JP2004080321A - Transmission method and transmission apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an encode rate in matching with an environment and a state when wirelessly transmitting digital data. <P>SOLUTION: A broadcast reception section 10 is provided with: an encoder 15 for encoding main data; a transmission circuit 16 for assembling the main data encoded by the encoder 15 into data frames and transmitting the data frames; and a reception circuit 16 for receiving a returned ACK frame; and a circuit 18 for calculating a successful rate of transmission of the data frames on the basis of the transmitted number of the data frames and the number of returned ACK frames every time the transmission circuit 16 transmits a prescribed number of the data frame; and a control circuit 18 setting a transmission rate of the data frames and the encode rate of the main data on the basis of the calculated successful rate. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and a device for transmitting digital data.
[0002]
[Prior art]
As shown in FIG. 6, there is a television receiver in which a broadcast receiving unit 10 and a display unit 20 are provided separately. In this case, the broadcast receiving unit 10 receives a television broadcast and demodulates a video signal and an audio signal. In the example of FIG. 6, a VTR 1 and a DVD player 2 are also connected as external AV devices. ing. The broadcast receiving unit 10 is placed at a corner of a room or the like.
[0003]
Then, in the broadcast receiving unit 10, one set of a video signal and an audio signal by television broadcasting and a video signal and an audio signal reproduced by the AV devices 1 and 2 is selected, and the selected pair is transmitted by radio waves. Is transmitted to the display unit 20. The video signal and the audio signal to be transmitted are encoded (data compression) by, for example, the MPEG method, are converted into data frames according to IEEE802.11, and are transmitted.
[0004]
On the other hand, the display unit 20 has a battery as a power source and an image display means configured with an LCD panel. Then, the display unit 20 decodes the original video signal and audio signal from the encoded signal transmitted by the broadcast reception unit 10, and outputs video and audio. Therefore, according to this television receiver, the user can easily watch a television program in a favorite place such as a living room, a bedroom, or a garden.
[0005]
[Problems to be solved by the invention]
In the case of the above-described television receiver, the quality of the video and audio output from the display unit 20 can be increased by increasing the encode rate when the broadcast receiving unit 10 encodes the video signal and the audio signal.
[0006]
However, the transmission rate (transmission rate) when the broadcast receiving unit 10 transmits the MPEG encoded signal to the display unit 20 must be higher than the encoding rate when the video signal and the audio signal are encoded. The state of radio waves between the broadcast receiving unit 10 and the display unit 20 differs depending on where the broadcast receiving unit 10 and the display unit 20 are used. For example, it differs depending on the distance between the broadcast receiving unit 10 and the display unit 20, the presence or absence of walls and furniture, and the like.
[0007]
Further, if the display unit 20 is moved to another place, the state of the radio wave also changes. Furthermore, even if the place where the display unit 20 is used is fixed, the radio wave condition may change even if a person passes between or approaches the broadcast receiving unit 10 and the display unit 20.
[0008]
For this reason, generally, the transmission rate when the broadcast receiving unit 10 transmits the MPEG encoded signal is set to be low, and the transmission state is secured. However, in such a case, the encoding rate of the MPEG encoded signal cannot be increased, and as a result, the quality of video and audio is limited.
[0009]
The present invention is intended to solve such a problem.
[0010]
[Means for Solving the Problems]
In the present invention, for example,
In a communication method, a transmitting side encodes main data, converts the data frame into a data frame, and transmits the data frame. When a receiving side normally receives the transmitted data frame, the receiving side returns an ACK frame to the transmitting side. ,
Each time a predetermined number of the data frames are transmitted, a success rate of the data frame transmission is calculated from the number of the transmitted data frames and the number of the returned ACK frames,
The transmission method is such that the transmission rate of the data frame and the encoding rate of the main data are set based on the calculated success rate.
Therefore, the transmission rate of the data frame is dynamically changed in accordance with the environment or state at that time, and the encoding rate is also dynamically changed to a speed corresponding to the transmission rate.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
{Circle around (1)} When data such as AV data is wirelessly transmitted according to IEEE 802.11 for a protocol and a data frame at the time of wireless transmission of data, as shown in FIG.
