JPS5850464B2 - Communication device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a communication device having an error retransmission function.

In general, high speed and high reliability are always required in communications, but especially high reliability is required in data transmission because input information inherently has little redundancy, and various methods have been considered for error correction.

Examples of these are (1) a method that uses codes that can correct errors, and (2) an error retransmission request that uses a reverse communication line to request retransmission of an error detection block when an error is detected on the receiving side. (3) A method that combines both of these methods.

Among these methods, the error retransmission request method is considered to be superior in terms of device simplification and economic efficiency.

Conventionally, there has been a communication device shown in FIG. 1 as a communication device having an error retransmission request function.

In the figure, 1 is a transmitter, 2 is a receiver, 3 is a communication line for transmitting signals from the transmitter 1 to the receiver 2, and 4 is a reverse communication line for transmitting signals from the receiver 2 to the transmitter 1.

Furthermore, 5 is an encoder provided in the transmitter 1, which divides the input data 6 into blocks and adds an error detection code to each block; A first demodulator 8 demodulates the detection signal, and a receiver 2 receives the output 9 of the first demodulator γ.
When there is a retransmission request from the encoder 5, the first storage device 11 that stores the block to be retransmitted out of the output 10 of the encoder 5 normally sends the encoder 50 output 10 to the first modulation device 12 and receives the block. When there is a retransmission request from the unit 2, the data 8a stored in the first storage device 8 is transferred to the first modulation device 12.
A retransmission controller 12 is the aforementioned first modulation device, which converts the output signal 13 of the retransmission controller 11 into a frequency band suitable for the communication line 3 and transmits it as a modulated signal 14.

Reference numeral 15 denotes a second demodulating device of the receiving section 2. Errors occur in the communication line 3 due to the addition of various distortions, and a signal 16 in which the error occurs is input to the second demodulating device 15.

Reference numeral 17 denotes a decoder to which the demodulated output 18 of the second demodulator 15 is input, and the decoder 17 decodes the decoded output 18 to determine whether or not each block has an error.

19 is a second storage device that stores the data output 20 of the decoder 17 and is controlled by the error detection signal output 21 of the decoder 17; This becomes the output.

23 is a second modulator that modulates the error detection signal output 21 of the decoder 17 and sends it to the reverse communication line 4; its output 24 passes through the reverse communication line 4, and the signal 25 is transmitted to the first The signal is transmitted to the demodulator 7.

Next, the operation will be explained.

The input data 6 is added with an error detection code for each block by the encoder 5.

Input data 10 to which an error detection code has been added passes through a retransmission controller 11, is modulated by a first modulation device 12, and is sent to a communication line 3.

The data signal 16 that has passed through the communication line 3 is sent to the second demodulator 15
The decoder 17 decodes the error detection code.

If no error is detected at this time, the output 2 of the decoder 17
0 directly passes through the second storage device 19 and becomes the output 22 of the receiving section 2.

If an error is detected in the decoder 1γ, the error detection signal output 21 is applied to the second modulator 23 and sent to the transmitter 1 via the reverse communication line 4.

The modulated error detection signal 25 sent to the transmitter 1 is the first
The signal is demodulated by the demodulator 7 and transmitted to the first storage device 8 and the retransmission controller 11.

When the retransmission controller 11 receives this signal 9, it will receive N+1 (N
is a positive integer) The transmission is performed again from the previous block.

There is a delay in the communication line 3, and if retransmission is performed, the order of the received sequences may be reversed. To prevent this, retransmission is performed from the N+1 block before.

The error detection signal 21 of the decoder 17 is also transmitted to the second storage device 19 of the receiving section 2, and the block in which the error occurred and the subsequent N blocks are erased, and the error detection signal 21 is transmitted to the N blocks sent again. If there are no errors, it will be stored and output.

This type of error retransmission request method is G o -back -
N-type ARQ (Automatic Repeat Re
It is called the ``quest'' method.

A conventional communication device having an error retransmission request function is configured as described above, and data transmission with sufficiently high reliability is possible even on a communication channel where many errors occur.

Since the opening of telephone lines, facsimile transmission using telephone lines has increased, but telephone lines are intended for voice calls, and digital communications such as facsimile data are subject to various distortions in the line. Errors occur, and an error retransmission request method has often been adopted.

By the way, unlike data transmission, in document transmission such as facsimile, the degree of redundancy is inherently very high, so even if some errors occur in the received information, this hardly interferes with the image quality.

