JPH07336336A - Data transmitter - Google Patents

Abstract

PURPOSE:To improve transmission efficiency and to make a circuit scale small by switching to a system for retransmitting only erroneous blocks when a reception buffer overflows during transmission by a selective retransmission SR system. CONSTITUTION:Blocks are continuously transmitted from a transmission side in a selective retransmission SR mode and error detection is successively performed for the received blocks on a reception side. During the transmission in the SR mode, the block 12 and the succeeding blocks overflow OFW, the SR mode is switched to an OFW mode corresponding to it and the blocks are transmitted on the transmission side. In the OFW mode, all the error detected blocks among the blocks present in the reception butter are repeatedly transmitted. For instance, the blocks 7 and 11 are retransmitted, the blocks 7 and 11 are alternately transmitted and when both are correctly received, the SR mode is returned and the next transmission is continued. At the time, the overflowed blocks 12, 13, 14, 7 and 11 from the time of overflow until the time when the blocks 7 and 11 are correctly received are abandoned. Thus, transmission efficiency characteristics are improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital data transmission device, and more particularly to a digital data transmission device having an error control function using an automatic repeat request system.

[0002]

2. Description of the Related Art In systems requiring high reliability such as digital data communication, error control by the ARQ (automatic repeat request) method has been widely used. AR
The Q method can be classified into the following three basic methods depending on the retransmission procedure.

(1) Stop-And-Wait (SAW) method When a signal block is transmitted, the transmitting side stops the transmission and waits until there is a response from the receiving side, and ACK (acknowledgement, here, acknowledgment) ), The next block is transmitted, and if NAK (negative response, here, retransmission request response), the same block is retransmitted.

(2) Go-Back-N (GBN) method Blocks are continuously transmitted even during the return delay time (RTD), and when an ACK is returned, the next block is continuously transmitted, and NAK is transmitted. Upon returning, the block currently being transmitted is completely transmitted, and then the block in error is returned and retransmitted. Here, N represents the number of blocks that can be transmitted during RTD. This method has a good communication path and RT
When D is short, the efficiency is very good, but when the condition of the communication path is bad, and when RTD is long, the efficiency is extremely deteriorated.

(3) Selective-Repeat (SR) method Blocks are continuously transmitted during the return delay time (RTD), and only the block for which NAK is returned is retransmitted. Therefore, it has a buffer to store the correct block received after the erroneous block, and when the retransmitted signal becomes an ACK, the user is in the order sent with the block recorded in the buffer. Output. This method is the most efficient method among these three methods, but the logic becomes complicated and a huge capacity buffer is required on the receiving side.

As a means for solving this problem, MJMill
er et al. have proposed a method of preventing buffer overflow by combining the SR protocol and the GBN protocol. For this method, for example, IEEE ON COMMUNIC
STATES COM-29 Volume 4, MJ Miller et al. “The Analysis of Some Selective-repeat ARQ with Fi
nite Receiver Buffer ”.

[0007] In this system, when the ARQ system of the SR mode is operated, all the blocks which are first judged to have an error on the receiving side are NAK for ν retransmissions and are judged on the transmitting side. In this case, the mode is switched from the SR mode to the GBN mode ARQ method and transmission is performed. Then, the block that is first determined to be erroneous on the transmitting side is ACK.
If it is determined, the mode is returned to the SR mode again and the transmission is performed.

FIG. 4 shows an example in which N = 5 and ν = 1. Explaining this example in detail with reference to the drawings, the receiving side first returns NAK to the transmitting side for the blocks 2, 4, and 7 which are judged to be erroneous by the receiving side, and the transmitting side first sets the SR mode. And resend.