(A) The transmitting device transmits a data frame (MAC data frame) having main data.
(B) When the receiving device has successfully received the MAC data frame, the receiving device returns a frame having ACK data (ACK frame) until the period TID specified by the transmitting device has elapsed.
If not, do nothing.
(C) When receiving the ACK data within the period TID, the transmitting device transmits the next MAC data frame.
If ACK data cannot be received within the period TID, the previous MAC data frame is retransmitted.
(D) The above process is repeated for each MAC data frame.
Is performed.
[0012]
FIG. 2 shows the configuration of the data frame. This data frame is defined by IEEE 802.11, but as shown in FIG. 2A, one data frame is composed of a PLCP preamble, a PLCP header, a PSDU, tail bits, and the like. In this case, the transmission rate (transmission rate) of the PLCP preamble and the PLCP header is fixed to 6 Mbps, but the transmission rates of the PSDU and the tail bits are variable as described later.
[0013]
Then, the PLCP header has data such as data DR and data LENGTH, as shown in FIG. 2B. In this case, the data DR indicates the transmission rate of the PSDU and the tail bit, and the data LENGTH indicates the length of the main data included in the PSDU.
[0014]
Here, the data DR indicates the transmission rate of the PSDU and the tail bit as described above, but is 4 bits, and the data DR and the transmission rate have a relationship as shown in FIG. 3, for example. I have. For example, when DR = "1101", the transmission rate of PSDU and tail bits is 6 Mbps, and when DR = "0101," the transmission rate is 12 Mbps. If this transmission rate is set low, wireless transmission is stable, but transmission and reproduction of high-quality video and audio cannot be performed. Conversely, if this transmission rate is set high, it is vulnerable to various obstacles. .
[0015]
When the data frame is a MAC data frame, as shown in FIG. 2C, the PSDU includes a MAC header, main data, and a frame checksum FCS. The MAC header includes a frame control FC, data DRID, address ADDR, and the like. In this case, the frame control FC has data such as the transmission direction of the data frame, whether or not the main data is encrypted, and whether the data frame is the first transmission or the retransmission.
[0016]
The data DRID indicates the time limit TID in the above item (C), and is generally TID = 2 to 3 ms. Further, the address ADDR is a source MAC address, a destination MAC address, a BSSID for specifying a wireless area, and the like.
[0017]
The main data is data to be transmitted. In this case, the main data is a video signal and an audio signal that have been subjected to MPEG encoding. The frame checksum FCS is used to check whether or not the receiving device has normally received the MAC data frame, as shown in section (B).
[0018]
Further, when the data frame is an ACK frame, as shown in FIG. 2D, the PSDU includes a MAC header and a frame checksum FCS, and the MAC header has data RA.
[0019]
(2) MPEG encoding rate and transmission rate When data is encoded by the MPEG method and transmitted wirelessly, even if the transmission rate of the wireless module (transmission / reception circuit) is set to the value RTX, one data frame is retransmitted. If the transmission is performed once (assuming that the transmission is performed twice in total including the initial transmission), the success rate of the transmission is 1/2, and the actual transmission rate is RTX / 2. If retransmission is performed twice (assuming that transmission is performed three times in total), the transmission success rate is 1/3, and the actual transmission rate is RTX / 3.
[0020]
Therefore,
RTX: Transmission rate set for wireless module p: Success rate of transmission 0 ≦ p ≦ 1
REF: Assuming a substantial transmission rate of the wireless transmission system,
REF = RTX · p (1)
It becomes.
[0021]
When data is encoded by the MPEG method and transmitted wirelessly,
RENC: If the encoding rate of the MPEG encoder on the transmitting side is used, the decoding rate when the MPEG encoded signal is decoded on the receiving side is also the value RENC. And at all,
RENC <REF (2)
Must. That is, if the state of RENC> RTX is continuously set, the data necessary for the MPEG decoder to reproduce a moving image is depleted, and the moving image cannot be reproduced.
