JP5736237B2 - Video transmission device - Google Patents

Description

  The present invention relates to a video transmission apparatus that transmits video data by a wireless LAN.

  IEEE802.11 is known as a standard that standardizes various procedures related to wireless communication, and video transmission apparatuses using a series of transmission methods according to this standard are widely used. Using this transmission method, live video captured by a web camera is generally transmitted from a remote place by a wireless LAN. Since video data of live video is large, when live video is transmitted, encoding processing is performed to reduce high-frequency video components that are difficult for human eyes to detect, and live video data compression processing is performed. There are many cases.

  In a system that transmits video data using a wireless LAN, the bit rate (transmission rate) that can be transmitted per frequency band varies depending on the carrier-to-noise ratio (C / N ratio). That is, the propagation state of the wireless transmission path changes and the transmission rate varies depending on the distance between the transmission / reception devices that transmit video data over the wireless LAN or the presence or absence of an obstacle that prevents radio wave propagation between the transmission / reception devices.

  In such a wireless transmission path, when the transmitting device encodes video data at a fixed compression rate (encoding rate) and transmits the video data at a constant transmission rate, the propagation status of the wireless transmission path When the transmission rate decreases due to a change in the video data, all video data cannot be transmitted. In this case, since the receiving device cannot receive the video data satisfactorily, the video displayed on the screen is disturbed.

  Also, in a wireless LAN defined in IEEE 802.11, a plurality of video transmission apparatuses share video transmission data of the same channel using a CSMA (Carrier Sense Multiple Access) method. Each video transmission device temporarily stops video data transmission and waits for video data to be transmitted when other video transmission devices are transmitting video data to avoid interference on the wireless propagation path Let However, in such a propagation state of the wireless transmission path, the transmission rate is lowered in each video transmission apparatus.

  In order to solve such a problem, a method of adaptively changing the compression rate of video data according to the propagation state of the wireless transmission path is known (see, for example, Patent Document 1). In this method, the video transmission apparatus lowers the transmission rate when the propagation state of the wireless transmission path deteriorates, and increases the transmission rate when it improves. Also, the encoding rate is controlled so that the encoding rate is equal to or lower than the transmission rate. Thereby, transmission errors of video data can be reduced, and video data can be transmitted satisfactorily even when the propagation state of the wireless transmission path changes.

JP 2007-329708 A

  However, in the method of Patent Document 1, since the encoding rate is controlled after the transmission rate is changed, when the propagation state of the wireless transmission path is changed and the transmission rate is lowered, the video data is changed until the encoding rate is switched. There is a problem that the video cannot be transmitted due to a loss of video, and the video during that period is interrupted. Also, in Patent Document 1, when a plurality of video transmission apparatuses transmit video data by sharing a wireless transmission path of the same channel according to the CSMA method, a situation in which a transmission rate is reduced at the time of simultaneous transmission, There is no explicit description on how to specifically control the encoding rate.

  Therefore, the present invention has been made in view of the above problems, and its purpose is that the transmission rate changes according to the propagation status of the wireless transmission path, or the transmission rate is lowered due to simultaneous transmission on the same transmission path. However, an object of the present invention is to provide a video transmission device capable of continuing transmission of video data without interruption.

In order to achieve the above object, a video transmission apparatus according to the present invention is a video transmission apparatus that generates encoded data by compressing and encoding a video signal, modulates the encoded data, and transmits the encoded data to a receiving apparatus via a wireless transmission path. A reception demodulator for receiving and demodulating data including an acknowledgment ACK for the transmitted encoded data from the receiving device; and an electric field strength measurement for measuring electric field strength of radio waves for the data transmitted by the receiving device A modulation scheme determination unit that determines a modulation scheme based on the electric field strength measured by the electric field strength measurement unit, and modulates the encoded data according to the modulation scheme determined by the modulation scheme determination unit, to the wireless transmission path A new modulation scheme is determined by a transmission section having a modulation transmission section to transmit, and a modulation scheme determination section of the transmission section; When switching to a new modulation method, an intermediate encoding rate is determined based on the current modulation method before the switching, the modulation method after the switching, and the electric field strength measured by the electric field strength measuring unit of the transmitting unit. A driver and an encoder that compresses and encodes a video signal at the encoding rate to generate encoded data, and the intermediate driver calculates a maximum transmittable rate based on the modulation scheme, and after the switching When the maximum transmittable rate in the modulation scheme is equal to or lower than the maximum transmittable rate in the current modulation scheme before switching, compression encoding is performed at an encoding rate equal to or lower than the maximum transmittable rate in the modulation scheme after switching. To output to the encoder, to output the instruction to the encoder, An instruction to switch to the new modulation method is output to the modulation transmission unit of the transmission unit after a predetermined time in which the modulation data of the transmission unit can be modulated by the modulation transmission unit of the transmission unit has elapsed. When the maximum transmittable rate in the modulation scheme after switching is higher than the maximum transmittable rate in the current modulation scheme before switching, an instruction for switching to the new modulation scheme is sent to the transmitting unit. The modulation transmission unit of the transmission unit outputs the modulation scheme switching completion indicating the switching to the new modulation scheme, or the instruction is sent to the modulation transmission unit of the transmission unit. After a predetermined time for switching to the new modulation scheme by the instruction after the output, the maximum transmission possible in the modulation scheme after the switching An instruction for compression encoding at an encoding rate equal to or less than a large rate is output to the encoder .

  In the video transmission device according to the present invention, when the electric field strength measured by the electric field strength measurement unit of the transmission unit is smaller than a predetermined threshold, the intermediate driver transmits the modulation and transmission to the modulation transmission unit of the transmission unit. The transmission is stopped and the encoded data is discarded, and when the electric field strength measured by the electric field strength measurement unit of the transmission unit is equal to or greater than a predetermined threshold, the modulation transmission unit of the transmission unit restarts the modulation and transmission It is characterized by that.

  The video transmission apparatus according to the present invention further includes a position information measuring unit and an encoding rate determining unit, wherein the position information measuring unit measures the position of the video transmission apparatus to generate position information, and the encoding rate The determination unit includes a table in which position information and an encoding rate are stored correspondingly, the position information generated by the position information measurement unit, the position information and the encoding rate stored in the table, and the transmission unit The encoding rate is determined based on the current modulation method used in the modulation transmission unit.

  In the video transmission apparatus according to the present invention, the encoding rate determination unit determines whether the position information generated by the position information measurement unit is stored in the table, and the position information is not stored. A current maximum transmittable rate is calculated based on the current modulation scheme, and the current maximum transmittable rate is stored in the table as an encoding rate corresponding to the position information. If stored, the encoding rate corresponding to the position information is read from the table.

  In the video transmission apparatus according to the present invention, the encoding rate determination unit calculates the current maximum transmittable rate based on the current modulation method, and reads the encoding corresponding to the position information read from the table. When the read encoding rate is equal to or less than the current maximum transmittable rate, the encoder performs compression encoding at the read encode rate. It is characterized by that.

  In the video transmission apparatus according to the present invention, the encoding rate determination unit may determine that the read encoding rate is higher than the current maximum transmittable rate after a predetermined time elapses or the current maximum transmittable rate. After the rate has increased to a predetermined rate, the encoder is caused to perform compression encoding at the read encoding rate.

  As described above, according to the present invention, transmission of video data can be continued without interruption, and a live video is not interrupted.

It is the schematic which shows the whole structure of the transmission system containing the transmission apparatus (video transmission apparatus) by embodiment of this invention. It is a flowchart which shows the transmission process by the wireless LAN physical layer of a transmitter. It is a block diagram which shows the structure of the transmitter by the 1st Embodiment (Example 1) of this invention. 6 is a flowchart illustrating processing related to an encoding rate and a modulation method by an intermediate driver according to the first exemplary embodiment. It is a block diagram which shows the structure of the transmitter by the 2nd Embodiment (Example 2) of this invention. 10 is a flowchart illustrating encoding rate calculation processing by an encoding rate calculation unit according to the second embodiment. It is a block diagram which shows the structure of the transmitter by the 3rd Embodiment (Example 3) of this invention. 10 is a flowchart illustrating an encoding rate calculation process by an encoding rate calculation unit according to the third embodiment. It is a block diagram which shows the structure of the transmitter by the 4th Embodiment (Example 4) of this invention. 14 is a flowchart illustrating processing related to an encoding rate and a modulation method by a position-transmission rate table holding unit according to the fourth embodiment. It is a block diagram which shows the structure of the transmitter by the 5th Embodiment (Example 5) of this invention.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.
[Overall system]
First, a transmission system including a transmission device (video transmission device) according to an embodiment of the present invention will be described. FIG. 1 is a schematic diagram showing the overall configuration of a transmission system. This transmission system includes a transmission device 1 and a reception device 2, and performs live video transmission over a wireless LAN. The transmission device 1 inputs a video signal, performs processing such as encoding and modulation, transmits data to the reception device 2 wirelessly, and receives ACK and the like from the reception device 2. The receiving device 2 receives the data transmitted from the transmitting device 1, performs processing such as demodulation and decoding, restores the original video signal, and outputs it. In addition, when receiving data normally, the receiving device 2 transmits ACK to the transmitting device 1 and transmits other data to the transmitting device 1 as necessary.

