JP2006129277A - Communications device, communication method, communication program, recording medium storing the communication program and communications system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communications device requiring no feedback from the receiving station side and being capable of conducting a data type change control, such as translation control having fast reaction rate to the change in communication environment, an error-resistance control or the like on the transmission station side, when a stream data, in real time, is transmitted in various communication statuses and a communication setting. <P>SOLUTION: The communication device 1 has a encoding-rate control unit 102 controlling an encoding rate in an encoding-rate changer 103 changing the encoding rate of the stream data to be transmitted. The communications device 1 further has an error-resistance control unit 106 for controlling an error resistance in an error-resistance adder adding the error resistance to a packet, and a communication-channel status measuring section measuring the communication status of the communications medium. The encoding-rate control unit and the error-resistance control unit 106 conduct controls on the basis of the measured communication status on the basis of a transmission, confirming packet in the communication-channel status measuring section. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a communication apparatus, a communication method, a communication program, a recording medium storing a communication program, and a communication system that transmit stream data or the like via a communication path in which the communication status of a transmission path such as wireless communication varies greatly It is about.

  In recent years, with the development of communication technology, the complexity of wiring at the time of LAN (Local Area Network) construction has been eliminated, communication connection between AV sources such as tuners arranged at a distance and AV playback devices such as displays, etc. As a purpose, a wireless communication system using wireless communication is used.

  In addition, as one of means for connecting to the Internet, use of a power line communication system using an existing power line has been proposed and is expected as a next generation communication system.

  However, the wireless communication system has a problem that the longer the transmission distance in wireless communication, the more susceptible to multipath fading. In addition, the power line communication system has a problem that it is easily affected by noise from home appliances used in the home. These problems cause image disturbance due to deterioration of the communication environment when transmitting stream data that requires real-time characteristics such as video. Therefore, a situation occurs in which the user cannot enjoy viewing the stream data comfortably. In order to solve such a problem, in the wireless communication system and the power line communication system as described above, it is necessary to perform control in which QoS (Quality of Service) indicated by transmission error rate and jitter (delay information) is ensured. Become.

  One method for suppressing image disturbance is a method called translation. The transrate means that when the communication status deteriorates, the encoded stream data is transmitted with a higher compression rate (lower encoding speed), and when the communication status becomes better, the compression rate. This is a method of adjusting the amount of packets that are actually transmitted by lowering (increase the encoding speed). Here, the case where the communication environment deteriorates indicates a state where the effective bandwidth of the transmission path is reduced. That is, when the communication environment deteriorates, it is possible to reduce image disturbance by reducing the amount of packets to be transmitted as described above.

  As a known technique using this translation, for example, Patent Document 1 described later discloses the following communication control method. This communication control method uses RTP (Real-time Transport protocol) and RTCP (RTP Control Protocol). Then, information on jitter and packet loss rate measured at the receiving station is transmitted to the transmitting station, and the transmitting station estimates the transmission path state and adjusts the bit rate of the data to be transmitted.

  As another communication control method, for example, Patent Document 2 described later discloses the following method. First, the receiving station measures the reception level to calculate the required value of the transmission rate, performs the operation for n samples, and calculates the average value. Then, the receiving station issues a content rate change instruction to the transmitting station in consideration of past results. The transmitting station changes the content rate according to the change instruction from the receiving station.

  Patent Document 1 and Patent Document 2 disclose a technique that can suppress image disturbance even when the effective bandwidth of a transmission path is reduced by adjusting the rate of stream data. On the other hand, as another method for suppressing image disturbance, there is a method for controlling to ensure a stable transmission path, or a method for controlling to increase the effective band that has been reduced due to deterioration of the transmission path condition. .

  For example, in the field of wireless LAN, a standard (hereinafter referred to as 802.11e) formulated by IEEE 802.11 TGe (Task Group E) has been proposed as a standard considering QoS (see Non-Patent Document 1). .

  In 802.11e, communication control by distributed control type EDCA (Enhanced Distributed Channel Access) and communication control by central control type HCCA (Hybrid Coordinator Function Control Access) are performed. EDCA is communication control that enables each communication station to access a communication channel stochastically (best effort). On the other hand, HCCA is communication control that enables each communication station to access a communication channel under the direction of HC (Hybrid Coordinator). When stream data is transmitted, it is preferable that a bandwidth is secured by communication control by HCCA. In this way, when the band is managed by the HC, it is ensured that a certain communication band is allocated to the transmitting station in a predetermined period, so that stable transmission is possible.

  However, even when the bandwidth is secured by HCCA, when wireless communication is performed, problems such as hidden terminals that occur when the distance between communication stations exceeds the communicable range, communication distance limitations, etc. Depending on the case, errors may occur frequently. In such a case, it may be possible to reduce transmission errors by changing the error tolerance in data transmission to a stronger one, thereby increasing the effective bandwidth.

  Means for changing error resilience include a method of applying an error correction code (FEC) such as a Read Solomon code or a turbo code to transmission data, and a type of transmission rate (hereinafter referred to as a PHY rate) in the physical layer. There is a way to change. The PHY rate is determined by a combination of a modulation scheme such as BPSK, QPSK, and QAM and a coding rate of the convolutional code.

  However, there is usually a trade-off between increasing error resilience and increasing communication bandwidth. That is, if the error tolerance is increased when the communication state is good, the communication band is reduced.

Furthermore, recently, a communication system that transmits and receives stream data using a mobile phone or a PDA has been proposed. Since mobile phones and PDAs are battery-driven, low power consumption is required. That is, in communication control, there is a need to perform control in consideration of power consumption in addition to the above-described technology related to high-quality transmission. On the other hand, for example, Patent Document 3 described later proposes a technique for reducing power consumption by adjusting the stream data rate and shortening the communication time.
JP 2002-204278 A (publication date July 19, 2002) JP 2004-153610 A (publication date May 27, 2004) JP 2000-69556 A (publication date March 3, 2000) IEEE STD 802.11e Draft 8.0 February 2004

  According to the methods disclosed in Patent Document 1 and Patent Document 2, the receiving station estimates the band state using the jitter and packet loss rate information, or the reception level, and feeds back the information to the transmitting station. High-quality video transmission can be performed by the transmission station translating. However, since the receiving station measures the communication state and feeds back the information to the transmitting station, the state of the communication path suddenly changes due to changes in the environment such as passage of a shield such as a person or device through the communication path. If it is changed, the follow-up of the translation rate may be delayed.

  Further, it is not easy for the transmitting station to estimate the band state based on the jitter and packet loss rate measured by the receiving station or the reception level. More specifically, when the communication state deteriorates and the encoding speed of the real-time data is lowered, the tracking of the translation can be performed relatively quickly. However, when the communication state is recovered and the encoding speed is increased, the stream data rate is kept low, and the throughput does not increase immediately. In this case, a method of increasing the rate little by little with reference to a table or the like is usually performed. However, such a method has a problem that the follow-up of the translation rate becomes slow.

  Furthermore, the receiving station requires a mechanism for measuring the communication path condition and a mechanism for feeding back the communication path condition to the transmitting station, which complicates the circuit configuration of the receiving station and causes an increase in cost. There is a problem.

  On the other hand, as a technique for ensuring a stable communication band, it is effective to secure a communication band by communication control by HCCA disclosed in Non-Patent Document 1. In addition, when errors occur frequently due to problems with hidden terminals or restrictions on communication distance, the communication control by HCCA should be performed more strictly, or the error tolerance in data transmission should be changed to a stronger one. As a result, the effective bandwidth can be increased. However, in the current technology, as disclosed in Patent Document 1 and Patent Document 2, a method for controlling error resilience is that a receiving station measures jitter and a packet loss rate, or a reception level, and the information is transmitted to the transmitting station. In general, a method of controlling error resilience by feeding back to the network is performed. Therefore, as in the case of translation, it is not easy to estimate how weak the error resilience can be changed when the communication environment is improved.

  At present, there are few communication devices that perform transmission while securing a band by communication control by HCCA, and there are overwhelmingly more communication devices that perform best-effort communication. Therefore, it is necessary to perform control in consideration not only when the bandwidth is secured by communication control by HCCA but also when performing best-effort communication such as EDCA.

  Furthermore, as a technique for reducing power consumption, as disclosed in Patent Document 3, in the low power consumption mode, the transmission time is shortened by performing a translation that sets the real-time data rate low. In addition, low power consumption can be achieved. However, in the technique disclosed in Patent Document 3, the real-time data rate is considered, but the transmission rate and transmission power in the physical layer are not considered at all.

  The present invention has been made in view of the above problems, and its purpose is to require feedback from the receiving station side when transmitting stream data with real-time characteristics in various communication conditions and communication settings. In addition, a communication device, a communication method, a communication program, and a communication program that can perform data format change control such as translation control and error resilience control with a fast response speed to changes in the communication environment on the transmitting station side. To provide a recorded recording medium and a communication system.

  A communication device according to the present invention is a communication device that transmits stream data, which requires real-time transmission, to an external communication device via a communication medium by packet communication in order to solve the above problem. A data format changing unit that changes the stream data to a data format suitable for transmission on the communication medium, a data format management unit that controls a data format set in the data format changing unit, and a communication status in the communication medium A communication path status measurement unit that measures the data based on a delivery confirmation packet sent from the external communication device, the data format management unit based on the communication status measured by the communication path status measurement unit Thus, the data format is controlled.

  The communication method according to the present invention is a communication method for transmitting stream data that requires real-time transmission to an external communication device via a communication medium by packet communication in order to solve the above-described problem. A data format changing step for changing the stream data to a data format suitable for transmission on the communication medium, a data format managing step for controlling the data format set in the data format changing step, and A communication path status measurement step for measuring a communication status based on a delivery confirmation packet sent from the external communication device, and the communication status measured by the communication path status measurement unit in the data format management step The data format is controlled based on the above.

  In the above configuration and method, first, the data format for the stream data to be transmitted can be changed. Examples of this data format include, but will not be limited to, the encoding rate of stream data and the error tolerance given to transmitted packets, as will be described later. This data format is changed based on the communication status measured based on the delivery confirmation packet sent from the external communication device on the receiving side. Here, the delivery confirmation packet indicates a packet indicating whether or not the transmitted packet has been properly received by the external communication apparatus on the receiving side. That is, by looking at the status of the delivery confirmation packet, it is possible to recognize the number of packets that have failed to be delivered on the receiving side and the number of packets that have been successfully delivered, and can be used as an indicator of the communication status.

  Conventionally, as described above, the transmission device receives information on the communication state measured on the reception device side from the reception device, and changes the coding rate based on this information. In this case, when the communication status is deteriorated, it is possible that reception of the information on the communication status sent from the receiving device itself may fail, thereby delaying the timing of changing the coding speed. was there. In addition, it has become necessary to provide the receiving device with means for measuring the communication state and transmitting information regarding the communication state to the transmission device.

