transmits a second request for disconnecting the communication connection via the communication connection, and the first communication means transmits the second request after the second request is transmitted. A parameter associated with the request is transmitted over the communication connection and the parameter is not received before a second time shorter than the first time elapses after the second request is received The second communication control means provides a communication system that disconnects the communication connection. According to this communication system, when the parameter from the first communication device is not received by the second communication device, the time during which the second communication device does not accept the operation is shortened.

  In a preferred aspect, the first communication device is an image display device, and the second communication means transmits a video signal via the communication connection. According to this communication system, when the second request is received, transmission of the video signal to the image display device is stopped even if the parameter from the first communication device is not received.

  In another preferred aspect, the first communication control means establishes a plurality of channels in the communication connection, and the first request, the response, the second request, and the parameter are the plurality of channels. The video signal is transmitted through another channel of the plurality of channels. According to this communication system, when the second request is received, the communication connections of the plurality of channels are disconnected.

  In another preferred aspect, the first communication means transmits the second request when the power of the first communication device is cut off. According to this communication system, when the power supply of the first communication device is cut off, the time until the communication connection is cut is shortened.

  In another preferred aspect, the first communication control means establishes a wireless communication connection, and the first communication means makes the second request when the signal strength in the radio falls below a predetermined level. It is characterized by transmitting. According to this communication system, when the wireless signal strength falls below a predetermined level, the time until the communication connection is cut is shortened.

  In another preferable aspect, the first communication control unit detects an error rate of the video signal transmitted by the second communication unit, and the first communication unit detects that the error rate exceeds a threshold value. The second request is transmitted. According to this communication system, when the error rate of the video signal exceeds the threshold, the time until the communication connection is cut is shortened.

  In another preferred aspect, the communication system includes a plurality of second communication devices, and the first communication means is determined after the communication connection is disconnected among the plurality of second communication devices. The parameter is transmitted to a second communication device to which the right is granted. According to this communication system, the time until the communication connection is cut for the second communication device to which the predetermined authority is not given is shortened.

  In another preferred aspect, the parameter indicates a time until the first communication control unit is allowed to re-establish the communication connection after the communication connection is disconnected. According to this communication system, it is possible to prevent an attempt to establish a communication connection between the first communication device and the second communication device before allowing the communication connection to be established again.

  In addition, the present invention includes a step in which a first communication device and a second communication device establish a communication connection, and a step in which the second communication device transmits a first request via the communication connection. The first communication device transmits a response to the first request via the communication connection, and the response before the first time elapses after the first request is transmitted. Is not received, the second communication device performs a predetermined process, and the first communication device transmits a second request for disconnecting the communication connection via the communication connection. The first communication device transmits a parameter associated with the second request via the communication connection after the second request is transmitted; and the second request includes: From the first time after being received If shorter second time is not received said parameters prior to lapse, the second communication device, to provide a communication method and a step of cutting the communication connection. According to this communication method, when the parameter from the first communication device is not received by the second communication device, the time during which the second communication device does not accept the operation is shortened.

  The present invention further includes a communication unit that communicates with an external device, a communication control unit that establishes a communication connection with the external device via the communication unit, and a processing unit that performs a predetermined process. If the first request is transmitted via the communication connection and a response to the first request is not received before the first time has elapsed since the first request was transmitted, the processing means Performs a predetermined process and before the second time shorter than the first time elapses after the second request for disconnecting the communication connection transmitted by the external device is received, When a parameter associated with the second request transmitted by the external device is not received after the second request is transmitted, the communication control unit provides a communication device that disconnects the communication connection. According to this communication device, when a parameter from an external device is not received, a time during which no operation is accepted is shortened.

Schematic of projection system PS. The block diagram which shows the functional structure of projection system PS. 2 is a block diagram showing a hardware configuration of the projector 1. FIG. The block diagram which shows the hardware constitutions of the tablet terminal 2. FIG. The sequence chart which shows the process in radio | wireless communication. 5 is a flowchart showing processing by the projector. The flowchart which shows the process by the tablet terminal 2. FIG. The sequence chart which shows the process in radio | wireless communication. FIG. 9 is a block diagram showing a functional configuration of a projector 1 according to Modification 1. 5 is a flowchart showing processing by the projector.

