JPS6342534A - Communication system - Google Patents

Abstract

PURPOSE:To eliminate the influence due to the error of a backward channel by transmitting not only the confirmation signal of a pertinent frame but also that of plural past frames in case of loop checking of the confirmation signal. CONSTITUTION:A confirmation signal generating part 28 adds redundant bits for error detection to the confirmation signal of L-number of past frames and loop checks these signals together with a frame identification number through a backward line 14 in accordance with an accepted error presence/absence detection result. A confirmation signal discriminating part 24 performs error detection based on a loop checked ACK/NACK signal: and if error is detected, the confirmation signal is abandoned because it is probable that the confirmation signal is erroneous, but otherwise, the received ACK/NACK signal is outputted to a transmission buffer 22. Thus, the influence of error of the backward communication line is loop checked reduced even if there is error in the backward communication line through which the confirmation signal is loop checked and a throughput approximating to the throughput for an errorless ideal case is obtained.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is directed to a retransmission request method (ARQ method) that detects whether there is an error in a received signal and requests retransmission if there is an error. Regarding communication systems.

(Prior Art) Various error control methods are known to reduce the effects of errors when transmitting information through a transmission path with errors, but among them, the ARQ method has a relatively simple device and is Because highly reliable communication can be performed, it is widely used not only in satellite communication but also in wired communication.

Various ARQ methods are already in use, including the Go-back-N method and the selective retransmission method.

However, all of these have been established on the assumption that the backward communication path for returning a confirmation signal indicating that there are no errors, that is, an ACK/NACK signal, is highly reliable.

The assumption that the conventional backward channel is highly reliable is because the ACK/NACK signal is, for example, 1 bit, which is extremely small compared to the amount of information to be transmitted. This is due to the fact that reliability can be sufficiently increased by adding a sufficiently large number of bits.

However, in recent years, with the development of data communication, for example, HDLC (High Level Dah)
aL ink Control Process
As in the signal transmission procedure using e), when transmitting data in both directions, the number of cases in which a confirmation signal for ARQ is transmitted together with the own transmission signal is increasing. In such a case, sufficient redundant bits cannot be added to the confirmation signal due to transmission capacity limitations.

Therefore, if there is an error in the backward communication channel, the error in the backward communication channel causes the ACK/N
There is also a possibility that the ACK signal will disappear. On the transmitting side, when a NACK signal is received and when an ACK/NACK signal is not received within a certain period of time, the transmitted information must be retransmitted, so the number of retransmissions of the transmitted information increases and the line throughput decreases. There was a problem.

(Problem to be Solved by the Invention) As described above, in the communication system using the conventional retransmission request method, if there is an error in the backward communication path, the confirmation signal disappears and the number of retransmissions of the transmitted information increases. , This caused a problem in that line throughput decreased.

The present invention has been made in view of the above points, and an object of the present invention is to provide a communication system using a retransmission request method in which throughput hardly decreases even when there is an error in the backward communication path.

[Structure of the Invention] (Means for Solving the Problem) The present invention provides confirmation f of the frame when returning the confirmation signal.
This system is characterized in that it eliminates the influence caused by errors in the backward channel by simultaneously sending not only the S number but also confirmation signals for frames of the past number of stages.

(Operation) When the history of confirmation signals of multiple past frames is returned,
Even if an error occurs when returning a confirmation signal in a certain frame and the confirmation signal disappears, it is possible to check whether an error occurred in the transmitted information in the previous frame by checking the history of confirmation signals in the next frame. can be determined.

That is, according to the present invention, if the confirmation signals of the past frames are returned, the confirmation signal will not be lost unless errors occur for L consecutive frames on the backward channel, so the retransmission probability can be reduced. This can be significantly reduced, and as a result, throughput can be improved.

(Embodiment) Hereinafter, an embodiment in which the present invention is applied to a selective retransmission communication system will be described based on the drawings.

FIG. 1 is a diagram showing the configuration of this communication system.
1 and the receiving section 12 are connected via a forward communication path 13 and a backward communication path 14.

The transmitting unit 11 includes a transmitting buffer 22 that holds transmitting data inputted from a terminal 21 and assigning a frame identification number, and a transmitting buffer 22 that assigns a frame identification number to the transmitting data outputted from the transmitting buffer 22 for error detection. a redundant bit addition circuit 23 that adds redundant bits and sends it to the forward communication path 13; and a confirmation signal that discriminates the confirmation signal input manually via the backward communication channel 14 and outputs the discrimination result to the transmission buffer 22. The determination unit 24 includes a determination unit 24.