  On the other hand, according to the above configuration and method, the data format of the stream data is changed based on the communication status measured based on the delivery confirmation packet sent from the external communication device on the receiving side. It has become so. Therefore, the communication state is measured without delay in the communication device on the transmission side, and the data format is changed based on this measurement, so that it is possible to control the change of the data format that quickly follows the change in the communication state. Become. In addition, it is possible to eliminate the need for a special configuration in the external communication device on the receiving side.

  Further, in the communication device according to the present invention, in the above configuration, the data format management unit calculates a predicted throughput as a predicted value of a data transfer rate at which data transfer is substantially performed, and the predicted throughput and the above The data format may be controlled based on the communication status.

  According to the above configuration, the predicted throughput is calculated, and the data format is controlled based on the predicted throughput and the communication status. In other words, since the actual speed of data transfer is predicted and the data format is controlled based on this prediction, data with a fast response speed not only when the communication status deteriorates but also when the communication status improves It is possible to perform format change control.

  The predicted throughput may be, for example, the predicted maximum throughput as the maximum value of the predicted value of the actual data transfer speed, but is not particularly limited to this, and the actual data transfer speed is not limited to this. Any value may be used as long as it is an index of the predicted value.

  Further, in the communication device according to the present invention, in the above configuration, the data format changing unit is an encoding rate changing unit that sets an encoding rate of the stream data, and the data format managing unit is the encoding unit. A coding rate management unit for controlling a coding rate set in the rate changing unit, wherein the coding rate management unit determines the coding rate based on a communication situation measured by the channel state measurement unit. It is good also as a structure to control.

  According to the above configuration, the encoding rate of the stream data is changed based on the communication status measured based on the delivery confirmation packet sent from the external communication device on the receiving side. . Therefore, the communication state is measured without delay in the communication device on the transmission side, and the coding speed is changed based on this measurement. Therefore, it is possible to perform coding speed change control that quickly follows the change in the communication state. It becomes possible. In addition, it is possible to eliminate the need for a special configuration in the external communication device on the receiving side.

  In the communication device according to the present invention, in the above configuration, the data format changing unit is an error resilience adding unit that imparts error resilience to a transmitted packet, and the data format managing unit is configured to add the error resilience An error resilience management unit that controls error resilience provided in a unit, and the error resilience management unit may control the error resilience based on a communication state measured by the communication path state measurement unit. .

  According to the above configuration, the error tolerance given to the transmitted packet is changed based on the communication status measured based on the delivery confirmation packet sent from the external communication device on the receiving side. It has become. Therefore, the communication state is measured without delay in the communication device on the transmission side, and the error resilience is changed based on this measurement, so it is possible to perform error resilience change control that quickly follows changes in the communication state. Become. In addition, it is possible to eliminate the need for a special configuration in the external communication device on the receiving side.

  Further, in the communication apparatus according to the present invention, in the above configuration, the data format changing unit assigns error resistance to the encoding rate changing unit that sets the encoding rate of the stream data, and the packet to be transmitted. An error resilience adding unit, wherein the data format management unit is configured to control an encoding rate set in the encoding rate changing unit, and an error resilience provided in the error resilience adding unit. An error resilience management unit for controlling, wherein the coding rate management unit controls the coding rate based on a communication state measured by the communication path state measurement unit, and the error resilience management unit The error tolerance may be controlled based on the communication status measured by the communication path status measurement unit.

  According to said structure, based on the communication condition measured based on the delivery confirmation packet sent from the external communication apparatus used as the receiving side, it attaches to the encoding rate of stream data, and the packet transmitted. The error resilience is changed. Therefore, the communication state is measured without delay in the communication device on the transmission side, and the coding speed and error resilience are changed based on this, so that the coding speed and error resilience that quickly follows the change in the communication state can be changed. Change control can be performed. In addition, it is possible to eliminate the need for a special configuration in the external communication device on the receiving side.

  Further, the communication device according to the present invention is a range in which, in the above configuration, an upper limit value and / or a lower limit value for controlling the coding rate is set for the coding rate management unit based on an instruction from the outside. It is good also as a structure further provided with the setting part.

  According to said structure, based on the instruction | indication from the outside, it becomes possible to set the upper limit and / or lower limit of coding rate control. Here, the instruction from the outside corresponds to, for example, an instruction input from the user directly to the communication apparatus, an instruction input from the external apparatus via the communication medium, or the like. In this way, it becomes possible to set the upper limit value of the encoding speed, so that the encoding band is set higher than the required communication quality, thereby occupying the communication band more than necessary, It is possible to suppress the occurrence of many transmission failures when the communication environment deteriorates. In addition, since it becomes possible to set the lower limit value of the coding rate, it is possible to ensure the minimum communication quality.

  Further, the communication device according to the present invention includes a communication unit having a function as a physical layer when performing data transmission via the communication medium in the above configuration, and the communication path state measurement unit is configured to be the communication unit. And further measures the physical layer communication speed set by the physical layer in the error layer, and the error resilience management unit determines the error resilience based on the physical layer communication speed and the communication state measured by the communication path state measurement unit. It is good also as a structure which controls.

  According to the above configuration, error tolerance control is performed based on the physical layer communication speed in addition to the communication status. Therefore, it is possible to grasp the situation in the communication medium more accurately, and it is possible to perform error tolerance control more accurately.

  In the communication apparatus according to the present invention, in the above configuration, the error resilience management unit performs control to change error resilience added to a packet to be transmitted by the error resilience adding unit. The physical layer communication speed set by the physical layer in the unit is changed, and the upper limit value and / or the lower limit of the control of the physical layer communication speed for the error resilience management unit based on an instruction from the outside It is good also as a structure further provided with the range setting part which sets a value.

  According to said structure, based on the instruction | indication from the outside, it becomes possible to set the upper limit and / or lower limit of control of a physical layer communication speed. Here, the instruction from the outside corresponds to, for example, an instruction input from the user directly to the communication apparatus, an instruction input from the external apparatus via the communication medium, or the like. As described above, the upper limit value of the physical layer communication speed can be set, so that the error tolerance becomes too weak due to the increase in the physical layer communication speed, and the range in which stable communication is possible is reduced. This can be avoided. In addition, it becomes possible to set the lower limit value of the physical layer communication speed, and it becomes possible to suppress the decrease in throughput by increasing the error resistance more than necessary by lowering the physical layer communication speed. Become.

  In the communication apparatus according to the present invention, in the above configuration, the error resilience management unit instructs the error resilience adding unit to change the encoding scheme and / or encoding parameter of the error correction code. It is good also as a structure which controls error tolerance by this.

  In the above, the encoding method of the error correction code corresponds to, for example, a modulation method of an error correction code described later, and the encoding parameter corresponds to, for example, an encoding rate described later. According to the above configuration, the error tolerance is changed by changing the encoding method and / or the encoding parameter of the error correction code, so that the error tolerance can be accurately controlled.

  Further, in the communication device according to the present invention, in the above configuration, the error tolerance management unit calculates a predicted throughput as a predicted value of a data transfer rate at which data transfer is substantially performed, and a current throughput, A comparison may be made with the predicted throughput after changing the error resilience, and when it is determined that changing the error resilience results in higher throughput, control to change the error resilience may be performed.

  According to the above configuration, when it is determined that the throughput is higher when the error tolerance is changed based on the predicted throughput, the control for changing the error tolerance is performed. Therefore, it is possible to increase the possibility that throughput is increased by performing error resilience control.

  The communication apparatus according to the present invention further includes a transmission buffer for temporarily storing data to be transmitted in the above configuration, and the error tolerance management unit has a predetermined amount of data accumulated in the transmission buffer. It is good also as a structure which controls so that error tolerance may be weakened when it falls below the threshold value.

  According to the above configuration, when the amount of data stored in the transmission buffer falls below a predetermined threshold, error resilience is changed weakly. Here, the case where the amount of data stored in the transmission buffer falls below a predetermined threshold indicates that the data to be transmitted is being transmitted smoothly, indicating that the communication status is good. Will be. That is, according to the control as described above, it is possible to quickly recognize that the communication status has been improved and perform control to quickly increase the communication speed accordingly.

  Further, the communication device according to the present invention includes a communication unit having a function as a physical layer when performing data transmission via the communication medium in the above configuration, and the communication path state measurement unit is configured to be the communication unit. Further, the physical layer communication speed set by the physical layer may be further measured, and the data format management unit may calculate the predicted throughput based on the physical layer communication speed.

  According to the above configuration, the predicted throughput is calculated based on the physical layer communication speed. Here, for example, when HCCA communication control is being performed, if the physical layer communication speed is known, the predicted throughput can be estimated with relatively high accuracy based on the allocated communication band. That is, for example, by preparing a table indicating the relationship between the physical layer communication speed value and the predicted throughput, the predicted throughput can be easily calculated.

  Further, in the communication device according to the present invention, in the above configuration, the communication path condition measurement unit further measures a communication band allocated to the communication device in a predetermined period, and the data format management unit The predicted throughput may be calculated based on information on the physical layer communication speed and the communication band.

  According to the above configuration, the predicted throughput is calculated based on the information on the communication band allocated to the communication device in a predetermined period in addition to the physical layer communication speed. Therefore, when bandwidth allocation is performed by an external communication control device, even if the bandwidth allocated to the communication device becomes small when the communication status with the communication control device deteriorates, The predicted throughput can be calculated based on the allocated bandwidth. Therefore, it is possible to predict the predicted throughput with higher accuracy.

  Further, in the communication device according to the present invention, in the above configuration, the communication path condition measurement unit further measures the occupied bandwidth and the free bandwidth occupied by the communication device in a predetermined period, and the data format management The unit may calculate the predicted throughput based on the physical layer communication speed, and information on the occupied bandwidth and the free bandwidth.

  According to the above configuration, in addition to the physical layer communication speed, the predicted throughput is calculated based on the information on the communication device occupation bandwidth and the free bandwidth in a predetermined period. Therefore, for example, even when communication is performed by the best effort type, the predicted throughput can be calculated more accurately.

  In the communication device according to the present invention, in the above configuration, the range setting unit accepts a data transmission instruction in the high quality mode and a data transmission instruction in the low power consumption mode from the outside, and corresponds to the instructed mode. Thus, an upper limit value and / or a lower limit value for controlling the coding speed may be set.

  According to the above configuration, the upper limit value and / or the lower limit value of the control of the coding rate is set based on the mode setting instruction from the outside. Therefore, it is possible to switch between a mode that prioritizes video quality and a mode that prioritizes long-time use, reflecting the user's intention. Note that high-quality video transmission is possible in the high-quality mode, and transmission time is shortened by reducing the quality in the low-power consumption mode, so that low power consumption can be achieved.