[0022]
Therefore, from Expressions (1) and (2), RENC <RTX · p (3)
It becomes. However, in practice, the data output from the wireless module on the transmitting side contains various information in addition to the original video signal and audio signal, Since the time for waiting for the ACK frame is required or the time for processing the ACK frame is also required, the encoding rate RENC of the MPEG encoder on the transmitting side needs to be suppressed to about 80%.
[0023]
As a result, equation (3) furthermore
RENC <0.8 × RTX · p (4)
It becomes. That is, when the communication condition is good and the transmission rate RTX and the success rate p increase, the image quality can be improved by increasing the encode rate RENC accordingly.
[0024]
Therefore, the present invention judges or detects the communication status, and when the communication status is poor, lowers the encoding rate RNC to reduce the image quality, but enables the reproduction of moving images without dropouts or discontinuities. The image quality is improved by increasing the rate RENC.
[0025]
(3) Example of transmitting device and receiving device FIG. 4 shows an example in which the transmitting device according to the present invention is applied to the above-described broadcast receiving unit 10. Also, an example of the display unit 20 serving as a receiving device is shown. Then, the broadcast wave signal of the television broadcast received by the antenna 11 is supplied to a receiving circuit 12 to extract a video signal and an audio signal of an arbitrary channel, and this signal is supplied to a switch circuit 13 for input switching. Video signals and audio signals are output from the VTR 1 and the DVD player 2, and these signals are also supplied to the switch circuit 13.
[0026]
Then, one set of the video signal and the audio signal supplied thereto is selected by the switch circuit 13, and the selected video signal and audio signal are supplied to the A / D converter 14, and the digital data is converted into an A / D signal. After being D-converted, it is supplied to the MPEG encoder 15 and is encoded into an MPEG encoded signal. The MPEG encoded signal is supplied to the wireless module 16 and is formed into the IEEE 802.11 MAC data frame described in the item (1). The OFDM signal is further transmitted to the display unit 20 via the antenna 17.
[0027]
The broadcast receiving unit 10 has a control circuit 18. The control circuit 18 controls the entire operation of the broadcast receiving unit 10 including switching of the switch circuit 13, and is constituted by a microcomputer. Further, the control circuit 18 controls the encoding rate when the MPEG encoder 15 encodes the data into the MPEG encoded signal and the transmission rate when transmitting the MAC data frame to optimal values.
[0028]
Therefore, the control circuit 18 is provided with, for example, a routine 100 as shown in FIG. 5 as a part of a program executed by the microcomputer. The details of the routine 100 will be described later, but in FIG. 5, only the part related to the present invention is extracted from the routine 100.
[0029]
On the other hand, in the display unit 20 serving as a receiving device, the OFDM signal transmitted from the broadcast receiving unit 10 is received by the antenna 21, and the received MPEG encoded signal is demodulated when the received signal is supplied to the wireless module 22. Taken out. Then, the MPEG encoded signal is supplied to an MPEG decoder circuit 24 through a buffer circuit 23 and is decoded into original digital data. The digital data is supplied to a D / A converter 25 to be converted into an original video signal and audio signal. D / A conversion is performed, and these signals are supplied to the LCD panel 27 and the speaker 28 through the drive circuit 26, and video and audio are output.
[0030]
In this case, the wireless module 22 checks whether or not the MAC data frame has been normally received by obtaining the frame checksum FCS for each received MAC data frame, as described in the section (B). , The ACK frame is returned to the wireless module 16 of the broadcast receiving unit 10 before the period TID elapses. If the reception is not successful, nothing is returned.
[0031]
Further, as described in the section (C), the radio module 16 of the broadcast receiving unit 10 checks whether or not an ACK frame is returned each time a MAC data frame is transmitted. The presence or absence indicates the success rate p in the equation (4).