Facsimile signals encoded to suppress redundancy are naturally vulnerable to errors (and the impact on image quality will increase slightly when an error occurs, but if the conventional error retransmission request method is used) , the reliability in a normal line is much better than the reliability required to not affect image quality.

Furthermore, in some cases, a considerable number of errors occur over telephone lines, which has the disadvantage of increasing retransmissions and thus increasing transmission time.

In facsimile, emphasis is placed on shortening transmission time, that is, increasing transmission efficiency, in order to reduce telephone costs, etc., so the increase in transmission time described above is a fatal drawback.

In addition, if the delay time of international lines etc. is large, Go-
The value of N in the back-N type ARQ method increases to 1
Another drawback is that the transmission time added by multiple retransmissions increases significantly.

In addition, in view of these points, conventionally, JP-A-53-758
As shown in Publication No. 18, the transmitter determines the importance of the information to be transmitted, and when an error occurs in the information transmission at the receiver, the retransmission request is controlled according to the importance of the information. There was something I did.

However, performing the above-mentioned processing in the transmitting section has the drawback that it is extremely difficult to design the hardware system, and it also has the disadvantage that, for example, when the importance of information is small in the transmitting section, ', and if an error occurs when transmitting the judgment signal and the receiving unit receives it as 'large', the receiving unit issues a retransmission request, but the transmitting unit ignores the request. There was a problem in that the receiving section would have to repeatedly request retransmission.

This invention was made in order to eliminate such drawbacks of the conventional system.Retransmission control is performed only in the receiving section, and even if some errors are detected, they are not transmitted to the transmitting section and the second storage device. By doing so, it is an object of the present invention to provide a communication device having an error retransmission request function that has a simple configuration, improves reliability to some extent, and improves transmission efficiency.

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 2, the transmitter 1, communication line 3, and reverse communication line 4 are the same as in FIG. 1, and are therefore not shown.

26 is a determiner in the receiving unit 2 that selects a desired error detection signal from among the error detection signal outputs 21 from the decoder 17 and adds the output 27 to the second modulation device 23 and the second storage device 19. It is.

FIG. 3 shows an example of the configuration of the determiner 26.

In the figure, 28 is a quinary counting circuit into which the error detection signal 21 of the decoder 17 is input, 29 is an inverter that inverts the output 30 of the quinary counting circuit 28, and 31 is an error detection signal 21.
This is an AND gate that multiplies the output 32 of the inverter 29 and the output 27 of the determiner 26.

Next, the operation of this determiner 26 will be explained with reference to FIG. 4 showing signal waveforms at each part.

When the error detection signal 21 is input to the quinary counting circuit 28,
The quinary counting circuit 28 counts the pulses of the error detection signal 21.

Since the output 32 of the inverter 29 is "1" until the output of the quinary counting circuit 28 becomes "1", the AND gate 31 is open, and the error detection signal 21 is passed directly to the output 27 of the determiner 26. Become.

When the quinary counting circuit 28 counts the pulse of the error detection signal 21 five times, the output 30 of the quinary counting circuit 28 becomes "1", the output 32 of the inverter 29 becomes "O", and the AND gate 31 closes, indicating an error. The fifth pulse of the detection signal 210 does not appear at the output 27 of the determiner 26.

Therefore, as can be seen from the waveform of the signal 27 in FIG. 4, the determiner 26 ignores the pulse of the error detection signal 21 once in five times.

In FIG. 4, l is one block length.

Further, FIG. 5 shows another embodiment of the determiner 26.

In the figure, 33 is set by the error detection signal 21 and indicates that there is no error in each block.
4 is input into a quinary counting circuit, 35 is an error detection signal 21
36 is the delay circuit 3 that delays by one block.
A flip-flop, 39, in which the output 37 of 5 is input to the R input, and the output 38 of the 5-ary counting circuit 33 is used to the S input.
is an inverter that inverts the output 40 of the flip-flop 36, and 41 is the output 42 of the inverter 39 and the error detection signal 2.
This is an AND gate that takes the product with 1 and uses the output as the output 27 of the determiner 26.

Note that the error-free detection signal 34 can be obtained more easily than the error detection signal 21.

Next, the operation of this determiner circuit will be explained with reference to FIG. 6, which shows signal waveforms at various parts.

The quinary counting circuit 33 counts the pulses of the error-free detection signal 34, but since the quinary counting circuit 33 is reset by the error detection signal 21, unless the pulse of the error-free detection signal 34 is counted five times in a row, , the output of the quinary counting circuit 33 does not become "1".