  In the communication device according to the present invention, in the above configuration, the range setting unit accepts a data transmission instruction in the high quality mode and a data transmission instruction in the low power consumption mode from the outside, and corresponds to the instructed mode. The upper limit value and / or lower limit value of the physical layer communication speed control and the transmission power in the communication unit may be set.

  According to the above configuration, the upper limit value and / or the lower limit value of the control of the physical layer communication speed is set based on the mode setting instruction from the outside. Therefore, it is possible to switch between a mode that prioritizes video quality and a mode that prioritizes long-time use, reflecting the user's intention. In the high quality mode, high-quality video transmission is possible, and in the low power consumption mode, it is possible to reduce the power consumption by lowering the physical layer communication speed by lowering the transmission power. .

  The communication apparatus according to the present invention may further include a display unit that displays whether the high-quality mode or the low-power consumption mode is controlled in the above configuration.

  According to the above configuration, it is displayed whether the communication apparatus is controlled in the high quality mode or in the low power consumption mode. Therefore, the user can confirm which mode is currently controlled by displaying, so that it is possible to take measures as necessary at an early stage.

  In addition, a communication system according to the present invention includes the communication device according to the present invention, and a reception device capable of communicating with the communication device via a communication medium and receiving stream data from the communication device. It is a feature.

  Thereby, it is possible to construct a communication system in which appropriate data transmission is performed according to the communication state in the communication medium.

  As described above, the communication apparatus according to the present invention controls the data format set in the data format change unit and the data format change unit that changes the stream data into a data format suitable for transmission on the communication medium. A data format management unit, and a communication path status measurement unit that measures a communication status in the communication medium based on a delivery confirmation packet sent from the external communication device, the data format management unit, The data format is controlled based on the communication status measured by the communication path status measurement unit. As a result, the communication state is measured without delay in the communication device on the transmission side, and the data format is changed based on the measurement. Therefore, it is possible to perform the data format change control that quickly follows the change in the communication state. It has the effect of becoming. In addition, there is an effect that it is possible to eliminate the necessity of having a special configuration in the external communication device on the receiving side.

  An embodiment of the present invention will be described with reference to FIGS. 1 to 13 as follows.

(Communication system configuration)
FIG. 2 is a schematic configuration diagram illustrating an example of a communication system according to the present embodiment. As shown in the figure, a network system 207 included in the communication system includes a transmission device (communication device) 201 and a reception device 202. The transmission device 201 and the reception device 202 are connected to each other via a communication medium 203.

  The transmission device 201 includes a communication band management function and a data transmission function for performing transmission control and / or error resilience control regarding transmission of stream data such as video and audio that require real-time transmission. Yes. The receiving device 202 has a stream data receiving function.

  The communication band management function included in the transmission device 201 means HCCA and EDCA communication control by the HC defined in 802.11e. Hereinafter, the communication band management function is referred to as the HC function. FIG. 2 shows an example in which the HC function and the data transmission function are included in the same device, but in actuality, they may be realized by separate devices. That is, a communication control device having an HC function and a transmission device having a data transmission function may be provided.

  For the sake of simplicity, FIG. 2 shows an example in which one transmission device 201 and one reception device 202 are provided in the network system 207. A plurality of transmission devices and reception devices may be provided. In addition, although the transmission device and the reception device are shown separately, the transmission device may have a function as a reception device, or the reception device may have a function as a transmission device. .

  As the communication medium 203, various communication media can be used and are not particularly limited. An example of the communication medium 203 is a wireless communication medium using 802.11a, which is a 5 GHz band wireless standard. When this wireless communication medium is used, for example, a network system in which various devices are connected to each other wirelessly as a home LAN can be realized. In this example, a configuration example in which the transmission device 201 functions as a home server such as an STB (set top box) that manages all wireless communication devices and video sources in the home is assumed. The transmission apparatus 201 as a home server has a configuration having a function of receiving stream data such as video and audio from a broadcasting station 204 such as BS / CS broadcasting and digital terrestrial broadcasting, and a public network 205 such as the Internet. It is assumed that In addition, the receiving device 202 is assumed to have a configuration including a display function such as a television and an audio output function. According to such a system, the transmission device 201 as a home server performs translation control and / or error resilience control while looking at the communication status in the communication medium 203, and uses stream data input from the outside as a television. A specific embodiment of transmitting to the receiving device 202 can be realized.

  In the above example, it is assumed that digital data is input to the transmission device 201 as the home server. However, for example, a DVD (Digital Versatile Disc) player, a BD (Blu-ray Disc) player, It is also possible to adopt a configuration in which analog data is input from an analog AV source 206 as a media player such as an HD DVD player or a video player. In this case, the transmission apparatus 201 as a home server can cope with this by providing a function of performing an encoding process such as an MPEG encoder. Further, for example, the media player itself may have a configuration in which the transmission device 201 is built.

  In the above example, a 5 GHz band wireless communication medium is given as an example of the communication medium 203, but a 2.4 GHz band wireless communication medium, a millimeter wave band wireless communication medium, and a communication medium using a power line are used. There may be.

  Here, a flow of processing of stream data transmission / reception in the network system 207 as described above will be briefly described. First, the transmission apparatus 201 and the reception apparatus 202 negotiate information regarding the QoS of stream data, such as jitter information, the size of a buffer to be prepared, and the amount of data to be transmitted. Then, in consideration of the negotiation result and information regarding whether to transmit by HCCA or EDCA, it is determined whether or not the HC function in the transmission apparatus 201 can secure a communication band. If the communication band can be secured, transmission of stream data is permitted by the HC function. At this time, when data transmission is performed based on HCCA communication control, a band for data transmission is allocated by the HC function, and the transmission apparatus 201 actually transmits stream data using the allocated band. To start. Further, when data transmission is performed based on EDCA communication control, the transmission apparatus 201 starts transmission of stream data by best effort.

(Configuration of transmitter)
Next, the transmission apparatus 201 will be described below with reference to FIG. FIG. 3 shows a configuration example of the transmission apparatus 201. As shown in the figure, the transmission device 201 includes a data transmission unit 1, an input unit 2, a display unit 3, a tuner unit 4, a wide area communication unit 5, an encoding unit 6, and an HC function unit 7. ing.

  The input unit 2 receives an instruction input from the user to the transmission device 201. The input unit 2 includes various buttons provided on the transmission device 201, a remote controller, and the like, for example.

  The display unit 3 displays an operation status in the transmission device 201. The display unit 3 includes, for example, various indicator lamps and a liquid crystal display device.

  The tuner unit 4 performs processing for receiving digital broadcasts such as BS / CS broadcasts and terrestrial digital broadcasts sent from the broadcast station 204. The wide area communication unit 5 performs processing for receiving content data from the public network 205 such as the Internet. The wide area communication unit 5 is configured by a modem, for example. The encoding unit 6 performs an encoding process for receiving analog data as an AV source from the analog AV source 206 and converting it into digital data such as MPEG2.

  The HC function unit 7 is a block that realizes the above-described HC function. That is, when data transmission / reception is performed between the transmission device 201 and the reception device 202 based on HCCA communication control, the HC function unit 7 performs bandwidth allocation for data transmission. Here, the HC function unit 7 negotiates information regarding QoS of stream data, such as jitter information, the size of a buffer to be prepared, and the amount of data to be transmitted, which is performed between the transmission device 201 and the reception device 202. Based on this, bandwidth allocation is performed. Note that this HC function unit 7 may not be provided when data transmission / reception between the transmission device 201 and the reception device 202 is all performed by EDCA best effort.

  The data transmission unit 1 performs processing for transferring the stream data transmitted from the tuner unit 4, the wide area communication unit 5, and the encoding unit 6 to the reception device 202 via the communication medium 203. In this transfer process, the data transmission unit 1 performs translation control and / or error resilience control according to the communication status at that time. Details of translation control and error resilience control in the data transmission unit 1 will be described later.

  When HCCA communication control is performed by the HC function unit 7, the data transmission unit 1 performs data transmission within the band range allocated by the HC function unit 7.

  In addition, the data transmission unit 1 controls the display unit 3 to display the current communication mode setting status and the communication status, and based on the input of the communication mode setting change instruction by the user, the input unit 2 is performed to receive the control information sent from 2. Here, examples of communication modes that can be set by the user include a high quality mode and a low power consumption mode. The high quality mode is a mode that prioritizes increasing the quality of stream data over suppressing power consumption, and the low power consumption mode is a mode that prioritizes suppressing power consumption over quality of stream data. . The display unit 3 performs processing for displaying the information to the user according to the setting of the current communication mode and the notification of the communication status from the data transmission unit 1.

(Configuration of data transmitter)
Next, the configuration of the data transmission unit 1 will be described below with reference to the functional block diagram shown in FIG. As shown in the figure, the data transmission unit 1 includes an application (range setting unit) 101, a coding rate management unit 102, a coding rate change unit 103, a channel condition measurement unit 107, a transmission buffer 104, and an error resilience management unit. 106, an error resilience adding unit 105, a communication unit 108, an antenna 109, and a table storage unit 110.

  The application 101 gives the display unit 3 information on the current communication mode setting, information on the coding rate in the coding rate management unit 102, information on error resilience being performed in the error resilience management unit 106, and the like. Processing to notify the communication status of In addition, the application 101 sets the type of transmission rate and the upper limit of transmission power in the physical layer to be used for the coding rate management unit 102 based on the setting of the communication mode. Here, the setting of the communication mode may be performed by an instruction input received by the input unit 2, or a setting instruction may be performed by communication from an external device such as the receiving device 202 via the communication unit 108. It may be. The application 101 controls communication processing in the communication unit 108 based on communication control by the HC function unit 7.

  The encoding rate management unit 102 performs encoding within the range of the upper limit value and the lower limit value of the encoding rate set by the application 101 in accordance with the current communication status of the communication medium 203 measured by the communication path status measurement unit 107. The encoding rate changing unit 103 is controlled to set the encoding rate. Details of the coding speed setting control, that is, translation control will be described later.

  The coding rate changing unit 103 performs a translation process according to the coding rate set by the coding rate managing unit 102. That is, the encoding speed changing unit 103 receives stream data from at least one of the tuner unit 4, the wide area communication unit 5, and the encoding unit 6, and sets the set code for the stream data. The encoding speed is changed according to the encoding speed.

  The transmission buffer 104 packetizes the stream data whose coding speed has been changed by the coding speed changing unit 103 and temporarily stores the stream data. The transmission buffer 104 is configured by a high-speed rewritable recording medium such as a RAM.

  The error resilience management unit 106 falls within the range of the upper limit value of the transmission rate and transmission power in the physical layer set by the application 101 in accordance with the current communication state in the communication medium 203 measured by the communication path state measurement unit 107. Thus, error tolerance setting control is performed on the error tolerance adding unit 105. Details of the error resilience control will be described later.

