JP3431124B2 - Transmission control device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a low transmission quality in a wireless section or the like as compared with a wired transmission line, and for example, a transmission line whose transmission quality greatly changes depending on a positional relationship between a base station and a mobile device, The present invention relates to a transmission control device that transmits real-time data. Here, unlike ordinary computer data, real-time system data refers to data such as voice, music, and moving images that need to arrive while satisfying the time constraint for the receiving-side upper layer device such as a decoder.

[0002]

2. Description of the Related Art When transmitting real-time data, it is necessary to correct a transmission error that an individual frame suffers during transmission and to reproduce the original sound or the original image as close as possible. Also, when the data is reproduced on the receiving side, even if the data is periodically transmitted from the transmitting side, the data does not arrive periodically due to the variation in the transmission delay of each frame due to the transmission control, and the data cannot be reproduced. There is a case where the receiving side does not have data to be reproduced next to the finished data.

In the case of transmitting general data, GBN (Go-Back N), SR (Se
lective-Repeat) etc. automatic repeat request (ARQ: Automat)
icRepeat reQuest) method is used. On the other hand, when transmitting real-time data, in order to absorb the variation in the transmission delay time of each frame described above,
There is a method in which the data arriving at the receiving side is buffered in the delay difference absorbing buffer and then the reproduction is started so as to keep the state where the data to be reproduced next always exists at the receiving side.

FIG. 5 shows an operation example according to the conventional SR-ARQ system. In the figure, 51 is a time series of transmission frames, 52 is a time series of reception frames, 53 is a time series of the buffering state of the delay difference absorption buffer, and 54 is a time series of reproduction data. The numbers 0, 1, 2, ... Show the frame numbers, the alphabets a, b, c, ... Show the payload data, “X” is the data in which the transmission error occurs, and the retransmission request Nak of the frame is transmitted. Sent back to.

Here, the round-trip delay time in the transmission path is set to a constant value Tr, and the transmitting side detects that the frame transmitted at time Tc-Tr is erroneous at the time Tc when the Nak returned from the receiving side is received. I shall. In this case, as compared with the case where the round-trip delay time varies, the frames are less likely to be redundantly transmitted, so that the transmission delay time due to the retransmission control of each frame is reduced.

From the time T0, the transmitting side transmits the real-time data {a, b, c, d, ...} In accordance with the SR-ARQ system. The receiving side starts reproduction from time T9 when the buffering of the data a, b, c, d, e, f into the delay difference absorption buffer is completed. After time T9, the data buffered in the delay difference absorption buffer is used to continue the reproduction while absorbing the transmission delay time difference.

Although not shown in FIG. 5, a frame arriving after a retransmission request for frame 6 (data g) in which a transmission error has occurred is temporarily buffered in the retransmission control buffer. Then, when the frame 6 (data g) arrives without a transmission error (time T13), the frame 6 (data g) and the previously arrived frame 7 (data h) are buffered in the delay difference absorption buffer. To be done. The same applies to the frame 8 (data i) and thereafter.

[0008]

In the conventional method using transmission control by the SR-ARQ system, the following problems occur. This will be described below with reference to FIG. In FIG. 6, 61 is a time series of transmission frames, 62 is a time series of reception frames, 63 is a time series of the buffering state of the delay difference absorption buffer, and 64 is a time series of reproduction data.

Here, since a transmission error has occurred in frame 1 (data b) and frame 2 (data c), the receiving side requests retransmission of frames 1 and 2, and the retransmitted frame arrives at the receiving side. The reproduction is started from the time T11 when the buffering of the data a, b, c, d, e, f is completed. Thus, in the case of FIG. 6, data a, b, c,
The waiting time until the reproduction starts becomes longer than that in the case where no transmission error occurs during the buffering of d, e, and f (FIG. 5). That is, if a transmission error occurs during buffering, it takes a long time to buffer a prescribed amount of frames. When the transmission delay is large, the increase in the buffering time due to the influence of the transmission error becomes even larger.

Therefore, when the transmission quality is poor, the waiting time before the start of reproduction becomes long. If operations such as fast-forward, rewind, skip, etc. are performed during playback on the receiving side and the order of playback frames is changed,
Playback interruption time becomes long. In addition, the data a,
Playback is started after b, c, d, e, and f have been buffered, but while the frame 6 (data g) to be played next is retransmitted a plurality of times, as at times T17 to T19, The data in the delay difference absorption buffer may be consumed, and reproduction may be interrupted. When the transmission quality deteriorates in this way and the same frame is retransmitted multiple times, the transmission delay time of the frame exceeds the reproduction time according to the amount of data buffered in the delay difference absorption buffer, Playback is interrupted. It should be noted that there is a case where the reproduction is interrupted even if the frame 14 (data o) is retransmitted only once, as at time T23 shown in FIG.

