JP2011130027A - Server device, communication system, and control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication system that prevents the occurrence of a reception error in each client terminal while considering communication with each client terminal when executing wireless transmission of video data. <P>SOLUTION: A server device (1) specifies a client terminal (for example, 2-1) whose reception error rate is the highest in the reception error rates of respective client terminals (2-1-2-N; N is an arbitrary integer). A value of transmission power, used for wireless transmission, of the server device (1) is changed so that the reception error rate of the specified client terminal (2-1) becomes lower than or equal to a prescribed threshold. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a communication system that wirelessly transmits video data from a server device to a client terminal.

  In recent years, as shown in FIG. 13, video data (digital broadcast data or the like) received by the server apparatus 1 ′ from the broadcast antenna 3 ′ or the like is transmitted from the server apparatus 1 ′ to a plurality of client terminals 2-1 ′ to 2-N. There is a communication system that wirelessly transmits to '(N' is an arbitrary integer) and outputs and displays on a display device or the like at each client terminal 2-1 'to 2-N'.

  However, in the above-described communication system that performs wireless transmission, when the received power value of the received signal received by each of the client terminals 2-1 ′ to 2-N ′ is too strong or too weak than the specified received power allowable range In addition, there is a possibility that a reception error occurs in each of the client terminals 2-1 ′ to 2-N ′.

  When a reception error occurs, a technique for restoring video reproduction using a correction / detection method such as an error correction code or CRC (Cyclic Redundancy Check), or a retransmission control method can be used. By using these methods, in the case of best effort communication or low bit rate stream communication, even if a reception error occurs, video reproduction can be recovered without any problem thereafter.

  However, when video data such as high-definition video is transmitted wirelessly, the occurrence of a reception error becomes a serious problem. This is because when video data such as high-definition video is transmitted wirelessly, it is necessary to perform high bit rate stream communication and transmit video data without interruption. This is because a high bit rate stream communication cannot be performed.

  For this reason, in the communication system shown in FIG. 13 described above, when wirelessly transmitting video data that requires a high bit rate, such as a high-definition video, each client terminal 2-1 ′ to 2-N ′. It is necessary to prevent reception errors from occurring at each of the client terminals 2-1 ′ to 2-N ′ in consideration of communication with the client.

  In addition, as a technical document filed prior to the present invention, there is a document that discloses a technique for controlling transmission output power of a communication partner based on a signal transmitted from the communication partner (for example, Patent Document 1, 2).

  In Patent Literature 1, the electric field strength or S / N ratio of a received signal is measured, and the measured information (measurement information) is sent to the wireless communication device on the communication partner side. The point which increases / decreases transmission output power based on information is disclosed.

  In Patent Document 2, the mobile station measures the reception quality of the received signal from the base station, and compares the measured reception quality with a predetermined target reception quality. If the measured reception quality falls below the target reception quality, an uplink TPC (Transmission Power Control) bit that increases the downlink transmission power is transmitted to the base station. Conversely, it is disclosed that when the measured reception quality exceeds the target reception quality, an uplink TPC bit that lowers the downlink transmission power is transmitted to the base station.

JP-A-4-180414 JP 2007-36633 A

  However, the transmission output power control disclosed in Patent Documents 1 and 2 is a method performed at the time of general wireless communication, and as in the present invention, wireless transmission of video data that requires a high bit rate such as a high-definition video. It does not prevent reception errors from occurring at each client terminal 2-1 'to 2-N' while considering communication with each client terminal 2-1 'to 2-N' when transmitting. .

  The present invention has been made in view of the above circumstances, and when performing wireless transmission of video data, which is the problem described above, a reception error occurs in each client terminal while considering communication with each client terminal. It is an object of the present invention to provide a server device, a communication system, and a control method that can be avoided.

  In order to achieve this object, the present invention has the following features.

<Server device>
The server device according to the present invention includes:
A server device that wirelessly transmits video data to a plurality of client terminals,
A means for identifying a client terminal having the highest reception error rate among the reception error rates of each client terminal,
Control means for changing a transmission power value used for the wireless transmission of the server device so that a reception error rate of the client terminal specified by the specifying means is a predetermined threshold value or less;
It is characterized by having.

<Communication system>
A communication system according to the present invention includes:
A communication system having a server device and a plurality of client terminals, and wirelessly transmitting video data from the server device to the plurality of client terminals,
The server device
A means for identifying a client terminal having the highest reception error rate among the reception error rates of each client terminal,
Control means for changing a transmission power value used for the wireless transmission of the server device so that a reception error rate of the client terminal specified by the specifying means is a predetermined threshold value or less;
It is characterized by having.

<Control method>
The control method according to the present invention includes:
A control method performed by a server device that wirelessly transmits video data to a plurality of client terminals,
A specific step of identifying a client terminal having the highest reception error rate among the reception error rates of each client terminal,
A control step of changing a transmission power value used for the wireless transmission of the server device so that a reception error rate of the client terminal specified in the specifying step is equal to or less than a predetermined threshold;
It is characterized by having.

  According to the present invention, when video data is wirelessly transmitted, it is possible to prevent a reception error from occurring at each client terminal while considering communication with each client terminal.

It is a figure which shows the system configuration example of the communication system of 1st Embodiment. It is a figure which shows the internal structural example of the server apparatus 1 and the client terminals 2-1 to 2-N which comprise a communication system. A general relational expression in which the impedance of the space between the server apparatus 1 and an arbitrary client terminal 2 and the reception error rate generated at the arbitrary client terminal 2 are associated with each other; FIG. It is. It is a figure for demonstrating the moving direction of relational expression; A when the transmission power value used for the wireless transmission of the server apparatus 1 is changed. It is a figure for demonstrating the example of the power control in case the three client terminals (C1, C2, C3) exist. It is a figure which shows the processing operation example in the communication system of 1st Embodiment. It is a figure for demonstrating the relational expression; A and B used in 2nd Embodiment. It is a figure which shows the example of a processing operation in the communication system of 2nd Embodiment. It is a figure for demonstrating the value of the weight according to the number of packets. It is a figure for demonstrating the relational expression; A, B, and C used in 3rd Embodiment. It is a figure for demonstrating the example of the power control of 4th Embodiment. It is a figure which shows the processing operation example in the communication system of 4th Embodiment. It is a figure which shows the system configuration example of the communication system relevant to this invention.

<Outline of communication system>
First, an outline of a communication system according to the present embodiment will be described with reference to FIG.

  The communication system of the present embodiment includes a server device 1 and a plurality of client terminals 2-1 to 2-N (N is an arbitrary integer), and video data is transmitted from the server device 1 to a plurality of client terminals 2. This is a communication system for wireless transmission from -1 to 2-N.

  The server device 1 according to the present embodiment identifies a client terminal (for example, 2-1) having the highest reception error rate among the reception error rates of the client terminals 2-1 to 2-N. Then, the transmission power value used for the wireless transmission of the server device 1 is changed so that the reception error rate of the identified client terminal 2-1 is equal to or less than a predetermined threshold. As a result, when wireless transmission of video data is performed, the server device 1 causes a reception error in each client terminal 2-1 to 2-N while considering communication with each client terminal 2-1 to 2-N. It can be prevented from occurring. Hereinafter, the communication system of the present embodiment will be described in detail with reference to the accompanying drawings.