  The error resilience adding unit 105 performs error resilience addition processing according to the error resilience setting set by the error resilience management unit 106. That is, the error resilience adding unit 105 reads a packet temporarily stored in the transmission buffer 104, adds error resilience, and then performs a process of transmitting the packet to the communication unit 108.

  The communication unit 108 performs processing for transmitting the packet to which the error tolerance is added by the error tolerance adding unit 105 to the receiving apparatus 202 via the communication medium 203. Further, when the communication unit 108 receives the reception response confirmation from the receiving device 202 and recognizes that the transmitted packet is an error, an error has occurred among the transmitted packets temporarily stored in the transmission buffer 104. The transmission buffer 104 is instructed to retransmit the packet corresponding to the packet. In addition, the communication unit 108 performs processing for transmitting and receiving control information such as a command input from the application 101 to and from the receiving device 202. As a result, the control information received from the receiving apparatus 202 can be notified to the application 101.

  The communication path status measurement unit 107 acquires the reception status of the packet reception response confirmation from the reception device 202 from the communication unit 108, and calculates a packet error rate (PER) based on the reception status information. Perform the process. Instead of the packet error rate calculation process, a process of counting the number of transmission success packets and transmission failure packets may be performed. Further, the communication path status measurement unit 107 performs processing for observing information on the PHY rate (physical layer communication speed) currently used.

  The table storage unit 110 stores a table indicating the relationship between the PHY rate and the predicted maximum throughput. Details of this table will be described later. The table storage unit 110 is configured by a nonvolatile recording medium such as a ROM.

(Receiver configuration)
Next, the receiving apparatus 202 will be described below with reference to FIG. FIG. 4 shows a configuration example of the receiving device 202. As shown in the figure, the receiving apparatus 202 includes a display unit 301, a decoding unit 302, an application 303, a reception buffer 304, an error resilience decoding unit 305, a communication unit 306, an antenna 307, and an input unit 308. ing.

  The input unit 308 receives an instruction input from the user to the receiving device 202. The input unit 308 is configured by various buttons provided in the receiving device 202, for example.

  The display unit 301 performs processing for displaying information such as the current communication setting and communication status notified from the application 303 and the stream data decoded by the decoding unit 302. The display unit 301 is configured by a display device capable of displaying an image, such as a liquid crystal display, a plasma display, and a CRT (Cathode Ray Tube).

  The decoding unit 302 performs processing for decoding the stream data stored in the reception buffer 304.

  The application 303 performs a process of receiving control information sent from the input unit 308 based on a user's communication mode setting change instruction input and transmitting the control information to the transmission apparatus 201 via the communication unit 306. . Here, the setting of the communication mode may be performed by an instruction input received by the input unit 308, or a setting instruction may be performed by communication from an external device such as the transmission device 201 via the communication unit 306. It may be. The application 303 performs control to display the current communication setting and communication status on the display unit 301.

  The reception buffer 304 is a buffer for temporarily storing the packet sent from the error resilience decoding unit 305, and the packet stored at the timing required by the decoding unit 302 as a stream data is decoded by the decoding unit. Processing to output to 302 is performed.

  The error resilience decoding unit 305 receives the packet received from the communication unit 306 and performs a process of decoding the error resilience added by the transmission device 201. The packet decoded by the error resilience decoding unit 305 is transmitted to the reception buffer 304.

  The communication unit 306 performs reception processing for packets transmitted from the transmission device 201. In addition, when the communication unit 306 recognizes that the received packet is an error, the communication unit 306 requests the transmitting apparatus 201 to retransmit the corresponding packet using reception response confirmation. In addition, the communication unit 306 performs processing for transmitting and receiving control information such as a command input from the application 303 to and from the transmission apparatus 201. As a result, the control information received from the transmission apparatus 201 can be notified to the application 303.

(Translate control)
Next, the flow of translation control in the coding rate management unit 102 will be described with reference to the flowchart shown in FIG. Here, a case where the communication mode is set to the high quality mode will be described. In this case, the application 101 sets the lower limit value of the encoding rate to 1 Mbps and does not set the upper limit value. Further, it is assumed that the HC function unit 7 secures a band by HCCA communication control so that stream data can be transmitted at a maximum of 8 Mbps when the transmission rate (PHY rate) of the physical layer is 36 Mbps.

  In addition, the transmission buffer 104 of the transmission device 201 and the reception buffer 304 of the reception device 202 are prepared as buffers capable of storing stream data for 256 ms. As a result, the maximum delay (jitter) when stream data is transmitted and received is 256 ms.

  Here, when stream data is transmitted and received, the time (reproduction time) for decoding a predetermined packet by the decoding unit 302 of the receiving apparatus 202 needs to be before the expiration date of the packet. That is, it is important that the transmission apparatus 201 transmits a packet so that the reception apparatus 202 performs reproduction before the expiration date.

  However, in wireless communication, there may be a case in which a packet is frequently retransmitted due to a temporary deterioration of the communication status in the communication medium 203 and a packet that cannot be reproduced before the expiration date. In this case, the transmission apparatus 201 needs to discard the corresponding packet temporarily stored in the transmission buffer 104.

  On the other hand, when the transmission buffer 104 and the reception buffer 304 are buffers of 256 ms as described above, the transmission buffer 104 sets the lifetime indicating the packet expiration date to 256 ms when the packet is generated. Is set in consideration of. When a retransmission request is received from the communication unit 108, the transmission buffer 104 compares the current time with the lifetime, discards the packet whose lifetime has passed, and does not retransmit it. In this case, since the receiving device 202 cannot reproduce the packet discarded on the transmitting device 201 side, the video displayed on the display unit 301 is disturbed as a result.

  Next, the actual processing flow will be described. First, before the transmission of the stream data as described above, after the parameter setting relating to QoS is performed between the HC function unit 7 and the reception device 202 in the transmission device 201, the transmission device 201 Is started (start in FIG. 5). Thereafter, the coding rate management unit 102 collects information on the currently used PHY rate and information on the packet error rate (PER) in a predetermined measurement period from the communication path state measurement unit 107 (step 101 and thereafter). , Referred to as S101). The predetermined measurement period for calculating the packet error rate is basically a period between the current time and a predetermined time.

  The communication path status measurement unit 107 counts the number of packets successfully transmitted and the number of packets unsuccessfully transmitted based on the delivery confirmation packet transmitted from the receiving device 202, and the number of packets successfully transmitted. , And measure the packet error rate based on the number of packets that failed to be transmitted. The delivery confirmation packet sent from the receiving apparatus 202 indicates whether or not each packet sent from the transmitting apparatus 201 has been successfully received. This delivery confirmation packet may be, for example, Normal Ack (a method in which one delivery confirmation packet is transmitted for each packet) defined in 802.11e, or Burst Ack (delivery confirmation for a plurality of packets). (A method in which information is collectively transmitted in one delivery confirmation packet).

  Next, the coding rate management unit 102 determines the predicted maximum throughput (TH (PHY)) by referring to the table stored in the table storage unit 10 based on the PHY rate information collected in S101. (S102).

  Here, the predicted maximum throughput means that when the transmission apparatus 201 performs data transmission using all the bands allocated in the predetermined measurement period, the communication status in the communication medium 203 is good and the packet error rate is high. It shows the maximum throughput that can be achieved when assuming zero. As shown in the example shown here, when a band is secured by the communication control of HCCA, it is guaranteed that a certain communication band is allocated for a predetermined period. The predicted maximum throughput can be uniquely determined by the rate.

  FIG. 6 shows an example of a table stored in the table storage unit 10. In the example shown in the figure, it is assumed that the PHY rate to be used is any one of 36 Mbps, 24 Mbps, 18 Mbps, and 12 Mbps. However, the type of PHY rate is not limited to this example. For example, the table may include the relationship with the predicted maximum throughput for PHY rates of 54 Mbps, 48 Mbps, 9 Mbps, and 6 Mbps. good.

  Thereafter, the coding rate management unit 102 determines whether or not the packet error rate has been measured (S103). If the packet error rate cannot be measured (NO in S103), the current translation control process is terminated. To do. Here, the case where the packet error rate cannot be measured corresponds to the case where there is no packet to be transmitted. In this case, since the communication status cannot be determined, the encoding speed setting for the current stream data is maintained. However, when stream data is transmitted, there should normally be a packet to be transmitted constantly, so it is considered very unlikely that NO will be determined in S103.

On the other hand, if YES in S103, that is, if it is determined that the packet error rate has been measured, the encoding rate management unit 102 sets the encoding rate (NR) of the stream data to be set next in the encoding rate changing unit 103. It is determined by the following equation (S104).
NR = TH (PHY) × (1-PER) × α (1)
Here, α is a constant satisfying 0 <α ≦ 1. In the present embodiment, α = 0.9 is set in order to leave a bandwidth for performing retransmission.

When stream data is transmitted, both video data and audio data are often transmitted. Audio data has a much smaller amount of data to be transmitted per unit time than video data. That is, the ratio of audio data to stream data is extremely small. Therefore, the video data is subjected to the translation control as described above, while the audio data may be fixed at a fixed rate without performing the translation control. In this case, the above equation (1) is expressed as follows.
NR = TH (PHY) × (1-PER) × α-BWaudio (2)
Here, BWaudio is set as a fixed rate of audio data + 200 KBps. The fixed rate of audio data is specifically about 224 KBps, for example. The reason why 200 Kbps is added to the BWaudio with respect to the fixed rate of the audio data is that the rate of the video data calculated based on the above equation (2) without adding 200 Kbps to the BWaudio is the actual video data. This is because it has been proved by experiments that the rate is reduced by about 200 KBps.

  Next, the coding rate management unit 102 compares the NR calculated by the above equation (1) with the lower limit value (1 Mbps) of the coding rate set by the application 101. Then, the coding rate management unit 102 adjusts the NR value so as not to fall below the lower limit value, and instructs the coding rate changing unit 103 to perform translation. That is, the coding rate management unit 102 sets the NR value to the lower limit value when the NR calculated by the above equation (1) is lower than the lower limit value.

  In the above example of translation control, the transmission apparatus 201 includes the HC function unit 7, and the band is secured by the HCCA communication control by the HC function unit 7, so that how much band can be secured. It has become clear. Therefore, once the PHY rate is determined, the predicted maximum throughput can be calculated by using the above table.

  On the other hand, in an actual system, the HC function may be realized by a communication device other than the transmission device 201. In this case, when the transmission apparatus 201 receives a packet indicating bandwidth allocation (QoS CF-Poll packet in 802.11e) from a communication device having the HC function, the bandwidth is secured in a predetermined period thereafter. The transmission device 201 transmits a packet. That is, even when the HC function is realized by a communication device other than the transmission apparatus 201, it is usually possible to perform translation control as in the case where the HC function is provided in the transmission apparatus 201.

