KR0123087B1 - Apparatus and method for viterbi decoding - Google Patents

Abstract

A decoding apparatus having an adaptive truncation length and method thereof are disclosed. The decoding apparatus comprises: a Viterbi decoder(110) for outputting a data minimized an error probability of the transferred data, and estimating and generating an error bit; and an error detecting and correcting unit(120) for detecting an error by the inputted the error bit and performing feedback a control signal of the truncation length to the Viterbi decoder(110) by variably setting the truncation length in responsive to the bit error rate. Thereby, it is possible to exactly perform the decoding in real-time.

Description

Viterbi decoding apparatus and method with adaptive truncation length

1 is a schematic block diagram illustrating a Viterbi decoding apparatus of the present invention.

2 is a detailed block diagram of the error detection and correction unit shown in FIG.

3 is a graph showing a relationship for setting a step size versus a bit error required in an embodiment of the present invention.

4 is a block diagram showing a decision byte of the present invention.

* Explanation of symbols for main parts of the drawings

110: Viterbi decoder 120: error detection and correction unit

121: Mode and step size information generation unit 122: BER register

123: cutting length determining unit 124: cutting length changing unit

The present invention relates to a method of demodulating a trellis code (TCM) in a digital image demodulation system, and more particularly in a Viterbi decoder in a TCM scheme. A Viterbi decoding apparatus and method having an adaptive truncation length that adaptively sets the size of a truncation length (tau).

The digital image demodulation system is for demodulating data received by being digitally modulated and restoring the original signal. During transmission of such digital data, an error, that is, a value of the transmission data may change due to characteristics of a transmission channel, and thus a method for correcting such an error of the data has been devised.

One of the proposed schemes for correcting an error is a method of convolutionally encoding data to be transmitted, and one of the proposed schemes for correcting an error of convolutional coded data is a Viterbi decoding algorithm.

The most important thing in determining the accuracy of error correction in this Viterbi decoding scheme depends on how many convolutional code data are used to make the decision. In other words, rather than performing error correction with only 10 convolutional code data, determination with 20 data becomes more error correcting capability. Therefore, in order to make the most accurate decision in the Viterbi decoding algorithm, the larger the number of data for determination, the higher the error correction capability.

However, when the number of convolutional code data for the execution of the Viterbi decoding algorithm is increased, the execution time for error correction is increased, that is, a real-time processing problem of the system occurs. Therefore, when designing a Viterbi decoder that performs the Viterbi decoding algorithm, it is most desirable to determine the number of data to be error corrected in consideration of the decoder's error correction capability and real-time processing speed. The minimum number of data for such error correction is referred to as the truncation length tau in the Viterbi algorithm.

The truncation length, tau, is determined within a range that does not significantly degrade the decoding performance, and is typically determined as a multiple of 5 or 6 of the number of memories in the convolutional encoder on the transmitting side.

On the other hand, in the case of decoding data passing through a channel having no strong noise, almost no data error occurs in the transmission process, and even though the aforementioned tau is reduced, there is almost no error in the data decoded by the Viterbi decoder. can see.

That is, the above-mentioned tau is advantageous in real-time processing of the Viterbi decoder in which data bits generated in the data transmission process are adaptively set according to the error rate, but in the conventional Viterbi decoder, the decoding is performed using a constant tau as described above. As a result, there was a problem that the real-time processing of the Viterbi decoder is difficult.

The present invention has been made to solve such a problem, and an object of the present invention is to adaptively set the tau length according to the error rate of data transmitted by convolutional coding, thereby improving the adaptive truncation length of the Viterbi decoder. The present invention provides a Viterbi decoding apparatus and method.

The present invention is a device for decoding convolution coded data so that an error in data that can occur during transmission can be corrected at a decoding side. Viterbi decoder that corrects convolution data that has an error during transmission, and outputs a bit error rate, which is the percentage of convolution data that has an error during transmission, whenever the decoding of the bits of the convolution data corresponding to the truncation length ends. Wow; And an error detection and correction unit for outputting a truncation control signal corresponding to the bit error rate of the Viterbi decoder.

The present invention also includes the steps of correcting convolutional data in which an error occurred in a transmission process by decoding the convolutionally encoded data so that the decoding side can correct an error of data that may occur in a transmission decision; Calculating a bit error rate, which is a percentage of the convolution data in which an error occurs during the transmission, each time the decoding of the bits of the convolution data corresponding to the truncation length ends; Resetting the truncation length according to the calculated bit error rate.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention;

1 is a schematic block diagram of a Viterbi decoding apparatus of the present invention, and includes a Viterbi decoder 110 and an error detection and correction unit 120.