  The transmission device 1 includes an encoder 11, an intermediate driver 12, and a wireless LAN physical layer (transmission unit) 13. In addition, although the transmission apparatuses 1-1 to 1-5 of Examples 1 to 5 which will be described later are provided with components having basically the same functions as those in FIG. 1, in addition to the components in FIG. 1 may have a function, or may not have a part of the functions of each component in FIG. 1, and the processing content may be different.

  The encoder 11 receives a video baseband signal, which is a video signal, and also receives an encoding rate instruction from the intermediate driver 12, performs compression encoding of the video signal according to the encoding rate indicated by the encoding rate instruction, and generates encoded data To do.

  The intermediate driver 12 receives the encoded data from the encoder 11 and outputs the input encoded data to the wireless LAN physical layer 13. The intermediate driver 12 also receives reception information such as modulation method switching information and electric field strength from the wireless LAN physical layer 13, calculates an encoding rate based on the reception information, and outputs an encoding rate instruction to the encoder 11. Here, the intermediate driver 12 absorbs a difference associated with the implementation of the wireless LAN physical layer 13 which is a lower layer, and the same physical layer as viewed from the encoder 11 regardless of the type of the wireless LAN physical layer 13. It is an interface that makes it appear as if it is. Therefore, the intermediate driver 12 has different received input information and different processing contents depending on the type of the wireless LAN physical layer 13 to be mounted. This is because the wireless LAN physical layer 13 is provided by each manufacturer, and the modulation method determination method and the information output to the outside differ depending on the type of the wireless LAN physical layer 13.

  The wireless LAN physical layer 13 receives the encoded data from the intermediate driver 12, packetizes the encoded data, adds a sequence number, modulates it, and transmits it wirelessly to the receiving device 2. In this case, the wireless LAN physical layer 13 stores the input encoded data in the transmission buffer, reads the encoded data from the transmission buffer according to the actual transmission rate according to the propagation state of the wireless transmission path, performs the above-described processing, and transmits it. . Further, the wireless LAN physical layer 13 receives an ACK for the transmitted data from the receiving device 2. Thereby, the wireless LAN physical layer 13 can recognize that the transmitted data is correctly received by the receiving device 2.

  Depending on the propagation status of the wireless transmission path between the transmission device 1 and the reception device 2, noise may be added to the data transmitted from the transmission device 1, and the reception device 2 uses the data from the transmission device 1 as a result. It may not be possible to receive normally. In this case, the receiving device 2 cannot transmit ACK to the transmitting device 1.

  The receiving device 2 includes a wireless LAN physical layer 21, an intermediate driver 22, and a decoder 23. The wireless LAN physical layer 21 receives the data transmitted by the transmission device 1, demodulates the data in units of packets, and determines whether the data has arrived normally continuously based on the sequence number of the demodulated packets. Determine. Further, the wireless LAN physical layer 21 determines whether or not the data in the packet is broken based on the frame check sequence (FCS) portion of the demodulated packet. When the wireless LAN physical layer 21 determines that the data has arrived normally and the data in the packet is normal, the wireless LAN physical layer 21 transmits an ACK to the transmission device 1 as a reception confirmation response packet and receives the data normally. The processed data (encoded data) is output to the intermediate driver 22.

  The intermediate driver 22 inputs encoded data from the wireless LAN physical layer 21 and outputs the input encoded data to the decoder 23. Here, as with the intermediate driver 12 provided in the transmission apparatus 1, the intermediate driver 22 absorbs the difference associated with the implementation of the wireless LAN physical layer 21, which is a lower layer, and can be any type of wireless LAN physical layer 21. However, it is an interface for making it appear as if it is the same physical layer as seen from the decoder 23.

  The decoder 23 receives the encoded data from the intermediate driver 22, decodes the encoded encoded data, generates a video baseband signal that is the original video signal, and outputs it.

[Transmission processing by the wireless LAN physical layer of the transmission device]
Next, transmission processing by the wireless LAN physical layer 13 of the transmission apparatus 1 shown in FIG. 1 will be described. FIG. 2 is a flowchart showing the transmission processing. The wireless LAN physical layer 13 of the transmission apparatus 1 receives the encoded data from the intermediate driver 12, packetizes the encoded data, and adds a sequence number to the packetized data (step S201). Then, the wireless LAN physical layer 13 modulates and transmits the packet to which the sequence number is added (step S202). The wireless LAN physical layer 13 waits for an ACK transmitted from the receiving device 2.

  When receiving and demodulating the packet, the receiving device 2 determines the continuity of the packet based on the sequence number added to the data, and determines that the received packet is not broken based on the FCS part of the packet. If it is determined that the packet has arrived normally and the received packet is normal, an ACK is returned to the transmitting apparatus 1. Further, when the receiving device 2 determines that the packet has not arrived normally or the received packet is not normal, the receiving device 2 does not return an ACK.

  The wireless LAN physical layer 13 of the transmission device 1 determines whether or not an ACK for the transmitted packet has been received from the reception device 2 (step S203), and determines that an ACK has been received (step S203: Y). And the process of step S201 is performed on the next packet. As described above, when the wireless LAN physical layer 13 transmits a packet in step S201 to step S203 and receives an ACK from the receiving device 2, the wireless LAN physical layer 13 repeats the process of transmitting the next packet and waiting for the reception of the ACK.

  If the wireless LAN physical layer 13 determines in step S203 that no ACK has been received after waiting for a predetermined time (step S203: N), the number of times the packet has been retransmitted in step S206, which will be described later, and the predetermined maximum number of retransmissions To determine whether the number of retransmissions is equal to or greater than the maximum number of retransmissions (step S204). If the wireless LAN physical layer 13 determines in step S204 that the number of retransmissions is not equal to or greater than the maximum number of retransmissions (step S204: N), the wireless LAN physical layer 13 waits for a predetermined random time to retransmit the packet (step S205). Here, the predetermined random time is longer than the time when the packet was retransmitted last time. That is, in step S205, the wireless LAN physical layer 13 sets a time longer than the time waited when the previous packet was retransmitted as a predetermined random time for retransmitting the current packet, in accordance with the retransmission of the packet. And wait for the predetermined random time. Then, the wireless LAN physical layer 13 retransmits the same packet to the receiving device 2 (step S206), and proceeds to step S203. Thus, when the wireless LAN physical layer 13 does not receive the ACK from the receiving device 2 within a predetermined time after packet transmission or retransmission, the number of retransmissions of the same packet has not reached the predetermined maximum number of retransmissions. The same packet is retransmitted to the receiving device 2.

  If the wireless LAN physical layer 13 determines in step S204 that the number of retransmissions is equal to or greater than the maximum number of retransmissions (step S204: Y), the wireless LAN physical layer 13 determines that an ACK cannot be received even if the retransmission process is performed. A time-out process is performed (step S207), and the process ends.

  If the wireless LAN physical layer 13 cannot normally transmit the packet to the receiving device 2 even after performing the transmission process shown in FIG. 2, that is, if the packet is not recovered by the retransmission process, the encoder 11 In order to cause the wireless LAN physical layer 13 to retransmit the packet, the encoded data corresponding to the packet may be output again to the wireless LAN physical layer 13 via the intermediate driver 12. Further, the wireless LAN physical layer 13 may generate an error correction packet including error correction data for correcting data included in the transmitted packet and transmit the error correction packet to the reception device 2. In this case, the wireless LAN physical layer 21 of the reception device 2 receives the error correction packet from the transmission device 1 and corrects the data determined to be not normal using the error correction data included in the error correction packet.

  Hereinafter, specific examples in which the transmission apparatus 1 illustrated in FIG. 1 performs live video transmission will be described in detail with reference to Examples 1 to 5. The first embodiment is an example in which the encoding rate is controlled in accordance with modulation system switching information determined based on RSSI (Received Signal Strength Indication). In the second embodiment, the encoding rate is controlled according to the amount of data temporarily held in the transmission buffer. Example 3 is an example in which the encoding rate is controlled according to the amount of data that could not be transmitted during the ACK timeout period (the amount of data that could be transmitted when ACK was returned as expected). The fourth embodiment is an example in which the encoding rate is controlled according to the position information of the transmission device acquired by GPS (Global Positioning System) or the like. The fifth embodiment is a modification of the first to fourth embodiments, in which the encoder of the transmission device and the wireless LAN physical layer in the first to fourth embodiments are not integrated, and are configured as separate devices. This is an example where the layer is installed outside as a wireless LAN access point or a wireless LAN bridge device.

