JPH0239141B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes an automatic repeat method, which is a type of error control method in data transmission.
Request (abbreviated as ARQ method) is particularly useful for data transmission that continuously sends data blocks over a line with a long response delay time, and can achieve high throughput (transmission This invention relates to a highly efficient automatic retransmission method that can obtain characteristics (efficiency).

The automatic retransmission method, or ARQ method, is an error correction method using automatic retransmission that has a response line, and is a continuous ARQ method that continuously sends data blocks.
Generally known methods include the GBN ( Go Back - N ) method and the SR ( Selective Repeat ) method. In the GBN method, when the transmitting side receives a retransmission request signal ( negative acknowledgment , abbreviated as NACK) from the receiving side, the data block corresponding to the retransmission request signal, that is, NACK, and all subsequent data blocks are This method retransmits the same data block. On the other hand, the SR method selectively retransmits only the data block corresponding to the NACK from the receiving side. Each of these typical examples of conventional continuous ARQ systems has advantages and disadvantages, and will be briefly explained below with reference to FIGS. 1 and 2. Note that both Fig. 1 and Fig. 2 are examples of a line in which the response delay time is 7 blocks long, and Fig. 1 shows the transmission/reception method of the GBN system.
Figure 2 shows the SR method of transmission and reception.

In FIG. 1, a represents a transmission block sequence, b represents a reception block sequence, and c represents a reception output sequence, respectively.
D ₁ , D ₂ , D ₃ ... are data blocks, and ACK
is an acknowledgment signal (Acknowledgement). Also, an X mark placed at the bottom of the receiving block row indicates that an error has been detected, and the data block marked with an
A NACK is sent, and an ACK is sent to the sender for correct data blocks for which no errors were detected. Therefore, in the case of Figure 1, the first
Once the NACK is sent to the third data block _D3 , the response delay time of the line is seven blocks long, so the ninth data block
After D ₉ , seven data block groups D ₃ to D ₉ are transmitted again, and this retransmission is based on the data block D ₃ .
This process is repeated until an ACK is received (once in FIG. 1). The 10th data block _D3 in the receive block string for which ACK was sent is output to the receive output string, and the 3rd to 9th data blocks ( _D3 to _D9 ) in the receive block string in between are discarded and received. It is not output to the output column. Thereafter, if a NACK is received for data blocks D ₄ , D ₅ , . . . , the same retransmission as above is performed. However, the first
In the figure, the 11th and 12th data blocks D ₄ and D ₅ in the receive block sequence are correctly received, so
These data blocks D ₄ and D ₅ are output as they are to the reception output column. In this way, in the GBN system, among correctly received data blocks, only the data blocks in the correct numerical order are output as a received output string, and the others are discarded (FIG. 1c). In this way, the GBN method has the advantage of not requiring buffer memory on the receiving side, but once an error is detected, the correctly received data block may be discarded, so the GBN method given by the following equation (1) The drawback is that the throughput (transmission efficiency) η deteriorates significantly in the case of a line with a long response delay time, such as a satellite communication line.

η=1-P _B /1+P _B (N-1) (1) where P _B is the block error rate of the line, and N is the response delay time of the line expressed in the number of blocks.

In FIG. 2, a represents a transmission block sequence, b represents a reception block sequence, and c represents a reception buffer input sequence.
d indicates each received output string. In this SR method,
When a NACK is received for the third data block D ₃ , the data block is
Only D ₃ is sent, then D ₁₀ . Similarly, for other data blocks D ₆ , D ₁₁ etc. for which NACKs have been received, only those data blocks are retransmitted, and this selective retransmission is repeated until an ACK is received (in Figure 2, D ₃ is retransmitted three times). resend). Then, all correctly received data blocks in the received block sequence are sequentially input to the buffer memory (second
As shown in FIG. 2d, the buffer memory sequentially outputs D ₁ , D ₂ , D ₃ , D ₄ , . . . when the numerical order of the buffer input blocks becomes correct. Therefore, the throughput η in the SR method
is given by the following equation (2), and exhibits ideal throughput characteristics independent of response delay time.