(First embodiment)
<System configuration example of communication system>
First, a system configuration example of a communication system according to the present embodiment will be described with reference to FIG.

  The communication system of the present embodiment includes a server device 1 and a plurality of client terminals 2-1 to 2-N (N is an arbitrary integer).

  The server device 1 wirelessly transmits digital broadcast data received from the broadcast antenna 3 or the like to a plurality of client terminals 2-1 to 2-N, and the digital broadcast data is displayed on each client terminal 2-1 to 2-N. And so on. The server device 1 of the present embodiment does not switch the transmission power value used during wireless transmission with each client terminal 2-1 to 2-N individually for each client terminal 2-1 to 2-N. The transmission power values used during wireless transmission with each of the client terminals 2-1 to 2-N are switched at once.

  Each of the client terminals 2-1 to 2-N makes a recording reservation based on an EPG (Electric Program Guide) transferred from the server device 1, and the program data for which the recording reservation has been made is transmitted to each client terminal 2-1. Control to record at ~ 2-N.

<Configuration example of server device 1>
Next, a configuration example of the server device 1 according to the present embodiment will be described with reference to FIG.

  The server device 1 according to the present embodiment includes a wireless communication unit 11, a storage unit 12, a video generation unit 13, and a transmission power control unit 14.

  The wireless communication unit 11 stores digital broadcast data sequentially received from the broadcast antenna 3 and the like in a buffer (not shown) under the control of the video generation unit 13. The digital broadcast data received by the wireless communication unit 11 includes program data and information such as EPG (broadcast program information). The wireless communication unit 11 wirelessly transmits the digital broadcast data sequentially stored in a buffer (not shown) to each of the client terminals 2-1 to 2-N under the control of the video generation unit 13.

  The storage unit 12 stores various information used when controlling the server device 1.

  The video generation unit 13 executes a video generation function (function for reproducing / recording video data in each of the client terminals 2-1 to 2-N; a TV viewing application, etc.), and the wireless communication unit 11 is connected to the broadcast antenna 3 Control is performed to transmit the digital broadcast data received from the client terminals 2-1 to 2-N. The video generation unit 13 can start and end the operation of the video generation function according to instructions from the client terminals 2-1 to 2-N.

  The transmission power control unit 14 executes a transmission power control function, and performs switching control of a transmission power value used when the wireless communication unit 11 wirelessly transmits digital broadcast data to the client terminals 2-1 to 2-N.

  When the transmission power control unit 14 performs transmission power value switching control, the server device 1 needs to temporarily stop transmission of the digital broadcast data. For this reason, it is preferable to reduce the number of transmission power value switching performed by the transmission power control unit 14. Thereby, interruption of digital broadcast data can be suppressed.

  The transmission power control unit 14 includes a worst value specifying unit 141 and a power control unit 142. The worst value specifying unit 141 specifies the client terminal having the highest reception error rate among the reception error rates of the client terminals 2-1 to 2-N. As a result, the worst reception error rate among the reception error rates of the client terminals 2-1 to 2-N can be specified. The worst value specifying unit 141 includes an impedance calculating unit 1411 and a reception error rate calculating unit 1412.

  The impedance calculator 1411 calculates the impedance of the space between the server device 1 and each of the client terminals 2-1 to 2-N. The impedance of the space between the server device 1 and each of the client terminals 2-1 to 2-N can be obtained by the following equation.

Impedance = Transmit power value ÷ Receive power value However,
Transmit power value: Transmit power value currently used by server device 1 Receive power value: Received power value of received signal measured at each client terminal 2-1 to 2-N

  The reception error rate calculation unit 1412 calculates the reception error rate of each client terminal 2-1 to 2-N based on the impedance of each client terminal 2-1 to 2-N calculated by the impedance calculation unit 1411. The reception error rate calculation unit 1412 grasps in advance a relational expression (relational expression shown in FIG. 3; A) in which the impedance and the reception error rate are associated, and calculates the impedance based on the relational expression; A. The reception error rate corresponding to the impedance of each of the client terminals 2-1 to 2-N calculated by the unit 1411 is calculated.

  The worst value specifying unit 141 specifies the client terminal with the highest reception error rate based on the reception error rate of each of the client terminals 2-1 to 2-N calculated by the reception error rate calculation unit 1412. Thus, the worst value specifying unit 141 can specify the worst reception error rate among the reception error rates of the client terminals 2-1 to 2-N.

  The power control unit 142 changes the transmission power value used for the wireless transmission of the server device 1 so that the worst reception error rate specified by the worst value specifying unit 141 is equal to or less than a predetermined threshold.

  FIG. 3 shows a general relational expression A in which the impedance of the space between the server device 1 and a given client terminal 2 is associated with the reception error rate generated in the given client terminal 2. . Note that the relational expression A shown in FIG. 3 is obtained in advance through experiments and the like.

  As shown in FIG. 3, when the impedance is too low, the reception power of the client terminal 2 is too strong, and as a result, the reception error rate of the client terminal 2 becomes high. On the other hand, when the impedance is too high, the reception power of the client terminal 2 is too weak, and as a result, the reception error rate of the client terminal 2 becomes high.

  When the worst reception error rate specified by the worst value specifying unit 141 is higher than a predetermined threshold; α, the video stream cannot be viewed on the client terminal 2 or normal communication cannot be performed (viewing). Impossible).

  Therefore, the power control unit 142 changes the transmission power value used for the wireless transmission of the server device 1 so that the worst reception error rate specified by the worst value specifying unit 141 is a predetermined threshold; α or less, The relational expression A shown in FIG. 3 is moved left and right as shown in FIG.

  FIG. 4A shows a relational expression A ′ when the transmission power value of the server apparatus 1 is increased. By increasing the transmission power value of the server apparatus 1, the relational expression A shown in FIG. 3 moves in the direction in which the impedance is high as shown by the relational expression A ′ in FIG. 4A.

  FIG. 4B shows a relational expression A ′ when the transmission power value of the server apparatus 1 is reduced. By reducing the transmission power value of the server device 1, the relational expression A shown in FIG. 3 moves in a direction in which the impedance is weaker like the relational expression A ′ in FIG. 4B.

  FIG. 5 shows an example of power control when there are three client terminals (C1, C2, C3). In this case, the impedance calculation unit 1411 performs the server device 1 and each of the server devices 1 based on the reception power value measured by each client terminal (C1, C2, C3) and the transmission power value currently used by the server device 1. The impedance of the space between the client terminals (C1, C2, C3) is calculated.

