JPH05110539A - Digital transmission system - Google Patents

Abstract

(57) [Abstract] [Object] The present invention relates to a digital transmission system in which a transmission side encodes and transmits a transmission bit using an error correction code, while the reception side decodes the transmission bit and receives the bit. It is an object of the present invention to improve the utilization efficiency of a line by making it possible to change the coding rate of the error correction code according to the line status. [Structure] The receiving side detects the line state, and the detection result is fed back to the transmitting side to change the coding rate for error correction according to the line state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital transmission system in which a transmission side encodes a transmission bit by using an error correction code and transmits it, while a reception side decodes the transmission bit and receives the bit.

[0002]

2. Description of the Related Art Conventionally, in the digital transmission system as described above, a transmitting side encodes a transmission bit by using an error correction code having a fixed error correction rate and transmits it, and then the receiving side decodes this. is doing.

[0003]

However, in such a conventional digital transmission system, since the coding rate of the error correction code cannot be changed according to the measured line quality, the line state fluctuates. In such a communication path, when the line condition is bad, the error correction code is insufficient, and when the line condition is good, the correction bits are wasted.

As a result, in order to carry out communications requiring reliability, a large amount of correction codes must be used,
As a result, the line cannot be used effectively. Further, in this way, even if the voice is not required to have high reliability, the number of error correction bits is set more than necessary when the line condition is good. There is also a problem that the number of bits of cannot be effectively used.

The present invention was devised in view of the above problems, and it is possible to improve the utilization efficiency of the line by changing the coding rate of the error correction code according to the line condition. , And to provide a digital transmission system.

[0006]

FIG. 1 is a block diagram showing the principle of the first invention. In the apparatus shown in FIG. 1, a variable rate error correction encoder 2 is provided on the transmitting side. Here, the variable rate error correction encoder 2 changes the coding rate to adjust the error correction capability.

Further, the receiving side is provided with a decoder 3 for decoding the coded signal sent from the transmitting side, and a line state detecting section 4 for detecting the line state (claim 1). Further, FIG. 2 is a block diagram of the principle of the second invention,
In the configuration shown in FIG. 2, a variable coding rate encoder 1 and a variable rate error correction encoder 2 are provided on the transmitting side.

Here, the variable coding rate encoder 1 is capable of varying the coding rate of the information source, and the variable rate error correction encoder 2 requires the output from the variable coding rate encoder 1. The thinning process is performed to change the coding rate to adjust the error correction capability.

The receiving side is provided with a decoder 3 and a line state detecting section 4. Here, the decoder 3 is for decoding the coded signal sent from the transmitting side, The line state detector 4 detects the line state (claim 2).

Further, FIG. 3 is a block diagram of the principle of the third invention. In the one shown in FIG. 3, the transmitting side stores a storage unit (memory) 6 for holding an input bit for a certain time, and FIG. A variable rate error correction encoder 2 similar to that of the second invention shown is provided.

Further, the receiving side is also provided with the decoder 3 and the line state detecting section 4 as in the case of the second aspect of the present invention, but the receiving side further has a storage section (memory). 5 are provided. The storage unit 5 stores the decryption failure data (claim 3).

[0012]

In the digital transmission system according to the first aspect of the present invention shown in FIG. 1, the receiving side detects the line state and feeds back the detection result to the transmitting side to establish the line state. Accordingly, the variable rate error correction encoder 2 on the transmission side changes the coding rate for error correction.

In the digital transmission system according to the second aspect of the present invention shown in FIG. 2, the transmission side is fed back by feeding back the line state detected by the line state detection unit 4 on the reception side to the transmission side. Then, the coding rate in the variable coding rate encoder 1 and the coding rate for error correction in the variable rate error correction encoder 2 are changed according to the line state.

Further, in the digital transmission system according to the third aspect of the present invention shown in FIG. 3, when the decoding fails, the decoding failure data is stored in the storage unit 5,
In addition, the signal indicating that the decoding has failed is fed back to the transmission side together with the line state detected by the line state detection unit 4 on the reception side, so that the transmission side stores an additional correction code according to the line state in the storage unit. 6 is calculated from the stored data and transmitted to the receiving side, and the receiving side combines the received additional correction code with the data stored in the storage unit 5,
Decrypt.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. (A) Description of First Embodiment FIG. 4 is a block diagram showing a first embodiment of the present invention. In FIG. 4, A is a transmitter and B is a receiver. A and the receiver B are connected by a communication line 11 and a feedback line 12.