[Example 1]
First, Example 1 will be described. In the first embodiment, as described above, the encoding rate is controlled according to the switching information of the modulation scheme determined based on the RSSI.

  FIG. 3 is a block diagram illustrating the configuration of the transmission apparatus according to the first embodiment. The transmission device 1-1 includes an encoder 11, an intermediate driver 12-1, and a wireless LAN physical layer 13-1. As with the encoder 11 shown in FIG. 1, the encoder 11 inputs a video signal, inputs an encoding rate instruction from the intermediate driver 12, performs compression encoding of the video signal according to the encoding rate indicated by the encoding rate instruction, Encode data is generated, and the encode data is output to the wireless LAN physical layer 13-1 via the intermediate driver 12-1. As a result, a fixed amount of encoded data according to the encoding rate is always generated and output.

  The intermediate driver 12-1 receives encoded data from the encoder 11 and outputs the input encoded data to the wireless LAN physical layer 13. Further, the intermediate driver 12-1 inputs modulation scheme switching information, electric field strength, and received data from the wireless LAN physical layer 13-1, and sets a maximum transmittable rate for the modulation scheme after switching indicated by the modulation scheme switching information. calculate. When the intermediate driver 12-1 determines that the maximum transmittable rate after switching the modulation scheme is equal to or less than the current maximum transmittable rate, the wireless LAN physical layer 13-1 actually changes the modulation scheme. Before being performed, an encode rate instruction is output to the encoder 11 so that the encode rate is equal to or lower than the maximum transmittable rate after switching the modulation method. On the other hand, if the intermediate driver 12-1 determines that the maximum transmittable rate after switching the modulation scheme is higher than the current maximum transmittable rate, the modulation scheme is actually changed in the wireless LAN physical layer 13-1. After that, the encoding rate instruction is output to the encoder 11 so that the encoding rate is equal to or lower than the maximum transmittable rate after switching the modulation method. If the intermediate driver 12-1 determines that the wireless transmission path is completely shielded based on the electric field strength, the intermediate driver 12-1 causes the wireless LAN physical layer 13-1 to stop the modulation and transmission processing, and input and hold the encoded encoding. Discard the data. On the other hand, if the intermediate driver 12-1 determines that the wireless transmission path has been recovered based on the electric field strength, the intermediate driver 12-1 causes the wireless LAN physical layer 13-1 to resume modulation and transmission processing.

  FIG. 4 is a flowchart showing processing related to the encoding rate and modulation method by the intermediate driver 12-1. The intermediate driver 12-1 determines whether or not the modulation method switching information is input from the wireless LAN physical layer 13-1 (step S401), and determines that the modulation method switching information is not input (step S401: N), the process proceeds to step S408. On the other hand, if the intermediate driver 12-1 determines in step S401 that the modulation scheme switching information has been input (step S401: Y), the intermediate driver 12-1 corresponds to the modulation scheme after the switching indicated by the modulation scheme switching information. By performing a predetermined division process using the redundant data amount for error correction, the transmission protocol header amount, and the like, the maximum transmittable rate is calculated (step S402). Since the method for calculating the maximum rate that can be transmitted is known, detailed description thereof is omitted here.

  The intermediate driver 12-1 determines the maximum transmittable rate after switching the modulation scheme and the current maximum transmittable rate (the maximum transmittable rate after switching the modulation scheme calculated when the modulation scheme switching information was previously input). The rate is compared (step S403). If the intermediate driver 12-1 determines in step S403 that the maximum transmittable rate after switching the modulation scheme is equal to or less than the current maximum transmittable rate (step S403: ≦), the encoding rate is the modulation scheme. An encoding rate instruction is output to the encoder 11 so as to be equal to or lower than the maximum transmittable rate after switching (step S404), and after a predetermined time has elapsed, a modulation system switching instruction is output to the wireless LAN physical layer 13-1 (step S404). S405). Here, the predetermined time indicating the timing at which the modulation scheme switching instruction is output is the time after the encoding rate instruction is output. After the encoding rate of the encoder 11 is reduced, the wireless LAN physical layer 13-1 The time when the modulation method after switching can be applied to the encoded data whose encoding rate has been lowered by actually switching the modulation method.

  Thus, when it is determined that the maximum transmittable rate after switching the modulation scheme is equal to or less than the current maximum transmittable rate, before the modulation scheme is actually changed in the wireless LAN physical layer 13-1, The encoding rate of the encoder 11 is changed. Therefore, when the transmission rate is reduced as the modulation method is switched, the transmission rate is lowered after the encoding rate is lowered. As a result, it is possible to prevent data loss and to solve the problem that data cannot be transmitted. Further, the video is not interrupted in the receiving device 2.

  If the intermediate driver 12-1 determines that the maximum transmittable rate after switching the modulation scheme is higher than the current maximum transmittable rate (step S403:>), the intermediate driver 12-1 issues a modulation scheme switch instruction to the wireless LAN physical layer 13-. 1 (step S406). As a result, the modulation scheme is actually switched in the wireless LAN physical layer 13-1, and the modulation scheme switching completion is output from the wireless LAN physical layer 13-1 to the intermediate driver 12-1. The intermediate driver 12-1 then inputs an encoding rate instruction from the wireless LAN physical layer 13-1 so that the encoding rate is less than or equal to the maximum transmittable rate after switching the modulation method. 11 (step S407).

  The intermediate driver 12-1 shifts from Step S401, Step S405, or Step S407, compares the electric field strength input from the wireless LAN physical layer 13-1 with a predetermined threshold (Step S408), and the electric field strength is greater than the threshold. Is determined to be small (step S408: <), it is determined that the wireless transmission path is not completely propagated and communication is not possible, that is, the maximum transmittable rate is 0, and the discard instruction is transmitted wirelessly. The data is output to the LAN physical layer 13-1 (step S409). As a result, the wireless LAN physical layer 13-1 stops the modulation and transmission processing based on the discard instruction, discards the input encoded data without retaining it in the transmission buffer, and encodes the transmission buffer. Discard the data.

  If the intermediate driver 12-1 determines in step S408 that the electric field strength is greater than or equal to the threshold value (step S408: ≧), the modulation processing or the like is stopped in the wireless LAN physical layer 13-1 due to the output of the data discard instruction. It is determined whether or not (step S410). If the intermediate driver 12-1 determines in step S410 that the modulation processing or the like is stopped in the wireless LAN physical layer 13-1 based on the output of the data discard instruction (step S410: Y), the propagation of the wireless transmission path It is determined that the situation has improved, and a process resumption instruction is output to the wireless LAN physical layer 13-1 (step S411). As a result, the wireless LAN physical layer 13-1 restarts the modulation and transmission processing for the input encoded data based on the processing restart instruction. On the other hand, if the intermediate driver 12-1 determines in step S410 that the data discard instruction has not been output and the modulation process or the like has not stopped in the wireless LAN physical layer 13-1 (step S410: N). The process is terminated, and the process returns to step S401 to repeat the process.

  As described above, when the wireless transmission path is interrupted, the encoded data is discarded without being held in the transmission buffer, and transmission stops. Therefore, when the wireless transmission path is restored, the modulation and transmission processing for the encoded data is performed. The reception apparatus 2 resumes the live video decoding promptly.

  As described above, the intermediate driver 12-1 inputs modulation scheme switching information including the modulation scheme determined by the wireless LAN physical layer 13-1. On the other hand, when the wireless LAN physical layer 13-1 does not have a function of determining the modulation method, the intermediate driver 12-1 performs modulation based on the electric field strength input from the wireless LAN physical layer 13-1. You may make it determine a system. Further, the intermediate driver 12-1 calculates the maximum transmittable rate, but the wireless LAN physical layer 13-1 calculates the maximum transmittable rate, and the intermediate driver 12-1 The maximum rate that can be transmitted may be directly input from the layer 13-1.