  FIG. 1 is a schematic diagram of a projection system PS (an example of a communication system) according to an embodiment of the present invention. The projection system PS includes a projector 1 (an example of a first communication device) and a plurality of tablet terminals 2 (an example of a second communication device). The projector 1 is an image display device that projects an image indicated by a video signal onto a screen SC. The tablet terminal 2 is a video source that outputs a video signal to the projector 1. The tablet terminal 2 is wirelessly connected peer-to-peer with the projector 1 by Wi-Fi (Wireless Fidelity: registered trademark) direct connection (connection using Wi-Fi Direct established by the Wi-Fi Alliance). The projector 1 projects an image corresponding to the video signal output from at least one tablet terminal 2 among the plurality of tablet terminals 2 on the screen SC. In the projection system PS, when a video signal is output from a plurality of tablet terminals 2, the projector 1 synthesizes images corresponding to the video signals output from the tablet terminals 2 (hereinafter referred to as “individual images”). The single image (hereinafter referred to as “composite image”) is projected onto the screen SC. In the example of FIG. 1, the projector 1 projects a composite image 50 obtained by combining the individual images 40 (40A and 40B) of the tablet terminals 2A and 2B onto the screen SC.

  FIG. 2 is a block diagram showing a functional configuration of the projection system PS. The projector 1 includes a communication unit 11, a communication control unit 12, and a display unit 13. The communication unit 11 communicates with the tablet terminal 2. The communication control unit 12 controls communication via the communication unit 11. The communication control means 12 establishes a communication connection with the tablet terminal 2 via the communication means 11 (hereinafter referred to as “peer-to-peer communication” because it includes peer-to-peer communication). The display unit 13 displays an image corresponding to the video signal output from the tablet terminal 2. The tablet terminal 2 includes a communication unit 21, a communication control unit 22, and a processing unit 23. 2 shows a functional configuration of one tablet terminal 2 among a plurality of tablet terminals 2 included in the projection system PS for convenience of explanation. The communication unit 21 communicates with the projector 1. The communication control unit 22 controls communication via the communication unit 21. The processing unit 23 performs predetermined processing according to communication with the projector 1.

  FIG. 3 is a block diagram illustrating a hardware configuration of the projector 1. The projector 1 includes a communication unit 101, a video signal receiver 102, an image processing circuit 103, a light source 104, a light source driving circuit 105, a liquid crystal panel 106, a projection lens 107, a power supply unit 108, an MCU (Micro Control). Unit) 109, ROM (Read Only Memory) 110, and RAM (Random Access Memory) 111. The communication unit 101 performs wireless communication with an external device such as the tablet terminal 2 according to a predetermined communication standard. The video signal receiver 102 acquires a video signal from the tablet terminal 2 via the communication unit 101. The image processing circuit 103 performs image processing on the video signal acquired by the video signal receiver 102. When the video signal receiver 102 acquires video signals from the plurality of tablet terminals 2, the image processing circuit 103 performs image processing for generating the composite image 50. The image processing circuit 103 outputs a signal corresponding to the image processing to the liquid crystal panel 106. The light source 104 is a device serving as a light source for projection, for example, a lamp such as a high-pressure mercury lamp, a halogen lamp, or a metal halide lamp, or a solid light source such as a semiconductor laser or an LED (Light Emitting Diode). The light source driving circuit 105 drives the light source 104. The liquid crystal panel 106 is an optical modulator that modulates the light emitted from the light source 104 in accordance with a signal supplied from the image processing circuit 103. The projection lens 107 is a lens that projects an image indicated by the light modulated by the liquid crystal panel 106 onto the screen SC. The power supply unit 108 supplies power to each unit of the projector 1 such as the image processing circuit 103 and the light source driving circuit 105. The power supply unit 108 has a battery or a capacitor for maintaining the supply of power. As a result, the power supply unit 108 has a predetermined time (for example, when the power cord is unplugged without being operated to turn off the power supply) when the supply of power to the power supply unit 108 is interrupted (for example, when the power cord is disconnected without being operated to turn off the power supply). Wireless communication with an external device can be continued (for example, several tens of milliseconds). The MCU 109 is a control device that controls each unit of the projector 1 by executing a program. The ROM 110 is a non-volatile storage device that stores various programs and data. The RAM 111 is a volatile storage device that stores data. In the projector 1, the communication unit 101 is an example of the communication unit 11. The MCU 109 executing the program is an example of the communication control unit 12. The liquid crystal panel 106 controlled by the MCU 109 executing the program is an example of the display unit 13.