η=1−P _B ...(2) However, in this SR method, until the numerical order of the buffer input blocks is correct, it is necessary to store all previously correctly received data blocks in the buffer memory to avoid overflow. Therefore, a disadvantage is that a large capacity (theoretically infinite) buffer memory must be prepared on the receiving side.

Therefore, we improved these shortcomings of the conventional method and
Just by installing a small buffer memory on the receiving side
We have previously proposed a method that aims to obtain throughput characteristics close to those of the SR method (patent application filed in 1983).
-27137). In this method (hereinafter referred to as method A), the number of retransmissions n of the same data block is determined in advance,
Retransmission is performed using the SR method until the number of retransmissions exceeds n, and at the point when the number of retransmissions exceeds n, the oldest error data block is continuously retransmitted. The throughput characteristics of this system are shown in FIG. 7 as results obtained by computer simulation. In Figure 7, the solid line indicates the case where the response delay time is 64 blocks.
The relationship between the block error rate (P _B ) and the throughput (η) when P = 1 is shown. Note that the throughput characteristics in the GBN method given by equation (1) and the throughput characteristics in the SR method given by equation (2) are shown in the figure by dashed lines and dotted lines, respectively, for reference comparison. As can be seen from the figure, the throughput characteristics of method A are significantly improved compared to the GBN method, but there is still room for further improvement in the throughput characteristics compared to the SR method.

Therefore, the present invention aims to further improve the throughput characteristics of the method A described above, and its purpose is to simply prepare a small-capacity buffer memory on the receiving side when data blocks are continuously sent over a line with a long response delay time. The object of the present invention is to provide an ARQ method that can obtain throughput characteristics close to ideal values. To achieve this objective, in the present invention, normally, as in the SR method, on the receiving side, only the correctly received new data block and the first correctly received retransmitted data block are input into the buffer memory. When the buffer memory overflows, the oldest error data block is efficiently retransmitted. In other words, the sending side can detect an overflow based on a retransmission request from the receiving side due to an overflow, or if it knows the capacity of the buffer memory in advance, so the oldest retransmitted data block is sent out preferentially at that time. Based on the technical idea of
Furthermore, the method for requesting retransmission from the receiver of the oldest data block mentioned above is the normal NACK.
How to add a retransmission request block number to
In addition to ACK and NACK, there is a method of providing a new acknowledgment signal (response signal) and using this new acknowledgment signal to request retransmission of the oldest error data block. On the other hand, when the transmitting side voluntarily retransmits the oldest error data block, the receiving side sends the data block stored in the buffer memory of the receiving side due to correct reception and the data block that has not yet been stored due to an error. ACK that has been received
Since it can be determined based on the NACK, if the capacity of the buffer memory is known in advance, it can be known at what point the overflow has occurred, so it is only necessary to send out the oldest error data preferentially at this point.

When the receiving side requests retransmission of the oldest error data block using the above-mentioned new confirmation signal, the following signal may be considered as the new confirmation signal, for example. For example, if we consider a case where data blocks are stored in the buffer memory on the receiving side at reserved (allocated) addresses, each time the contents are cleared, the number of the next data block group to be stored is determined, and the number of the other data blocks is determined. There is no room for storing. In other words, if a reserved data block is received, whether it is correct or incorrect, there will be no free space in the buffer memory, and an overflow occurs unless all data blocks are correctly received. Therefore, when there is no free space in the buffer memory and a correctly received data block is reserved for input to the buffer memory and is the oldest data block that has been retransmitted due to an error. , a signal indicating correct reception of this retransmitted data block and requesting retransmission of the oldest erroneous data block is transmitted as a new confirmation signal. This new confirmation signal can be referred to as an affirmative retransmission request signal due to its function, so it will be abbreviated as follows.

The automatic retransmission system of the present invention will be explained below using an example in which the receiving side requests retransmission of the oldest error data block using the above-mentioned affirmative retransmission request signal, and then a specific example of the circuit configuration will be explained. . First, the transmission and reception control procedures in the automatic retransmission system of this example will be explained in general terms.