Here, the Viterbi decoder 110 cuts the received data (convolutional coded) into the number of bits of the truncation length corresponding to the tan control signal TCS of the error detection and correction unit 120, and cuts the number of bits. By performing the Viterbi decoding algorithm on the data of, the error of the data generated in the transmission process is corrected and output. In addition, the Viterbi decoder 110 of the present invention estimates a bit error rate (hereinafter, referred to as BER), that is, a bit error rate that is a percentage of convolution data in which an error occurs during the transmission process. Provided by 120.

The error detection and correction unit 120 inputs the BER provided from the Viterbi decoder 110 and provides the tau control signal TCS to the Viterbi decoder 110 in response to the amount of change in the BER.

2 is a detailed block diagram of the error detection and correction unit 120.

As shown, the error detection and correction unit 120 includes a BER register 122 and a cut length changing unit 124, and the cut length changing unit 124 cuts all and step size information generation units 121 and cut. The length determining unit 123 is included.

In FIG. 2, the BER applied from the Viterbi decoder 110 to the error detection and correction unit 120 is called NBER (New BER). As described above, the reason for naming the NBER is that the BER provided to the mode and step size government generation unit 121 is obtained from the BER and BER registers 122 provided from the Viterbi decoder 110. BER (OBER (Old BER)) exists to distinguish between the two.

That is, the BER register 122 inputs and stores the NBER provided by the Viterbi decoder 110 and outputs the stored NBER as an OBER when a new NBER is applied.

The mode and step size information generation unit 121 calculates a mode and step size to be described later by using a decision algorithm in which performance does not decrease as the length of the tau increases. To provide.

That is, the mode and step size information generation unit 121 determines tau according to the above-described NBER and OBER and the information byte (OBYTE (old decision byte)) applied from the truncation length determination unit 123, and determines the determined tan. The cutting length determination unit 123 is applied to the byte (NOBYTE (new decision byte)).

FIG. 3 is a graph showing a determination variable for setting the mode and the step size information generation unit tau.

Here, the x-axis represents a value obtained by dividing the absolute value of the difference between OBER and NBER by OBER and multiplying by 100, and the y-axis represents size information, that is, step size, indicating increase or decrease in tau length for x-axis transformation. In other words, the step size indicating increase or decrease in the length of tau is changed by the x-axis value. For example, if the previous to current bit error rate on the x-axis is about 5, the step size is 0, and if it is 5 to about 45, the step size is determined as shown correspondingly.

4 shows the construction of OBYTE and NBYTE.

As shown, the information byte consists of 8 bits, i.e., 1 byte, as shown. Here, the most significant two bits (md0, md0) represent mode information indicating wmdrak of tau length, the blank portion is a dummy bit, and the least significant four bits (m3, m2, m1, m0) are step size information. Indicates.

That is, if Mode 1 (md1) and Mode 0 (md0) are '00', there is no change, '01' indicates an increase in tau length, and '10' indicates a decrease in tau length. And the least significant 4 bits represent a step size having 0 to 15 levels.

The step size determination is set in the above-described mode and step size information generation unit 121 as shown in the graph shown in FIG. 3, and the mode decision is determined by several current states as follows.

When the ODBYTE provided by the first current cut length determiner 123 is '01' (tau length increase), three cases of NBEROBER, NBEROBER, and NBER = OBER may occur.

1. NBEROBER

If the NBER is larger than the OBER, the tau is increased in the previous step, but the bit error rate of the Viterbi decoder 110 is increased. This is not a problem of tau. Adopt methods such as maintaining.

2. When NBER = OBER

If the NBER and the OBER are the same, the above-described decision byte NDBYTE is set so that the mode is fixed to '00', that is, the size of tau is fixed and the step size is not changed to maintain the real-time processing performance of the Viterbi decoder 110. Must be set.

3. NBEROBER

If the NBER is smaller than the OBER, the decision byte (NDBYTE) is set to reduce the size of tau (10), that is, reduce the size of tau and improve the size of the step so that the real-time processing performance is improved.

Second, as the mode is '10' (tau length reduction) in the current ODBYTE, three cases may also occur in this case, NBEROBER, NBEROBER, and NBER = OBER.

1. NMBEROBER

First, when the NBER is larger than the OBER, the bit error rate of the Viterbi decoder 110 is increased, so that the mode is set to '01', that is, the size of tau is increased, and the decision byte is set to increase the step size.