The one-no-j1 receiving unit 12 includes an error detection circuit 25 that receives transmission information input via the forward communication path 13 and performs error detection, and a reception information a receive buffer 27 that holds the received data and outputs the received data to the terminal 26 in the order of frame identification numbers;
A series of confirmation signals are generated based on the detection results of the error detection circuit 25 and sent to the transmitter 11 via the backward communication path 14.
and a confirmation signal generation section 28 that returns the confirmation signal to the confirmation signal generator 28.

In the communication system configured as above, first,
The transmission information inputted from the terminal 21 and consisting of bits per block is introduced into the transmission buffer 22, where an h-bit header indicating a frame identification number is added. This information is held in the transmission buffer 22. The +h bits of information held in the transmission buffer 22 are input to the redundant bit adding circuit 23, where -h bits are added to the redundant bits n- for error detection, and the information is sent to the redundant bit adding circuit 23, where -h bits are added to the redundant bits n- for error detection, and an n-bit signal is sent to the Funaword communication channel. Sent on 13th. Various codes can be used for this error detection, but here, the transmitted information is expressed as an n-1 degree polynomial, and the remainder when divided by a generator polynomial g (x) modulo 2 is added as a redundant bit. We will discuss the case where this method is adopted.

In the receiving section 12, an error detection circuit 25 detects the presence or absence of an error. Errors can be detected by dividing the received n-bit signal by the same generator polynomial g (x) as the sender. This is because if there is no error, it is divisible by g (x), and if there is an error, it is not divisible.

If redundant focusing for error detection is increased, g (x
), that is, the probability of overlooking an error, can be made sufficiently small.

The error detection result obtained by the error detection circuit 25 is output to the confirmation signal generation section 28 together with the frame identification number.

At this time, if there is no error, the bits of reception information are output to the reception buffer 27 together with the frame identification number. On the other hand, if there is an error, output to the reception buffer 27 is prohibited.

The reception buffer 27 checks the frame 1 individual number of the received information, and outputs the received data to the terminal 26 if frames are being received continuously.

If the frames are not consecutive, output to the terminal 26 is stopped and the received information is stored in the reception buffer 27 as it is. Frames that have not been accumulated in the reception buffer 27 are discarded due to errors during transmission, and are correctly received by the subsequent retransmission procedure. Then, when it is correctly received, it is stored in the reception buffer 27, and is outputted to the terminal 15 in the correct frame order along with the information already stored in subsequent frames.

On the other hand, the confirmation signal generation unit 28 generates a confirmation signal of the past L frames, that is, ACK, according to the received detection result of no error 9.
The /NACK signal is returned via the backward line 14 with a frame identification number and redundant bits added for error detection. For example, if the ACK signal is displayed as "0°" and the NACK signal is displayed as ``1'', and the history of ACK/NACK signals of the past eight received signals including the received signal is returned, at time t, the confirmation signal generation unit The signal output from 28 is, for example, "t frame identification signal 010011".
It takes the form of 10"10 redundant bits".

This means that an error was detected at times t-1, t-4, t-5, and t-6, and that the signals received at times t, t-2, t-3, and t-8 were correctly received. It means.

Similarly, if the error determination result of signal f8 received at time t+1 is that there is no error, the signal returned at time t+1 will be "frame identification number 001001 of t+1".
1 bit + redundant bit.

The confirmation signal discriminator 24 checks the returned ACK/NACK.
Error detection is performed based on the signal. If there is an error, the confirmation signal may be incorrect and is discarded. If there is no error, the received ACK/ACK signal is stored in the transmission buffer 22.
Outputs a NACK signal.

When the transmission buffer 22 receives an ACK signal, it erases the stored transmission data, and when it receives a NACK signal, it retransmits the transmission data with the frame identification signal that was multiplied by #, so the transmission data is changed to redundant bits. Additional circuit 2
Output again in 3.

Only the storage order of this retransmitted data is changed in the transmission buffer 22, and the data is continuously stored until an ACK signal is received.