  The reception error rate calculation unit 1412 calculates the impedance of each client terminal (C1, C2, C3) calculated by the impedance calculation unit 1411 using a relational expression (impedance and impedance) based on the transmission power value currently used in the server device 1. Plot on the relational expression with the reception error rate; A). FIG. 5A shows a state where the impedance of each client terminal (C1, C2, C3) is plotted on the relational expression A;

  In the case of the state shown in FIG. 5 (a), the reception error rate of the client terminal (C2, C3) is equal to or less than a predetermined threshold; α, so that the server device 1 and the client terminal (C2, C3) It can be seen that the communication state is good. However, since the reception error rate of the client terminal (C1) is greater than a predetermined threshold; α, it can be seen that the communication state between the server device 1 and the client terminal (C1) is poor.

  For this reason, the power control unit 142 changes the transmission power value currently used in the server device 1 so that the reception error rate of the client terminal (C1) is equal to or less than a predetermined threshold; α. FIG. 5B shows the reception error rate of each client terminal (C1, C2, C3) when the transmission power value currently used in the server apparatus 1 is changed. As shown in FIG. 5B, the transmission power value of the server apparatus 1 is reduced, the relational expression shown in FIG. 5A is moved to the left, and the relational expression shown in FIG. Thus, the reception error rate of the client terminal (C1) can be set to a predetermined threshold; α or less. Therefore, the power control unit 142 reduces the transmission power value currently used by the server device 1 so that the reception error rate of the client terminal (C1) is equal to or less than a predetermined threshold; α. Thereby, the reception error rate of each client terminal (C1, C2, C3) can be optimized.

<Configuration example of client terminals 2-1 to 2-N>
Next, a configuration example of the client terminals 2-1 to 2-N according to the present embodiment will be described with reference to FIG.

  The client terminals 2-1 to 2-N of the present embodiment acquire digital broadcast data wirelessly transmitted from the server device 1, and display or record the acquired digital broadcast data on a display device or the like. . The client terminals 2-1 to 2-N of the present embodiment include a wireless communication unit 21, a storage unit 22, a video reproduction unit 23, and a received power monitoring unit 24.

  The wireless communication unit 21 receives the digital broadcast data wirelessly transferred from the server device 1 under the control of the video reproduction unit 23.

  The storage unit 22 stores various information used when controlling the client terminal 2. For example, recording reservation information and the like when recording reservation is set in the client terminal 2 are stored.

  The video playback unit 23 executes a video playback function (a function for playing back and recording video data in the client terminal 2), and outputs or records the digital broadcast data received by the wireless communication unit 21 to a display device or the like. Or For example, the video playback unit 23 displays digital broadcast data on the display device of the client terminal 2 or displays digital broadcast data on an external display device. In addition, the video reproduction unit 23 records the digital broadcast data received by the wireless communication unit 21 based on the recording reservation information stored in the storage unit 22.

  The received power monitoring unit 24 performs monitoring control of received power of a signal received by the wireless communication unit 21. The reception power monitoring unit 24 includes a reception power measurement unit 241 and a reception power notification unit 242.

  The reception power measurement unit 241 measures the reception power value of the reception signal received by the wireless communication unit 21. The reception power value measurement method is not particularly limited as long as the reception power value of the reception signal received by the wireless communication unit 21 can be measured, and various known measurement methods can be applied.

  The reception power notification unit 242 notifies the server device 1 of the reception power value measured by the reception power measurement unit 241 through the wireless communication unit 21.

<Example of processing operation in communication system>
Next, an example of processing operation in the communication system of the present embodiment will be described with reference to FIG.

  The communication system of this embodiment needs to guarantee the video quality of digital broadcast data that is played back or recorded in the client terminals 2-1 to 2-N. For this reason, while the video playback function of the client terminals 2-1 to 2-N is operating, the transmission power control function of the server device 1 is operated, and transmission when the server device 1 transmits digital broadcast data. Power output control is to be executed.

<Example of processing operation of client terminals 2-1 to 2-N>
First, an example of processing operations of the client terminals 2-1 to 2-N will be described with reference to FIG.

  When the video playback unit 23 starts operation of the video playback function (Step A0 / Yes), the received power monitoring unit 24 starts monitoring the received power (Step A1). ), The received power measuring unit 241 measures the received power value (step A2).

  The reception power notification unit 242 notifies the server device 1 of the reception power value measured by the reception power measurement unit 241 (step A3).

  Next, the received power monitoring unit 24 determines whether or not the video playback function is operating (step A4). If the video playback function is operating (step A4 / Yes), the received power measurement unit 241 Measure the power value (step A5). The reception power notification unit 242 notifies the server device 1 of the reception power value measured by the reception power measurement unit 241 (step A6).

  When the transmission power notification unit 242 notifies the server device 1 of the reception power value (step A6), the reception power monitoring unit 24 determines again whether or not the video reproduction function is operating (step A4).

  If the received power monitoring unit 24 determines that the video playback function is not in operation (step A4 / No), it stops monitoring the received power (step A7).

  The client terminals 2-1 to 2-N according to the present embodiment notify the server apparatus 1 of the received power value measured by the received power measurement unit 241 when the video playback function starts, and the client terminals 2-1 to 2-N In accordance with the received power value of the signal received by the server device 1, the transmission power value used for the wireless transmission of the server device 1 is changed in the server device 1 so that no reception error occurs in each of the client terminals 2-1 to 2-N The transmission power of the server device 1 can be changed.

  Furthermore, the client terminals 2-1 to 2-N of the present embodiment notify the server apparatus 1 of the received power value measured by the received power measuring unit 241 during the video playback function operation, and the client terminals 2-1 to 2 The transmission power value used for the wireless transmission of the server device 1 is changed in the server device 1 according to the received power value of the signal received by -N, and no reception error occurs in each client terminal 2-1 to 2-N As described above, the transmission power of the server device 1 can be changed.

  As a result, the client terminals 2-1 to 2-N of the present embodiment can prevent reception errors from occurring on the client terminals 2-1 to 2-N when performing wireless transmission of video data. it can. As a result, it is possible to guarantee the video quality of the digital broadcast data to be played back or recorded in each client terminal 2-1 to 2-N.

<Processing example of server device 1>
Next, a processing operation example of the server apparatus 1 will be described with reference to FIG. In the following description, when one client terminal is shown among the plurality of client terminals 2-1 to 2-N, it will be described as the client terminal 2.

  In the server device 1, when the video generation unit 13 starts the operation of the video generation function according to an instruction from the client terminal 2, the transmission power control unit 14 starts transmission power control.

  The worst value specifying unit 141 determines whether or not the received power of the client terminal 2 has been updated based on the received power value notified from the client terminal 2 (step B0).

  The worst value specifying unit 141 determines whether or not the received power of the client terminal 2 has been updated when the received power value is notified from one client terminal 2, or all the client terminals 2- When the reception power value is notified from 1 to 2-N, it is also possible to determine whether or not the reception power of each client terminal 2-1 to 2-N has been updated.

  When the worst value specifying unit 141 determines that the received power has been updated (step B0 / Yes), the impedance calculating unit 1411 receives the received power value notified from each of the client terminals 2-1 to 2-N and the server Based on the transmission power value currently used by the device 1, the impedance of the space between the server device 1 and each of the client terminals 2-1 to 2-N is calculated (step B1).