  Returning to FIG. 3, the wireless LAN physical layer 13-1 includes a modulation / transmission unit 131-1, a reception / demodulation unit 132, an electric field strength measurement unit 133, and a modulation method determination unit 134. The modulation / transmission unit 131-1 includes a transmission buffer that temporarily holds the encoded data when it is transmitted. The modulation / transmission unit 131-1 receives the encoded data from the intermediate driver 12-1 and switches the modulation method from the modulation method determination unit 134. Input the information, store the input encoded data in the transmission buffer, read the encoded data from the transmission buffer according to the actual transmission rate according to the propagation status of the wireless transmission path, packetize the encoded data and add the sequence number, Data is modulated in accordance with the modulation scheme indicated by the modulation scheme switching information, an error correction code having a predetermined redundancy corresponding to the modulation scheme is added, and transmitted to the receiving apparatus 2 by radio. Also, the modulation / transmission unit 131-1 receives a modulation method switching instruction from the intermediate driver 12-1, switches to the modulation method indicated by the modulation method switching information input from the modulation method determination unit 134, and follows the modulation method after switching. Modulate data. Then, the modulation / transmission unit 131-1 outputs the modulation scheme switching completion to the intermediate driver 12-1. Also, the modulation / transmission unit 131-1 receives ACK from the reception / demodulation unit 132, and recognizes that the transmitted data is correctly received by the reception device 2. In this case, the modulation / transmission unit 131-1 transmits the next data (packet) after inputting the ACK.

  The reception / demodulation unit 132 receives data such as ACK transmitted by the reception device 2, demodulates the received data such as ACK, outputs the ACK to the modulation / transmission unit 131-1, and data other than ACK Are output to the intermediate driver 12-1 as received data. Also, the reception / demodulation unit 132 outputs the reception data before demodulation to the electric field strength measurement unit 133.

  The electric field strength measuring unit 133 receives the reception data before demodulation from the reception / demodulation unit 132, measures the electric field strength such as the C / N ratio based on the reception data before demodulation, and modulates the measured electric field strength. The data is output to the determination unit 134 and the intermediate driver 12-1.

  The modulation method determination unit 134 receives the electric field strength from the electric field strength measurement unit 133, and uses the predetermined conversion method table to determine the modulation method corresponding to the input electric field strength as a new modulation method. Then, when the modulation scheme changes, the modulation scheme determination unit 134 outputs the modulation scheme switching information to the intermediate driver 12-1 and the modulation / transmission unit 131-1. In the conversion method table, for example, the electric field strength such as the C / N ratio and the modulation method are stored as a pair, and the modulation method is uniquely determined based on the electric field strength.

  The modulation scheme determination unit 134 may determine the modulation scheme based not only on the C / N ratio but also on the basis of the non-arrival frequency of the ACK, the error information of the FCS unit, and the like. Good. In this case, the reception / demodulation unit 132 generates non-arrival frequency of ACK, error information of the FCS unit, and the like, and the modulation scheme determination unit 134 receives non-arrival frequency of ACK and error information of the FCS unit from the reception / demodulation unit 132. For example, when the non-arrival frequency of ACK is high, the modulation scheme is determined such that the maximum transmittable rate is further reduced. The algorithm for determining the modulation method in the modulation method determination unit 134 is not defined by the wireless LAN standardization method, and differs depending on the implementation of the wireless LAN physical layer 13-1. In the first embodiment, the intermediate driver 12-1 determines the encoding rate according to the modulation method determined by the wireless LAN physical layer 13-1, and can be applied regardless of the modulation method determined by any algorithm. Yes (the same applies to Examples 2 to 5).

  In the first embodiment, when the intermediate driver 12-1 determines that the maximum transmittable rate after switching the modulation scheme is higher than the current maximum transmittable rate, the intermediate driver 12-1 issues a modulation scheme switch instruction to the wireless LAN physical layer. 13-1 and after the completion of modulation system switching input from the wireless LAN physical layer 13-1, an encode rate instruction is output to the encoder 11. On the other hand, a modulation system switching instruction is output to the wireless LAN physical layer 13-1, and after a predetermined time has elapsed (after waiting for a time for the actual switching of the modulation system), an encoding rate instruction is output to the encoder 11. Good.

  In addition, a delay unit is provided before and after the modulation method determination unit 134 of the wireless LAN physical layer 13-1 (the first delay unit, the modulation method determination unit 134, and the like between the modulation method determination unit 134 and the intermediate driver 12-1). The intermediate driver 12-1 determines that the maximum transmittable rate after switching the modulation scheme is equal to or less than the current maximum transmittable rate. In this case, the modulation method switching information input from the modulation method determination unit 134 is immediately output to the intermediate driver 12-1 to the first delay unit, and the modulation method determination unit 134 receives the second delay unit. The input modulation method switching information is output to the modulation / transmission unit 131-1 after a predetermined time has elapsed. On the other hand, when the intermediate driver 12-1 determines that the maximum transmittable rate after switching the modulation scheme is higher than the current maximum transmittable rate, the intermediate driver 12-1 inputs the first delay unit from the modulation scheme determination unit 134 The modulation system switching information is output to the intermediate driver 12-1 after a predetermined time has elapsed, and the modulation system switching information input from the modulation system determination section 134 is immediately transmitted to the second delay section as the modulation / transmission section 131-. 1 is output. In this case, the intermediate driver 12-1 does not perform the processing of step S404 to step S407 shown in FIG. Further, when the modulation / transmission unit 131-1 receives the modulation method switching information, the modulation / transmission unit 131-1 immediately switches to the modulation method.

  As described above, according to the transmission device 1-1 of the first embodiment, the intermediate driver 12-1 calculates the maximum transmittable rate after switching the modulation scheme, and this maximum rate is the current maximum transmittable rate. If it is determined that the encoding rate is less than or equal to the encoding rate instruction, the encoding rate instruction is output to the encoder 11 so that the encoding rate is equal to or lower than the maximum transmission rate after switching the modulation method. It was made to output to the layer 13-1. As a result, the encoding rate of the encoder 11 can be lowered before the modulation method is actually changed in the wireless LAN physical layer 13-1 and the transmission rate is lowered. Therefore, when the transmission rate is reduced due to the switching of the modulation method, it is possible to avoid a state in which the transmission rate is lowered after the encoding rate is lowered and the transmission rate is lower than the encoding rate, thereby preventing data loss. And the problem that data cannot be transmitted can be solved. That is, transmission of video data can be continued without interruption, and the live video is not interrupted.

  On the other hand, if the intermediate driver 12-1 determines that this maximum rate is higher than the current maximum transmittable rate, it outputs a modulation method switching instruction to the wireless LAN physical layer 13-1 to actually switch the modulation method. After that, the encode rate instruction is output to the encoder 11 so that the encode rate is equal to or lower than the maximum transmittable rate after switching the modulation method. As a result, the encoding rate of the encoder 11 can be increased after the modulation scheme is actually changed in the wireless LAN physical layer 13-1 and the transmission rate is increased. Therefore, when the transmission rate increases with the switching of the modulation method, it is possible to avoid a situation in which the encoding rate increases after the transmission rate increases and the encoding rate becomes higher than the transmission rate. It is possible to prevent such a problem that data cannot be transmitted. That is, transmission of video data can be continued without interruption, and the live video is not interrupted. The receiving device 2 according to the first embodiment may have a configuration according to the conventional wireless LAN standardization method (the same applies to the second to fifth embodiments).

[Example 2]
Next, Example 2 will be described. In the second embodiment, as described above, the encoding rate is controlled according to the amount of data temporarily held in the transmission buffer.

  FIG. 5 is a block diagram illustrating the configuration of the transmission apparatus according to the second embodiment. The transmission device 1-2 includes an encoder 11, an intermediate driver 12-2, a wireless LAN physical layer 13-2, and an encode rate calculation unit 14. The encoder 11 performs the same processing as in the first embodiment, inputs a video signal, receives an encoding rate instruction from the encoding rate calculation unit 14, performs compression encoding, generates encoded data, and generates an intermediate driver 12- 1 to the wireless LAN physical layer 13-2.

  The intermediate driver 12-2 receives the encoded data from the encoder 11, and outputs the input encoded data to the wireless LAN physical layer 13-2. Further, the intermediate driver 12-2 receives modulation method switching information, electric field strength, and received data from the wireless LAN physical layer 13-2, and outputs the input modulation method switching information to the encode rate calculation unit 14. Further, the intermediate driver 12-2 performs the processing of steps S408 to S411 shown in FIG. 4 using the input electric field strength, and is not in a propagation state in which communication is possible because the wireless transmission path is completely shielded. If it is determined that the wireless LAN physical layer 13-2 has discarded the input encoded data and the encoded data held therein, and it is determined that the propagation state of the wireless transmission path has been improved, the wireless LAN physical layer 13-2 Then, the modulation and transmission process is resumed.

  The encode rate calculation unit 14 receives the modulation method switching information from the intermediate driver 12-2 and also receives the buffer data amount (the amount of data temporarily stored in the transmission buffer) from the wireless LAN physical layer 13-2. Then, the encoding rate is calculated based on the modulation method switching information and the buffer data amount, and is output to the encoder 11.