  FIG. 4 is a block diagram illustrating a hardware configuration of the tablet terminal 2. The tablet terminal 2 includes a CPU 201, a ROM 202, a RAM 203, a communication unit 204, and a touch panel 205. The CPU 201 is a control device that controls each unit of the tablet terminal 2 by executing a program. The ROM 202 is a nonvolatile storage device that stores various programs and data. The RAM 203 is a volatile storage device that stores data. The communication unit 204 performs wireless communication with an external device such as the projector 1 according to a predetermined communication standard. The touch panel 205 is an input device in which a panel for sensing coordinates is provided on a display surface such as a liquid crystal display. For the touch panel 205, for example, an optical, resistive film, capacitance, or ultrasonic touch panel is used. In the tablet terminal 2, the communication unit 204 is an example of the communication unit 21. The CPU 201 executing the program is an example of the communication control unit 22 and the processing unit 23.

  FIG. 5 is a sequence chart showing processing in peer-to-peer communication between the projector 1 and the tablet terminal 2. In the projection system PS, the peer-to-peer communication between the projector 1 and the tablet terminal 2 includes a channel for communicating a video signal (hereinafter referred to as “video channel”) and a signal for controlling the peer-to-peer communication (hereinafter referred to as “video channel”). A channel (hereinafter referred to as “control channel”) for performing communication of “control signal”) is established. Hereinafter, communication in the control channel will be described. Note that video signal communication in the video channel is performed separately from the processing shown below. Hereinafter, for convenience of explanation, peer-to-peer communication between the projector 1 and one tablet terminal 2 among the plurality of tablet terminals 2 included in the projection system PS will be described.

  FIG. 5 shows processing in communication (so-called keep alive communication) for confirming that peer-to-peer communication between the projector 1 and the tablet terminal 2 is valid. The keep-alive communication is performed at predetermined time intervals after the peer-to-peer communication between the projector 1 and the tablet terminal 2 is established. In this example, the tablet terminal 2 transmits a packet for confirming that peer-to-peer communication is valid and has an empty payload portion (hereinafter referred to as “confirmation packet”) via the control channel to the projector 1. Send to. The tablet terminal 2 operates the timer after transmitting the confirmation packet, and before the predetermined timeout time (hereinafter referred to as “time T1”) elapses, the tablet terminal 2 responds to the confirmation packet from the projector 1 (hereinafter, “ When a response packet is received, it is confirmed that the peer-to-peer communication is valid. On the other hand, when the response packet is not received even after the time T1 has elapsed (that is, when a time-out occurs), the tablet terminal 2 performs a predetermined process. In the example illustrated in FIG. 5, when a timeout occurs, the tablet terminal 2 disconnects peer-to-peer communication with the projector 1.

  Upon receiving the confirmation packet, the projector 1 transmits a response packet to the tablet terminal 2 via the control channel. In FIG. 5, the confirmation packet transmitted by the tablet terminal 2 is an example of a first request, and the response packet transmitted by the projector 1 is an example of a response to the first request. Note that other wireless communication that also serves as keep-alive communication may be performed between the projector 1 and the tablet terminal 2. For example, even if it is confirmed that keep-alive communication is effective by sharing a key for encrypting a video signal in a HDCP (High-bandwidth Digital Content Protection system) at a predetermined time interval. Good.