The impedance is calculated by the following formula (1).
Formula (1)
Impedance = Transmit power value ÷ Receive power value However,
Transmit power value: Transmit power value currently used by server device 1 Receive power value: Received power value of received signal measured at each client terminal 2-1 to 2-N

  Next, the reception error rate calculation unit 1412 calculates the reception error rate of each client terminal 2-1 to 2-N based on the impedance of each client terminal 2-1 to 2-N calculated by the impedance calculation unit 1411. To do. The reception error rate calculation unit 1412 grasps in advance a relational expression (for example, the relational expression shown in FIG. 5A; A) in which the impedance and the reception error rate are associated with each other. Based on this, the reception error rate corresponding to the impedance of each of the client terminals 2-1 to 2-N calculated by the impedance calculation unit 1411 is calculated. Thereby, the reception error rate calculation unit 1412 obtains the reception error rate obtained when the impedances of the client terminals 2-1 to 2-N (C1, C2, and C3 in FIG. 5) are plotted on the relational expression A. Can be calculated.

  The worst value specifying unit 141 specifies the client terminal with the highest reception error rate based on the reception error rate of each of the client terminals 2-1 to 2-N calculated by the reception error rate calculation unit 1412. Thereby, the worst value specifying unit 141 receives the worst reception among the reception error rates of the client terminals 2-1 to 2-N (in FIG. 5A, the reception error rates of the client terminals C1, C2, and C3). The error rate (the reception error rate of the client terminal C1 in FIG. 5A) can be specified (step B2).

  Next, the power control unit 142 calculates an optimum transmission power value that can improve the worst reception error rate specified by the worst value specifying unit 141 (step B3).

  Specifically, the power control unit 142 causes the worst reception error rate specified by the worst value specification unit 141 (in FIG. 5A, the reception error rate of the client terminal C1) to be a predetermined threshold; α or less. The transmission power value (for example, the relational expression shown in FIG. 5B; the transmission power value for obtaining A ′) is calculated.

  Next, the power control unit 142 compares the calculated optimal transmission power value with the transmission power value currently used by the server device 1, and the optimal transmission power value is currently used. It is determined whether or not the value is different (step B4).

  When the optimum transmission power value is different from the currently used transmission power value (step B4 / Yes), the power control unit 142 determines that the currently used transmission power value is calculated as described above. To a new transmission power value (step B5).

  When the power control unit 142 is changed to the optimum transmission power value, the power control unit 142 waits for a predetermined time (step B6), and the worst value specifying unit 141 obtains reception power values for all the client terminals 2-1 to 2-N. It is determined whether or not (step B7).

  When the transmission power value of the server device 1 is changed to the optimum transmission power value in step B5, the reception power value of the reception signal received by each of the client terminals 2-1 to 2-N is changed. For this reason, by waiting for a predetermined time in step B6, a new received power value after changing the transmission power value can be acquired from each of the client terminals 2-1 to 2-N.

  When the worst value specifying unit 141 acquires the received power values for all the client terminals 2-1 to 2-N (step B7 / Yes), the impedance calculating unit 1411 determines that each of the client terminals 2-1 to 2-N The impedance of the space between the server device 1 and each of the client terminals 2-1 to 2-N is calculated based on the received power value notified from the server and the transmission power value currently used by the server device 1. (Step B1).

  The impedance calculation unit 1411 of the server device 1 according to the present embodiment is configured so that the server device 1 and each of the client terminals 2-1 to 2 are based on the received power values of the received signals measured by the client terminals 2-1 to 2-N. Calculate the impedance of the space between -N. The reception error rate calculation unit 1412 calculates the reception error rate of each client terminal 2-1 to 2-N based on the impedance of each client terminal 2-1 to 2-N calculated by the impedance calculation unit 1411. The worst value identification unit 141 identifies the client terminal having the highest reception error rate among the reception error rates of the client terminals 2-1 to 2-N calculated by the reception error rate calculation unit 1412, and determines the worst reception error. Identify rates. The power control unit 142 changes the transmission power value used for the wireless transmission of the server device 1 so that the worst reception error rate specified by the worst value specifying unit 141 is equal to or less than a predetermined threshold.

  Thus, the server device 1 of the present embodiment communicates with each of the client terminals 2-1 to 2-N when wirelessly transmitting video data to each of the client terminals 2-1 to 2-N. In consideration, it is possible to prevent a reception error from occurring in each of the client terminals 2-1 to 2-N. As a result, it is possible to guarantee the video quality of the digital broadcast data that is played back or recorded by each of the client terminals 2-1 to 2-N.

<Operation / Effect of Communication System of this Embodiment>
As described above, the server device 1 according to the present embodiment identifies the client terminal having the highest reception error rate among the reception error rates of the client terminals 2-1 to 2-N, and receives the identified client terminal. The transmission power value used for the wireless transmission of the server device 1 is changed so that the error rate is equal to or less than a predetermined threshold. As a result, the server device 1 of the present embodiment, when performing wireless transmission of video data, considers communication with each of the client terminals 2-1 to 2-N while considering the communication with each of the client terminals 2-1 to 2-N. It is possible to prevent a reception error from occurring.

(Second Embodiment)
Next, a second embodiment will be described.

  In the first embodiment, the reception error rate of each client terminal 2-1 to 2-N is uniformly calculated based on the impedance of each client terminal 2-1 to 2-N calculated by the impedance calculation unit 1411. I made it.

  However, when the reception error rate of a specific client terminal that is playing and recording video data of a specific application (for example, high bit rate such as high-definition video) becomes high, the video data of the specific application is played and recorded. The degradation of video quality will be more noticeable than normal client terminals that are not. Also, in the wireless environment, the received power value of the client terminal fluctuates according to changes in the surrounding environment, so the reception error rate of a specific client terminal that is playing and recording video data of a specific application is It is necessary to provide a certain amount of margin for impedance fluctuations.

  For this reason, in the communication system according to the present embodiment, the reception error rate of the client terminal that wirelessly transmits the video data of the specific application is weighted, and the reception error rate is calculated to be high. This allows a specific client terminal that wirelessly transmits video data of a specific application to receive errors more than a normal client terminal that wirelessly transmits normal video data other than the video data of the specific application. In a state where the rate is high, the transmission power value used for the wireless transmission of the server device 1 can be changed so that the reception error rate becomes a predetermined threshold value or less. Hereinafter, the second embodiment will be described. Note that the communication system of the second embodiment is configured in the same manner as in the first embodiment, and only the processing operations performed by the client terminals 2-1 to 2-N and the server device 1 are different. In the embodiment, only a processing operation example will be described.

  There are three client terminals (C1, C2, C3). The client terminal (C3) wirelessly transmits video data of a specific application. For the client terminals (C1, C2), An example of power control when normal video data other than video data of a specific application is wirelessly transmitted is shown in FIG.

  In this case, for the client terminals (C1, C2), the reception error rate is calculated by using the normal relational expression; A used in the first embodiment, and for the client terminal (C3) The reception error rate is calculated using the following relational expression: B;

  Thereby, the reception error rate of the client terminal (C3) can be calculated as a reception error rate higher than the reception error rate when calculated using the normal relational expression A. As a result, the reception error rate of the client terminal (C3) can have a certain margin against the fluctuation of impedance.