  However, when the communication status between the communication device having the HC function and the transmission device 201 is deteriorated, it is conceivable that a reception error of a packet indicating band allocation occurs. In this case, there is a possibility that the bandwidth allocated to the transmission apparatus 201 becomes small.

  In order to cope with such a case, when the communication apparatus having the HC function is different from the transmission apparatus 201, it is preferable to perform the following processing. First, the communication path state measurement unit 107 measures a communication band actually allocated in a predetermined period. Then, the coding rate management unit 102 calculates the predicted maximum throughput for each PHY rate when it is assumed that the allocated communication bandwidth is all used, the communication status is good, and the packet error rate is 0. Create a table based on the calculation results. This table is updated each time the communication bandwidth measurement unit 107 measures the communication band for each predetermined period. In this way, by performing the above-described translation control based on the table updated as needed, it is possible to cope with the case where the HC function is included in a device different from the transmission device 201.

  As described above, when the table is updated as needed, the table storage unit 10 is preferably configured by a rewritable nonvolatile recording medium such as an EEPROM (Electrically Erasable & Programmable ROM).

  Further, as described above, there are overwhelmingly more communication systems in which best-effort communication is performed than communication systems in which transmission of stream data is performed in a state where a bandwidth is secured by HCCA communication control as described above. . Therefore, control in consideration of the case where communication is performed by the best effort type such as communication control of EDCA is necessary. That is, when the best effort type communication is performed, it is preferable to perform the following processing. First, the communication path status measurement unit 107 communicates the bandwidth occupied by the transmission apparatus 201 probabilistically accessing the communication channel at best effort and actually transmitting a packet and any communication device during a predetermined period. Measure the free bandwidth that you have confirmed that you are not accessing the channel. A sum of these two bandwidths is regarded as a communication band that can be secured by the transmission apparatus 201. Then, the coding rate management unit 102 calculates the predicted maximum throughput for each PHY rate when all the communication bandwidth that can be secured is used and the communication state is good and the packet error rate is assumed to be zero. Then, a table based on the calculation result is created. This table is updated each time the communication bandwidth measurement unit 107 measures the communication band for each predetermined period. In this way, by performing the above-described translation control based on the table updated as needed, it is possible to cope with a case where communication is performed by a best effort type such as communication control of EDCA.

  Further, in addition to the band actually given or used as described above, the communication path state measurement unit 107 measures the C / N in the delivery confirmation packet sent from the receiving device 202, for example, and this C / N The coding rate management unit 102 may calculate the predicted maximum throughput using the value of N.

(Example of translation control results)
FIG. 7 is a graph showing an example of a result when the above-described translation control is actually performed. In the translation control, the processing shown in FIG. 5 is performed at regular intervals. Here, this interval is set to 15 ms. Further, the communication path state measurement unit 107 calculates the PER by counting the number of packets that have been successfully transmitted and the number of packets that have failed to be transmitted in order to calculate the packet error rate. However, since there are few samples of the number of packets at the 15 ms interval, the packet error rate is calculated by averaging four times of the information collected at the 15 ms interval.

As described above, when the PER is calculated by counting the number of packets successfully transmitted and the number of packets unsuccessfully transmitted, the above equation (1) is expressed as follows.
NR = TH (PHY) × (S / (S + US)) × α (3)
In the above equation, S indicates the number of packets that have been successfully transmitted, and US indicates the number of packets that have failed to be transmitted.

  Further, in order to make it easy to grasp the wireless situation, in the result shown in FIG. 7, the transmission success rate as a value obtained by dividing the average value of the number of successful transmission packets by the measurement interval instead of the packet error rate, and the transmission failure packet The transmission failure rate is shown as a value obtained by dividing the average value of the numbers by the measurement interval. In the result shown in FIG. 7, since the PHY rate is not changed, the predicted maximum throughput (TH (PHY)) is 8 Mbps.

  In FIG. 7, A <b> 1 indicates a change in the stream setting rate (NR) set by the coding rate management unit 102, and A <b> 2 indicates a change in the transmission success rate measured by the channel condition measurement unit 107. A3 indicates a change in the transmission failure rate measured by the communication path condition measuring unit 107, and A4 indicates a change in the number of packets waiting for transmission in the transmission buffer 104 (buffer size). A5 indicates a change in the set PHY rate, and A6 indicates the number of packets counted by the transmission buffer 104 that cannot be confirmed from the reception device 202 and have expired. This shows the change in (number of losses). The horizontal axis represents time, and the left side of the vertical axis represents the data rate (Mbps), which is the axes of A1, A2, and A3. The right side of the vertical axis represents the buffer size (number of packets), the PHY rate (Mbps), and the number of loss occurrences (number of packets), which are the axes of A4, A5, and A6. The effectiveness of the translation control can be judged by whether or not loss occurs.

  Here, the reason why the number of loss occurrences can be used as an index for verifying the effectiveness of translation control will be described. The loss occurrence number indicates the number of packets whose expiration date has passed without being able to confirm reception from the receiving apparatus 202 as described above. Therefore, there is a possibility that the receiving device 202 cannot receive the corresponding packet, and there is a possibility that the video is disturbed. However, in reality, the receiving apparatus 202 normally receives the stream data packet from the transmitting apparatus 201, but the reception confirmation packet from the receiving apparatus 202 cannot be normally received by the transmitting apparatus 201. It is done. That is, it can be said that judging effectiveness based on the number of occurrences of loss recognized by the transmitting apparatus 201 is a stricter index than judging whether or not the video is actually disturbed in the receiving apparatus 202.

  As shown in FIG. 7, in the vicinity of 39200 ms, the communication status becomes worse, the transmission success rate is lowered, and the transmission failure rate is raised. Along with this, the number of packets waiting for transmission in the transmission buffer 104 will increase, but the transmission buffer 104 will wait for transmission because the stream setting rate has been lowered following the communication status. The increase in packets that can be suppressed.

  Here, the speed at which packets waiting for transmission in the transmission buffer 104 increase depends on the time until the coding rate management unit 102 detects that the communication status has deteriorated, and the coding rate changing unit 103. It depends on how long it takes to translate and how much throughput is in between. Then, the communication state is unstable until around 39400 ms, and the communication state is recovered at a stretch around 39500 ms. As a result, the transmission success rate is increased, and the number of packets waiting for transmission in the transmission buffer 104 is reduced. In addition, the stream setting rate can be quickly increased following the recovery of the communication state. After that, not only when the communication state is bad, but also when the communication state is recovered, the stream setting rate can be set quickly following the communication state, so no loss occurs.

  From the above results, by performing the translation control as described above, not only when the communication status deteriorated, but also when the communication status recovered, the stream data set rate quickly followed the communication status. It turns out that it is possible to set in the state. In addition, since the transmission apparatus 201 determines the communication status, the reception apparatus 202 does not need a mechanism for performing feedback.

(Error tolerance control)
Next, error tolerance control in the error tolerance management unit 106 will be described. First, a case where loss generation cannot be suppressed only by the above-described translation control will be described. In the result shown in FIG. 6, the transmission success rate becomes 0 around 39700 ms, and transmission of all packets fails. At this time, when the above-described translation control is applied, the set rate of the stream is set to 1 Mbps. In the result shown in FIG. 6, since the communication state has recovered within 100 ms thereafter, no loss occurred, but in the following situation, loss occurs. Become. In other words, as described above, the transmission buffer 104 sets the lifetime indicating the expiration date in consideration of 256 ms for each packet, and thus the case where the transmission success rate of 0 continues for 256 ms or more. In this case, loss occurs and the image is disturbed.

  As a method for solving this problem, when the throughput is reduced in a situation where the communication success rate is 0, the throughput is reduced, and the transmission buffer 104 in the transmission apparatus 201 is controlled to increase the throughput. A method of increasing the buffer capacity of the reception buffer 304 in the reception device 202 can be considered.

  Here, in the method of increasing the buffer capacity, the maximum delay can be set larger than before. Therefore, even if the time until the communication state is recovered is somewhat longer, it is possible to reduce the video disturbance. However, when the buffer capacity is increased, there is a problem that the real-time property is lost due to an increase in the delay time of data transfer and a problem that the apparatus cost increases.

  Therefore, in the following, the flow of error resilience control in the error resilience management unit 106 will be described with reference to the flowchart shown in FIG. 8 as a method for controlling the throughput to increase when the throughput decreases.

  As means for changing error resilience, there are a method of changing an error correction code to be added to data, a method of changing a PHY rate, and the like. Here, as described above, there is usually a trade-off between increasing error resilience and increasing communication bandwidth, and increasing error resilience when communication conditions are good reduces communication bandwidth. Just do it. For example, when an error correction code is used, error tolerance can be increased by a redundant amount of data. However, since the packet becomes longer and the time required for transmission increases, the throughput decreases.

  FIG. 9 shows the relationship between the modulation scheme, coding rate, and error resistance at various PHY rates. As shown in the figure, the strength of error resilience depends on the modulation scheme and coding rate. FIG. 10 shows the relationship between input power and packet error rate at various PHY rates. As shown in the figure, the packet error rate decreases as the PHY rate decreases. Therefore, it can be seen that it is effective to control the PHY rate when the received power is reduced due to an environmental change such as passage of a shield such as a person or device through the communication path.

  In the following, PHY rate control will be mainly described in error resilience control. Here, the case where the communication mode is set to the high quality mode as in the case of the translation control will be described. In this case, the application 101 instructs the error resilience management unit 106 to use any one of the PHY rates of 36 Mbps, 24 Mbps, 18 Mbps, and 12 Mbps. In addition, the application 101 does not set an upper limit value of transmission power. Further, it is assumed that the HC function unit 7 secures a band by HCCA communication control so that stream data can be transmitted at a maximum of 8 Mbps when the transmission rate (PHY rate) of the physical layer is 36 Mbps.

  In addition, the transmission buffer 104 of the transmission device 201 and the reception buffer 304 of the reception device 202 are prepared as buffers capable of storing stream data for 256 ms. As a result, the maximum delay (jitter) when stream data is transmitted and received is 256 ms.

  First, before the transmission of the stream data as described above, after the parameter setting relating to QoS is performed between the HC function unit 7 and the reception device 202 in the transmission device 201, the transmission device 201 Is started (start in FIG. 8). Thereafter, the coding rate management unit 102 waits for transmission in the transmission buffer 104, information on the PHY rate currently used from the channel state measurement unit 107, information on the packet error rate (PER) in a predetermined measurement period, and the transmission buffer 104. Information on the number of packets (buffer size) is collected (S201). The predetermined measurement period for calculating the packet error rate is basically a period between the current time and a predetermined time.

  Next, the coding rate management unit 102 determines whether or not the PHY rate can be increased (S202). If it is determined that the PHY rate can be increased (YES in S202), an error is caused to increase the PHY rate. The tolerance adding unit 105 is controlled (S203), and all the processes are terminated.

