JPH0254639A - Data modulator/demodulator with error correction function - Google Patents

Abstract

PURPOSE:To reduce the effect of an error on a line and to improve data transmission efficiency by changing a trace back length (l) of a Viterbi decoder in response to the retransmission request frequency of an error control section applying error correction for a data packet by a retransmission system. CONSTITUTION:The tracing back time (l) of the history of the Viterbi decoder 7a (7b) is changed in response to the frequency of the retransmission request of a data packet by an error control section 3a (3b) and the tracing back length (l) of the Viterbi decoder 7a (7b) is extended when the retransmission request frequency is increased. Thus, the error correction capability of the Viterbi decoder 7a (7b) is improved and the retransmission request frequency of the error control section is lowered, then the data transmission efficiency as a whole is improved and the Viterbi decoder is operated with an optimum tracing back length (l).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a data modulation/demodulation device with an error correction function.

[Conventional technology]

In conventional data modulation and demodulation devices, the traceback length of the Viterbi decoder is fixed at a constant value.

When convolutionally encoded data is decoded by a Viterbi decoder, it is generally known that the longer the trace pack length, the higher the error correction ability of the Viterbi decoder. However, when the trace pack length is increased, a code sent later is required to decode one piece of data, resulting in an increase in data delay time.

Therefore, if there are few data errors on the line, the data transmission efficiency will be improved by shortening the traceback length and reducing the delay time.

On the other hand, if there are many errors in data on the line, it is better to increase the traceback length and improve the error correction ability, even if the delay time increases somewhat.

[Agenda that the invention attempts to solve]

In the conventional data modulation/demodulation equipment described above, the trace pack length is constant, so if the traceback length is determined to have the ability to correct data errors in the worst condition of the line, However, there was a problem in that the delay time was longer than necessary.

[Means to solve the problem]

A data modulation/demodulation device with an error correction function according to the present invention includes a modulation section that modulates transmission data, a demodulation section that demodulates reception data, and a received code that is convolutionally encoded and outputted from the demodulation section. The above-mentioned error υ control unit includes a Vitapi decoder that performs maximum likelihood decoding by tracing back the history for 2 (2: natural number) symbol times, and an error control unit that performs error correction using a data packet retransmission method. The time t for tracing back the history of the Viterbi decoder is changed depending on the frequency of data packet retransmission requests.

[Effect]

In the present invention, the trace length t of the Viterbi decoder is changed in accordance with the retransmission request frequency of an error control unit that performs error correction using a data packet retransmission method.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.

In the figure, 1m (1b) indicates the transmission data input, 2
m(2b) indicates the received data output.

3m (3b) is an error control unit that performs error correction using a data packet retransmission method; 4m (4b) is a convolutional encoder; 5m (5b) is a modulation unit that modulates transmission data; 8
'(6b) is a demodulation unit that demodulates received data, 7m (7
b) is a Viterbi decoder that performs maximum likelihood decoding by tracing back the history of 1 (1: natural number) symbol time of the convolutionally encoded received code output from the demodulator 6m (6b); 8 is a line; It is.

Then, depending on the frequency of data packet retransmission requests in the error control unit 3m (3b), the Viterbi decoder T & (7b)
The configuration is such that the time t for tracing back the history of is changed.

Next, the operation of the embodiment shown in FIG. 1 will be explained.

First, the transmission data inputted from the transmission data input 1m (1b) is sent to the convolutional encoder 4m (4b) as a data packet with information for error υ control added by the error control unit 3m (3b). It will be done. This convolutionally encoded data is then modulated by the modulation section 5a (5b) and transmitted via the line 8 to the demodulation section 6 of the data modulation/demodulation device on the other side.
Sent to b (6m).

Next, since the data demodulated by the demodulator 5b (5m) is convolutionally encoded, the Viterbi decoder 7b
It is decoded at (7a) and returned to the data packet form created by the error control unit 3m (3b). Then, this data packet is sent to the error control unit 3b (3m), and the error control unit 3b (3&) checks it using the control information added to the data packet to determine whether or not there is an error υ in the data packet. Judging as purple.