  In the case of the state shown in FIG. 7A, the reception error rate of the client terminal (C1, C2) is equal to or less than a predetermined threshold value α, and therefore, between the server device 1 and the client terminal (C1, C2). It can be seen that the communication state is good. However, since the reception error rate of the client terminal (C3) is greater than a predetermined threshold; α, it can be seen that the communication state between the server device 1 and the client terminal (C3) is poor.

  For this reason, the power control unit 142 changes the transmission power value currently used in the server device 1 so that the reception error rate of the client terminal (C3) is equal to or less than a predetermined threshold; α. FIG. 7B shows the reception error rate of each client terminal (C1, C2, C3) when the transmission power value currently used in the server apparatus 1 is changed. As shown in FIG. 7 (b), the transmission power value of the server apparatus 1 is increased, the relational expression shown in FIG. 7 (a) is moved to the right, and the relational expression shown in FIG. 7 (b); By setting A ′ and B ′, the reception error rate of the client terminal (C3) can be set to a predetermined threshold; α or less. For this reason, the power control unit 142 increases the transmission power value currently used in the server device 1 so that the reception error rate of the client terminal (C3) is equal to or less than a predetermined threshold; α. Thereby, the reception error rate of each client terminal (C1, C2, C3) can be optimized.

<Example of processing operation of client terminals 2-1 to 2-N>
First, an example of processing operations of the client terminals 2-1 to 2-N will be described with reference to FIG.

  The client terminals 2-1 to 2-N according to the present embodiment receive the received power notification unit 242 when playing / recording video data of a specific application (for example, a high bit rate such as a high-definition video). When notifying the server device 1 of the power value, the server device 1 is notified of the operation state that the video data of the specific application is being reproduced / recorded (steps A′3 and A′6). In FIG. 8, when the reception power notification unit 242 notifies the server device 1 of the reception power value, the server device 1 is notified of the operation state that the video data of the specific application is being reproduced / recorded. I made it. However, it is also possible to construct the server apparatus 1 so as to notify the received power value and the operating state separately.

<Processing example of server device 1>
Next, a processing operation example of the server apparatus 1 will be described with reference to FIG.

  The worst value specifying unit 141 determines whether or not the received power of the client terminal 2 has been updated based on the received power value notified from the client terminal 2 (step B0). When the worst value specifying unit 141 determines that the received power has been updated (step B0 / Yes), the impedance calculating unit 1411 receives the received power value notified from each of the client terminals 2-1 to 2-N and the server Based on the transmission power value currently used by the device 1, the impedance of the space between the server device 1 and each of the client terminals 2-1 to 2-N is calculated (step B1).

  Next, the reception error rate calculation unit 1412 calculates the reception error rate of each client terminal 2-1 to 2-N based on the impedance of each client terminal 2-1 to 2-N calculated by the impedance calculation unit 1411. To do.

  When the reception error rate calculation unit 1412 of the present embodiment calculates the reception error rate of each of the client terminals 2-1 to 2-N, with respect to the reception error rate of the specific client terminal that has accepted the operation state, Weighting is performed so that the reception error rate is increased.

  For example, it is assumed that the reception error rate calculation unit 1412 grasps in advance a relational expression (for example, the relational expression A shown in FIG. 7A) that associates the impedance with the reception error rate. Further, it is assumed that the reception error rate calculation unit 1412 has previously grasped a relational expression shown in FIG. 7A; a relational expression obtained by applying a predetermined weight to A; B. In this case, the reception error rate calculation unit 1412 calculates the reception error rate of a normal client terminal that has not received an operation state using the relational expression; A shown in FIG. The reception error rate of the client terminal is calculated using the relational expression B shown in FIG.

  The worst value specifying unit 141 specifies the client terminal with the highest reception error rate based on the reception error rate of each of the client terminals 2-1 to 2-N calculated by the reception error rate calculation unit 1412. As a result, the worst value specifying unit 141 receives the worst reception error rate among the reception error rates of the client terminals 2-1 to 2-N (reception error rates of the client terminals C1, C2, and C3 in FIG. 7A). The error rate (the reception error rate of the client terminal C3 in FIG. 7A) can be specified (step B′2).

  Next, the power control unit 142 calculates an optimum transmission power value that can improve the worst reception error rate specified by the worst value specifying unit 141 (step B′3).

  Specifically, the power control unit 142 causes the worst reception error rate specified in the worst value specification unit 141 (in FIG. 7A, the reception error rate of the client terminal C3) to be equal to or less than a predetermined threshold value α. A transmission power value (for example, the relational expression shown in FIG. 7B; transmission power values for obtaining A ′ and B ′) is calculated.

  Note that the processing operations in Step B4 to Step B7 are substantially the same as those in the first embodiment, and thus specific processing operations are omitted.

<Operation / Effect of Communication System of this Embodiment>
As described above, the server device 1 according to the present embodiment weights the reception error rate of the client terminal that wirelessly transmits the video data of the specific application, and calculates the reception error rate to be high. . This allows a specific client terminal that wirelessly transmits video data of a specific application to receive errors more than a normal client terminal that wirelessly transmits normal video data other than the video data of the specific application. In a state where the rate is high, the transmission power value used for the wireless transmission of the server device 1 can be changed so that the reception error rate becomes a predetermined threshold value or less.

  In the above embodiment, the reception error rate calculation unit 1412 uses the relational expression A shown in FIG. 7A as the reception error rate of a normal client terminal that does not wirelessly transmit video data of a specific application. The reception error rate of a specific client terminal that wirelessly transmits video data of a specific application is calculated using the relational expression B shown in FIG. However, the present embodiment is not limited to two relational expressions; A and B, but a plurality of relations with different weights according to the video data type and video data bit rate of a specific application. It is also possible to use a formula to calculate the reception error rate of each client terminal. For example, the reception error rate of each client terminal using a plurality of relational expressions with different weights according to the types of stream video data such as high-definition video, normal stream video data, and stream video data by normal Internet access. Can also be calculated.

  As a result, the reception error rate of the client terminal that wirelessly transmits the video data of the specific application is weighted according to the video data of the specific application and is calculated so as to increase the reception error rate. be able to.

(Third embodiment)
Next, a third embodiment will be described.

  In the second embodiment, when each client terminal 2-1 to 2-N reproduces and records video data of a specific application (for example, a high bit rate such as a high-definition video), the specific application The server device 1 is notified of the operation status indicating that the video data is being played back / recorded, and the server device 1 is configured for the reception error rate of the client terminal that wirelessly transmits the video data of the specific application. We decided to perform weighting according to the video data of a specific application so that the reception error rate would be high.

  In the third embodiment, the reception error rate of each client terminal 2-1 to 2-N depends on the number of packets transmitted and received between the server device 1 and each client terminal 2-1 to 2-N. The reception error rates of the client terminals 2-1 to 2-N are calculated so that the reception error rate increases as the number of packets increases. As a result, each client terminal 2-1 to 2-N has a higher reception error rate as the number of packets transmitted and received between the server device 1 and each client terminal 2-1 to 2-N increases. A reception error rate can be calculated. Hereinafter, a third embodiment will be described.