(1) Transmission procedure When an ACK is received from the receiving side, a new data block is sent, and when a NACK is received, the corresponding data block is retransmitted.
However, even if a NACK is received, if an ACK for the corresponding data block has already been received, a new data block is sent. Up to this point, it is the same as the SR method.

However, a positive retransmission request signal from the receiving side
When an ACK is received, instead of transmitting a new data block, it retransmits the oldest erroneous data block at that time, using the time slot that would have originally transmitted a new data block.

(2) Receiving procedure On the receiving side, the procedure as shown in A and B below differs depending on whether there is free space in the buffer memory or not.

(i) Reception procedure A - When there is free space in the buffer memory: Depending on whether the received data block was correctly received, ACK, ACK, etc. are sent as in the SR method.
Assume that a NACK is sent to the sending side.

(ii) Reception procedure B - When there is no free space in the buffer memory: When a data block is received by mistake
Send NACK. Furthermore, even if the data block is correctly received, if it is not reserved in the buffer memory and cannot be input, a NACK is sent.

When the correctly received data block is the oldest erroneous data block, an ACK is sent.

If the correctly received data block is not the oldest but is reserved in the buffer memory and can be input, an affirmative retransmission request signal is sent.

The throughput of this example method obtained by the transmission/reception procedures of (1) and (2) is as follows: η=
This approaches the ideal value of 1-P _B (formula (2)), but if the response delay time is N block length, a sufficiently good throughput can be obtained by setting the buffer memory capacity to about 2N. The throughput characteristics of this system were determined by computer simulation using the buffer memory capacity B on the receiving side as a parameter, and the results are shown in FIG. In Fig. 8, the solid lines are taken as an example when N=64, B=64, B=128, and B=192.
The relationship between block error rate (P _B ) and throughput (η) in the case of FIG. In addition, the throughput characteristics and formula in the GBN method given by formula (1)
The throughput characteristics of the SR method given in (2) are shown in the same figure by dashed-dotted lines and dotted lines, respectively, for reference comparison. On the other hand, in method A, N=64, n
When =1, the buffer memory capacity that should be prepared on the receiving side is 128 blocks. Therefore, the eighth
It can be seen that the characteristics when B=128 in the figure and the characteristics of method A in FIG. 7 are the throughput characteristics when the reception buffer memory capacity is the same, and the method of the present invention clearly exhibits higher throughput characteristics.

FIG. 3 specifically shows the transmission/reception method of the present invention when using an example in which the response delay time is N=7 blocks long and the buffer memory capacity (B) on the receiving side is 7 blocks. It is something that In FIG. 3, D ₁ , D ₂ , . . . indicate data blocks with transmission numbers 1, 2, . . . , respectively, a is a transmission block sequence, b is a reception block sequence,
c indicates a receiving buffer input string, and d indicates a receiving output string. Data blocks that were received in error are also marked with an X.

In FIG. 3a, transmission according to the SR method is performed from time t ₀ to t ₁ . Since it was received at time _t1 , the transmitting side retransmits the first error data block ( _D3 ). Furthermore, since an ACK for data block D ₃ is received at time t ₂ , a new data block (D ₁₇ ) is sent even if a NACK for D ₃ is received thereafter. In FIG. 3b, since there is space in the buffer memory between times _T0 and _T1 , confirmation signals ACK and NACK are sent out according to reception procedure A. There is no free space in the buffer memory between time T ₁ and T ₂ , so reception procedure B is performed.
Confirmation signals ACK and NACK are sent. For example, _D10 was received correctly but is not reserved in the buffer memory, so a NACK is sent. _D5 is not the oldest but is a retransmission data block reserved in the buffer memory, and is sent out if it is correctly received. Also,
After time _T2 , a data block is output from the buffer memory and the overflow is eliminated, so the confirmation signal is sent out again according to reception procedure A.