  In the projector 1, there may be an event that makes it difficult to maintain peer-to-peer communication with a tablet terminal. This event is related to the power supply, for example, when the power supply to the projector 1 is suddenly cut off, for example, when the power cord of the projector 1 is disconnected or when a power failure occurs. In another example, the event may be related to the quality of peer-to-peer communication, such as a radio signal strength falling below a predetermined level. When such an event occurs, according to the process shown in FIG. 5, the tablet terminal 2 does not disconnect the peer-to-peer communication with the projector 1 until the time T1 has elapsed. In this case, if the projector 1 becomes unable to communicate with the peer-to-peer communication established, there may occur a problem that the operation by the user cannot be accepted in the tablet terminal 2. In order to deal with this problem, when the power supply to the projector 1 is cut off, the projector 1 uses a charge stored in the battery or the capacitor to cut off the peer-to-peer communication (hereinafter referred to as “disconnect request”). Is transmitted to the tablet terminal 2. When receiving the disconnection request, the tablet terminal 2 disconnects the peer-to-peer communication with the projector 1, so the above problem is solved. The disconnect request is an example of a second request in the present invention.

  In the present embodiment, a communication standard in which predetermined parameters are transmitted from the projector 1 to the tablet terminal 2 following this disconnection request is employed. Hereinafter, this parameter is referred to as “accompanying parameter”. The accompanying parameter indicates, for example, information on the determined authority given to the tablet terminal 2 after the peer-to-peer communication is disconnected. The determined authority includes, for example, authority (so-called group owner authority) that assumes a role as an access point. In another example, the accompanying parameter indicates a time (hereinafter referred to as “allowable time”) until the projector 1 is allowed to establish peer-to-peer communication with the tablet terminal 2 again after the peer-to-peer communication is disconnected.

  In this communication standard, when a disconnection request is received from the projector 1, the tablet terminal 2 stands by until an associated parameter is received. However, after the disconnection request is transmitted, the charge stored in the battery or the capacitor may be exhausted, and the accompanying parameter may not be transmitted. In this case, the tablet terminal 2 continues to wait until it receives the associated parameter. Since this is inconvenient, a timeout is also set for the time to wait for this accompanying parameter. Since it is better that the time from receiving the disconnection request to disconnecting the peer-to-peer communication is shorter, the time-out time (hereinafter referred to as “time T2”) after receiving the disconnection request in this embodiment is the keep-alive communication. It is set shorter than time T1. Below, the process by the projector 1 and the process by the tablet terminal 2 are each demonstrated.

  FIG. 6 is a flowchart showing processing by the projector 1. FIG. 6 illustrates a process in which the projector 1 transmits a disconnection request to the tablet terminal 2 when power supply to the projector 1 is suddenly interrupted. The following process is started in a state where power is supplied to the power supply unit 108 of the projector 1.

  In step SA1, the MCU 109 determines whether or not the power supply to the power supply unit 108 is interrupted. The determination as to whether or not the supply of power has been interrupted is performed using a signal from the power supply unit 108, for example. In this case, a signal line for transmitting a signal indicating that power is supplied to the power supply unit 108 is wired from the power supply unit 108 to the MCU 109. The MCU 109 monitors the signal on this signal line, and determines that the supply of power to the power supply unit 108 is cut off when the signal is turned off. If it is determined that the supply of power to the power supply unit 108 has been cut off (SA1: YES), the MCU 109 shifts the processing to step SA2. If it is determined that the supply of power to the power supply unit 108 is not interrupted (SA1: NO), the MCU 109 waits for processing until the supply of power is interrupted.

  In step SA2, the MCU 109 determines whether peer-to-peer communication with the tablet terminal 2 has been established. Specifically, the MCU 109 stores a list of identifiers of the tablet terminals 2 for which peer-to-peer communication has been established in the RAM 111, and depends on whether the identifier of any tablet terminal 2 is included in this list. To determine whether peer-to-peer communication has been established. If it is determined that peer-to-peer communication with the tablet terminal 2 has been established (SA2: YES), the MCU 109 proceeds to step SA3. When it is determined that peer-to-peer communication with the tablet terminal 2 has not been established (SA2: NO), the MCU 109 ends the process.