Conventionally, in order to solve the above problems, a method of increasing the buffering amount of the delay difference absorbing buffer on the receiving side has been adopted. However, with this method, the buffering time is increased and the probability of a transmission error occurring during buffering is high, so that the waiting time until the start of reproduction may be extremely long as described above.

According to the present invention, when transmitting real-time data through a transmission line whose transmission quality is lower than that of a wired transmission line and whose transmission quality greatly changes, there is a waiting time before starting reproduction or interruption of reproduction. It is an object of the present invention to provide a transmission control device that can shorten the time and realize reproduction with less interruption.

[0013]

A transmission control apparatus according to the present invention comprises a delay difference absorption buffer for buffering a fixed amount of received data and then outputting it to an upper layer apparatus;
Equipped with one retransmission control means. When the received data has a transmission error, the first retransmission control means requests the transmitting side to retransmit the frame, and sends the retransmitted data having no transmission error to the delay difference absorption buffer.

The second re- transmission control means converts the received data into
Even if there is a transmission error, the transmission side does not request the frame to be retransmitted, and the data in which the error in the payload part is allowed is sent to the delay difference absorption buffer. Retransmission control method change control
The means is to buffer the data in the delay difference absorption buffer.
Monitoring amount, and if the buffering amount is greater than the transition value,
If the first retransmission control means is selected, the buffering amount is selected.
Is smaller than the transition value, the second retransmission control means is selected.
To do . As a result, the buffering time at the start of reception is shortened, the buffering amount for delay difference absorption is always secured with a buffering amount equal to or greater than the transition value, and data can be supplied to the host device on the receiving side at a constant bit rate. it can.

Further, the frame of the present invention includes error correction detection.
The header part with the code added and the error detection code
Composed of a payload section, the second retransmission control means confirms the frame number of the header information restored by the added error correction detection code in the header portion of the frame, the delay difference absorbing the data allows the error of the payload portion It may be configured to send the data to the buffer for use.

[0016]

1 shows an example of the configuration of a transmission control device of the present invention. In the figure, the transmitting side comprises a transmitting side retransmission control means 11, a transmission waiting buffer 12, and a transmitting side retransmission control buffer 13. The receiving side includes retransmission control method change control means 21, receiving side retransmission control means A22, receiving side retransmission control buffer A23, receiving side retransmission control means B24, receiving side retransmission control buffer B25, delay difference absorbing buffer 2
It is composed of 6. Here, a solid line arrow shows a data flow, and a broken line shows a control relationship.

The data sent from the upper layer device on the transmission side is input to the transmission side retransmission control means 11 via the transmission waiting buffer 12 and the transmission side retransmission control buffer 13.
The frame is formed into a frame structure as shown in FIG. 2 and sequentially transmitted to the transmission path. In the frame structure, an error correction detection code is added to the header part (control bit) and an error detection code is added to the payload part (data). The transmission side retransmission control unit 11 reads the frame for which a retransmission request is issued from the reception side from the transmission side retransmission control buffer 13 and retransmits the frame.

On the receiving side, the received frame is buffered in the receiving side retransmission control buffer A23 and the receiving side retransmission control buffer B25 via the receiving side retransmission control means A22 and the receiving side retransmission control means B24, respectively. A certain amount of the data buffered in the reception side retransmission control buffer A23 and the reception side retransmission control buffer B25 is buffered in the delay difference absorption buffer 26, and is further output to the reception side upper layer device at a constant bit rate. . When the buffering amount of data in the delay difference absorbing buffer 26 is larger than the transition value, the retransmission control method change control unit 21 selects the retransmission control by the reception side retransmission control unit A22, and the buffering amount is larger than the transition value. If the number is small, the retransmission control by the reception side retransmission control means B24 is selected.

Here, the retransmission control operation by the reception side retransmission control means A22 or the reception side retransmission control means B24 will be described with reference to FIG. In FIG. 3, frame X (data g), frame X + 1 (data h), frame X + 2
(Data i) and frame X + 3 (data j) are sequentially received, and the case where frame X contains an error is shown. When the receiving side retransmission control means A22 detects an error in the frame X (data g), it controls the retransmission of the frame X. Upon detecting an error in the frame X (data g), the receiving side retransmission control means B24 restores the header information by the error correction code added to the header part, and controls the receiving side retransmission control of the data g'having an error in the payload part. Buffer in buffer B25.