On the receiving side, only the first correctly received data block _D3 , which has been retransmitted a plurality of times as shown in FIG. 3c, is input into the buffer memory. As shown in FIG. 3d, after the correctly received new data blocks D ₁ and D ₂ are output from the buffer memory, until the retransmitted data block D ₃ is input to the buffer memory, the data blocks that have already been input to the buffer memory are The six subsequent data blocks _D4 to _D9 remain stored and are not output.

FIG. 4 shows the general configuration of a data transmission device that implements the above-described example of the system of the present invention. In the figure,
1 is an input control circuit and a transmission buffer memory. The input control circuit is a circuit that sends a new data block to the data transmitter 2 and inputs it to the transmit buffer memory only when it receives signals b, c, and m from the transmitter controller 4. The transmission buffer memory is a memory that holds the transmitted data block n, and the memory capacity may be the length of N blocks, which is the same as the response delay time of the line. Reference numeral 2 denotes a data transmitter, which transmits input data n from the input control circuit and the transmission buffer memory 1 in a predetermined format. Reference numeral 3 denotes a receiving device on the transmitting side, which detects whether an acknowledgment (response) signal from the receiving side is an ACK or a NACK. 4 is a transmission control device;
Detection signal (ACK/
This is a device that controls data blocks to be sent to the data transmitting device 2 according to ACK/NACK)f, g, and h. Reference numeral 5 denotes a data receiving device, which receives a transmission data block from the transmitting side. Reference numeral 6 denotes a reception monitoring device, which is a device for determining whether or not the data receiving device 5 correctly receives a data block. Reference numeral 7 denotes a reception output control device which controls the reception data blocks O of the data reception device 5 according to the determination result of the reception monitoring device 6 and the state of the built-in reception buffer memory, and outputs only correctly received data blocks P in numerical order. It is a device for outputting. Reference numeral 8 denotes a receiving side transmitting device, which is a device for sending ACK or NACK as a response signal to the transmitting side according to the determination result signals r and s of the receiving monitoring device 6 and the receiving output control device 7. 9 is a communication line. In the device configuration shown in FIG. 4, the transmission control device 4 on the transmitting side and the reception output control device 7 on the receiving side each perform conventional continuous ARQ.
The structure is significantly different from that of the conventional method. Hereinafter, a specific example of the configuration of the transmission control device 4 will be explained with reference to FIG. 5, and a specific example of the configuration of the reception output control device 7 will be explained with reference to FIG.

FIG. 5 shows the transmission control device 4 (within the two-dot chain line) together with the input control circuit and the transmission buffer memory 1. The transmission buffer memory is realized by random access memory. The input control circuit is a circuit that inputs the input data block a only when there is a write enable signal b from the write address designation circuit 12. The transmission control device 4 includes a block number detection circuit 1
0, a block number holding memory 11, a write address designation circuit 12, a read address designation circuit 13, a NACK determination circuit 14, and an ACK unconfirmed block number storage memory 15.
That is, the block number detection circuit 10 is a circuit for detecting the block number of the input data block ^a1 to the transmission buffer memory. The write address designation circuit 12 is a logic circuit, and based on the ACK signal f from the transmitting receiving device 3 or the determination signal i from the NACK determination circuit 14, the write enable signal b and the write address c are input to the control circuit and the transmission buffer memory. 1, and also sends a similar write address c to the block number holding memory 11. That is, data blocks for which ACK has already been received are sequentially erased in the transmission buffer memory by the write address designation circuit 12, and data blocks for which ACK has not yet been received, including new data blocks, are stored in N blocks corresponding to the line response delay time. The block number is stored in the block number holding memory 11 in correspondence with the data block in the transmission buffer memory. On the other hand, the read address designation circuit 13 is also a logic circuit,
Upon receiving the ACK signal g or the judgment signal j from the NACK judgment circuit 14, the block number e from the block number holding memory 11, and the unconfirmed block number l from the ACK unconfirmed block number holding memory 15, it should be read from the transmission buffer memory. It sends out an address signal m specifying the address number of the data block. The NACK determination circuit 14 receives the NACK signal h from the transmitting receiving device 3 and the unconfirmed block number k from the ACK unconfirmed block number holding memory 15, and determines whether or not the data block for the received NACK has already received an ACK. If it has already received an ACK, it sends an ACK judgment signal i to the write address designation circuit 12, and if it has not yet received an ACK, it sends a NACK judgment signal j to the read address designation circuit 13. Send. The ACK unconfirmed block number holding memory 15 identifies the transmitted block number upon receiving the block number e from the block number holding memory 11, and stores the transmitted data until it receives the ACK signal f or signal g from the transmitting receiving device 3. The block numbers of the blocks are memorized and held in order. Therefore, the signals k and l output by this memory 15 are signals whose information is the block number of a data block that has not yet been correctly received by the receiving side.