2. NBER = OBER

If NBER and OBER are the same, the mode is set to '00' and fixed to maintain performance, and the step size is not changed.

3. NBEROBER

If the NBER is smaller than the OBER, it cannot be generated, but if the NBER and the OBER coincide with each other in order to improve the performance, the processing is the same.

Lastly, in the current ODBYTE, the mode is '00' (tau length is fixed). In this case, three cases of NBEROBER, NBEROBER, and NBER = OBER may occur.

1. NBEROBER

If the NBER is larger than the OBER, the bit error rate of the Viterbi decoder 110 is increased. In this case, the mode is set to '01' and the step size is increased.

2. NBER = OBER

If NBER and OBER are the same, the modules are fixed by setting them to zero to maintain performance, and do not change the step size.

3. NBEROBER

If the NBER is less than OBER, the bit error rate of the Viterbi decoder 110 is reduced. In this case, the mode is set to '10', that is, the reduction direction, and the least significant 4 bits of the decision byte are combined so that the step size is also reduced. Let's do it.

On the other hand, the cut length determiner 123 stores the decision byte NDBYTE in the current step provided by the above-described mode and step size information generation unit 121, and uses this value and the decision byte ODBYTE set in the previous step. The final tau is determined, the determined tau is transmitted to the Viterbi decoder 110 as a tau control signal TCS, and the stored decision byte value is transmitted to the decision direction and size information generation unit 121 to be used in the next step. .

As described above, according to the decoding apparatus and method having the adaptive truncation length according to the present invention, the truncation length is adapted by setting a new decision length according to the truncation length of the previous step and the bit error rate provided by the Viterbi decoder. This can be changed to solve real-time problems and to improve decoding accuracy.

Claims (6)

A device for decoding data transmitted by convolutional coding so that an error in data generated in a transmission process can be corrected by a decoding side, wherein the convolution data is Viterbi decoded by bit length of a truncation length corresponding to a truncation control signal. Each time the decoding of the convolutional data having an error in the transmission process is performed, and the decoding of the convolution data of the number of bits corresponding to the truncation length is completed, the bit error rate, which is a percentage of the convolution data having an error in the transmission process, is terminated. An output Viterbi large coder 110; Viterbi decoding apparatus having an adaptive truncation length including an error detection and correction unit for outputting the truncation control signal corresponding to the bit error rate of the Viterbi decoder (110). The bit error rate (NBER) provided by the Viterbi decoder 110 is stored, and when the bit error rate (NBER) is applied, the error detection and correction unit 120 stores the bit error rate. A BER register 122 for outputting the stored bit error rate NBER as a bit error rate OBER; Adaptive truncation length including a truncation length changer 124 for outputting the truncation control signal corresponding to the difference between the bit error rate NBER of the Viterbi decoder 110 and the bit error rate OBER of the BER register 122. Viterbi decoding device having a. The cutting length changing unit 124 of claim 2, wherein the truncation length changing unit 124 includes a first decision byte (ODBYTE) representing the previous truncation length performed by the Viterbi decoder 110, and the bit error rate (NBER, OBER). A mode and step size information generation unit 121 for increasing the truncation length of the Viterbi decoder 110 and providing a new decision byte (NDBYTE) for designating the truncation length corresponding to the? The cutting length is determined by the determination byte NDBYTE of the mode and step size information generating unit 121, and the cutting length control signal corresponding to the determined cutting length is provided to the Viterbi decoder 110. A Viterbi decoding apparatus having an adaptive truncation length including a truncation length determiner (123) for providing a decision byte (NOBYTE) to the mode and step size generation unit (121) as a decision byte (ODBYTE). 4. The Viterbi decoding device according to claim 3, wherein the decision bytes (NDBYTE, ODBYE) have an adaptive truncation length set to have two bits indicating an increase / decrease of the truncation length. 5. The Viterbi decoding device according to claim 4, wherein the decision bytes (NDBYTE, ODBYTE) have an adaptive truncation length set to further have 4 bits indicating the set truncation length. Viterbi decoding the convolutionally coded data so that the decoding side can correct an error of data that may occur in the transmission process, and the error in the transmission process by viterbi decoding the convolution data by bit unit of a preset truncation length. Correcting convolutional data generated; Calculating a bit error rate that is a percentage of the convolution data in which an error occurs during the transmission process each time decoding of the convolution data of the number of bits corresponding to the truncation length ends; And resetting the truncation length in accordance with the calculated bit error rate.