The transmission buffer 22 stores transmission data arranged in the order of transmission. If there is no error in the backward communication channel 14, ACK/NAC of the most accumulated fortune-telling data
It should receive the K signal. Backward communication channel 14
When an error occurs and the ACK/NACK signal is discarded and disappears, when the correct ACK/NACK signal is received, history information of past ACK/NACK signals is checked and stored information is deleted or retransmitted.

If the transmission buffer 22 does not receive an ACK/NACK signal within a certain period of time Tout after storing the transmission data, it assumes that the ACK/NACK signal has disappeared and starts a retransmission procedure. T out is set to be slightly longer than the longest time required for an ACK/NACK signal for the transmission data to be returned to the transmission buffer 22 after the transmission data is output from the transmission buffer 22 . Therefore, if the transmission path delay is the same,
The larger the history to be sent back, the larger Tout will be.

FIG. 2 is a diagram showing a more specific example of the retransmission procedure described above.

In the figure, t is the time, a is the data stored in the transmission buffer 22, b is the frame identification number of the signal sent from the redundant bit addition circuit 23, and C is the data stored in the forward communication path 13 and backward communication path 14. The transmission status (x indicates that an error has occurred), d is the frame identification number of the signal output from the error detection circuit 25 to the reception buffer 27, and e is the reception buffer 27
The signals output from to the terminal 26 are shown respectively.

At time t-1, transmitted frame 1 is immediately output from terminal 26 because it has been correctly transmitted.

Frame 2 sent out at time t-2 has an error on the forward communication channel 13, so a NACK signal is sent back. This NACK signal is returned to the transmission buffer 22 at time t-4. Therefore, at time t-5, frame number 2 is taken out by +1 from the transmission buffer 22 and retransmitted, and the storage position in the transmission buffer 22 is also moved to the rear end. Here, the transmission data of J retransmission frame 2 was transmitted to the receiving section without error, but this time an error occurred in the ACK signal on the backward communication path 14, so the ACK/NACK signal was determined at time t-7. Can not. Similarly, since an error occurred in the backward communication channel 14 in the NACKrf signal of frame 5, only a correct determination can be made at time t-3. These frames 2 and 5 are stored in the transmission buffer 22 when the NACK signal of frame 6 at time t-9 is received. Therefore, the past history of the ACK/N ACK signal received at time t-9 is referred to. At time t-9, "+100010" is received as the history, and it can be seen that the previous frame 5 is a NACK signal, and the previous frame 2 is an ACK signal. Based on this, frame 2 is deleted and frames 5 and 6 are retransmitted.

On the other hand, in the receiving section 12, the frame 1 is immediately sent to the terminal 15.
However, since an error was detected in frame 2, it is discarded. Frame 3.4 is received at times t-4 and t-5, but since frame 2 has not been received, the information of frame 3.4 remains stacked # in the reception buffer 27. Then, when frame 2 is received at time t-6, frames 2, 3.4 are arranged in order in the reception buffer 27, so
It is output to terminal T26.

Furthermore, in this communication system, frame 8 is correctly transmitted on the forward communication channel 13, and the ACK signal is determined by the transmitting side at time t=12 by history determination, so retransmission does not occur. Due to the disappearance of the ACK signal due to an error in the communication path, 41i transmission was always required.

By the way, in a communication system using the conventional selective retransmission method, the probability of retransmitting data once transmitted is P r
Consider epl. This probability Prcpl is the probability that an error will occur in the transmitted λ frame block on the forward channel, and the probability that an error will occur in the λ frame block transmitted on the forward channel, but when the ACK/NACK signal is returned,
Since it is the sum of the probability that a frame block error including the CK signal will occur, Prepl=Pr+(1-Pr) -Pb-Pr+Pb
It can be expressed as -Pr-Pb=.(1).

Note that here, Pr is the block error rate of the forward channel, and Pb is the block error rate of the backward channel.

Now, for simplicity, let Pr-Pb, Prcpl = 2Pf - Pi" - (2)
Then, the line throughput η1 is n+ −I Pr Pr (I Pr) −(3
).