FIG. 6 shows the configuration of a reception output control device 7 on the reception side, which includes a reception buffer memory 16 and a write address designation circuit 17.
, a read address designation circuit 18 , and a buffer memory monitoring circuit 19 . The reception buffer memory 16 is realized as a random access memory, and its function is to write only the first correctly received data block O from the data reception device 5 according to the determination result from the reception monitoring device 6, and to The data blocks are outputted to the outside as output data blocks P until they are in the correct numerical order.
This writing/reading is controlled by a write address designation circuit 17 and a read address designation circuit 18.
and the buffer memory monitoring circuit 19. The write address designation circuit 17 receives the first correctly received block number v from the buffer memory monitoring circuit 19 and sends the address number t of the correct data block to be written to the reception buffer memory 16 to the reception buffer memory 16. The read address designation circuit 18 selects the block numbers w of the data blocks written in the reception buffer memory 16 whose block numbers are in the correct numerical order and which can be output to the outside by the buffer memory monitoring circuit 1.
9 and sends out an address signal u indicating the address number to be read. The buffer memory monitoring circuit also receives ACK/ACK from the reception monitoring device 6.
NACK signal and corresponding block number q
The write address designation circuit 17 determines whether to send the ACK or the signal s.
This is a logic circuit that sends out a block number v to be written to, and also sends out a block number w that can be output from the reception buffer memory 16 to the read address designation circuit 18.

Above, the present invention in the example explained in detail
In the ARQ method, that is, the automatic retransmission method, automatic retransmission is performed based on the SR method when there is free space in the buffer memory on the receiving side, and in addition to the SR method when there is no free space in the buffer memory. It sends a NACK for a data block that cannot be input, and an affirmation requesting retransmission of the oldest erroneous data block if it is correctly received and this data block can be input to the buffer memory. Sends a retransmission request signal. Therefore, compared to the previously proposed method (method A), it is possible to improve the throughput characteristics when using a small-capacity receive buffer memory, and the ideal throughput of the SR method is realized for the first time using a large-capacity receive buffer memory. It is possible to obtain characteristics that are extremely close to the characteristics.

By the way, the method of the present invention normally performs transmission and reception using the SR method, and when there is no free space in the buffer memory on the receiving side, the oldest error data block is preferentially retransmitted in addition to the SR method. The instruction to retransmit old erroneous data blocks may be given from the receiver to the sender, or by the sender itself.
Moreover, when receiving instructions from the receiving side, in addition to the method of using the affirmative retransmission request signal as explained by way of example,
Any method may be used as long as it requests retransmission of the oldest error data block when the buffer memory overflows, such as adding a retransmission request block number to the NACK described above. In addition, in order to spontaneously retransmit from the transmitting side, as mentioned above, when an overflow of the receiving buffer memory is detected from the previously known capacity of the receiving buffer memory and the NACK and ACK sent from the receiving side, Just resend it.