If there is no error in the data packet, the data portion is output to the received data output 2b (2m). If an error is detected, a control packet is sent back to request retransmission of the erroneous data packet. When the other error controller 3m (3b) receives the control packet of the retransmission request, it retransmits the requested data packet. By retransmitting data packets in this way between these two error control units 3m and 3b,
After obtaining correct data, the obtained data is output to the reception data outputs 2m and 2b.

FIG. 2 shows the convolutional encoder 41 (4b) in FIG.
It is a block diagram which shows the example of -.

B1%B4 in this figure 2 is the data kalpa of 4 points υ,
Yo l Yl + Ql to Q4 are the outputs of convolutionally encoded 5-bit codes, including one redundant bit. This 5-bit code is sent to the modulation section 5m (5b) shown in FIG.

In this figure 2, 10.11...14 is 1
Bit data delay element, 15.18...
20 is an exclusive OR gate;
21 and 22 are AND gates.

Now, let the input data string at time t be Bt” (BtB wealth BI
B4), the output data string Qt = (Y.

YI Qsnow Qs Qa) is Qt”F
'(Bt Bt-1Bt-2'...#t-n) However, n is the number F of data strings B that have been input so far. As a function of the input data string, all information is included.

On the other hand, the Viterbi decoder on the receiving side decodes the code Qt sent via the signal fIs8 and demodulated by the demodulator to obtain output data B. Here, if there is no error due to noise or the like on the line, the encoder demodulated by the demodulator should match the output of the encoder on the transmitting side. In reality, Q is affected by noise on the line, so it does not necessarily match the town.

By the way, as mentioned above, since the convolutionally encoded code includes information on previous data, Qt
+l (1 is a natural number) K also includes information about the town. Then, the Viterbi decoder corrects the error received on the line by performing maximum likelihood decoding by going through the code history of NQ, ~Qt+t (L is a natural number), and outputs Ht. In the decoder, t is called the traceback length. The longer this trace pack length t is, the closer the output of the Tavi decoder is to BtK (the fewer errors occur). However, if the trace pack length t is increased, B,
Because it is necessary to wait for the code (Jt+6) to be input to the decoder in order to obtain the output, the data delay time becomes large.

If there are fewer errors on the line, sufficient error correction can be made even if the trace pack length t is short, and in order to reduce the delay time, it is better to make t as short as possible. On the other hand, if there are many errors on the line, it is better to increase the in correction capability by increasing t even if the delay time becomes longer.

Now, when t is a certain constant value, as the number of errors on the line increases, the frequency of retransmission requests by the error control unit 3b (3m) in FIG. 1 increases. If the frequency of retransmission requests increases, increasing the length of the Viterbi decoder 7b (7m) h race pack will increase the error correction ability of the Viterbi decoder 7b (7m). The benefit is that the frequency of retransmission requests in the control unit is reduced, and overall data transmission efficiency is improved.
Also, the Viterbi decoder will operate with an optimal traceback length t.

〔Effect of the invention〕

As explained above, the present invention enables data packets to be processed on the line by changing the trace puncture length t of the Viterbi decoder in accordance with the retransmission request frequency of the error control unit that performs error correction using the data packet retransmission method. This has the effect of reducing the impact of errors and improving data transmission efficiency.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing an example of the convolutional encoder in FIG. 1. ja, [b・劎・・Transmission data input, 2m, 2b...
Received data output, 3m, 3b...Fist error controller, 4m
, 4b...e convolutional encoder, 5a. 5b...1111 modulation section, 5 &, 6b@ * @ @
Demodulator, 7a. 7b...Viterbi decoder.

Claims (1)

[Claims] A modulation unit that modulates transmitted data, a demodulation unit that demodulates received data, and a history of l (l: natural number) symbols of the convolutionally encoded received code output from this demodulation unit. The Viterbi decoder includes a Viterbi decoder that performs maximum likelihood decoding using a data packet retransmission method, and an error control unit that performs error correction using a data packet retransmission method. 1. A data modulation/demodulation device with an error correction function, characterized in that the time l for tracing back the history of a decoder is changed.