If the system of the above embodiment sends the history of past L frames, for example, the ACK of the mth frame
Even if an error occurs when returning the /NACK signal and this signal is lost, there is no need for the transmitting side to immediately retransmit the signal of the mth frame, and the A CK /N of the next (m+1)th frame is
ACK of mth frame when receiving A CK signal
/NACK result can be determined. Similarly, even if the (m+1)th frame is deleted, it is sufficient to have the (m+2)th frame. That is,
ACK/NACK caused by error in backward communication channel
Since signal loss occurs only when L frames are consecutively erroneous on the backward channel, the +lG transmission probability P rcp2 in this system is Prcp2 = Pf' +
(1-Pr) Pb = 14). Here, if Pr-Pb is used for Simplified 1i, then Prcp2-Pr+P ``L(1-Pi') = 15
), and the throughput η2 is 772-1-Pr-Pr' (1-Pr)-(
6). If L becomes large, the third term can be ignored and η2
ζ1-PI'. This is equivalent to the throughput when there is no error in the backward communication path 14, and is equivalent to the case where the block error rate is reduced to approximately 1/2 compared to the throughput η1 of the conventional system.

Figure 3 shows the effects of this system as described above, where A is the block error rate vs. throughput characteristic of the conventional selective retransmission method, and B is the A CK/
The same characteristics when the number of N CK signals is L-2, C is also L
-4 shows the same characteristic, and D shows the same characteristic when there is no error in the backward communication path. This figure also shows the magnitude of the throughput improvement effect of this system.

Another important point is that as L increases, the characteristic approaches the ideal value.

Furthermore, according to the above system, past ACK/NACK
Although the amount of returned information increases slightly due to the transmission of the history of , a relatively small value of L is enough to obtain a throughput close to the ideal in a general communication channel.

It should be noted that although the above embodiments have been described with reference to unidirectional communication, the present invention also operates in a particularly q-effective manner in bidirectional communication. In the case of bidirectional communication, the redundant bits for error detection added to the transmission data of the own station and the redundant bits for error detection added to the ARQ confirmation signal sent back to the opposing station can be shared. That is, when the transmission data is N bits and the return data is M bits, redundant bits for error detection are added to the N+M bits and then transmitted.

During bidirectional communication, both transmission processing and reception processing are performed within the own station, but the error detection functions of the error detection circuit 25 and confirmation signal control section 24 performed in the above embodiment can be shared. In the case of bidirectional communication, the frame length of transmitted data is generally several hundred bits to several thousand bits, and the increase in information by the present invention, for example, 8 bits, is sufficiently negligible with respect to the frame length.

The present invention is not limited to the above embodiments, and various modifications are possible.

For example, although the above embodiment describes the selective retransmission method among the ARQ methods, the present invention applies to all ARQ methods that return ACK/NACK signals, including the Go-back-N method.
Applicable to any method.

In addition, in the above embodiment, the frame identification number is ACK/NAC
The ACK/NACK signal was sent back with the K signal, but if the return delay time of the ACK/NACK signal for the signal sent on the sending side is constant, the ACK/NACK signal for which transmission signal is determined by the reception time of the ACK/NACK signal. Since the frame identification number can be identified, the frame identification number is not necessarily necessary.

[Effects of the Invention] As described above, according to the present invention, even if there is an error in the bank word communication path for returning the confirmation signal, the influence can be reduced, and the throughput is almost the same as that in an ideal case without errors. Equal throughput can be obtained.

Therefore, according to this method, high-speed ARQ transmission is possible.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a selective retransmission communication system according to an embodiment of the present invention, FIG. 2 is a diagram specifically explaining the operation of the system, and FIG. 3 is a block diagram of the system. FIG. 4 is a characteristic diagram of block error rate versus throughput for explaining the effect in comparison with a conventional example. DESCRIPTION OF SYMBOLS 11... Transmission part, 12... Receiving part, 13... Forward F communication path, 14... Backward communication path.

Claims (3)

[Claims] (1) A means for adding redundant bits for error detection to the transmission information sent frame by frame from the transmission section to the reception section, and detecting whether or not there is an error in the transmission information in the reception section, and checking the detection result. means for sending the signal back to the transmitter as a signal;
and a means for retransmitting the transmitted information from the transmitting section according to the return status of the confirmation signal, wherein the receiving section returns the confirmation signals for a plurality of past frames. Communications system. (2) The communication system according to claim 1, wherein the transmitting section retransmits the transmitted information when the confirmation signal from the receiving section indicates that there is an error. (3) The communication system according to claim 1, wherein the transmitter retransmits the transmitted information when the confirmation signal from the receiver is not returned within a certain period of time.