[0032]
Therefore, in the present invention, the success rate p is obtained from the presence or absence of the return of the ACK frame, and the encode rate RENC of the MPEG encoder 15 and the transmission rate RTX of the wireless module 16 are controlled to appropriate values according to the success rate p. . The control is realized by the microcomputer of the control circuit 18 executing, for example, a routine 100 shown in FIG.
[0033]
That is, when the broadcast receiving unit 10 starts transmitting the MPEG encoded signal, the processing of the microcomputer of the control circuit 18 starts from step 101 of the routine 100, and then, in step 102, the encoding rate RENC of the MPEG encoder 15 and The transmission rate RTX of the wireless module 16 is set to their highest value.
[0034]
Subsequently, in step 111, transmission (including retransmission) of the MAC data frame is performed, for example, 1000 times. In this case, the encode rate RENC and the transmission rate RTX are the maximum values set in step 102. At this time, if the transmission of the MAC data frame is successful, an ACK frame is returned from the display unit 20, and the number nACK of the returned ACK frames is counted.
[0035]
Next, in step 112,
p = nACK / 1000 (5)
, The success rate p of the transmission of the MAC data frame is calculated, and in step 113, it is determined whether the expression (4) is satisfied.
[0036]
Then, when the expression (4) does not hold, it means that the transmission rate RTX is too high. Therefore, the process proceeds from step 113 to step 114, and in this step 114, it is determined whether or not the transmission rate RTX can be reduced. , It is determined whether the transmission rate RTX is the lowest value.
[0037]
In this case, since the transmission rate RTX is the highest value in step 102 and therefore is not the lowest value, the process proceeds from step 114 to step 115. In this step 115, the encoding rate RENC and the transmission rate RTX become 1 The rank is set to a lower value, and then the process returns to step 111.
[0038]
If the transmission rate RTX is the lowest value in step 114, that is, if the transmission rate RTX cannot be further reduced, the process returns from step 114 to step 111.
[0039]
Therefore, according to steps 111 to 115, every time the MAC data frame is transmitted 1000 times, it is checked whether or not the expression (4) is satisfied. If not, the encoding rate RENC and the transmission rate until the expression is satisfied are satisfied. The rate RTX is lowered.
[0040]
On the other hand, when equation (4) is satisfied in step 113, there is a margin in the transmission rate RTX, so the process proceeds from step 113 to step 124, where the transmission rate RTX can be increased. It is determined whether or not the transmission rate RTX is the highest value.
[0041]
If the transmission rate RTX is not the highest value, the process proceeds from step 124 to step 125. In step 115, the encoding rate RENC and the transmission rate RTX are set to values higher by one rank, and then the process returns to step 111. .
[0042]
If the transmission rate RTX is the highest value in step 124, that is, if the transmission rate RTX cannot be increased any more, the process returns from step 124 to step 111.
[0043]
Therefore, according to steps 111 to 113, 124, and 125, every time a MAC data frame is transmitted 1000 times, it is checked whether or not expression (4) is satisfied. The rate RENC and the transmission rate RTX are increased.
[0044]
Therefore, according to the routine 100, the transmission rate RTX becomes the maximum value allowed in the environment or state at that time, and the encoding rate RENC also becomes a corresponding speed.
[0045]
{Circle around (4)} According to the broadcast receiving unit 10 described above, the success rate p when transmitting the MAC data frame from the returned ACK frame is obtained, and the transmission rate RTX at that time is determined according to the success rate p. The encoding rate RENC is set to the highest value allowed by the transmission rate RTX, as well as being set to the highest value allowed by the environment and conditions. Therefore, even when the broadcast receiving unit 10 and the display unit 20 are used or during use, even if the environment and the state change, it is possible to always obtain the optimal video and audio, and to eliminate the lack of the video and audio. It does not occur.
[0046]
Moreover, for that purpose, there is no need to change or add hardware of the broadcast receiving unit 10, and only the software needs to be changed. Further, the display unit 20 does not need to change hardware and software, and can use the existing one as it is.