FIG. 6 is a flowchart showing the encoding rate calculation processing by the encoding rate calculation unit 14. First, the encode rate calculation unit 14 receives the modulation method switching information from the intermediate driver 12-2 and also receives the buffer data amount from the wireless LAN physical layer 13-2 (step S601). Then, the encoding rate calculation unit 14 performs a predetermined division process on the modulation scheme after switching indicated by the modulation scheme switching information using the redundant data amount for error correction and the transmission protocol header amount corresponding to the modulation scheme. By doing so, the maximum transmittable rate is calculated (step S602), and the temporal change of the buffer data amount is obtained to calculate the data rate in the transmission buffer (step S603). Then, the encode rate calculation unit 14 calculates the encode rate using the following mathematical formula (step S604), and outputs an encode rate instruction to the encoder 11 (step S605).
(Formula 1)
Encoding rate = maximum transmittable rate−data rate in transmission buffer (1)
Accordingly, the encoder 11 performs compression encoding so as to be within a predetermined rate in accordance with the encoding rate instruction from the encoding rate calculation unit 14.

  Here, when the modulation method is switched during data transmission and the maximum transmittable rate is lower than the current encoding rate, the data is temporarily held in the transmission buffer of the wireless LAN physical layer 13-2. In this case, since the maximum rate that can be transmitted becomes lower, the encode rate calculation unit 14 calculates an encode rate lower than before using the equation (1) and outputs an encode rate instruction to the encoder 11. As a result, the amount of encoded data output by the encoder 11 decreases, and the amount of data held in the transmission buffer decreases as the wireless LAN physical layer 13-2 reads and transmits data from the transmission buffer. At this time, since the data rate in the transmission buffer becomes low, the encode rate calculation unit 14 calculates an encode rate higher than before by the equation (1) and outputs an encode rate instruction to the encoder 11. As a result, the encoded data output by the encoder 11 increases.

  In this way, when the modulation method is switched and the maximum transmittable rate is lower than the current encoding rate, the encoding rate is temporarily lowered so that the data to be transmitted can be transmitted from the transmission buffer, and the data in the transmission buffer is transmitted. However, the encoding rate gradually increases as the amount of data in the transmission buffer decreases. As a result, the encoding rate calculation unit 14 calculates the encoding rate according to the mathematical expression (1) and controls the encoding rate of the encoder 11 so that all data can be sent within a predetermined time. It is possible to transmit the live video satisfactorily without the video being interrupted.

  Returning to FIG. 5, the wireless LAN physical layer 13-2 includes a modulation / transmission unit 131-2, a reception / demodulation unit 132, an electric field strength measurement unit 133, and a modulation method determination unit 134. The modulation / transmission unit 131-2 includes a transmission buffer that temporarily holds the encoded data when it is transmitted. The modulation / transmission unit 131-2 receives the encoded data from the intermediate driver 12-2 and also switches the modulation method from the modulation method determination unit 134. Information is input, and the input encoded data is stored in the transmission buffer as in the first embodiment, and the encoded data is read from the transmission buffer according to the actual transmission rate according to the propagation state of the wireless transmission path, and the encoded data is packetized. Then, the sequence number is added, the data is modulated according to the modulation scheme indicated by the modulation scheme switching information, an error correction code of a predetermined redundancy corresponding to the modulation scheme is added, and transmitted to the receiving apparatus 2 by radio. Also, the modulation / transmission unit 131-2 receives ACK from the reception / demodulation unit 132, and recognizes that the transmitted data has been correctly received by the reception device 2. In this case, the modulation / transmission unit 131-2 transmits data after inputting the ACK. Also, the modulation / transmission unit 131-2 calculates the amount of data held in the transmission buffer, and outputs the data amount to the encode rate calculation unit 14 as the buffer data amount.

  Since the reception / demodulation unit 132, the electric field strength measurement unit 133, and the modulation scheme determination unit 134 are the same as those in the first embodiment, the description thereof is omitted.

  The data temporarily stored in the transmission buffer provided in the modulation / transmission unit 131-2 of the wireless LAN physical layer 13-2 includes retransmission data processed by a communication method higher than the wireless LAN transmission method. Is also included. That is, when data is lost on the wireless transmission path, the data is held in the transmission buffer, so the encoding rate calculation unit 14 increases the data rate in the transmission buffer, and the above equation (1) A low encoding rate is calculated, and the amount of encoded data output by the encoder 11 is reduced. As a result, the overall transmission rate does not exceed the maximum transmittable rate of the wireless transmission path, data loss can be prevented, and lost data is retransmitted using the transmission buffer.

  Regardless of the second embodiment, the receiving apparatus 2 generally includes a receiving buffer for temporarily holding data before starting decoding, and after holding a certain amount of encoded data in the receiving buffer. Start decoding. Even in the case where the modulation method is switched and the maximum transmission rate is reduced in the transmission device 1-2, the transmission apparatus 1-2 does not have a certain amount of encoded data in the reception buffer (before the reception buffer becomes empty). When the encoding rate calculation unit 14 of the transmission device 1-2 controls the encoding rate and the modulation / transmission unit 131-2 of the wireless LAN physical layer 13-2 can transmit data, the reception device In 2, live video can be transmitted without interruption.

  The intermediate driver 12-2 may include the encode rate calculation unit 14, and the modulation / transmission unit 131-2 of the wireless LAN physical layer 13-2 may determine the buffer data amount by using the intermediate driver 12-2. May be output to the encode rate calculation unit 14 via

  In the wireless LAN, a plurality of transmission apparatuses 1-2 and a plurality of reception apparatuses 2 share the same wireless transmission path and transmit data by the CSMA method. While the first transmission device 1-2 is transmitting data, other transmission devices 1-2 sharing the wireless transmission path cannot transmit data. That is, the transmission rate of the first transmission device 1-2 changes depending on the transmission status of the other transmission device 1-2 in addition to the propagation status of the wireless transmission path. While the other transmission device 1-2 is transmitting data, the data to be transmitted by the first transmission device 1-2 is transmitted to the modulation / transmission unit 131-2 of the wireless LAN physical layer 13-2. Temporarily held in a buffer. Then, since the data is held in the transmission buffer, the encoding rate calculation unit 14 increases the data rate in the transmission buffer, calculates an encoding rate lower than before by the above equation (1), and outputs it by the encoder 11. The amount of encoded data is reduced. As a result, the encoding rate becomes a value commensurate with the propagation state of the wireless transmission path, so that it is possible to transmit live video without interruption of video in the receiving device 2.

  As described above, according to the transmission device 1-2 of the second embodiment, the encode rate calculation unit 14 calculates the maximum transmittable rate based on the modulation scheme switching information, and calculates the buffer data amount in the transmission buffer. The data rate in the transmission buffer is calculated by obtaining the temporal change, and the encoding rate is calculated by the equation (1). The encoder 11 performs compression encoding according to the encoding rate calculated by the encoding rate calculation unit 14 to generate encoded data. As a result, when the modulation method is switched and the maximum transmittable rate is lower than the current encoding rate, the encoding rate is temporarily lowered so that the data to be transmitted can be transmitted from the transmission buffer, and the data in the transmission buffer is transmitted. However, as the data in the transmission buffer decreases, the encoding rate gradually increases. That is, the encoding rate is controlled in consideration of the amount of data temporarily held in the transmission buffer, and not only follows the change in the maximum transmittable rate depending on the propagation state of the wireless transmission path, but also other transmission devices 1 -2 also follows the transmission rate that changes depending on the transmission status, so that data loss can be prevented, video data transmission can be continued without interruption, and live video is not interrupted.

Example 3
Next, Example 3 will be described. As described above, the third embodiment is an example in which the encoding rate is controlled according to the amount of data that could not be transmitted during the ACK timeout period (the amount of data that could be transmitted when ACK was returned as expected). is there.

  FIG. 7 is a block diagram illustrating the configuration of the transmission apparatus according to the third embodiment. The transmission device 1-3 includes an encoder 11, an intermediate driver 12-3, a wireless LAN physical layer 13-3, a virtual transmission amount count unit 15, and an encode rate calculation unit 19. The encoder 11 performs the same processing as in the first and second embodiments, and outputs the generated encoded data to the wireless LAN physical layer 13-3 via the intermediate driver 12-3. Since the intermediate driver 12-3 is the same as that of the second embodiment, the description thereof is omitted.

  The encode rate calculation unit 19 receives the modulation method switching information from the intermediate driver 12-3, and is expected to have been able to transmit the virtual transmission amount (if the ACK is returned as expected) from the virtual transmission amount counting unit 15. The amount of data) is input, the encoding rate is calculated based on the modulation scheme switching information and the virtual transmission amount, and is output to the encoder 11.