  In the communication system of the present embodiment, the number of packets transmitted / received between the server device 1 and each of the client terminals 2-1 to 2-N; n ′ is measured for each client terminal 2-1 to 2-N. . The reception error rate of each client terminal 2-1 to 2-N is weighted according to the number of packets of each client terminal; n ′, and the reception error rate increases as the number of packets; n ′ increases. Next, the reception error rate of each of the client terminals 2-1 to 2-N is calculated.

  FIG. 9 shows an example of weighting values according to the number of packets transmitted and received between the server apparatus 1 and each of the client terminals 2-1 to 2-N; n ′. As shown in FIG. 9, when the number of packets; n ′ is in the range from 0 to n, the weighting value is set to 1 and the reception error rate of each client terminal 2-1 to 2-N is used as it is. . Further, when n ′ is larger than n, the weighting value is F (n ′ / n), and the number of packets with respect to the reception error rate of each of the client terminals 2-1 to 2-N; The reception error rate of each client terminal 2-1 to 2-N is calculated so that the reception error rate increases as the number of packets; n ′ increases.

  Note that if the server device 1 can grasp the number of packets transmitted and received between the server device 1 and each of the client terminals 2-1 to 2-N; For example, measurement may be performed on the server device 1 side, and measurement may be performed on the client terminal 2-1 to 2-N side, and the measured number of packets; n ′ may be notified to the server device 1. It is also possible to configure.

  However, it is preferable that the server apparatus 1 is constructed so as to measure the number of packets; n ′. This is because it is not necessary to notify the server device 1 of the number of packets; n from the client terminals 2-1 to 2-N, so that the load on the network can be reduced or the processing operations at the client terminals 2-1 to 2-N This is because the amount can be reduced.

<Example of processing operation of client terminals 2-1 to 2-N>
First, an example of processing operations of the client terminals 2-1 to 2-N will be described with reference to FIGS.

  The client terminals 2-1 to 2-N of the present embodiment perform the same processing as that of the first embodiment shown in FIG. 6 when measuring the number of packets; n ′ on the server device 1 side.

  Further, when measuring the number of packets n ′ on the client terminals 2-1 to 2-N side, the same processing as that of the second embodiment shown in FIG. 8 is performed. In this case, the client terminals 2-1 to 2-N notify the server apparatus 1 of the number of packets measured on the client terminals 2-1 to 2-N side; n ′ as an operating state (step A′3 , A'6).

<Processing example of server device 1>
Next, a processing operation example of the server apparatus 1 will be described with reference to FIG.

  The worst value specifying unit 141 determines whether or not the received power of the client terminal 2 has been updated based on the received power value notified from the client terminal 2 (step B0). When the worst value specifying unit 141 determines that the received power has been updated (step B0 / Yes), the impedance calculating unit 1411 receives the received power value notified from each of the client terminals 2-1 to 2-N and the server Based on the transmission power value currently used by the device 1, the impedance of the space between the server device 1 and each of the client terminals 2-1 to 2-N is calculated (step B1).

  Next, the reception error rate calculation unit 1412 calculates the reception error rate of each client terminal 2-1 to 2-N based on the impedance of each client terminal 2-1 to 2-N calculated by the impedance calculation unit 1411. To do.

  The reception error rate calculation unit 1412 of the present embodiment calculates the reception error rate of each client terminal 2-1 to 2-N based on the impedance of each client terminal 2-1 to 2-N calculated by the impedance calculation unit 1411. When calculating, the number of packets transmitted and received between the server apparatus 1 and each of the client terminals 2-1 to 2-N is weighted according to n ′, and the reception error rate increases as the number of packets; n ′ increases. So that the reception error rate of each of the client terminals 2-1 to 2-N is calculated.

  For example, the reception error rate calculation unit 1412 grasps in advance a relational expression (for example, the relational expression shown in FIG. 10A; A) in which an impedance is associated with a reception error rate.

  The reception error rate calculation unit 1412 calculates the reception error rate according to the impedance of each of the client terminals 2-1 to 2-N calculated by the impedance calculation unit 1411 based on the relational expression A. In this case, as shown in FIG. 9, the client terminal in the range of the number of packets; n ′ ranging from 0 to n sets the weighting value to 1, and uses the relational expression; A shown in FIG. Calculate the rate. Further, as shown in FIG. 9, the client terminal having the number of packets n ′ greater than n sets the weighting value to F (n ′ / n), and the relational expression shown in FIG. A reception error rate is calculated using a relational expression with weights F (n ′ / n) corresponding to the numbers n ′ and B and C.

  In the case of FIG. 10, the client terminal (C1) calculates the reception error rate using the relational expression; A because the number of packets; n ′ ranges from 0 to n. Further, since the client terminal (C2) has the number of packets; n ′ is larger than n, the relational expression; the relational expression obtained by applying weighting F (n ′ / n) corresponding to the number of packets; Is used to calculate the reception error rate. Further, since the client terminal (C3) has the number of packets; n ′ is larger than n, the relational expression; the relational expression obtained by applying a weight F (n ′ / n) corresponding to the number of packets; Is used to calculate the reception error rate. Thereby, the reception error rate can be calculated so that the reception error rate increases as the number of packets; n ′ increases.

  The worst value specifying unit 141 specifies the client terminal with the highest reception error rate based on the reception error rate of each of the client terminals 2-1 to 2-N calculated by the reception error rate calculation unit 1412. Thereby, the worst value specifying unit 141 receives the worst reception among the reception error rates of the client terminals 2-1 to 2-N (reception error rates of the client terminals C1, C2, and C3 in FIG. 10A). The error rate (in FIG. 10A, the reception error rate of the client terminal C3) can be specified (step B′2).

  Next, the power control unit 142 calculates an optimum transmission power value that can improve the worst reception error rate specified by the worst value specifying unit 141 (step B′3).

  Specifically, the power control unit 142 causes the worst reception error rate specified by the worst value specification unit 141 (in FIG. 10A, the reception error rate of the client terminal C3) to be equal to or less than a predetermined threshold value α. A transmission power value (for example, a relational expression shown in FIG. 10B; transmission power values for obtaining A ′, B ′, and C ′) is calculated.

  Note that the processing operations in Step B4 to Step B7 are substantially the same as those in the first embodiment, and thus specific processing operations are omitted.

<Operation / Effect of Communication System of this Embodiment>
As described above, the server device 1 according to the present embodiment, between the server device 1 and each of the client terminals 2-1 to 2-N, with respect to the reception error rate of each of the client terminals 2-1 to 2-N, The number of packets to be transmitted / received is weighted according to n ′, and the reception error rate of each client terminal 2-1 to 2-N is calculated so that the reception error rate increases as the number of packets; n ′ increases. Thus, based on the reception error rate calculated by weighting according to n ′, the number of packets transmitted and received between the server device 1 and each of the client terminals 2-1 to 2-N, the reception error rate Can be changed so that the transmission power value used for the wireless transmission of the server device 1 is less than or equal to a predetermined threshold.