As a result, the blocks 2 and 4 are now judged by the receiving side to be error-free, and an ACK is returned to the transmitting side. On the other hand, since the block 7 is again judged to be an error by the receiving side, the receiving side returns NAK to the transmitting side. This NA
On the transmitting side receiving K, the mode is changed from SR mode to GBN.
Switch to the mode and send. That is, the retransmission block 7 and the following four blocks are transmitted by the GBN protocol until ACK is returned to the block 7. Then, when it is determined that the ACK is received for the block 7 on the transmitting side, the mode is returned to the SR mode again and the subsequent block is transmitted.

As another means, the paper of MJ Miller et al.
It proposes a combination method of Stutter (ST) mode that continuously transmits until CK returns. This method operates in the SR mode first, and at this time, all the blocks judged to have an error are NAK for ν retransmissions.
When it is determined by the transmitting side, the mode is switched from the SR mode to the ST mode and transmission is performed. Then, the block judged to be erroneous is continuously transmitted, and if an ACK is received by the transmitting side, the mode is returned to the SR mode again and the next transmission is performed.

This example is shown in FIG. 5 for the case of N = 4 and ν = 1. Explaining this example with reference to the drawing, with respect to blocks 5 and 7 judged to be erroneous by the receiving side, NAK is returned from the receiving side to the transmitting side, and the transmitting side retransmits again in SR mode. However, since the block 5 also encountered NAK, the transmitting side switches from the SR mode to the ST mode and continuously retransmits until an ACK is returned to the block 5. Then, when it is determined that the ACK is received on the transmitting side, the mode is returned to the SR mode again and the subsequent transmission is performed. However, since the block 5 was NAK again, the transmission side switches the mode from SR to ST. Then, the block 5 is continuously transmitted until it becomes ACK. When it is determined that ACK is received on the transmitting side for block 5, the mode is returned to the SR mode again and the subsequent blocks are transmitted.

The method proposed by these MJ Miller et al.
You can prevent the overflow of the receive buffer,
There is a drawback that the algorithm is complicated because a plurality of logics are switched. In GBN mode and ST mode, R
Since the throughput is extremely deteriorated in a system having a large TD, the throughput characteristic of the entire system is not so improved due to the influence thereof.

[0013]

As described above, in the conventional ARQ system, when the communication state is poor, the capacity of the receiving buffer becomes large, and the throughput suddenly deteriorates. In many cases, the algorithm was often complicated when trying to prevent the overflow of.

Therefore, in the present invention, the protocol is as simple as possible with the goal of improving these problems so that digital data communication can be performed in a system having a long RTD such as a satellite communication system using a small portable terminal. Another object of the present invention is to construct a system in which the buffer is as small as possible and the power consumption of the terminal is as small as possible so that the device can be downsized and the throughput can be maximized.

[0015]

In order to achieve the above object, the present invention provides a data transmission apparatus which retransmits data from the transmitting side when the data transmitted from the transmitting side is judged to be erroneous by the receiving side. In the above, transmitting means for continuously transmitting signal blocks to a communication path having a loopback delay time corresponding to the transmission time length of N blocks of data signals,
Detecting means for receiving the data signal transmitted by the transmitting means, sequentially detecting errors in each received signal block using the error detecting bit added to each signal block on the transmitting side in advance, and the detecting means. If no error is detected as a result of error detection, the signal block is output to the user and at the same time an acknowledgment (A
CK), and when an error is detected, the signal block is not output to the user and a resending request response (NAK) is sent back to the sending side, and the response sent by the responding means is received. If the response is a retransmission request response (NAK), a retransmitting unit that immediately retransmits the signal block in which an error is detected, and a block that is received following the signal block in which the error is detected by the detecting unit. Receive buffer means having a receive buffer of kN blocks (k is a natural number) for holding a block in which no error is detected, and when the receive buffer means overflows, the received block is discarded regardless of whether or not there is an error. And overflow notification means for notifying the transmitting side that the receiving side has overflowed at the same time as the retransmission request response (NAK). Upon receiving the notification of the overflow notification unit, switches the data transmission method on the transmitting side, i-k on the basis of the first overflow the i-th block
An erroneous block continuous retransmitting means for retransmitting only an erroneous block from the Nth block to the i-1th block in a continuous manner, and the ikkNth block by the erroneous block continuous retransmitting means. When all the erroneous blocks in the i-1th block from the block are received correctly, a transmission restoration means for returning to the original data transmission system to perform transmission is provided.