FIG. 8 is a flowchart showing the encoding rate calculation processing by the encoding rate calculation unit 19. First, the encoding rate calculation unit 19 inputs modulation scheme switching information from the intermediate driver 12-3 and also inputs a virtual transmission amount from the virtual transmission amount counting unit 15 (step S801). Then, the encoding rate calculation unit 19 performs a predetermined division process on the modulation scheme after switching indicated by the modulation scheme switching information using the redundant data amount for error correction and the transmission protocol header amount corresponding to the modulation scheme. By doing so, the maximum transmittable rate is calculated (step S802). Then, the encode rate calculation unit 19 calculates the encode rate using the following formula (step S803), and outputs an encode rate instruction to the encoder 11 (step S804).
(Formula 2)
Encoding rate = Maximum rate that can be transmitted-Virtual transmission amount (2)
Accordingly, the encoder 11 performs compression encoding so as to be within a predetermined rate in accordance with the encoding rate instruction from the encoding rate calculation unit 19.

  Here, when data is not normally transmitted from the transmission device 1-3 to the reception device 2 due to the propagation state of the wireless transmission path, or when another transmission device 1-3 is transmitting data, the reception device ACK may not be returned from 2. In this case, the virtual transmission amount is counted by a virtual transmission amount counting unit 15 described later. Since the virtual transmission amount becomes large, the encode rate calculation unit 19 calculates an encode rate lower than before by the mathematical formula (2), and outputs an encode rate instruction to the encoder 11. Thereby, the amount of encoded data output by the encoder 11 is reduced. Therefore, the encoding rate calculation unit 19 reduces the encoding rate of the encoder 11 by lowering the encoding rate from the originally assumed rate according to Equation (2) according to the virtual transmission amount that is the amount of data that could not be transmitted. Since the control is performed, loss of data can be prevented, all data can be transmitted within a predetermined time, and a live video can be transmitted without interruption of video in the receiving device 2.

  Returning to FIG. 7, the wireless LAN physical layer 13-3 includes a modulation / transmission unit 131-3, a reception / demodulation unit 132, an electric field strength measurement unit 133, and a modulation method determination unit 134. The modulation / transmission unit 131-3 includes a transmission buffer that temporarily holds the encoded data when it is transmitted. The modulation / transmission unit 131-3 inputs the encoded data from the intermediate driver 12-3 and also switches the modulation method from the modulation method determination unit 134. As in the first and second embodiments, the input encoded data is stored in the transmission buffer, and the encoded data is read from the transmission buffer according to the actual transmission rate according to the propagation state of the wireless transmission path. It is packetized, a sequence number is added, data is modulated according to the modulation scheme indicated by the modulation scheme switching information, an error correction code with a predetermined redundancy corresponding to the modulation scheme is added, and transmitted to the receiving apparatus 2 by radio. Further, the modulation / transmission unit 131-3 receives ACK from the reception / demodulation unit 132 and recognizes that the transmitted data is correctly received by the reception device 2. In this case, the modulation / transmission unit 131-3 transmits data after inputting ACK. In addition, the modulation / transmission unit 131-3 outputs ACK not received to the virtual transmission amount counting unit 15 when ACK is not input within a predetermined time after data is transmitted.

  Since the reception / demodulation unit 132, the electric field strength measurement unit 133, and the modulation scheme determination unit 134 are the same as those in the first and second embodiments, the description thereof is omitted.

  When the virtual transmission amount counting unit 15 receives ACK not received from the modulation / transmission unit 131-3 of the wireless LAN physical layer 13-3, the reception / demodulation unit 132 temporarily receives the ACK, and the modulation / transmission unit 131- If ACK was input as expected in 3, the amount of data expected to have been transmitted (the amount of data expected to have been transmitted when ACK was returned as expected) is used as the virtual transmission amount. The virtual transmission amount is counted and output to the encode rate calculation unit 19.

  The wireless LAN physical layer 13-3 may include a virtual transmission amount counting unit 15, or the virtual transmission amount counting unit 15 may calculate the encoding rate via the intermediate driver 12-3. You may make it output to the part 19. FIG. Further, the intermediate driver 12-3 may include an encoding rate calculation unit 19.

  Further, in the wireless LAN standardization method, a block ACK method for returning ACKs of a plurality of packets collectively is defined. Similarly in this case, the virtual transmission amount counting unit 15 counts the data amount of the packet that has not been acknowledged in the block ACK as the virtual transmission amount, and outputs the virtual transmission amount to the encode rate calculation unit 19. Thereby, the encoding rate can be controlled by the same method as described above.

  As described above, according to the transmission device 1-3 of the third embodiment, the virtual transmission amount counting unit 15 is expected to have been able to transmit when ACK not received is input and ACK is returned as expected. The amount of data is counted as a virtual transmission amount, and the encode rate calculation unit 19 calculates the maximum transmittable rate based on the modulation scheme switching information. The maximum transmittable rate and the virtual transmission are calculated according to the equation (2). The encoding rate was calculated from the amount. Then, the encoder 11 performs compression encoding according to the encoding rate calculated by the encoding rate calculation unit 19 to generate encoded data. Thereby, depending on the propagation state of the wireless transmission path, data may not be normally transmitted from the transmission device 1-3 to the reception device 2, or data may be being transmitted by another transmission device 1-3. When ACK is not returned from 2, the encoding rate is temporarily lowered, and when ACK is returned, the encoding rate is increased. In other words, the encoding rate can be controlled to follow the transmission rate that changes depending on the propagation status of the wireless transmission path or the transmission status of other transmission apparatuses 1-3 that share the wireless transmission path, thereby preventing data loss. Thus, it is possible to transmit the live video without interruption of the video in the receiving device 2.

Example 4
Next, Example 4 will be described. As described above, the fourth embodiment is an example in which the encoding rate is controlled according to the position information of the transmission device acquired by GPS or the like. In the fourth embodiment, it is assumed that the receiving device 2 is a fixed station that does not move.

  FIG. 9 is a block diagram illustrating the configuration of the transmission apparatus according to the fourth embodiment. The transmission apparatus 1-4 includes an encoder 11, an intermediate driver 12-4, a wireless LAN physical layer 13-4, a position information measurement unit 16, and a position-transmission rate table holding unit (encoding rate determination unit) 17. The encoder 11 performs the same processing as in the first to third embodiments, and outputs the generated encoded data to the wireless LAN physical layer 13-4 via the intermediate driver 12-4.

  The intermediate driver 12-4 receives the encoded data from the encoder 11 and outputs the input encoded data to the wireless LAN physical layer 13-4. The intermediate driver 12-4 receives an encoding rate instruction from the position-transmission rate table holding unit 17 and outputs the input encoding rate instruction to the encoder 11. Further, the intermediate driver 12-4 inputs the modulation system switching information, the electric field strength, and the reception data from the wireless LAN physical layer 13-4, and sets the maximum transmittable rate for the modulation system after switching indicated by the modulation system switching information. calculate. Then, the intermediate driver 12-4 performs the processing of steps S401 to S407 illustrated in FIG. 4 and outputs an encoding rate instruction to the encoder 11. Further, the intermediate driver 12-4 performs the processing of step S408 to step S411 shown in FIG. 4 using the input electric field strength, and is not in a propagation situation in which communication is possible because the wireless transmission path is completely shielded. If it is determined that the wireless LAN physical layer 13-4 has discarded the input encoded data and the encoded data held therein, and it is determined that the propagation state of the wireless transmission path has been improved, the wireless LAN physical layer 13-4 Then, the modulation and transmission process is resumed. The intermediate driver 12-4 normally outputs the encoding rate instruction generated by the processing in steps S401 to S407 shown in FIG. 4 to the encoder 11, and inputs the encoding rate instruction from the position-transmission rate table holding unit 17. In this case, the input encoding rate instruction is output to the encoder 11.

  The position information measurement unit 16 measures the current position of the transmission device 1-4 using GPS or the like, generates position information, and outputs the position information to the position-transmission rate table holding unit 17. The position-transmission rate table holding unit 17 holds a predetermined table, inputs the position information of the transmission device 1-4 from the position information measurement unit 16, and the current modulation method from the modulation method determination unit 137 described later. Enter. Then, the position-transmission rate table holding unit 17 reads a transmission rate (encoding rate) corresponding to the input position information from the table, and outputs an encoding rate instruction to the encoder 11 via the intermediate driver 12-4. In this case, the position-transmission rate table holding unit 17 outputs an encoding rate instruction after a predetermined time elapses when the encoding rate is higher than the current maximum transmittable rate. In addition, the position-transmission rate table holding unit 17 determines whether the transmission rate (encoding rate) corresponding to the input position information exists in the table with the intermediate driver 12-1 of the first embodiment for the input current modulation method. Similarly, the current maximum transmittable rate is calculated, and the current maximum transmittable rate is stored in the table as a transmission rate (encoding rate) corresponding to the position information. Here, the table stores position information, a transmission rate (encoding rate) corresponding to the position information, and the like, and the position information is information indicating a predetermined range centered on the reference position.