When the amount of data buffered in the delay difference absorbing buffer 26 is larger than the transition value, and the frame X (data g) retransmitted by the transmitting side is received by the receiving side without error, the frame X is received. (Data g) and frame X + 1 (data h) to frame X + 3 (data j) buffered in the reception side reproduction control buffer A23.
Are sent to the delay difference absorbing buffer 26. As described above, when the buffering amount of data in the delay difference absorbing buffer 26 is large and the data can be continuously supplied to the upper layer device at a constant bit rate, the existing SR- by the reception side retransmission control means A22. Retransmission control equal to ARQ is performed, and error-free transmission can be performed.

On the other hand, when the buffering amount of the data in the delay difference absorbing buffer 26 is smaller than the transition value, the retransmission control by the reception side reproduction control means B24 is selected and buffered in the reception side reproduction control buffer B25. Frame X (data g ') containing an error
+1 (data h) to frame X + 3 (data j) are sent to the delay difference absorption buffer 26. As described above, when the buffering amount of data in the delay difference absorption buffer 26 is small and it becomes impossible to supply the data to the upper layer device at a constant bit rate, the error difference-allowed data is absorbed in the delay difference absorption. It is sent to the buffer 26. further,
By sending the next frame without re-sending,
The buffering amount of data in the delay difference absorbing buffer 26 can be recovered, and the data supply to the upper layer device at a constant bit rate can be continued.

FIG. 4 shows an operation example of the transmission control device of the present invention. In the figure, 41 is a time series of transmission frames, and 42 is
Is a time series of the received frame, 43 is a time series of the buffer for the delay difference absorption buffer, and 44 is a time series of the reproduction data. The numbers 0, 1, 2, ... Show the frame numbers, the alphabets a, b, c, ... Show the payload data, “X” is the data in which the transmission error occurs, and the retransmission request Nak of the frame is transmitted. Sent back to.

Here, the round-trip delay time on the transmission path is set to a constant value Tr, and the transmitting side detects that the frame transmitted at time Tc-Tr is erroneous at the time Tc when the Nak returned from the receiving side is received. I shall. Also,
Even if an error occurs in the frame, it is assumed that the header information is restored by the error correction code added to the header part.

On the receiving side, from the time T2 when the frame 0 (data a) arrives to the time T5, the buffering amount of data in the delay difference absorbing buffer 26 is equal to or less than the transition value. The retransmission control B is performed by the control means B24. At this time, the frame 1 (data b) and the frame 2 (data c) suffer errors during transmission, but the header information is restored by the error correction code to check the frame number, and the error is received in the payload part. It is buffered in the side retransmission control buffer B25 and sent to the delay difference absorbing buffer 26. In the figure, data in which errors are allowed are shown as b'and c '.

As a result, although the reproduced data b'and c'include an error, the data a to f are stored in the delay difference absorbing buffer 26.
The buffering time of can be shortened compared to the case of retransmitting frames 1 and 2 (FIG. 6). That is, the reproduction can be started from time T9 as in the case of FIG. From time T5 to time T12, the buffering amount of the data in the delay difference absorbing buffer 26 exceeds the transition value, and therefore the retransmission control A by the reception side retransmission control means A22 is performed. At this time, frame 6 (data g)
And frame 8 (data i) suffers errors during transmission,
Nak under the retransmission control is returned to the transmission side, and the data g and the subsequent data are not buffered in the delay difference absorption buffer 26. However, the data g ', h, i', j are buffered in the receiving side retransmission control buffer B25.

When the buffering amount of data in the delay difference absorbing buffer 26 becomes equal to or less than the transition value at time T12, the retransmission control B by the reception side retransmission control means B24 starts. At this time, the retransmitted frame 6 (data g) contains an error again, but the retransmission request is not returned and is buffered as data g'in the reception side retransmission control buffer B25.
By this retransmission control B, the data g ′, h buffered in the reception side retransmission control buffer B25 at time T13
Is sent to the delay difference absorbing buffer 26, and the buffering amount in the delay difference absorbing buffer 26 is recovered.