[0047]
{Circle around (5)} In the above description, after step 102, a MAC data frame having null data (for example, data whose values are all FFh) as main data is transmitted, for example, 100 times, and thereafter, step 112 and thereafter are executed You can also. By doing so, the MAC data frame having the original MPEG encoded signal can be transmitted from the beginning at an appropriate speed. At this time, the time required for transmitting null data is 10 ms or less even when RTX = 10 Mbps, and since null data is not reproduced as video or audio, there is no problem in viewing video and audio.
[0048]
In the above description, the encode rate RENC and the transmission rate RTX are set to the highest values in step 102, but they may be set to the median value or the lowest value.
[0049]
[List of abbreviations used in this specification]
A / D: Analog to Digital
ACK: ACKnowledgment
AV: Audio and Visual
BSSID: Basic Service Set IDentification
D / A: Digital to Analog
DVD: Digital Versatile Disc
IEEE: Institute of Electrical and Electronics Engineers
LCD: Liquid Crystal Display
MAC: Media Access Control address
MPEG: Motion Picture Image Coding Experts Group
OFDM: Orthogonal Frequency Division Multiplex
PLCP: Physical Layer Convergence Procedure
PSDU: Physical layer Service Data Unit
VTR: Video Tape Recorder
[0050]
【The invention's effect】
According to the present invention, optimal images and sounds can always be obtained even when the environment and conditions change each time or during use of the transmitting device and the receiving device, and the images and sounds can be obtained. There is no loss. In addition, there is no need to change or add hardware to the transmitting device. Further, the receiving device does not need to change both hardware and software, and can use the existing device as it is.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining the present invention.
FIG. 2 is a diagram for explaining the present invention.
FIG. 3 is a diagram for explaining the present invention.
FIG. 4 is a system diagram illustrating one embodiment of the present invention.
FIG. 5 is a flowchart illustrating one embodiment of the present invention.
FIG. 6 is a diagram for explaining the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Broadcast receiving part, 12 ... Receiving circuit, 14 ... A / D converter, 15 ... MPEG encoder, 16 ... Wireless module, 20 ... Display part, 22 ... Wireless module, 24 ... MPEG decoder, 25 ... D / A converter, 27 ... LCD panel

Claims (6)

In a communication method, a transmitting side encodes main data, converts the data frame into a data frame, and transmits the data frame. When a receiving side normally receives the transmitted data frame, the receiving side returns an ACK frame to the transmitting side. ,
Each time a predetermined number of the data frames are transmitted, a success rate of the data frame transmission is calculated from the number of the transmitted data frames and the number of the returned ACK frames,
A transmission method wherein the transmission rate of the data frame and the encoding rate of the main data are set based on the calculated success rate. The transmission method according to claim 1,
If the above settings are
A process of setting the transmission rate of the data frame to the highest value based on the success rate,
A transmission method wherein the encoding rate of the main data is set to a maximum value based on the set transmission rate. In the transmission method according to claim 1 or claim 2,
A transmission method in which the main data is a video signal and an audio signal. A communication apparatus in which a transmitting side encodes main data, converts the data frame into a data frame and transmits the data frame, and a receiving side returns an ACK frame to the transmitting side when the transmitted data frame is normally received. ,
An encoder for encoding the main data,
A transmission circuit that converts the encoded main data into the data frame and transmits the data frame;
A receiving circuit for receiving the returned ACK frame;
A circuit for calculating a success rate of transmission of the data frame from the number of transmitted data frames and the number of returned ACK frames each time the transmission circuit transmits a predetermined number of the data frames; ,
And a control circuit for setting a transmission rate of the data frame and an encoding rate of the main data based on the calculated success rate. The transmission device according to claim 4,
The setting made by the control circuit is
A process of setting the transmission rate of the data frame to the highest value based on the success rate,
A transmitting apparatus, wherein the encoding rate of the main data is set to a maximum value based on the set transmission rate. In the transmission device according to claim 4 or claim 5,
A transmission device wherein the main data is a video signal and an audio signal.

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