  In step SA3, the MCU 109 transmits a disconnection request to the tablet terminal 2. Specifically, the MCU 109 transmits a disconnection request via the control channel to each of the tablet terminals 2 that have established peer-to-peer communication with the projector 1. The MCU 109 transmits a disconnection request using the electric charge stored in the battery or capacitor of the power supply unit 108. In step SA4, the MCU 109 transmits an accompanying parameter via the control channel to the tablet terminal 2 to which the disconnection request has been transmitted. When the accompanying parameter indicates information regarding the determined authority, the MCU 109 transmits the accompanying parameter to the tablet terminal 2 to which the determined authority is given. As a specific example, when the communication device (group owner) serving as an access point is the projector 1 in the projection system PS, the projector 1 has a plurality of tablets whose peer-to-peer communication with its own device is disconnected. The associated parameter is transmitted to the tablet terminal 2 which becomes the new group owner among the terminals 2. The tablet terminal 2 that becomes a new group owner is determined by the MCU 109 according to the temporal order in which peer-to-peer communication with the projector 1 is established, for example.

  When the accompanying parameter indicates an allowable time, the accompanying parameter is transmitted to each of the tablet terminals 2 with which peer-to-peer communication with the projector 1 is established. For example, the allowable time is determined according to an expected time until the projector 1 can project an image on the screen SC again when power supply to the power supply unit 108 is resumed. In this example, the predicted time is the time required for warming up the light source 104, and the MCU 109 calculates the predicted time based on the temperature of the light source 104 detected by the temperature sensor.

  FIG. 7 is a flowchart showing processing by the tablet terminal 2. FIG. 7 shows a process in which the tablet terminal 2 disconnects the peer-to-peer communication with the projector 1 when a disconnection request is received. The following process is started in a state where peer-to-peer communication between the projector 1 and the tablet terminal 2 is established.

  In step SB1, the CPU 201 determines whether or not a disconnection request has been received from the projector 1. When it is determined that the disconnect request has been received (SB1: YES), the CPU 201 activates the timer and shifts the processing to step SB2. If it is determined that a disconnection request has not been received (SB1: NO), the CPU 201 waits for processing until a disconnection request is received. In step SB2, the CPU 201 determines whether or not an accompanying parameter is received from the projector 1. If it is determined that the accompanying parameter has been received (SB2: YES), the CPU 201 stores the accompanying parameter in the RAM 203, and the process proceeds to step SB3. If it is determined that the accompanying parameter has not been received (SB2: NO), the CPU 201 shifts the processing to step SB4.

  In step SB3, the CPU 201 performs processing according to the received accompanying parameter. Specifically, when the accompanying parameter indicates information regarding the authority of the group owner, the CPU 201 performs processing for establishing peer-to-peer communication with another tablet terminal 2 with which peer-to-peer communication with the projector 1 has been established. Note that information for identifying another tablet terminal 2 that has established peer-to-peer communication with the projector 1 is received from the projector 1 when, for example, an accompanying parameter is received. In another example, the information for identifying the other tablet terminal 2 that has established peer-to-peer communication with the projector 1 is another communication device different from the projector 1, and the peer-to-peer communication with the tablet terminal 2 has been established. You may receive from a communication apparatus. Note that if there is no process according to the accompanying parameter and performed before the peer-to-peer communication with the projector 1 is disconnected, step SB3 is omitted.

  In step SB4, the CPU 201 determines whether or not the time T2 has elapsed since the disconnection request was received. As described above, time T2 is shorter than time T1 in keep-alive communication. When it is determined that the time T2 has elapsed (SB4: YES), the CPU 201 shifts the processing to step SB5. When it is determined that the time T2 has not elapsed (SB4: NO), the CPU 201 shifts the processing to step SB2. In step SB5, the CPU 201 performs processing for disconnecting peer-to-peer communication with the projector 1.