When the buffering amount of the data in the delay difference absorbing buffer 26 exceeds the transition value at time T13, the process returns to the retransmission control A by the reception side retransmission control means A22. Next, when the buffering amount of the data in the delay difference absorption buffer 26 becomes equal to or less than the transition value at time T14, the retransmission control B by the reception side retransmission control means B24 is performed. The frame 8 (data i) retransmitted at this time is received by the receiving side retransmission control buffer B2.
5 is buffered as data i. By this retransmission control B, the retransmission control buffer B25 on the receiving side at time T15
The data i, j, and k buffered in the delay difference absorption buffer 26 are sent to the delay difference absorption buffer 26.
The buffering amount in 6 is recovered.

The same applies hereinafter, but the frame 14 (data o) retransmitted at time T22 is received without error, but is discarded because it overlaps with the timing at which the error data o'is reproduced. In this way, when the buffering amount of the data in the delay difference absorbing buffer 26 becomes equal to or less than the transition value, the retransmission control B by the reception side reproduction control means B24 is made to function, and the error-allowed data is transmitted to the reception side. The buffering amount is restored by sending it from the retransmission control buffer B25 to the delay difference absorption buffer 26.
As a result, although the reproduction quality is deteriorated due to the influence of the data including the transmission error, it is possible to avoid the state where the reproduction difference is lost due to the lack of the data buffered in the delay difference absorption buffer 26.

In the above description, assuming a system in which the round-trip delay time of the transmission path is known, the receiving side sends back Nak to request the retransmission of the frame transmitted one round-trip delay time earlier. However, the RN, which is the smallest frame number among the frames returned from the receiving side and not accepted by the receiving side, is shown on the transmitting side.
Even when retransmission is performed based on (Request Number), the transmission control device of the present invention can be used in the same manner.

[0030]

As described above, the transmission control apparatus of the present invention accepts a frame in which a transmission error is allowed on the receiving side and makes a retransmission request when the buffering amount of the delay difference absorbing buffer is small. Dynamically switch to no transmission control. As a result, the buffering amount of the delay difference absorption buffer can be reduced, and the real-time system data can be transferred to SR-ARQ
Even if the transmission is controlled by the method, it is possible to shorten the waiting time until the reproduction is started and the reproduction interruption time due to the buffering of the delay difference absorption buffer.

Further, even if the transmission quality is deteriorated and the transmission delay time of an arbitrary frame becomes large due to the effect of retransmission, the delay difference absorption buffer is prevented from becoming empty, so that the reproduction is interrupted. It can be avoided. However, since the data for which a transmission error has been allowed is temporarily buffered in the delay difference absorption buffer, a reduction in reproduction quality cannot be avoided. In that case, by the encoding method in which the deterioration of the reproduction quality due to the mixing of errors is relatively small,
The compressed real-time data may be transmitted.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of a transmission control device of the present invention.

FIG. 2 is a diagram showing a structure of a frame to be transmitted.

FIG. 3 is a diagram for explaining a retransmission control operation in the transmission control device of the present invention.

FIG. 4 is a timing chart showing an operation example of the transmission control device of the present invention.

FIG. 5 is a timing chart showing an operation example according to a conventional SR-ARQ method.

FIG. 6 is a timing chart showing an operation example according to a conventional SR-ARQ method.

[Explanation of symbols]

11 Retransmission control means for transmitting side 12 Waiting buffer 13 Transmit side retransmission control buffer 21 Retransmission control method change control means 22 Retransmission control means A on receiving side 23 Retransmission control buffer A on receiving side 24 Retransmission control means B on receiving side 25 Retransmission control buffer B on receiving side 26 Delay difference absorption buffer

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Claims (2)

(57) [Claims] 1. A buffer for absorbing a fixed amount of received data, which is output to an upper layer device, and a transmission request of a frame to the transmitting side when the received data has a transmission error. The first retransmission control means for sending the retransmitted data having no transmission error to the delay difference absorption buffer, and the transmission side requesting the retransmission of the frame even if the received data has a transmission error. made without a second retransmission control means for sending the data allows the error of the payload portion to the delay difference absorbing buffer, buffering the data of the delay difference in the absorption buffer
The amount of buffering is monitored and the constant
Value ”), the first retransmission control means
If the buffering amount is less than the transition value,
Is a retransmission control method change for selecting the second retransmission control means
Transmission control device being characterized in that a control means. 2. The transmission control device according to claim 1 , wherein the frame is a header to which an error correction detection code is added.
Part and payload part with error detection code added
Is, the second retransmission control means, frame header information restored by the error correction detection code added to the header portion of the frame
A transmission control device, which is configured to check a system number and send data in which an error in a payload part is allowed to the delay difference absorption buffer.