(Fourth embodiment)
Next, a fourth embodiment will be described.

  In the first to third embodiments described above, the transmission power value used for the wireless transmission of the server device 1 is set so that the reception error rates of all the client terminals 2-1 to 2-N are equal to or less than a predetermined threshold. I decided to change it. However, there is a case where the transmission power value used for the wireless transmission of the server device 1 cannot be changed so that the reception error rates of all the client terminals 2-1 to 2-N are below a predetermined threshold value.

  An example of this is shown in FIG. FIG. 11 shows a case where the difference in impedance between the client terminals (C1, C4) is too large. In this case, even if the transmission power value used for the wireless transmission of the server apparatus 1 is changed and the relational expression shown in FIG. 11 (a); A is shifted left and right, all client terminals (C1, C2, C3, C4 ) Cannot be set to a predetermined threshold; α or less.

  For this reason, in this embodiment, the client terminal (C4) having the worst reception error rate is excluded from the control target so that the reception error rates of the remaining client terminals (C1, C2, C3) are equal to or lower than a predetermined threshold. Then, the transmission power value used for the wireless transmission of the server device 1 is changed. Thereby, it is possible to prevent a reception error from occurring in the remaining client terminals (C1, C2, C3). Hereinafter, the communication system of the present embodiment will be described with reference to FIG.

<Example of processing operation of client terminals 2-1 to 2-N>
First, an example of processing operations of the client terminals 2-1 to 2-N will be described with reference to FIG.

  The client terminals 2-1 to 2-N of the present embodiment perform the same processing as that of the first embodiment shown in FIG.

<Processing example of server device 1>
Next, a processing operation example of the server device 1 will be described with reference to FIG.

  The worst value specifying unit 141 determines whether or not the received power of the client terminal 2 has been updated based on the received power value notified from the client terminal 2 (step B0).

  When the worst value specifying unit 141 determines that the received power has been updated (step B0 / Yes), the impedance calculating unit 1411 receives the received power value notified from each of the client terminals 2-1 to 2-N and the server Based on the transmission power value currently used by the device 1, the impedance of the space between the server device 1 and each of the client terminals 2-1 to 2-N is calculated (step B1).

  Next, the reception error rate calculation unit 1412 calculates the reception error rate of each client terminal 2-1 to 2-N based on the impedance of each client terminal 2-1 to 2-N calculated by the impedance calculation unit 1411. To do. The reception error rate calculation unit 1412 grasps in advance a relational expression (for example, the relational expression shown in FIG. 11A; A) in which the impedance and the reception error rate are associated with each other. Based on this, the reception error rate corresponding to the impedance of each of the client terminals 2-1 to 2-N calculated by the impedance calculation unit 1411 is calculated. Thereby, the reception error rate calculation unit 1412 plots the impedance of each of the client terminals 2-1 to 2-N (in FIG. 11A, the client terminals C1, C2, C3, and C4) on the relational expression A. The reception error rate obtained at this time can be calculated.

  The worst value specifying unit 141 specifies the client terminal with the highest reception error rate based on the reception error rate of each of the client terminals 2-1 to 2-N calculated by the reception error rate calculation unit 1412. As a result, the worst value specifying unit 141 has the worst reception error rate of each of the client terminals 2-1 to 2-N (in FIG. 11A, the reception error rates of the client terminals C1, C2, C3, and C4). A specific reception error rate (in FIG. 11A, the reception error rate of the client terminal C4) can be specified (step B2).

  Next, the power control unit 142 calculates an optimum transmission power value that can improve the worst reception error rate specified by the worst value specifying unit 141 (step B3).

  Specifically, the power control unit 142 causes the worst reception error rate specified by the worst value specifying unit 141 (in FIG. 11A, the reception error rate of the client terminal C4) to be equal to or less than a predetermined threshold value α. A correct transmission power value is calculated.

  Next, the power control unit 142 compares the calculated optimal transmission power value with the transmission power value currently used by the server device 1, and the optimal transmission power value is currently used. It is determined whether or not the value is different (step B4).

  When the optimum transmission power value is different from the currently used transmission power value (step B4 / Yes), the power control unit 142 changes the currently used transmission power value to the calculated optimum transmission power value. In this case, it is determined whether or not all the client terminals 2-1 to 2-N (in FIG. 11A, the client terminals C1, C2, C3, and C4) can be included in the viewable range (step C1). .

  When the power control unit 142 determines that all the client terminals 2-1 to 2-N (in FIG. 11A, the client terminals C1, C2, C3, and C4) are not within the viewable range (Step S1). C1 / No), the client terminal having the worst reception error rate specified by the worst value specifying unit 141 (in FIG. 11A, the client terminal C4) is excluded from the control target (step C4). Then, the worst value specifying unit 141 again receives the reception error rate of each of the client terminals 2-1 to 2-N (in FIG. 11A, client terminals C1, C2, and C3) calculated by the reception error rate calculation unit 1412. Based on the above, the client terminal with the highest reception error rate is identified. Thereby, the worst value specifying unit 141 receives the worst reception among the reception error rates of the client terminals 2-1 to 2-N (reception error rates of the client terminals C1, C2, and C3 in FIG. 11A). The error rate (the reception error rate of the client terminal C1 in FIG. 11A) can be specified (step B2).

  Next, the power control unit 142 calculates an optimum transmission power value that can improve the worst reception error rate specified by the worst value specifying unit 141 (step B3).

  Specifically, in the power control unit 142, the worst reception error rate specified again by the worst value specifying unit 141 (in FIG. 11A, the reception error rate of the client terminal C1) is a predetermined threshold; α or less. Such a transmission power value is calculated.

  Next, the power control unit 142 compares the calculated optimal transmission power value with the transmission power value currently used by the server device 1, and the optimal transmission power value is currently used. It is determined whether or not the value is different (step B4).

  When the optimum transmission power value is different from the currently used transmission power value (step B4 / Yes), the power control unit 142 changes the currently used transmission power value to the calculated optimum transmission power value. In this case, it is determined whether or not all client terminals 2-1 to 2-N (in FIG. 11A, client terminals C1, C2, and C3) can be included in the viewable range (step C1).

  If the power control unit 142 determines that all the client terminals 2-1 to 2-N (in FIG. 11A, the client terminals C1, C2, and C3) are within the viewable range (step C1 / Yes) ), The currently used transmission power value is changed to the optimum transmission power value calculated above (step B5).

  When the power control unit 142 is changed to the optimum transmission power value, the power control unit 142 waits for a predetermined time (step B6), and the worst value specifying unit 141 selects all the client terminals 2-1 to 2-N (in FIG. 11A). Then, it is determined whether or not the received power values for the client terminals C1, C2, C3) have been acquired (step B7).

  When the worst value specifying unit 141 acquires the received power values of all client terminals 2-1 to 2-N (in FIG. 11A, client terminals C1, C2, and C3) (step B7 / Yes), Based on the received power value notified from each of the client terminals 2-1 to 2-N and the transmission power value currently used by the server apparatus 1, the impedance calculating unit 1411 The impedance of the space between 2-1 and 2-N is calculated (step B1).