  Here, as a criterion for determining that the PHY rate can be increased, the fastest PHY rate set by the application 101 is not set, that is, the current PHY rate is not 36 Mbps, and The condition is that the buffer size is zero. Here, the condition is that the buffer size is 0, but the condition may be that the buffer size falls below a certain threshold. Further, when the communication status is still poor when the PHY rate is increased, the PHY rate is decreased again. However, in such a case, the condition that the PHY rate is increased when it can be determined that no video disturbance occurs on the receiving side. But you can.

  On the other hand, if NO in S202, that is, if the PHY rate cannot be increased, the coding rate management unit 102 determines the relationship between the current PHY rate information and the PHY rate and predicted maximum throughput as shown in FIG. The predicted maximum throughput ((TH (current)) and (TH (new))) is determined with reference to the table shown (S204).

  Here, as described above, the predicted maximum throughput means that the communication status in the communication medium 203 is good when the transmission apparatus 201 performs data transmission using all the bands allocated in the predetermined period. It shows the maximum throughput that can be achieved when the packet error rate is assumed to be zero. TH (current) indicates the predicted maximum throughput that can be achieved at the current PHY rate, and TH (new) indicates the predicted maximum throughput that can be achieved when the PHY rate is lowered by one level from the current level. . Here, reducing the PHY rate by one step means changing the PHY rate registered in the table to a PHY rate that is one step lower than the current PHY rate. TH (new) is not limited to a PHY rate that is one step lower than the current PHY rate, and may be any PHY rate lower than the current PHY rate.

  Thereafter, the coding rate management unit 102 determines whether or not the packet error rate can be measured (S205). If the packet error rate cannot be measured (NO in S205), all the processes are terminated. Here, the case where the packet error rate cannot be measured corresponds to the case where there is no packet to be transmitted. In this case, since the communication status cannot be determined, the current error resilience setting is maintained. However, when stream data is transmitted, there should normally be packets that should be transmitted constantly, so it is considered very unlikely that the determination in S205 will be NO.

  On the other hand, if YES in S205, that is, if it is determined that the packet error rate has been measured, the coding rate management unit 102 determines whether or not the throughput is increased by lowering the PHY rate in the current communication state. . This determination is made based on whether TH (new) is greater than TH (current) × (1-PER) (S206).

  If it is determined that the throughput does not increase (NO in S206), the current error resilience setting is maintained and all the processes are completed. On the other hand, if YES in S206, that is, if it is determined that the throughput is increased by lowering the PHY rate, the coding rate management unit 102 instructs the error resilience adding unit 105 to lower the PHY rate. (S207) All processing is completed.

  In the example of the error resilience control described above, the transmission apparatus 201 includes the HC function unit 7, and the band is secured by the HCCA communication control by the HC function unit 7, so how much band can be secured. It has become clear. Therefore, once the PHY rate is determined, the predicted maximum throughput can be calculated by using the above table.

  On the other hand, in an actual system, the HC function may be realized by a communication device other than the transmission device 201. In this case, as described above, even when the HC function is realized by a communication device other than the transmission device 201 by using the packet information indicating the band allocation, the HC function is normally transmitted by the transmission device 201. It is possible to perform error resilience control as in

  However, as described above, when the communication state between the communication device having the HC function and the transmission device 201 is deteriorated, it is conceivable that a reception error of a packet indicating allocation of a band occurs. In this case, there is a possibility that the bandwidth allocated to the transmission apparatus 201 becomes small.

  In order to cope with such a case, as described above, when the communication device having the HC function is different from the transmission device 201, the following processing is preferably performed. First, the communication path state measurement unit 107 measures a communication band actually allocated in a predetermined period. Then, the coding rate management unit 102 calculates the predicted maximum throughput for each PHY rate when it is assumed that the allocated communication bandwidth is all used, the communication status is good, and the packet error rate is 0. Create a table based on the calculation results. This table is updated each time the communication bandwidth measurement unit 107 measures the communication band for each predetermined period. In this way, by performing the error resilience control as described above based on the table updated as needed, it is possible to cope with the case where the HC function is in a device other than the transmission device 201.

  Further, as described above, when the best effort type communication is performed, it is preferable that the following processing is performed. First, the communication path state measurement unit 107 measures the bandwidth occupied by the transmission apparatus 201 and the free bandwidth that no communication device uses the bandwidth in a predetermined period. A sum of these two bandwidths is regarded as a communication band that can be secured by the transmission apparatus 201. Then, the coding rate management unit 102 calculates the predicted maximum throughput for each PHY rate when all the communication bandwidth that can be secured is used and the communication state is good and the packet error rate is assumed to be zero. Then, a table based on the calculation result is created. This table is updated each time the communication bandwidth measurement unit 107 measures the communication band for each predetermined period. Thus, by performing the error resilience control as described above based on the table updated as needed, it is possible to cope with the case where communication is performed in a best effort type such as EDCA communication control.

  Further, as described above, in addition to the band actually given or used as described above, the channel state measurement unit 107 performs C / N in a delivery confirmation packet sent from the receiving device 202, for example. The coding rate management unit 102 may calculate the predicted maximum throughput using the C / N value.

(Example of results of error resilience control)
FIG. 11 is a graph showing an example of a result when the error resilience control as described above is actually performed. In this example, error resilience control and translation control are performed simultaneously. First, a case where only error resilience control is performed alone will be described. For example, as described above, when a bandwidth of 8 Mbps is secured by HCCA communication control, the stream data rate is set to 7 Mbps in consideration of the bandwidth to be retransmitted, and error resilience control as described above is performed. Let's consider the case where is done.

  It is assumed that when communication is performed in a state where the PHY rate is set to 36 Mbps, the PHY rate is lowered to 24 Mbps due to deterioration of the communication state. In this case, the actual throughput is improved because the error tolerance is higher than when communication is performed with the PHY rate set to 36 Mbps. However, if communication is performed with the PHY rate set to 24 Mbps, as shown in FIG. 6, the throughput is about 4.5 Mbps even when all bands are used. Therefore, while the communication status is poor, the corresponding data is stored in the transmission buffer 104 of the transmission apparatus 201. Then, when the communication status is recovered thereafter, the data stored in the transmission buffer 104 is decreased by increasing the PHY rate again, and as a result, the video disturbance can be reduced.

  However, as is clear from the above description, data during a poor communication state is stored in the transmission buffer 104 of the transmission device 201. Therefore, when the communication status deteriorates, it is possible to reduce the amount of data stored in the transmission buffer 104 by simultaneously performing the translation control. Therefore, in the example shown in FIG. 11, both error resilience control and translation control are performed.

  In the translation control and the error resilience control, the processing shown in FIG. 5 and the processing shown in FIG. 8 are performed at a constant interval. Here, this interval is 15 ms. Further, the communication path state measurement unit 107 calculates the PER by counting the number of packets that have been successfully transmitted and the number of packets that have failed to be transmitted in order to calculate the packet error rate. However, since there are few samples of the number of packets at the 15 ms interval, the packet error rate is calculated by averaging four times of the information collected at the 15 ms interval.

  As described above, when the PER is calculated by counting the number of packets successfully transmitted and the number of packets unsuccessfully transmitted, the processing in S206 is as follows: TH (new) is TH (current) × ( A determination is made as to whether or not it is greater than S / (S + US)). Here, S indicates the number of packets that have been successfully transmitted, and US indicates the number of packets that have failed to be transmitted.

  Furthermore, in order to make it easy to grasp the wireless situation, in the result shown in FIG. 11, the transmission success rate as a value obtained by dividing the average value of the number of successful transmission packets by the measurement interval instead of the packet error rate, and the transmission failure packet The transmission failure rate is shown as a value obtained by dividing the average value of the numbers by the measurement interval.

  In FIG. 11, A <b> 1 indicates a change in the stream setting rate (NR) set by the coding rate management unit 102, and A <b> 2 indicates a change in the transmission success rate measured by the channel condition measurement unit 107. A3 indicates a change in the transmission failure rate measured by the communication path condition measuring unit 107, and A4 indicates a change in the number of packets waiting for transmission in the transmission buffer 104 (buffer size). A5 indicates a change in the set PHY rate, and A6 indicates the number of packets counted by the transmission buffer 104 that cannot be confirmed from the reception device 202 and have expired. This shows the change in (number of losses). The horizontal axis represents time, and the left side of the vertical axis represents the data rate (Mbps), which is the axes of A1, A2, and A3. The right side of the vertical axis represents the buffer size (number of packets), the PHY rate (Mbps), and the number of loss occurrences (number of packets), which are the axes of A4, A5, and A6.

  As shown in FIG. 11, in the vicinity of 3700 ms, the communication status is deteriorated, the transmission success rate is lowered, and the transmission failure rate is raised. Along with this, the number of packets waiting to be transmitted in the transmission buffer 104 increases, but the PHY rate is changed from 36 Mbps to 24 Mbps in accordance with the communication status, and the stream setting rate is changed according to the change in the PHY rate. Has been lowered. As a result, an increase in the number of packets waiting for transmission in the transmission buffer 104 can be further suppressed as compared with the case where only the translation control shown in FIG. 7 is used.

  Here, the speed at which packets waiting for transmission in the transmission buffer 104 increase depends on the time until the coding rate management unit 102 detects that the communication status has deteriorated, and the coding rate changing unit 103. It depends on how long it takes to translate and how much throughput is in between. The stable communication state continues by lowering the PHY rate to around 4300 ms, and the PHY rate is increased to 36 Mbps when the buffer size becomes 0 around 4400 ms. As the stream setting rate is increased accordingly, a stable communication band can be secured.

  From the above results, it is possible to perform error resilience control and translation control with high followability not only when the communication state deteriorates but also when the communication state recovers. In addition, since the transmission apparatus 201 determines the communication status, the reception apparatus 202 does not need a mechanism for performing feedback.

(Communication mode control processing)
Next, communication mode control processing set in the application 101 of the transmission apparatus 201 will be described below with reference to the flowchart shown in FIG. As described above, the settable communication modes include the high quality mode and the low power consumption mode. The high quality mode is a communication mode in which priority is given to improving the quality of stream data over suppressing power consumption. The low power consumption mode is a communication mode in which priority is given to suppressing power consumption over the quality of stream data.

  The communication mode may be set according to control information sent from the input unit 2 such as a button or a remote control, or may be set by receiving control information from the receiving device 202 via the communication unit 108. According to the setting of the communication mode, the application 101 sets the upper limit value and the lower limit value of the encoding rate for the encoding rate management unit 102, and the transmission rate in the physical layer to be used for the error resilience management unit 106. And set the upper limit of transmission power.

  First, the application 101 determines whether or not the communication mode has been changed (S301). When it is determined that there is no change (NO in S301), the application 101 ends all processing without changing the communication mode. On the other hand, if YES in S301, that is, if it is determined that the communication mode has been changed, the application 101 determines whether the change is to the low power consumption mode or to the high quality mode. (S302).