The response means includes error rate measuring means for measuring or estimating the error rate of the received signal block,
When the error rate obtained by the error rate measuring means is lower than a predetermined value, a permissible processing means for considering the signal block in which an error has been detected as having no error detected is further provided.

[0017]

According to the present invention, when the receiving buffer overflows during transmission in the selective retransmission (SR) system, the system is switched to the system in which only the erroneous block is retransmitted.
It is possible to efficiently clear the overflowed reception buffer and quickly return to the selective retransmission (SR) method, improve the throughput, and reduce the circuit scale.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A digital data transmission device according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a diagram for explaining the basic concept of one embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of the digital data transmission device of the present invention.

As shown in FIG. 2, the digital data transmission apparatus includes an information source 1, an information source encoder 2, a channel encoder 3, a modulator (recording unit) 4, a transmission channel 5, a demodulator (reproducing unit). ) 6, a channel decoder 7, an information source decoder 8 and a destination 9.

On the transmitting side, the signal output from the information source 1 is coded by the information source encoder 2 in a form suitable for the information source to become the signal u, and the channel encoder 3 adapts it to the channel. After being encoded into a signal v, which is modulated by the modulator 4. It is sent to the receiving side via the transmission channel 5. At this time, noise is mixed into the signal in the transmission channel 5.

On the receiving side, the modulated signal from the transmission channel 5 is demodulated by the demodulator 6 to obtain the signal r, which is then decoded by the channel decoder 7 to obtain the signal u ', and further the information source decoder After being combined in 8, the information is sent to the destination 9.

According to the present invention, when the input u of the channel encoder 3 shown in FIG. 2 is transmitted, the output u'of the channel decoder 7 is transmitted.
If there is an error in the packet, it relates to a method of repeating the retransmission of u until it is correctly received.

Return delay time (RTD) in FIG.
If N (N = 5 in this example) blocks can be transmitted, a reception buffer having a buffer size of kN blocks (here, k = 1 and buffer size kN = 5) is configured. At this time, blocks are continuously transmitted from the transmitting side in SR mode, and the receiving side sequentially detects errors in the received blocks. In this example, N for block 2, block 4, block 7, and block 10
AK is returned, and ACK is returned to the other blocks.

When the transmitting side receives NAK, the block is immediately retransmitted. In the figure, blocks 2 and 4 were correctly received in one retransmission. In block 7, since an error was detected on the receiving side in the first retransmission, NAK was transmitted again, and the transmitting side performed the second retransmission. By the way, in this case, the reception buffer records the received block until the block is correctly received after transmitting the NAK of a block, but since the size of the reception buffer is limited to N (= 5), Then, the block 12 and subsequent blocks overflow, and accordingly, the transmitting side switches the SR mode to the overflow mode and transmits the block.

In the overflow mode, all blocks in the receive buffer in which an error has been detected are repeatedly retransmitted. In the case of the example, the block 11 as well as the block 7 retransmits. Then, block 7 and block 11 are alternately transmitted, and when the two blocks are correctly received, the mode is returned to the SR mode and the next transmission is continued. At this time,
As shown in the figure, the block 13, the block 14, the block 7, and the block 11 following the overflowed block 12 from the overflow until the blocks 7 and 11 are correctly received are discarded.