In the present embodiment, the case of voice communication will be described as an example. Here, the transmitter A uses a coded transmission bit obtained by sampling voice as the transmission data, and adds an error correction code to the encoded transmission bit for transmission. Therefore, the transmitter A is, as shown in FIG.
It is provided with a rate variable punctured convolutional encoder 2 as a variable rate error correction encoder.

The variable coding rate encoder 1 is configured as a speech encoder capable of varying the coding rate of the information source according to the line quality. Further, the variable rate punctured convolutional encoder 2 changes the error correction coding rate according to the channel quality like the variable coding rate encoder 1. Therefore, the variable rate error correction encoder 2 , A convolutional encoder 21 and a puncturing table (bit decimating table) 22.

First, the convolutional encoder 21 obtains a convolutional code by performing mod2 addition of an input bit and a fixed number of bits preceding it, and outputs the convolutional code.

Further, the puncturing table 22 is
The error correction capability is adjusted by changing the coding rate by thinning the output bits from the convolutional encoder 21 following the line quality.

By the way, the receiver B decodes the output from the transmitter A and receives a desired bit. Therefore, the receiver B, as shown in FIG. Error rate conversion table (line status detector) 4
And a Viter-Bidego decoder (decoder) 3 provided with a path metric calculation device 31.

Here, the path metric / channel error rate conversion table 4 has the smallest path metric calculated at the time of decoding (the smallest difference between the code sequence obtained from the encoder on the transmission side and the received code sequence). This value is related to the error rate of the communication path)
The channel quality is obtained from the degree of increase in the puncturing rate, and the result is fed back to the variable coding rate encoder 1 and the puncturing table 22 in the variable rate punctured convolutional encoder 2.

The bitterbide degoder 3 is used as a decoder for decoding the convolutionally coded signal sent from the transmitting side. Further, the path metric calculator 31 provided in the bitterbide degoder 3 obtains the difference between the code sequence obtained from the encoder on the transmission side and the received code sequence, and further calculates the minimum path metric which is the smallest of them. Then, decoding is performed based on this, and the above calculation result is output to the path metric / line error rate conversion table 4.

With the above configuration, the input speech sent to the variable coding rate encoder 1 is first encoded by the variable coding rate encoder 1. At this time,
The coding rate is determined according to the line quality information output from the receiving side via the feedback line 12.

The encoded input speech is output to the convolutional encoder 21 in the rate variable punctured convolutional encoder 2, where the input bit and a fixed number of bits preceding it are mod2 added. , To a convolutional code.

The input speech converted into the convolutional code is output to the puncturing table 22 which receives the output of the line quality detection result from the feedback line 12, and the output bit thinning processing following the line quality detection result is performed here. Is given.

As a result, by performing the thinning-out process on the output bits, the coding rate can be changed and the error correction capability can be adjusted according to the line. After that, the convolved code signal is input to the Viterbi degoder 3 of the receiver B via the communication line 11.

The convolved coded signal input to the Viterbi degodard 3 of the receiver B via the communication line 11 is decoded and output by the bitterbide degoder 3.

From the convoluted coded signal, the path metric calculation device 31 provided in the Viterbi degodard 3 obtains the code sequence and the reception code sequence obtained from the encoder on the transmission side. Of the code sequences is calculated, and the minimum path metric, which is the smallest of the differences, is calculated.

The calculation result is output to the path metric / line error rate conversion table 4, and the line quality is obtained from the degree of increase of the minimum path metric by the path metric / line error rate conversion table 4.

The line quality detection result thus obtained is obtained by the coding rate variable encoder 1 provided in the transmitter A,
It is fed back to the puncturing table 22 in the rate variable punctured convolutional encoder 2 via the feedback line 12.

As a result of this feedback, when the line quality is good, the puncturing table 22 reduces the error correction code and increases the number of bits of the transmitted voice, so that the quality of the transmitted voice becomes good. To be done.