  With the above processing, even when the accompanying parameter is not received, processing for disconnecting the peer-to-peer communication due to timeout is performed when the time T2 elapses. Therefore, when the incidental parameter is not received (for example, when the charge stored in the battery or the capacitor is exhausted in the projector 1), the tablet terminal 2 continues to wait until the incidental parameter is received, and the operation by the user is not accepted. It is prevented. Also, the time T2 is set shorter than the time T1 in keep-alive communication. Therefore, when the accompanying parameter is not received, the time until the peer-to-peer communication is disconnected is shortened compared to the case where the peer-to-peer communication is disconnected based on the keep-alive communication.

  FIG. 8 is a sequence chart showing processing in wireless communication between the projector 1 and the tablet terminal 2. FIG. 8 shows processing when a cutting request is transmitted by the projector 1. FIG. 8A shows a process in the case where an accompanying parameter is received by the tablet terminal 2 before the time T2 elapses after the disconnection request is received. In this case, the tablet terminal 2 performs a process according to the accompanying parameter, and then performs a process of disconnecting the peer-to-peer communication with the projector 1. FIG. 8B shows a process in the case where the accompanying parameter is not received by the tablet terminal 2 before the time T2 elapses after the disconnection request is received. In this case, the tablet terminal 2 performs a process of disconnecting the peer-to-peer communication with the projector 1 when the time T2 has elapsed.

<Modification>
The present invention is not limited to the above-described embodiments, and various modifications can be made. Hereinafter, some modifications will be described. Of the modifications described below, two or more may be used in combination.

(1) Modification 1
The event that makes it difficult to maintain peer-to-peer communication with the tablet terminal is not limited to the case where the supply of power to the power supply unit 108 is interrupted. For the peer-to-peer communication with the tablet terminal 2, the projector 1 may transmit a disconnection request when the wireless signal strength falls below a predetermined level. In this case, in step SA1, the MCU 109 determines whether or not the wireless signal strength has fallen below a predetermined level. In this case, the process of step SA2 is omitted.

  FIG. 9 is a block diagram illustrating a functional configuration of the projector 1 according to the first modification. In the first modification, the projector 1 includes a detection unit 14 in addition to the functional configuration illustrated in FIG. The detecting means 14 detects that the intensity of the wireless signal is below a predetermined level. The communication unit 11 transmits a disconnection request and an accompanying parameter when the detection unit 14 detects that the signal strength in the radio is below a predetermined level. In the first modification, the MCU 109 executing the program is an example of the detection unit 14.

  FIG. 10 is a flowchart illustrating an example of processing in which the projector 1 determines whether or not the wireless signal strength has fallen below a predetermined level. In this example, the projector 1 decrypts the encrypted video signal, and when the error rate of the decrypted video signal exceeds a threshold value, the projector 1 determines that the wireless signal strength has fallen below a predetermined level.

  In step SA11, the MCU 109 starts obtaining an encrypted video signal from the tablet terminal 2. In step SA12, the MCU 109 decodes the acquired video signal. In step SA13, the MCU 109 determines whether or not the error rate of the decoded video signal exceeds a threshold value. The threshold value is stored in the ROM 110 in advance. If it is determined that the error rate exceeds the threshold (SA13: YES), the MCU 109 shifts the processing to step SA3. When it is determined that the error rate does not exceed the threshold value (SA13: NO), the MCU 109 shifts the processing to step SA14.

  In step SA14, the MCU 109 determines whether or not the acquisition of the video signal from the tablet terminal 2 has been completed. If it is determined that the acquisition of the video signal has ended (SA14: YES), the MCU 109 ends the process. If it is determined that the acquisition of the video signal has not ended (SA14: NO), the MCU 109 proceeds to step SA12. Note that it may be determined whether or not the wireless signal strength has fallen below a predetermined level by a process other than the process shown in FIG. For example, when peer-to-peer communication is performed via radio waves, the projector 1 may determine whether or not the radio signal strength has fallen below a predetermined level by detecting the radio wave strength.