In this state, the output 40 of the flip 70 tube 36 becomes "0", the output 42 of the inverter 39 becomes "1", the AND gate 41 is opened, and the error detection signal 21 becomes the output 27 of the determiner 26 as it is.

When the quinary counting circuit 33 counts the pulses of the error-free detection signal 34 five times in succession, its output 40 becomes 1", and the output 40 of the flip-flop 36 becomes 1" until the output 37 of the delay circuit 35 rises. "bawl.

Then, the AND gate 41 is closed via the inverter 39 only while the output 40 is "1", and the output 37 of the delay circuit 35 is the pulse of the error detection signal 21 delayed by one block. , this signal 37
The pulse of the error detection signal 21 that causes the error does not appear at the output 27 of the determiner 26.

Therefore, as can be seen from the waveform of signal 27 in FIG. 6, when an error is detected, this determiner 26 will ignore the error detection signal if five blocks before that block have errors. ing.

In addition, in the embodiments of the two judgers described above, a 5-counting circuit is used, and the error detection signal is ignored once every 5 times, or when an error is detected, it is determined that the error is present in the 5 blocks before that block. I configured it to ignore this error if I throw it, but 5
It is not necessary to limit the number of times or five blocks, but an appropriate value should be selected depending on the characteristics of the line.

Furthermore, in the second embodiment, if there is no error in the output of the decoder 17 for a certain period of time, the error detection signal is ignored.

By the way, in an actual communication device, there is an information source encoder that divides the signal from the information source into blocks and adds an error detection code.
In some cases, there is an information source decoder that performs error detection and decoding on the receiving side, but in that case, as shown in FIG. For example, the output 44 of the information source decoder 43 may be added to the determiner, and the error detection code may be ignored.

In addition, although the encoder 5 in the first embodiment described above has an error detection code added thereto, an error correction code having a correction function may also be added thereto.

As described above, according to the communication device of the present invention, in the communication device having the error retransmission request function, a determiner for selecting an error detection signal is provided on the receiving side, and the determination device selects the error detection signal output from the determiner. By performing retransmission and reducing the number of retransmissions of input data, it is possible to improve transmission efficiency even if the reliability is reduced to some extent, and to reduce the decrease in transmission efficiency even when line distortion is large. There are effects that can be achieved with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional communication device having an error retransmission request function, FIG. 2 is a block diagram of a receiving section of a communication device according to an embodiment of the present invention, and FIG. 3 is a block diagram of a determining unit of FIG. 4 is a diagram showing signal waveforms of each part of the circuit in FIG. 3, FIG. 5 is a circuit diagram showing another embodiment of the determiner in FIG. 2, and FIG. FIG. 5 is a diagram showing signal waveforms of each part of the circuit, and FIG. 7 is a partial block diagram of a communication device according to another embodiment of the present invention. 1... Transmitting section, 2... Receiving section, 3...
...Communication line, 4...Reverse direction communication line, 5
. . . encoder, 7 . . . first demodulator,
8...First storage device, 11...Retransmission controller, 12...First modulation device, 15...
. . . second demodulator, 17 . . . decoder, 19
. . . second storage device, 23 . . . second modulation device, 26 . . . In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An encoder that divides human data into blocks and adds an error detection code to each block, and a first encoder that demodulates the modulated error detection signal sent from the receiver through the reverse communication line. a demodulator; a first storage device that stores input data to which an error detection code has been added by the encoder according to the output of the first demodulator; A transmission comprising: a retransmission controller that selects either the output of the encoder or the input data stored in the first storage device; and a first modulation device that modulates the output of the retransmission controller and sends it to a communication line. a second demodulator that demodulates the output of the first modulator transmitted through the communication line; a decoder that decodes the output of the second demodulator and detects errors; and the decoder. the second to store the data output of
a receiving unit having a storage device, a determiner that selects the error detection signal output of the decoder, and a second modulator that modulates the output of the determiner and sends it to a reverse communication line, A communication device characterized in that input data is retransmitted according to an output signal of the determiner. 2 The determiner selects N+1 (N
2. The communication device according to claim 1, wherein N error detection signals are selected from among the error detection signals (where N is a positive integer). 3 Claims characterized in that the determiner ignores one error detection signal that follows when there is no error detection signal in N consecutive blocks (N is a positive integer) in the error detection signal output of the decoder The communication device according to item 1.