When the line quality is poor, the number of bits of the transmitted voice is reduced to reduce the quality of the transmitted voice, but the error correction code is increased to reduce the resultant deterioration of the received voice. It

As described above, the coding rate is changed by the coding rate variable encoder 1 capable of varying the coding rate and the output from the coding rate variable encoder 1 to the transmitter A by performing a necessary thinning process. In addition to the rate variable punctured convolutional encoder 2 provided with a puncturing table 22 for changing the error correction capability, the receiver B is also provided with a bitterbide degoder for decoding the coded signal transmitted from the transmitter A. 3, a path metric calculation device 31 for calculating the minimum path metric provided in the bitterbide degoder 3, and a path metric / line error rate conversion table 4 for detecting the line status. By feeding back the line status detected in
In the transmitter A, the coding rate in the variable coding rate encoder 1 and the coding rate for error correction in the variable rate punctured convolutional encoder 2 can be changed according to the line state.

As a result, even in a communication path in which the line condition fluctuates, when the line condition is poor, an error correction code is added to the normal level to assist the correction capability on the receiving side, and vice versa.
When the line condition is good, it is possible to reduce the correction bit more than usual so as to improve the data quality and prevent the waste of the correction bit, thereby making it possible to effectively use the line.

Further, as a result of the above feedback, when the line condition is good, the number of error correction bits is reduced and the number of bits of transmission data is increased, so that the data quality is improved even for transmission data that is not particularly required to be reliable. The flexibility of being able to raise is effective.

In this way, reliable communication can be performed while effectively using the line, and the error correction code has flexibility in a communication line in which the line state changes. The amount of error correction code can be adjusted to an appropriate amount according to the quality of the line.

Further, even in a case where reliability is not required, such as voice, when the line condition is good, it is possible to increase flexibility by reducing the number of error correction bits and increasing the number of bits of transmitted voice. You can

(B) Description of Second Embodiment FIG. 5 is a block diagram showing a second embodiment of the present invention. In FIG. 5, A'is a transmitter and B'is a receiver. The transmitter A'and the receiver B'are connected by the communication line 11 and the feedback line 12.

Here, as shown in FIG. 5, the transmitter A'has an input bit storage memory (storage unit) 6 for storing the input bits for a predetermined time, and the convolutional encoder 2
1 and a puncturing table 22 for variable rate punctured convolutional encoder 2.

Further, the receiver B ', as in the first embodiment described above, has a path metric / line error rate conversion table (line state detector) 4 and a Viter-Bidego decoder (decoder) provided with a path metric calculator 31. ) 3, but further comprises a decoding failure data storage memory (storage unit) 5.

The Viterbi degodar 3 provided with the path metric / line error rate conversion table 4 and the path metric calculator 31 is the same as that of the first embodiment described above, and therefore its explanation is omitted. .. Further, the decoding failure data storage memory 5 is a memory for storing the decoding failure data when the Viterbi degoder 3 of the receiver B ′ fails in decoding.

With this configuration, in the second embodiment, the ARQ system is obtained by adding the success or failure of the line quality to the information to be fed back, and if the decoding fails on the receiving side, the decoding failure data storage memory 5 is used. The received signal (decoding failure data) is stored in the NAK signal (Non AcKnowledge) of the signal indicating that the decoding has failed.
Signal) to the path metric / line error rate conversion table 4
It is fed back to the transmission side together with the line status detected in.

On the transmitter A'side, an additional correction code corresponding to the line state is calculated from the input bits stored in the memory 6 and transmitted to the receiver B'side, and on the receiver side.
Additional correction code received and decoding failure data storage memory 5
It is re-decoded by combining with the previously received data stored in. If the re-decoding cannot be performed once, the above processes are repeated until the decoding succeeds.

In this way, on the transmission side, the memory 6 which stores the input bits for a certain period of time, and the required thinning-out processing is performed on the output from the variable coding rate encoder 1 to change the coding rate and improve the error correction capability. The receiver B'includes a variable rate punctured convolutional encoder 2 which adjusts the rate, and a receiver B'that decodes the coded signal sent from the transmitter A ', and a path metric detecting a line state.
By providing the line error rate conversion table 4 and the decoding failure data storage memory 5 for storing the decoding failure data, the following effects can be obtained.

That is, when the decoding fails, the decoding failure data is stored in the decoding failure data storage memory 5,
In addition, the signal indicating that the decoding has failed, together with the line status detected by the path metric / line error rate conversion table 4,
Since feedback is provided to the transmitter A ', the transmitter A'
In, the additional correction code corresponding to the line state can be transmitted, and in the receiver B ′, the received additional correction code and the data stored in the decoding failure data storage memory 5 are combined to perform re-decoding. As a result, high reliability, high throughput, short average delay time, etc. can be realized.