(2) Modification 2
The confirmation packet may be transmitted from the projector 1 to the tablet terminal 2. In this case, when receiving the confirmation packet, the tablet terminal 2 transmits a response packet to the projector 1. If the response packet is not received before the time T1 elapses after the confirmation packet is transmitted, the projector 1 performs a predetermined process. Further, the disconnect request may be transmitted from the tablet terminal 2 to the projector 1. In this case, the process illustrated in FIG. 6 is performed by the tablet terminal 2, and the process illustrated in FIG. 7 is performed by the projector 1.

(3) Modification 3
The image projected by the projector 1 is not limited to the composite image described in the embodiment. For example, the projector 1 may project an individual image of one tablet terminal 2 selected from the plurality of tablet terminals 2 onto the screen SC. Further, all of the tablet terminals 2 wirelessly connected to the projector 1 may not output video signals to the projector 1. Furthermore, a single tablet terminal 2 may be used in the projection system PS.

(4) Modification 4
In the keep-alive communication, the predetermined process performed by the tablet terminal 2 is not limited to the disconnection of the peer-to-peer communication. For example, the tablet terminal 2 may retransmit the confirmation packet as the predetermined process. In this case, the tablet terminal 2 may disconnect the peer-to-peer communication with the projector 1 when the time-out continues for the determined number of times.

(5) Modification 5
The first communication device is not limited to the projector 1. As long as the first communication device is a communication device that performs peer-to-peer communication with the second communication device, for example, a liquid crystal display device having a liquid crystal display or the like may be used. In another example, the first communication device may be an audio device such as a speaker or an AV amplifier. In this case, the second communication device may output an audio signal to the first communication device. Further, the second communication device is not limited to the tablet terminal 2. The second communication device may be, for example, a mobile phone or a personal computer as long as it is a communication device that performs peer-to-peer communication with the first communication device.

(6) Modification 6
The information indicated by the accompanying parameter is not limited to the information shown in the embodiment. The accompanying parameter may indicate, for example, information on a frame rate of a video signal communicated in a video channel or a color space. In another example, the accompanying parameter may indicate an identifier for identifying the projector 1 that transmits the disconnection request. In another example, when the first communication device is an audio device, the accompanying parameter may indicate information related to audio.

(7) Modification 7
When the accompanying parameter is transmitted to the tablet terminal 2 that newly becomes the group owner, the method for the MCU 109 to determine the tablet terminal 2 is not limited to the method described in the embodiment. The MCU 109 may determine, for example, one tablet terminal 2 that outputs a video signal when a disconnection request is transmitted as a tablet terminal 2 that becomes a new group owner. In another example, a tablet terminal 2 that becomes a new group owner may be determined according to an order determined by the identifiers of the tablet terminals 2 (for example, alphabetical order of identifiers or numerical order). In yet another example, each tablet terminal 2 is given a unique numerical value, and the tablet terminal 2 that becomes a new group owner may be determined according to the magnitude of this numerical value.

(8) Modification 8
The video channel and the control channel established in the peer-to-peer communication between the projector 1 and the tablet terminal 2 are not limited to one each. For example, two control channels may be established in the peer-to-peer communication described above. In this case, the keep-alive communication and the communication of the disconnection request and the accompanying parameters may be performed via different control channels. Further, the number of channels established in the peer-to-peer communication between the projector 1 and the tablet terminal 2 may be one. In this case, video signal communication and control signal communication are performed through one established channel.

(9) Modification 9
The hardware configurations of the projector 1 and the tablet terminal 2 are not limited to the configurations shown in FIGS. The projector 1 and the tablet terminal 2 may have any hardware configuration as long as the processing of each step shown in FIGS. 5 to 9 can be executed. For example, a volatile storage device may be used instead of the ROM 110 or the ROM 202. In another example, the projector 1 may be configured by a method using a liquid crystal panel 106 and a color wheel, a method using a digital mirror device (DMD), a method using a DMD and a color wheel, or the like. .

(10) Modification 10
The projector 1 and the tablet terminal 2 are not limited to being wirelessly connected. The projector 1 and the tablet terminal 2 may be wiredly connected by peer-to-peer via an image signal cable, a USB (Universal Serial Bus) cable, or the like.