  If it is determined that the mode has been changed to the low power consumption mode (Yes in S302), the application 101 first instructs the coding rate management unit 102 to lower the upper limit value of the translation rate (coding rate). (S303). As a result, the amount of data input to the transmission buffer 104 is reduced. Thereafter, after a predetermined time, the application 101 instructs the error resilience management unit 106 to lower the upper limit value of the PHY rate (S304). Further, after a predetermined time, the application 101 instructs the communication unit 108 to reduce the transmission power (S305). Thus, by performing the processing of S303 to S305 step by step, it becomes possible to shift to the low power consumption mode without image disturbance.

  On the other hand, if NO in S302, that is, if the mode is a change to the high quality mode, first, the application 101 instructs the communication unit 108 to increase the transmission power (S306). Thereafter, after a predetermined time, the application 101 instructs the error resilience management unit 106 to increase the upper limit value of the PHY rate (S307). Thereafter, after a predetermined time, the application 101 instructs the coding rate management unit 102 to increase the upper limit value of the translation (coding rate) (S308). As a result, the amount of data input to the transmission buffer 104 is increased. As described above, by performing the processing of S306 to S308 step by step, it is possible to shift to the high quality mode without image disturbance.

  As shown in FIG. 13A, the effect is particularly exerted by performing the control as described above, when the transmission power is lowered and the power consumption is greatly reduced. In such a case, it is important to reduce transmission power in order to reduce power consumption. However, as shown in FIG. 10, in the receiving apparatus 202, the input power and the error rate are closely related, and if the transmission power is lowered, the communication environment is deteriorated. Therefore, it is necessary to lower the PHY rate so that the communication environment does not deteriorate even if the transmission power is lowered. However, when the PHY rate is lowered, if there is no change in the set rate of the stream, video disturbance occurs due to the data being stored in the transmission buffer 104 of the transmission apparatus 201 at an allowable amount or more. On the other hand, when the upper limit value of the stream setting rate in the translation control is lowered, the video quality is lowered, but the video is not disturbed, and the power consumption can be reduced.

  Here, in actual control, when shifting to the low power consumption mode, if processing is performed in the order of transmission power change, PHY rate change, and stream setting rate change, data transfer will fail. There is a possibility of coming. Therefore, as described above, it is preferable to perform processing in the order of changing the set rate of the stream, changing the PHY rate, and changing the transmission power. Then, when shifting to the high quality mode, as described above, it is preferable to perform the processing in exactly the opposite flow as when shifting to the low power consumption mode. However, the process is not limited to being performed in this order, and the process may be performed in a different order or may be performed at substantially the same timing.

  The control as described above is effective when the relationship between the transmission power and the power consumption is as shown in FIG. 13A. However, as shown in FIG. In the case where the power does not decrease much, the effect of reducing the power consumption by reducing the transmission power cannot be expected. Therefore, in such a case, the process from S304 to S305 illustrated in FIG. 12 may be changed to a process of increasing the upper limit value of the PHY rate and increasing the upper limit value of the transmission power. According to this method, the communication time is shortened by increasing the PHY rate and power consumption, and as a result, low power consumption can be achieved.

  Note that the application 101, the coding rate management unit 102, the coding rate change unit 103, the error resilience addition unit 105, the error resilience management unit 106, the channel condition measurement unit 107, and the communication unit 108 included in the data transmission unit 1 described above. Can be realized by an arithmetic unit such as a CPU executing a program stored in a storage unit such as a ROM (Read Only Memory) or a RAM and controlling a communication unit such as an interface circuit. Therefore, various functions and various processes included in the data transmission unit 1 of the present embodiment can be realized simply by a computer having these means reading the recording medium storing the program and executing the program. In addition, by recording the program on a removable recording medium, the various functions and various processes described above can be realized on an arbitrary computer.

  As the recording medium, a memory (not shown) such as a ROM may be used as a program medium for processing by the microcomputer, and a program reader is provided as an external storage device (not shown). It may be a program medium that can be read by inserting a recording medium therein.

  In any case, the stored program is preferably configured to be accessed and executed by the microprocessor. Furthermore, it is preferable that the program is read out, and the read program is downloaded to the program storage area of the microcomputer and the program is executed. Note that this download program is stored in advance in the transmission apparatus 201.

  The program medium is a recording medium configured to be separable from the main body, such as a tape system such as a magnetic tape or a cassette tape, a magnetic disk such as a flexible disk or a hard disk, or a disk such as a CD / MO / MD / DVD. Fixed disk system, card system such as IC card (including memory card), or semiconductor memory such as mask ROM, EPROM (Erasable Programmable Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), flash ROM, etc. In particular, there are recording media that carry programs.

  In addition, the recording medium is preferably a recording medium that fluidly carries the program so as to download the program from a communication network such as the Internet.

  Further, when the program is downloaded from the communication network in this way, it is preferable that the download program is stored in advance in the transmission device 201 or installed from another recording medium.

  As described above, the transmission device according to the present invention is a transmission device that transmits encoded stream data that requires real-time transmission, and the transmission device temporarily stores the stream data. A communication unit that transmits the data accumulated in the transmission buffer to an external communication device, and a communication path state measurement unit that measures a communication state in the communication unit. The calculation of the throughput and the packet error rate information in a predetermined period or the number of packets successfully transmitted and the number of packets unsuccessfully transmitted are measured, and control is performed so that real-time transmission is not interrupted based on the information. It is said.

  In such a transmission apparatus, when transmitting stream data that requires real-time transmission such as video and audio, the stream data is controlled by performing control based on the predicted maximum throughput and packet error rate that can be achieved in the transmission apparatus. Therefore, it is possible to perform control with a fast reaction speed not only when the communication status is deteriorated but also when the communication status is improved.

  The transmission apparatus according to the present invention includes an encoding rate changing unit that changes an encoding rate of the stream data, and an encoding rate managing unit that manages the encoding rate of the encoding rate changing unit, It is preferable that the encoding rate management unit issues an instruction to change the encoding rate based on the measurement result of the communication status in the communication status measurement unit.

  In this way, it is possible to reduce image disturbance by performing translation control based on the measurement result of the current communication state in the transmission device.

  The transmission apparatus according to the present invention includes an error tolerance adding unit that adds error tolerance to data accumulated in the transmission buffer, and an error tolerance management unit that manages the error tolerance adding unit, and the communication status measuring unit It is preferable that the error resilience management unit issues an error resilience change instruction based on the measurement result of the communication status in FIG.

Thus, by performing error resilience control based on the measurement result of the current communication status in the transmission device, it is possible to reduce image disturbance.
The transmission apparatus according to the present invention includes an encoding rate changing unit that changes an encoding rate of the stream data, an encoding rate managing unit that manages an encoding rate of the encoding rate changing unit, and the transmission buffer. An error resilience adding unit for adding error resilience to the data stored in step (b), and an error resilience managing unit for managing the error resilience adding unit, and the encoding based on the measurement result of the communication state in the communication state measuring unit It is preferable that an instruction to change the coding speed is given by the speed manager, and an instruction to change the error tolerance is given by the error tolerance manager.

  In this way, it is possible to reduce image disturbance by performing translation control and error resilience control based on the measurement result of the current communication status in the transmission device.

  In the transmission apparatus according to the present invention, it is preferable that the encoding rate management unit can set an upper limit value and / or a lower limit value, and issues an instruction to change the encoding rate within the range.

  In this way, by setting the upper limit value of the translation control, the stream data rate can be set higher than the required quality, and the communication bandwidth can be occupied more than necessary, or the communication environment can deteriorate. In this case, it is possible to avoid a situation in which image disturbance is likely to occur. In addition, by setting the lower limit value of the translation control, it is possible to ensure the minimum quality.

  In the transmission apparatus according to the present invention, the communication status measurement unit collects information on a PHY rate used in the communication unit, and the error resilience management unit issues an error resilience change instruction based on the information. It is preferable.

  Thus, by collecting information on the currently used PHY rate, it is possible to accurately grasp the current state of the communication path.

  In the transmission apparatus according to the present invention, the error resilience adding unit transmits stream data via the communication unit by specifying a PHY rate for the data accumulated in the transmission buffer, and the error resilience management It is preferable that the unit can set an upper limit value and / or a lower limit value of the PHY rate, and performs an error resilience change instruction by controlling the PHY rate based on the measurement result of the communication status.

  In this way, by changing the PHY rate, it is possible to improve the throughput by lowering the PHY rate when the communication situation deteriorates. In addition, by allowing the upper limit value of the PHY rate to be set, it is possible to avoid the increase in the PHY rate, the error tolerance being too weak, and the range in which stable communication can be stably reduced. By making it possible to set the lower limit value of the PHY rate, it is possible to avoid a situation where the PHY rate is lowered, error tolerance is increased more than necessary, and throughput is lowered.

  In the transmitter according to the present invention, the error resilience adding unit further adds an error correction code to the data accumulated in the transmission buffer and transmits stream data via the communication unit, and the error It is preferable that the tolerance management unit issues an error tolerance change instruction by controlling the coding method and / or the coding parameter of the error correction code based on the measurement result of the communication status.

  As described above, by adding the error correction code, when the communication situation deteriorates, it is possible to improve the throughput by adding the error correction code.

  In the transmission apparatus according to the present invention, the error tolerance adding unit further divides the data accumulated in the transmission buffer into smaller sizes and transmits stream data via the communication unit, and the error tolerance management Preferably, the unit issues an error resilience change instruction by controlling the size to be divided based on the measurement result of the communication status.

  In this way, by dividing the stream data into smaller sizes, it is possible to improve the throughput by controlling the size to be divided when the communication state deteriorates.

  In the transmission apparatus according to the present invention, the error resilience management unit compares the current throughput with the predicted maximum throughput after changing the error resilience based on the measurement result of the communication status, It is preferable to give an instruction to change the error resilience when it is determined that the throughput is improved by the change.

  In this way, by comparing how much throughput is obtained when it is assumed that the current throughput and error resilience have been changed, it is possible to control the throughput in a higher direction.

  Further, in the transmission device according to the present invention, the error resilience management unit issues an error resilience change instruction when the stored information in the transmission buffer falls below a predetermined threshold based on the measurement result of the communication status. Is preferred.

  In this way, once the error tolerance is increased, it is possible to determine at which timing the error tolerance can be reduced.

  In the transmission apparatus according to the present invention, the communication status measurement unit preferably measures information on a PHY rate used in the communication unit, and calculates a predicted maximum throughput using the information on the PHY rate. .

  In this way, in the case where the HC and the transmission device are configured by the same device, if the band is secured by HCCA, the prediction can be made only by measuring the currently used PHY rate. It is possible to calculate the maximum throughput.