  In addition, the position-transmission rate table holding unit 17 causes the second read out after the encoding rate corresponding to the first position information read out from the table as the position information changes due to the movement of the transmitting device 1-4. If the encoding rate corresponding to the position information is lower, an encoding rate lower than the encoding rate corresponding to the second position information is determined, and an encoding rate instruction is output to the intermediate driver 12-4. After a predetermined time has elapsed, a modulation scheme of the maximum transmittable rate corresponding to the determined encoding rate is determined, and a modulation scheme instruction is output to a modulation scheme determination section 137 described later. As a result, the modulation scheme determination unit 137 receives a modulation scheme instruction from the position-transmission rate table holding unit 17 and determines the modulation scheme.

  FIG. 10 is a flowchart showing processing related to the encoding rate and modulation method by the position-transmission rate table holding unit 17. First, the position-transmission rate table holding unit 17 inputs the position information of the transmission device 1-4 from the position information measurement unit 16, and also inputs the current modulation method from the modulation method determination unit 137 (step S1001). By performing a predetermined division process using the redundant data amount for error correction and the transmission protocol header amount corresponding to the modulation method, the current maximum transmittable rate is calculated (step S1002).

  The position-transmission rate table holding unit 17 determines whether an encoding rate corresponding to the position information exists in the table (step S1003), and determines that there is an encoding rate corresponding to the position information (step S1003). : Y), the encoding rate corresponding to the position information is read from the table, and a new encoding rate is determined (step S1004). On the other hand, if the position-transmission rate table holding unit 17 determines in step S1003 that there is no encoding rate corresponding to the position information (step S1003: N), the current maximum transmittable rate calculated in step S1002 Is set as the encoding rate corresponding to the position information and stored in the table (step S1005).

  The position-transmission rate table holding unit 17 shifts from step S1004 to compare the newly determined encoding rate with the current maximum transmittable rate (step S1006), and the determined encoding rate can be currently transmitted. When it is determined that the maximum rate is below the maximum rate (step S1006: ≦), an encoding rate instruction is output to the encoder 11 via the intermediate driver 12-4 (step S1007). As a result, the encoding rate of the encoder 11 quickly decreases and the data transmission amount decreases before the propagation rate of the wireless transmission path deteriorates and the maximum rate that can be actually transmitted decreases, thereby preventing data loss. And transmission with which the video is hardly interrupted can be realized.

  On the other hand, if the position-transmission rate table holding unit 17 determines in step S1006 that the determined encoding rate is higher than the current maximum transmittable rate (step S1006:>), the encoding rate instruction is given after a predetermined time has elapsed. Is output to the encoder 11 via the intermediate driver 12-4 (step S1008). As a result, the encoding rate of the encoder 11 is increased after waiting for data to be transmitted from the transmission buffer, so that data loss can be prevented and transmission without interruption of video can be realized.

  The position-transmission rate table holding unit 17 updates the position information in place of the process of step S1008, and the current maximum transmission rate calculated from the current modulation scheme is determined to be a predetermined rate (for example, determined). An encoding rate instruction for the encoding rate read from the table may be output after waiting for the value to reach a predetermined value close to the encoding rate.

  The position-transmission rate table holding unit 17 moves from step S1005, step S1007, or step S1008, and the encoding rate read from the table in step S1004 decreases as the position information changes due to the movement of the transmission device 1-4. It is determined whether or not (step S1009). For example, the position-transmission rate table holding unit 17 determines whether or not there is a tendency to decrease in time based on a plurality of encoding rates read from the table and the read times for a predetermined time. If the position-transmission rate table holding unit 17 determines in step S1009 that the encoding rate is decreasing (step S1009: Y), the encoding of the lowest value that is lower than the encoding rate corresponding to the position information at that time is performed. The rate is determined (step S1010). For example, the position-transmission rate table holding unit 17 subtracts a predetermined value from the encoding rate corresponding to the position information at that time, and determines the lowest value of the subtraction result as the encoding rate.

  The position-transmission rate table holding unit 17 outputs the encoding rate instruction of the lowest encoding rate determined in step S1010 to the encoder 11 via the intermediate driver 12-4 (step S1011). Further, the position-transmission rate table holding unit 17 determines a modulation scheme of the maximum transmittable rate corresponding to the lowest encoding rate determined in step S1010 after a predetermined time has elapsed (step S1012), and the modulation scheme The instruction is output to the wireless LAN physical layer 13-4 (step S1013), the process ends, and the process proceeds to step S1001. For example, the position-transmission rate table holding unit 17 determines a modulation scheme using a table in which the lowest encoding rate corresponds to the modulation scheme with the maximum transmittable rate.

  Here, when the transmitting apparatus 1-4 approaches a position where the maximum transmittable rate is low, the position-transmission rate table holding unit 17 first controls the encoding rate to a low value, and then wirelessly The modulation method is directly changed for the LAN physical layer 13-4. In general, when approaching a position where the maximum transmittable rate becomes low, packet loss occurs due to a decrease in electric field strength. However, the packet loss can be reduced by the processing of the position-transmission rate table holding unit 17. Therefore, it is possible to reduce the possibility that the video is interrupted.

  On the other hand, if the position-transmission rate table holding unit 17 determines in step S1009 that the encoding rate has not decreased (step S1009: N), the process ends and the process proceeds to step S1001.

  When the position information and the corresponding encoding rate exist in the table, the position-transmission rate table holding unit 17 determines that the encoding rate read from the table is higher than the current maximum transmittable rate in step S1006. If it is determined that the encoding rate is higher (step S1006:>), the encoding rate stored in the table may be updated to the current maximum transmittable rate that is equal to or lower than the encoding rate. As a result, a table adapted to the case where the propagation state of the wireless transmission path is most deteriorated is generated, and it becomes possible to perform control that makes it difficult to interrupt the video.

  Returning to FIG. 9, the wireless LAN physical layer 13-4 includes a modulation / transmission unit 131-4, a reception / demodulation unit 132, an electric field strength measurement unit 133, and a modulation method determination unit 137. The modulation / transmission unit 131-4 includes a transmission buffer that temporarily holds the encoded data when it is transmitted. The modulation / transmission unit 131-4 inputs the encoded data from the intermediate driver 12-4 and also switches the modulation method from the modulation method determination unit 137. Information is input, the input encoded data is stored in the transmission buffer in the same manner as in the first to third embodiments, the encoded data is read from the transmission buffer according to the actual transmission rate according to the propagation state of the wireless transmission path, and the encoded data is It is packetized, a sequence number is added, data is modulated according to the modulation scheme indicated by the modulation scheme switching information, an error correction code with a predetermined redundancy corresponding to the modulation scheme is added, and transmitted to the receiving apparatus 2 by radio. Also, the modulation / transmission unit 131-4 receives ACK from the reception / demodulation unit 132 and recognizes that the transmitted data is correctly received by the reception device 2. In this case, the modulation / transmission unit 131-4 transmits data after inputting the ACK.

  The modulation method determination unit 137 receives the electric field strength from the electric field strength measurement unit 133, determines a modulation method corresponding to the input electric field strength as a new modulation method using a predetermined conversion method table, and performs position-transmission. A modulation scheme instruction is input from the rate table holding unit 17, and the modulation scheme indicated by the modulation scheme instruction is determined as a new modulation scheme. Then, when the modulation method changes, the modulation method determination unit 137 outputs the modulation method switching information to the intermediate driver 12-4 and the modulation / transmission unit 131-4, and holds the current modulation method in the position-transmission rate table. To the unit 17. Since the reception / demodulation unit 132 and the electric field strength measurement unit 133 are the same as those in the first to third embodiments, the description thereof is omitted.

  The fourth embodiment is based on the configuration of the first embodiment, and further includes a position information measurement unit 16 and a position-transmission rate table holding unit 17, and controls the encoding rate in advance according to the position information acquired by GPS. is there. On the other hand, the modification of the fourth embodiment is based on the configuration of the second and third embodiments, and may further include a position information measurement unit 16 and a position-transmission rate table holding unit 17.

  The position-transmission rate table holding unit 17 outputs the encoding rate instruction to the encoder 11 via the intermediate driver 12-4, but directly outputs it to the encoder 11 without passing through the intermediate driver 12-4. You may make it do. Further, the intermediate driver 12-4 may include a position information measuring unit 16 and a position-transmission rate table holding unit 17.