[Brief explanation of drawings]

Figures 1 and 2 are explanatory diagrams for explaining two typical examples of conventional continuous ARQ methods, Figure 3 is an explanatory diagram for explaining an example of the method of the present invention, and Figure 4 is an explanatory diagram for explaining the method of the present invention. FIG. 5 is a block diagram showing an example of the main part of the transmitting side shown in FIG. 4, and FIG. 6 is an example of the main part of the receiving side shown in FIG. 4. Block diagram showing 7th
This figure is a graph showing the throughput characteristics of the conventional example, and FIG. 8 is a graph showing the throughput characteristics of the system of the present invention in comparison with that of the conventional system. In the drawing, 1 is an input control circuit and a transmission buffer memory, 2 is a data transmitter, and 3 is an ACK/ACK/buffer memory.
4 is a transmission control device, 5 is a data reception device, 6 is a reception monitoring device, 7 is a reception output control device, and 8 is an ACK/NACK detection device on the sending side for detecting ACK/NACK.
Receiving side transmitting device for sending ACK/NACK, 9 is a communication line, 10 is a block number detection circuit, 11 is a block number holding memory, 12 is a write address designation circuit, 13 is a read address designation circuit, 1
4 is a NACK judgment circuit, 15 is an ACK unconfirmed block number holding memory, 16 is a reception buffer memory,
17 is a write address designation circuit, 18 is a read address designation circuit, 19 is a reception buffer memory monitoring circuit, D ₁ , D ₂ , D ₃ , . . . are data blocks,
ACK is an acknowledgment signal, NACK is a retransmission request signal,
ACK is a confirmation signal representing an acknowledgment and a request for retransmission of the oldest erroneous data block, a and a' are input data blocks, b is a signal that controls the input of the data block, c is a signal that specifies the write address number, d and e is a signal indicating the block number, f
is a signal indicating ACK reception, g is a signal indicating reception, h is a signal indicating NACK reception, i is a signal indicating ACK from NACK determination circuit 14, j is NACK
A signal indicating NACK from the determination circuit 14, k and l are signals indicating the ACK unconfirmed block number, m
is a signal specifying the address number of the data block to be read from the transmission buffer memory, n is the transmission data block, o is the reception data block, p is the output data block, q is the block number of the reception data and a signal indicating correct or incorrect reception, r is the signal A signal that requests transmission of NACK, s is a signal that requests transmission of ACK or ,
v is a signal indicating the data block number to be written to the receiving buffer memory, and w is a signal indicating the data block number that can be output from the receiving buffer memory.

Claims (1)

[Scope of Claims] 1. The system has a line for a response from the receiving side to a data block from the sending side, and the sending side automatically retransmits the data block received in error, and the receiving side automatically retransmits the data block received correctly. In data transmission, the receiving buffer memory is provided with a receiving buffer memory for storing the retransmitted data block and the first correctly received retransmitted data block, and the data blocks are read out in the correct numerical order from the receiving buffer memory, the receiving buffer memory being a finite-length memory for at least one response delay time. As long as the receiving buffer memory does not overflow, only when the sending side receives a retransmission request signal indicating that the data was not received correctly, only the data block corresponding to the retransmission request signal is retransmitted, and the receiving buffer memory overflows. An automatic retransmission method for data transmission characterized by giving priority to retransmitting the oldest erroneous data block at that time. 2. Overflow of the receive buffer memory is detected on the receiving side, and upon detection of this overflow, the receiving side sends a signal requesting retransmission of the oldest error data block to the transmitting side, and the transmitting side uses this signal to send the oldest error data block. An automatic retransmission system in data transmission according to claim 1, characterized in that an erroneous data block is retransmitted. 3. Automatic data transmission in data transmission according to claim 1, characterized in that an overflow of the reception buffer memory is detected on the transmitting side, and upon detection of this overflow, the transmitting side voluntarily retransmits the oldest erroneous data block. Retransmission method. 4. On the receiving side, when the oldest retransmitted data block is correctly received and the retransmitted data block is stored in the reception buffer memory, the receiving side indicates correct reception of the retransmitted block and requests retransmission of the oldest erroneous data block. 3. The automatic retransmission system for data transmission according to claim 2, characterized in that the automatic retransmission system transmits a signal that