In FIG. 3, the block length is 1024 bits and N = 1.
The throughput characteristic in the example shown in FIG. 1 when the value is set to 28 is shown together with the conventional example of the SR + GNB system, the SR system (infinite buffer size), and the GNB system. From this figure, it can be seen that the example of FIG. 1 of the present invention exhibits excellent characteristics with the same buffer size as compared with the conventional example. In particular, the method of the present invention has a high improvement effect in a poor communication channel state, and is effective when applied to a system having a poor communication channel state such as a mobile band communication system.

When the error rate of the received signal block is lower than a predetermined value, the signal block in which the error is detected is not processed in the same manner as the signal block in which the error is not detected, and the throughput is improved. Can be further improved.

The present invention can further improve the transmission efficiency by combining with various error correction codes.

[0030]

As described above, according to the present invention, when the data transmitted from the transmitting side is judged to be erroneous by the receiving side, the data transmitting apparatus which retransmits the data from the transmitting side transmits in the SR mode. When the receive buffer of buffer size kN overflows and the i-th block and the subsequent kN-1 blocks are discarded, i-
The mode is switched to the mode in which only the erroneous block is continuously transmitted from the kNth block to the i−1th block. This allows you to efficiently clear the overflowed receive buffer and quickly return to SR mode.
It is possible to realize a data transmission device having good transmission efficiency, that is, throughput characteristics.

Further, the algorithm can be simplified, the buffer can have a finite length, the circuit scale can be reduced, and the power consumption of the terminal can be suppressed.

[Brief description of drawings]

FIG. 1 is a diagram showing a transmission procedure according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of the device of the present invention.

FIG. 3 is a graph showing the throughput characteristic of the embodiment of the present invention shown in FIG. 1 in comparison with the conventional example.

FIG. 4 is a diagram showing a transmission procedure of a conventional example.

FIG. 5 is a diagram showing another conventional transmission procedure.

[Explanation of symbols]

 1 Information Source 2 Information Source Encoder 3 Channel Encoder 4 Modulator 5 Transmission Channel 6 Demodulator 7 Channel Decoder 8 Information Source Decoder 9 Destination ACK Acknowledgment NAK Resend Request Response

Claims (2)

[Claims] 1. A data transmission device that retransmits data from a transmitting side when data transmitted from the transmitting side is judged to be erroneous by the receiving side, and a loopback corresponding to a transmission time length of a data signal of N blocks. Transmitting means for continuously transmitting a signal block to a communication path having a delay time, and a data signal transmitted by the transmitting means are received, and each received signal block is added in advance to each signal block on the transmitting side. Detecting means for sequentially detecting errors using the bit for error detection, and as a result of error detection by the detecting means, when no error is detected, the signal block is output to the user and an acknowledgment is sent to the transmitting side at the same time. When an error is detected, the signal block is not output to the user and a resending request response is sent back to the sending side. Retransmission means for receiving the response sent back by the response means, and when the response is a resend request response, retransmitting means for immediately retransmitting a signal block in which an error has been detected, and a signal in which an error has been detected by the detecting means. Receive buffer means having a receive buffer of kN blocks (k is a natural number) for holding a block in which an error is not detected among blocks received subsequently to the block, and the received block when the receive buffer means overflows. Discarding regardless of the presence or absence of error, overflow notifying means for notifying the transmitting side that an overflow occurs at the same time as the retransmission request response from the receiving side, and receiving the notification of the overflow notifying means, switching the data transmission method at the transmitting side, From the i-kNth block based on the i-th block that overflowed first An error block continuous retransmitting means for retransmitting only an erroneous block in the i-1th block continuously, and an i-kNth block to an i-kNth block by the error block continuous retransmitting means. A data transmission apparatus comprising: a transmission restoration means for returning to the original data transmission method and performing transmission when all erroneous blocks in the first block are correctly received. 2. An error rate measuring means for measuring or estimating an error rate of a received signal block, and an error rate if the error rate obtained by the error rate measuring means is lower than a predetermined value. 2. The data transmission apparatus according to claim 1, further comprising admissive processing means for considering that the signal block in which is detected as having no error detected.