<Operation / Effect of Communication System of this Embodiment>
As described above, the power control unit 142 of the server device 1 according to the present embodiment changes all the client terminals (in FIG. 11A, the client terminal) when the transmission power value used during the wireless transmission of the server device 1 is changed. When the reception error rate of C1, C2, C3, C4) does not fall below the predetermined threshold, the client terminal specified by the worst value specifying unit 141 (client terminal C4 in FIG. 11A) is excluded. Then, the worst value specifying unit 141 removes the client terminals (client terminal C4 in FIG. 11A) excluded by the power control unit 142 (in FIG. 11A, client terminals C1, C2). , C3), another client terminal having the highest reception error rate (in FIG. 11A, client terminal C1) is identified. Then, the power control unit 142 performs wireless transmission of the server device 1 so that the reception error rate of the client terminal (the client terminal C1 in FIG. 11A) specified by the worst value specifying unit 141 is equal to or less than a predetermined threshold. Change the transmission power value used for.

  As a result, the server apparatus 1 of the present embodiment is configured so that the reception error rate of all client terminals (client terminals C1, C2, C3, and C4 in FIG. 11A) is equal to or less than a predetermined threshold. Even if the transmission power value used for 1 wireless transmission cannot be changed, the client terminal having the worst reception error rate (client terminal C4 in FIG. 11A) is excluded from the control target, and the remaining client terminals (In FIG. 11A, it is possible to prevent a reception error from occurring in the client terminals C1, C2, and C3).

  The above-described embodiment is a preferred embodiment of the present invention, and the scope of the present invention is not limited to the above-described embodiment alone, and various modifications are made without departing from the gist of the present invention. Implementation is possible.

  For example, in the communication system described above, as shown in FIG. 1, it is assumed that the server device 1 wirelessly transmits digital broadcast data received from the broadcast antenna 3 or the like to the client terminals 2-1 to 2-N. However, the server device 1 is constructed so that the digital broadcast data (including EPG) is managed by the server device 1 and the digital broadcast data managed by the server device 1 is wirelessly transmitted to the client terminals 2-1 to 2-N. It is also possible to do.

  In the communication system described above, the server apparatus 1 identifies the client terminal having the highest reception error rate among the reception error rates of the client terminals 2-1 to 2-N, and receives the identified client terminal. The transmission power value used for the wireless transmission of the server device 1 is changed so that the error rate is equal to or less than a predetermined threshold. However, even when the reception error rate of the identified client terminal is equal to or less than a predetermined threshold, it is possible to sequentially change the transmission power value used for the wireless transmission of the server device 1. Thereby, even if the reception error rate of all the client terminals 2-1 to 2-N is equal to or less than a predetermined threshold, the transmission power value used for the wireless transmission of the server device 1 can be changed as needed.

  Further, the above-described communication system is based on the assumption that the client terminals 2-1 to 2-N and the server device 1 are installed in the home and perform private wireless transmission. However, it is also possible to install the server device 1 in an environment for the general public, not limited to the home, and construct public wireless transmission with an unspecified number of client terminals 2-1 to 2-N. .

  In addition, the control operation in each device configuring the communication system in the present embodiment described above can be executed using hardware, software, or a composite configuration of both.

  In the case of executing processing using software, it is possible to install and execute a program in which a processing sequence is recorded in a memory in a computer incorporated in dedicated hardware. Alternatively, the program can be installed and executed on a general-purpose computer capable of executing various processes.

  For example, the program can be recorded in advance on a hard disk or ROM (Read Only Memory) as a recording medium. Alternatively, the program can be stored (recorded) temporarily or permanently in a removable recording medium. Such a removable recording medium can be provided as so-called package software. Removable recording media include floppy (registered trademark) disks, CD-ROM (Compact Disc Read Only Memory), MO (Magneto optical) disks, DVDs (Digital Versatile Discs), Blu-ray disks, magnetic disks, and semiconductor memories. Can be mentioned.

  The program is installed on the computer from the removable recording medium as described above. In addition, it is wirelessly transferred from the download site to the computer. In addition, it is transferred to a computer via a network by wire.

  In addition, the communication system in the present embodiment is not only executed in time series according to the processing operation described in the above embodiment, but also the processing capability of the apparatus that executes the processing, or in parallel or individually as required. It is also possible to build to run on

DESCRIPTION OF SYMBOLS 1 Server apparatus 11 Wireless communication part 12 Storage part 13 Image | video production | generation part 14 Transmission power control part 141 Worst value identification part 1411 Impedance calculation part 1412 Reception error rate calculation part 142 Power control part 2-1 to 2-N Client terminal 21 Wireless communication Unit 22 storage unit 23 video reproduction unit 24 reception power monitoring unit 241 reception power measurement unit 243 reception power notification unit 3 broadcast antenna

Claims (7)

A server device that wirelessly transmits video data to a plurality of client terminals,
A means for identifying a client terminal having the highest reception error rate among the reception error rates of each client terminal,
Control means for changing a transmission power value used for the wireless transmission of the server device so that a reception error rate of the client terminal specified by the specifying means is a predetermined threshold value or less;
The server apparatus characterized by having. The control means includes
When the transmission power value is changed, if the reception error rate of all client terminals does not become a predetermined threshold or less, exclude the client terminal specified by the specifying means,
The specifying means is:
2. The server apparatus according to claim 1, wherein another client terminal having the highest reception error rate is specified among the reception error rates of the remaining client terminals excluding the client terminal excluded by the control means. The specifying means is:
First calculation means for calculating the impedance of the space between the server device and each client terminal based on the received power value of the received signal measured at each client terminal;
Second calculation means for calculating a reception error rate of each client terminal based on the impedance of each client terminal calculated by the first calculation means;
3. The server device according to claim 1, wherein the client terminal having the highest reception error rate among the reception error rates of the client terminals calculated by the second calculation unit is specified. The second calculation means includes:
The reception error rate of a client terminal that wirelessly transmits video data of a specific application is weighted according to the video data of the specific application, and is calculated so as to increase the reception error rate. The server device according to claim 3. The second calculation means includes:
The reception error rate of each client terminal is weighted according to the number of packets transmitted / received between the server device and each client terminal, so that the reception error rate increases as the number of packets increases. 4. The server device according to claim 3, wherein a reception error rate of the client terminal is calculated. A communication system having a server device and a plurality of client terminals, and wirelessly transmitting video data from the server device to the plurality of client terminals,
The server device
A means for identifying a client terminal having the highest reception error rate among the reception error rates of each client terminal,
Control means for changing a transmission power value used for the wireless transmission of the server device so that a reception error rate of the client terminal specified by the specifying means is a predetermined threshold value or less;
A communication system comprising: A control method performed by a server device that wirelessly transmits video data to a plurality of client terminals,
A specific step of identifying a client terminal having the highest reception error rate among the reception error rates of each client terminal,
A control step of changing a transmission power value used for the wireless transmission of the server device so that a reception error rate of the client terminal specified in the specifying step is equal to or less than a predetermined threshold;
A control method characterized by comprising:

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