(11) Modification 11
Since the projector 1 and the plurality of tablet terminals 2 only need to be able to communicate with each other by designating the other party, the connection is not limited to peer-to-peer communication. The projector 1 and the plurality of tablet terminals 2 may be at least part of a communication device group constituting a LAN (Local Area Network) by wire or wireless.

DESCRIPTION OF SYMBOLS 1 ... Projector, 2 ... Tablet terminal, 11 ... Communication means, 12 ... Communication control means, 13 ... Display means, 14 ... Detection means, 21 ... Communication means, 22 ... Communication control means, 23 ... Processing means, 101 ... Communication part , 102 ... Video signal receiver, 103 ... Image processing circuit, 104 ... Light source, 105 ... Light source drive circuit, 106 ... Liquid crystal panel, 107 ... Projection lens, 108 ... Power supply unit, 109 ... MCU, 110 ... ROM, 111 ... RAM, 201 ... CPU, 202 ... ROM, 203 ... RAM, 204 ... communication unit, 205 ... touch panel.

Claims (10)

A first communication device;
A second communication device,
The first communication device is:
First communication means for communicating with the second communication device;
First communication control means for establishing a communication connection with the second communication device via the first communication means,
The second communication device is:
Second communication means for communicating with the first communication device;
Second communication control means for controlling communication via the second communication means;
Processing means for performing predetermined processing, and
The second communication means transmits a first request via the communication connection;
The first communication means transmits a response to the first request via the communication connection;
If the response is not received before the first time has elapsed since the first request was transmitted, the processing means performs a predetermined process,
The first communication means transmits a second request for disconnecting the communication connection via the communication connection;
The first communication means transmits a parameter associated with the second request via the communication connection after the second request is transmitted;
If the parameter is not received before the second time shorter than the first time elapses after the second request is received, the second communication control means disconnects the communication connection. Communications system. The first communication device is an image display device;
The communication system according to claim 1, wherein the second communication means transmits a video signal via the communication connection. The first communication control means establishes a plurality of channels in the communication connection;
The first request, the response, the second request, and the parameter are transmitted via a channel of the plurality of channels;
The communication system according to claim 2, wherein the video signal is transmitted through another channel of the plurality of channels. 4. The communication system according to claim 2, wherein the first communication unit transmits the second request when power of the first communication device is cut off. 5. The first communication control means establishes a wireless communication connection;
The communication system according to any one of claims 2 to 4, wherein the first communication means transmits the second request when the signal strength in the radio falls below a predetermined level. The first communication control means detects an error rate of the video signal transmitted by the second communication means,
The communication system according to claim 5, wherein the first communication unit transmits the second request when the error rate exceeds a threshold value. The communication system includes a plurality of second communication devices,
The first communication unit transmits the parameter to a second communication device to which a predetermined authority is given after the communication connection is disconnected among a plurality of second communication devices. Item 7. The communication system according to any one of Items 1 to 6. 8. The parameter according to any one of claims 1 to 7, wherein the parameter indicates a time until the first communication control unit is allowed to re-establish the communication connection after the communication connection is disconnected. The communication system according to claim 1. Establishing a communication connection between the first communication device and the second communication device;
The second communication device transmitting a first request via the communication connection;
The first communication device transmitting a response to the first request via the communication connection;
If the response is not received before the first time has elapsed since the transmission of the first request, the second communication device performs a predetermined process;
The first communication device transmits a second request for disconnecting the communication connection via the communication connection;
The first communication device transmitting a parameter associated with the second request via the communication connection after the second request is transmitted;
If the parameter is not received before a second time shorter than the first time has elapsed since the second request was received, the second communication device disconnects the communication connection. And a communication method. A communication means for communicating with an external device;
Communication control means for establishing a communication connection with the external device via the communication means;
Processing means for performing predetermined processing, and
The communication means transmits a first request via the communication connection;
If a response to the first request is not received before the first time has elapsed since the first request was transmitted, the processing means performs a predetermined process,
The second request is transmitted before the second time shorter than the first time elapses after the second request for disconnecting the communication connection transmitted by the external device is received. A communication device that disconnects the communication connection when the parameter associated with the second request transmitted by the external device is not received.

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