  Further, in the transmission apparatus according to the present invention, the communication status measurement unit measures information on a PHY rate used in the communication unit and a communication band allocated in a predetermined period, and the information on the PHY rate and the communication band are measured. It is preferable to calculate the predicted maximum throughput using this information.

  In this way, when the HC and the transmission device are configured as separate devices, even when the bandwidth is secured by HCCA, the bandwidth actually allocated from the HC and the PHY rate that is currently being attempted It is possible to calculate the predicted maximum throughput by measuring.

  Further, in the transmission device according to the present invention, the communication status measurement unit measures the PHY rate information used in the communication unit and the bandwidth and free bandwidth occupied by the transmission device in a predetermined period, It is preferable to calculate the predicted maximum throughput using the information on the PHY rate and the information on the occupied bandwidth and the free bandwidth.

  In this way, even in the case where stream data is transmitted in the best effort type such as EDCA, a prediction can be made by measuring the bandwidth actually used by the transmission device, the free bandwidth, and the PHY rate. It is possible to calculate the maximum throughput.

  Further, in the transmission device according to the present invention, the transmission device can switch between the high quality mode and the low power consumption mode, and the encoding is performed based on the measurement result of the communication status in the mode and the communication status measurement unit. It is preferable that the rate management unit issues an instruction to change the coding rate, and the error tolerance management unit issues an error tolerance change instruction.

  In this way, it is possible to switch between a mode that prioritizes video quality and a mode that prioritizes long-time use, reflecting the user's intention.

  Further, when the transmission apparatus according to the present invention sets the upper limit value and / or lower limit value of the encoding rate set by the encoding rate management unit, when the transmission apparatus is controlled in the high quality mode, Set the upper limit value and / or lower limit value of the encoding speed higher than the specified value, and set the upper limit value and / or lower limit value of the encoding speed lower than the specified value when controlling in the low power consumption mode. It is preferable that the encoding rate management unit issues an instruction to change the encoding rate within the range.

  In this way, high-quality video transmission is possible in the high-quality mode, and transmission time is shortened by reducing the quality in the low-power consumption mode. It becomes possible.

  In the transmission device according to the present invention, the error resilience adding unit instructs the communication unit to transmit power when transmitting the encoded and modulated stream data via the transmission unit, and When the transmission apparatus is controlled in the high quality mode, the transmission power is set higher than the first specified value, and the upper limit value and / or the lower limit value of the coded modulation set by the error resilience management unit is set to the second value. If the control is performed in the low power consumption mode, the transmission power is set lower than the first specified value, and the upper limit value of the coded modulation set by the error resilience management unit and Preferably, the lower limit value is set lower than the second specified value, and the error resilience adding unit gives an instruction to change error resilience by controlling the coding modulation method within the range.

  In this way, high-quality video transmission is possible in the high quality mode, and in the low power consumption mode, the transmission power and the PHY rate are controlled to be reduced simultaneously, resulting in low power consumption. Electricity can be achieved.

  Moreover, it is preferable that the transmission apparatus according to the present invention displays whether the transmission apparatus is controlled in a high quality mode or a low power consumption mode.

  By doing so, it is displayed whether the transmission apparatus is controlled in the high quality mode or in the low power consumption mode. As a result, the user can know and / or confirm which mode is currently controlled, so that the user can take an action as needed.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately changed within the scope of the claims are also included in the technical scope of the present invention.

  The communication device and the communication system according to the present invention can be suitably used for a network system or the like in which a communication function such as wireless is built in, for example, a household appliance and these are connected to each other as a home LAN. is there. More specifically, the present invention can be applied to a communication device for connecting an AV source such as a tuner and an AV playback device such as a display arranged at a distance, a communication system including the communication device, and the like.

It is a block diagram which shows the function structure of the data transmission part with which the transmission apparatus which concerns on one Embodiment of this invention is provided. It is a block diagram which shows the outline of an example of the communication system which concerns on this embodiment. It is a block diagram which shows schematic structure of the transmitter which concerns on this embodiment. It is a block diagram which shows schematic structure of the receiver which concerns on this embodiment. It is a flowchart which shows the process sequence of translation control. It is a table which shows the relationship between a PHY rate and a prediction maximum throughput. It is a graph which shows an example of the result of translation control. It is a flowchart which shows the process sequence of error tolerance control. It is a table | surface which shows the relationship between a PHY rate and error tolerance. It is a graph which shows the relationship between input electric power and a packet error rate. It is a graph of an example of the result in the case of using translation control and error tolerance control simultaneously. It is a flowchart which shows the process sequence in control of a communication mode. The same figure (a) and the same figure (b) are graphs which show an example of the relationship between transmission power and power consumption.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Data transmission part 2 Input part 3 Display part 4 Tuner part 5 Wide area communication part 6 Coding part 7 HC function part 10 Table memory | storage part 101 Application (range setting part)
102 Encoding rate management unit 103 Encoding rate change unit 104 Transmission buffer 105 Error tolerance addition unit 106 Error tolerance management unit 107 Communication path state measurement unit 108 Communication unit 109 Antenna 110 Table storage unit 201 Transmission device (communication device)
202 receiving device 203 communication medium 204 broadcasting station 205 public network 206 analog AV source 207 network system 301 display unit 302 decoding unit 303 application 304 reception buffer 305 error resilience decoding unit 306 communication unit 307 antenna 308 input unit

Claims (21)

A communication device that transmits stream data that requires real-time transmission to an external communication device via a communication medium by packet communication,
A data format changing unit that changes the stream data to a data format suitable for transmission on the communication medium;
A data format management unit for controlling the data format set in the data format changing unit;
A communication path status measuring unit for measuring the communication status in the communication medium based on a delivery confirmation packet sent from the external communication device;
The data format management unit controls the data format based on the communication status measured by the communication path status measurement unit.   The data format management unit calculates a predicted throughput as a predicted value of a data transfer rate at which data transfer is substantially performed, and controls the data format based on the predicted throughput and the communication status. The communication apparatus according to claim 1, wherein: The data format changing unit is an encoding rate changing unit for setting an encoding rate of the stream data;
The data format management unit is a coding rate management unit that controls a coding rate set in the coding rate changing unit;
The communication apparatus according to claim 1 or 2, wherein the encoding rate management unit controls the encoding rate based on a communication state measured by the communication path state measuring unit. The data format changing unit is an error resilience adding unit that imparts error resilience to a transmitted packet,
The data format management unit is an error tolerance management unit that controls error tolerance given in the error tolerance addition unit,
The communication apparatus according to claim 1, wherein the error resilience management unit controls the error resilience based on a communication state measured by the communication path state measurement unit. The data format changing unit is an encoding rate changing unit for setting an encoding rate of the stream data, and an error tolerance adding unit for giving error tolerance to a packet to be transmitted;
The data format management unit includes a coding rate management unit that controls a coding rate set in the coding rate change unit, and an error resilience management unit that controls error resilience provided in the error resilience adding unit. Yes,
The coding rate management unit controls the coding rate based on the communication status measured by the channel status measurement unit, and the error tolerance management unit is measured by the channel status measurement unit. The communication apparatus according to claim 1, wherein the error tolerance is controlled based on a communication state.   4. A range setting unit for setting an upper limit value and / or a lower limit value of the encoding rate control for the encoding rate management unit based on an instruction from the outside. Or the communication apparatus of 5. A communication unit having a function as a physical layer when data transmission is performed via the communication medium,
The communication path condition measurement unit further measures the physical layer communication speed set by the physical layer in the communication unit,
5. The communication apparatus according to claim 4, wherein the error resilience management unit controls the error resilience based on a physical layer communication speed measured by the communication path state measurement unit and the communication state. The error resilience management unit controls the error resilience adding unit to change the error resilience added to the transmitted packet, thereby changing the physical layer communication speed set by the physical layer in the communication unit. As
The system further comprises a range setting unit for setting an upper limit value and / or a lower limit value of the control of the physical layer communication speed for the error resilience management unit based on an instruction from the outside. 7. The communication device according to 7.   5. The error resilience management unit controls error resilience by instructing the error resilience adding unit to change an encoding method and / or an encoding parameter of an error correction code. The communication device described.   The error resilience management unit calculates a predicted throughput as a predicted value of the data transfer rate at which data transfer is substantially performed, and compares the current throughput with the predicted throughput after changing the error resilience, 5. The communication apparatus according to claim 4, wherein control is performed to change error resilience when it is determined that changing the error resilience increases throughput. A transmission buffer for temporarily storing data to be transmitted;
The communication apparatus according to claim 4, wherein the error resilience management unit controls the error resilience to be weaker when the amount of data stored in the transmission buffer falls below a predetermined threshold. A communication unit having a function as a physical layer when data transmission is performed via the communication medium,
The communication path condition measurement unit further measures the physical layer communication speed set by the physical layer in the communication unit,
The communication apparatus according to claim 2, wherein the data format management unit calculates the predicted throughput based on the physical layer communication speed. The communication path condition measurement unit further measures the communication band allocated to the communication device in a predetermined period,
13. The communication apparatus according to claim 12, wherein the data format management unit calculates the predicted throughput based on information on the physical layer communication speed and the communication band. The communication path state measurement unit further measures the occupied bandwidth and the free bandwidth occupied by the communication device in a predetermined period,
13. The communication apparatus according to claim 12, wherein the data format management unit calculates the predicted throughput based on the physical layer communication speed, and information on the occupied bandwidth and the free bandwidth.   The range setting unit accepts a data transmission instruction in the high quality mode and a data transmission instruction in the low power consumption mode from the outside, and an upper limit value and / or a lower limit of the control of the coding rate corresponding to the instructed mode The communication apparatus according to claim 6, wherein a value is set.   The range setting unit accepts a data transmission instruction in the high quality mode and a data transmission instruction in the low power consumption mode from the outside, and an upper limit value of the physical layer communication speed control and / or corresponding to the instructed mode The communication apparatus according to claim 8, wherein a lower limit value and transmission power in the communication unit are set.   The communication apparatus according to claim 15 or 16, further comprising a display unit that displays whether the high quality mode or the low power consumption mode is being controlled. A communication method for transmitting stream data that requires real-time transmission to an external communication device via a communication medium by packet communication,
A data format changing step for changing the stream data to a data format suitable for transmission in the communication medium;
A data format management step for controlling the data format set in the data format change step;
A communication path status measurement step for measuring a communication status in the communication medium based on a delivery confirmation packet sent from the external communication device;
In the data format management step, the data format is controlled based on the communication status measured by the communication path status measurement unit.   A communication program for operating the communication device according to any one of claims 1 to 17, wherein the communication program causes a computer to function as each unit.   A computer-readable recording medium on which the communication program according to claim 19 is recorded. A communication device according to any one of claims 1 to 17,
A communication system, comprising: a receiving device capable of communicating with the communication device via a communication medium and receiving stream data from the communication device.

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