  As described above, according to the transmission device 1-4 of the fourth embodiment, the position-transmission rate table holding unit 17 reads the encoding rate corresponding to the position information of the transmission device 1-4 from the table, and issues an encoding rate instruction. When outputting to the encoder 11 via the intermediate driver 12-4, the encoding rate read from the table is compared with the current maximum transmittable rate calculated from the current modulation scheme, and the read encoding rate is The encoding rate instruction is output immediately when the maximum transmission rate is less than the maximum transmission rate, and when the read encoding rate is higher than the current maximum transmission rate, the encoding rate instruction is output after a predetermined time. . As a result, the data transmission amount can be reduced by lowering the encoding rate before the propagation state of the wireless transmission path deteriorates and the maximum rate that can be actually transmitted decreases. Therefore, it is possible to prevent data loss and transmit live video without interruption of video in the receiving device 2.

Example 5
Next, Example 5 will be described. As described above, the fifth embodiment is a modification of the first to fourth embodiments. The encoder 11 of the transmission apparatuses 1-1 to 1-4 and the wireless LAN physical layers 13-1 to 13-4 in the first to fourth embodiments. Are configured as separate devices, and the wireless LAN physical layers 13-1 to 13-4 are installed outside as wireless LAN access points or wireless LAN bridge devices.

  FIG. 11 is a block diagram illustrating a configuration of a transmission apparatus (transmission system) according to the fifth embodiment. The transmission apparatus 1-5 includes an encoder 20 and a wireless LAN access point 18. The encoder 20 includes the encoder 11 and the intermediate driver 12-1 of the first embodiment, the intermediate drivers 12-2 and 12-3 and the encode rate calculation units 14 and 19 of the second and third embodiments, or the intermediate driver 12 of the fourth embodiment. -4, the position information measuring unit 16 and the position-transmission rate table holding unit 17 are provided with the components of any of the embodiments. The encoder 20 receives a video signal, compresses and encodes the video signal at a predetermined encoding rate, generates encoded data, and transmits the encoded data to the wireless LAN access point 18 via a wired medium such as Ethernet (registered trademark). Further, the encoder 20 receives the electric field strength and modulation method switching information from the wireless LAN access point 18, calculates the maximum rate that can be transmitted, obtains the encoding rate in the same manner as in the first to fourth embodiments, and obtains the encoding data. Generate.

  The wireless LAN access point 18 includes a wireless LAN physical layer 13-5. Specifically, the wireless LAN physical layer 13-1 according to the first embodiment, the wireless LAN physical layer 13-2 according to the second embodiment, and the embodiment. 3 of the wireless LAN physical layer 13-3 and the virtual transmission amount counting unit 15 of the third embodiment, or the wireless LAN physical layer 13-4 of the fourth embodiment, and a configuration corresponding to the embodiment of the encoder 20 Department. The wireless LAN physical layer 13-5 has the same function as any of the wireless LAN physical layers 13-1 to 13-4 of the first to fourth embodiments. The wireless LAN access point 18 receives the encoded data from the encoder 20, transmits it to the receiving device 2 using the wireless LAN protocol, and receives the wireless LAN ACK and the like. In addition, the wireless LAN access point 18 measures the electric field strength, performs a process such as determining a modulation method, and transmits the electric field strength and the modulation method switching information to the encoder 20 via a wired medium.

  Although the encoder 20 includes the intermediate drivers 12-1 to 12-4 and the like, the wireless LAN access point 18 includes the intermediate drivers 12-1 to 12-4 other than the encoder 11 instead of the encoder 20. You may make it provide. In this case, the encoder 20 receives an encoding rate instruction from the wireless LAN access point 18.

  As described above, according to the transmission device 1-5 of the fifth embodiment, the wireless LAN physical layer 13-5 is provided in the wireless LAN access point 18 installed outside the encoder 20. Also in this case, as in the first to fourth embodiments, the transmission rate changes according to the propagation state of the wireless transmission path, or the simultaneous transmission occurs on the same transmission path and the transmission rate decreases. However, transmission of video data can be continued without interruption, and live video is not interrupted.

DESCRIPTION OF SYMBOLS 1 Transmission apparatus 2 Reception apparatus 11, 20 Encoder 12, 22 Intermediate driver 13 Wireless LAN physical layer (transmission part)
14, 19 Encoding rate calculation unit 15 Virtual transmission amount counting unit 16 Position information measurement unit 17 Position-transmission rate table holding unit 18 Wireless LAN access point 21 Wireless LAN physical layer (receiving unit)
22 Intermediate Driver 131 Modulation / Transmission Unit 132 Reception / Demodulation Unit 133 Electric Field Strength Measurement Units 134 and 137 Modulation Method Determination Unit

Claims (6)

In a video transmission apparatus that compresses and encodes a video signal to generate encoded data, modulates the encoded data, and transmits the encoded data to a receiving apparatus via a wireless transmission path.
A reception demodulator for receiving and demodulating data including an acknowledgment ACK for the transmitted encoded data from the receiving device, and an electric field strength measuring unit for measuring the electric field strength of radio waves for the data transmitted by the receiving device A modulation method determination unit that determines a modulation method based on the electric field strength measured by the electric field strength measurement unit, and modulates the encoded data according to the modulation method determined by the modulation method determination unit and transmits the data to the wireless transmission path A transmitter having a modulation transmitter, and
When a new modulation method is determined by the modulation method determination unit of the transmission unit and switched to the new modulation method, the current modulation method before switching, the modulation method after switching, and the electric field strength of the transmission unit An intermediate driver for determining an encoding rate based on the electric field strength measured by the measurement unit;
An encoder that compresses and encodes a video signal at the encoding rate and generates encoded data;
The intermediate driver is
Based on the modulation scheme, the maximum transmittable rate is calculated, and the maximum transmittable rate in the modulation scheme after switching is equal to or lower than the maximum transmittable rate in the current modulation scheme before switching,
An instruction for compressing and encoding at an encoding rate equal to or lower than the maximum transmittable rate in the modulation scheme after switching is output to the encoder, and the instruction is output to the encoder. An instruction for switching to the new modulation scheme is output to the modulation transmission unit of the transmission unit after a predetermined time that can be modulated by the modulation transmission unit of the transmission unit has elapsed,
When the maximum transmittable rate in the modulation scheme after switching is higher than the maximum transmittable rate in the current modulation scheme before switching,
An instruction for switching to the new modulation scheme is output to the modulation transmission section of the transmission section, and after the modulation scheme switching completion indicating the switching to the new modulation scheme is input from the modulation transmission section of the transmission section Alternatively, after the instruction is output to the modulation transmission unit of the transmission unit, after a predetermined time for switching to the new modulation method by the instruction has elapsed, the transmission rate is equal to or less than the maximum transmittable rate in the modulation method after the switching. An image transmission apparatus, wherein an instruction for compression encoding at an encoding rate is output to the encoder. The video transmission apparatus according to claim 1,
The intermediate driver is
When the electric field strength measured by the electric field strength measurement unit of the transmission unit is smaller than a predetermined threshold, the modulation transmission unit of the transmission unit stops the modulation and transmission and discards the encoded data, and the transmission unit A video transmission apparatus characterized in that, when the electric field strength measured by the electric field strength measuring unit is equal to or greater than a predetermined threshold, the modulation and transmission unit of the transmission unit restarts the modulation and transmission. The video transmission device according to claim 1 or 2 ,
Furthermore, a position information measurement unit and an encoding rate determination unit are provided,
The position information measurement unit generates position information by measuring the position of the video transmission device,
The encoding rate determination unit includes a table in which position information and an encoding rate are stored correspondingly, the position information generated by the position information measurement unit, the position information and the encoding rate stored in the table, and An image transmission apparatus, wherein an encoding rate is determined based on a current modulation method used in a modulation transmission unit of the transmission unit. The video transmission apparatus according to claim 3 ,
The encoding rate determination unit
It is determined whether or not the position information generated by the position information measurement unit is stored in the table. If the position information is not stored, the current transmittable maximum is determined based on the current modulation scheme. A rate is calculated, and the current maximum transmittable rate is stored in the table as an encoding rate corresponding to the position information. When the position information is stored, the encoding rate corresponding to the position information is stored in the table. A video transmission device that reads from The video transmission device according to claim 4 ,
The encoding rate determination unit
Based on the current modulation scheme, a current maximum transmittable rate is calculated, and the encoding rate corresponding to the position information read from the table is compared with the current maximum transmittable rate, The video transmission apparatus, wherein when the read encoding rate is equal to or lower than the current maximum transmittable rate, the encoder performs compression encoding at the read encoding rate. The video transmission apparatus according to claim 5 , wherein
The encoding rate determination unit
If the read encoding rate is higher than the current maximum transmittable rate, after a predetermined time elapses, or after the current maximum transmittable rate reaches a predetermined rate, the encoder A video transmission apparatus, wherein compression encoding is performed at a read encoding rate.

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