[0046]

As described in detail above, according to the digital transmission system according to the invention described in claims 1 and 2, a variable coding rate encoder capable of varying the coding rate is provided on the transmitting side. The output from the variable coding rate encoder is provided with a variable rate error correction encoder that performs required decimation processing to change the coding rate to adjust the error correction capability, and at the same time, it is sent from the transmitting side to the receiving side. It has a decoder that decodes the encoded signal and a line state detection unit that detects the line state, and the line state detected by the line state detection unit is fed back to the transmission side. Accordingly, the coding rate in the variable coding rate encoder and the coding rate for error correction in the variable rate error correction encoder can be changed, so that the line state changes with time. Communication path Oite also can be realized Takanobu and high throughput and low delay at the same time,
Further, there is an advantage that the bandwidth can be effectively used in voice transmission to improve the quality of the transmitted voice when the line condition is good and to secure the received voice quality above a certain level even when the line quality is poor.

Further, according to the digital transmission method of the invention described in claim 3, the receiving side further comprises a storage section for storing the decoding failure data, and when the decoding fails, the decoding section stores the decoding failure data. Save the failure data, and
By feeding back the signal indicating that the decoding has failed to the transmission side together with the line state detected by the line state detection unit, the transmission side transmits an additional correction code according to the line state, and the reception side receives it. Additional correction code and storage unit 5
Since it is possible to perform decoding by combining with the data stored in, the transmitting side can transmit the additional correction code according to the line state, and the receiving side can store the additional correction code and the received Re-decoding can be performed in combination with the data stored in the unit, which has the advantage of achieving high reliability, high throughput, short average delay time, and the like.

[Brief description of drawings]

FIG. 1 is a principle block diagram of a first invention.

FIG. 2 is a principle block diagram of a second invention.

FIG. 3 is a principle block diagram of a third invention.

FIG. 4 is a block diagram showing a first embodiment of the present invention.

FIG. 5 is a block diagram showing a second embodiment of the present invention.

[Explanation of symbols]

1 variable coding rate encoder 2 variable rate punctured convolutional encoder (variable rate error correction encoder) 3 Viterbid decoder (decoder) 4 path metric / line error rate conversion table (line state detection unit) 5 decoding failure data Storage memory (storage unit) 6 Input bit storage memory (storage unit) 11 Communication line 12 Feedback line 21 Convolutional encoder 22 Puncturing table 31 Path metric calculation device A, A'transmitter B, B'receiver

Claims (3)

[Claims] 1. In a digital transmission system in which a transmission side encodes and transmits a transmission bit using an error correction code, and a reception side decodes this to receive bits, the reception side detects a line state, A digital transmission system characterized by changing the coding rate for error correction according to the line status by feeding back the detection result to the transmitting side. 2. In a digital transmission system in which a transmission side encodes and transmits a transmission bit by using an error correction code, and a reception side decodes this to receive the bit, the transmission side encodes an information source. A variable coding rate encoder (1) capable of varying the rate, and error correction coding of the output from the variable coding rate encoder (1), and then performing a necessary thinning process to change the coding rate. A variable rate error correction encoder (2) that adjusts the error correction capability, and a decoder (3) that decodes the encoded signal sent from the transmitter to the receiver and the line state is detected by the receiver. A line state detection unit (4) is provided, and the line state detected by the line state detection unit (4) is fed back to the transmission side, so that the transmission side can change the coding rate according to the line state. Code in encoder (1) A digital transmission system characterized in that a coding rate and a coding rate for error correction in the variable rate error correction encoder (2) are changed. 3. In a digital transmission system in which a transmission side encodes and transmits a transmission bit by using an error correction code, and a reception side decodes this and receives bits, a constant input bit sequence is set on the transmission side. A storage unit (6) for holding time and a variable rate error correction encoder (2) for performing error correction coding and then performing required thinning processing to change the coding rate to adjust the error correction capability are provided. , A decoder (3) for decoding the encoded signal sent from the transmitting side to the receiving side, a line state detecting section (4) for detecting the line state, and a storage section (5) for storing the decoding failure data. When the decoding fails, the decoding failure data is stored in the storage unit (5), and the signal indicating the decoding failure is detected by the line state detection unit (4). Sender with line status By feeding back, the transmitting side calculates an additional correction code according to the line state from the data stored in the storage unit (6) and transmits it, and the receiving side compares the received additional correction code with the received additional correction code. The storage unit (5)
A digital transmission method characterized by performing decoding by combining with the data stored in.