KR20000045146A - Forward error correction method in bi-directional communication system - Google Patents

Abstract

PURPOSE: A forward error correction method is provided to improve an error correction performance by adjusting an interleaving depth according to an error number. CONSTITUTION: In a forward error correction method, when a signal is sent to a terminal from a base station, an RS encoder of a transmitter adds 2N parities every RS block. In a case where an error number generated at an RS decoder of a reception side is below N, an error correction is performed, and the error corrected data is sent to a convolution de-interleaver(46). To a micro processor unit of the terminal is inputted a zero as an error number value which indicates that the data is not corrected. A comparator of the micro processor unit(49) compares an output(a zero value) of the RS decoder(47) with a threshold value from a threshold value generator, and outputs a select control signal for selecting an 'OK' message when the error number generated from the RS decoder is below N. A multiplexer outputs either one of an 'OK' message and an 'NO' message according to the select control signal. A micro processor unit(40) of a head end side receiving an output of the multiplexer maintains a present depth of a convolution interleaver(43). In a case where the error number generated from the RS decoder(47) of a reception side exceeds a predetermined generation frequency and thus exists between (N+1) and 2N, the micro processor unit(49) of the terminal selects the 'NO' message. In a case where a generation frequency of the 'NO' message exceeds a predetermined limit, the micro processor unit(40) of the head end increases an interleaving depth of the convolution interleaver(43) by a predetermined amount.

Description

Method of correcting forward error and apparatus employing the same for use in bi-directional communication system

The present invention relates to a forward error correction (FEC) method and apparatus therefor in a bidirectional communication system.

In general, the receiving side of a bidirectional communication system such as a cable modem is used to improve the reception sensitivity by adjusting the gain by an automatic gain controller (AGC) according to the strength of the signal received from the transmitting side. Has been. This will be described in more detail with reference to FIG. 1.

The automatic gain control circuit of FIG. 1 is largely divided into an analog AGC unit and a digital AGC unit. The analog AGC unit includes a variable gain adjustment amplifier 11 and a low pass filter (LPF) 17. The digital AGC unit includes a rectifier 12, And a subtractor 13, threshold generator 14, loop filter 15 and pulse width modulator (PWM) 16.

The analog AGC unit receives the PWM modulated signal from the PWM 16 of the digital AGC unit, obtains a DC component by the LPF 17, and then optimally adjusts the gain of the variable gain adjustment amplifier 11 by this signal. The digital AGC unit outputs a control signal for gain adjustment according to the level of the input signal. The rectifier 12 rectifies the input signal and outputs the absolute value. The subtractor 13 outputs a threshold value and an absolute value of the input signal. The threshold generator 14 generates and stores a threshold value that is a reference for the input signal, and the loop filter 15 determines a bandwidth of the AGC as a kind of low pass filter (LPF). 16 pulse-modulates the output of the loop filter 15.

FIG. 2 illustrates an automatic gain control method in a bidirectional communication system such as a cable modem. Assuming that the terminal receives the signal, the receiver adjusts the level of the input signal to a level suitable for the receiver. It is designed to control the output signal level of a transmitter by sending it to a transmitter in a headend of a cable broadcasting (CATV) or a central office of a telephone company through an upstream channel.

However, in the bidirectional communication system, the automatic gain control method is not only easy to design the transmitter and receiver because it is used not only the digital block but also the analog amplifier. There is a problem that cannot be escaped from the effect of the digital receiver, which results in deterioration of the reliability of the digital receiver.

Therefore, the present invention has been proposed to solve the above-described problem, in the bidirectional communication system, if the error is out of the error correction ability of the Reed Solomon decoder of the receiver calculates the number of uncorrectable errors and informs the transmitter, It is an object of the present invention to provide a forward error correction method and apparatus for improving error correction capability by adjusting the interleaving depth according to the number of errors.

In order to achieve the above object, the forward error correction method of the present invention includes a transmitting end including a forward error correction encoding unit and a receiving end including a forward error correction decoding unit, wherein the forward error correction decoding unit includes: Determining whether the generated error is out of a set error correction capability; Maintaining the interleaving depth in the forward error correction encoder when the generated error does not depart from the error correction capability; And adjusting the interleaving depth in the forward error correction encoder according to an uncorrectable frequency of error from each receiver when the generated error is out of the error correction capability. .

In order to achieve the above object, a forward error correction apparatus of the present invention in a bidirectional communication system includes: a forward error correction encoding unit performing forward error correction encoding on a signal to be transmitted; A forward error correction decoding unit performing forward error correction decoding on a signal received through a channel; A threshold value generator for generating a predetermined threshold value according to the number of parity inserted by the forward error correction encoder; A comparator for determining whether the error correction capability generated by the forward error correction decoding unit deviates from the set error correction capability by comparing the number of uncorrectable errors generated with the threshold value; And MCU of the receiving end including a multiplexer for supplying the corresponding error state information according to the determination result of the comparator; And an MCU of a transmitter that adjusts an interleaving depth in the forward error correction encoder according to the contents and frequency of error state information output from the MCU of the receiver.

1 is a block diagram showing a general automatic gain control circuit;

2 is a view for explaining an automatic gain control method in a bidirectional communication system such as a cable modem;

3 illustrates a part of an FEC decoder in a general digital communication system;

4 is a conceptual diagram showing a FEC method according to the present invention in a bidirectional communication system; and

5 is a block diagram showing an FEC apparatus according to the present invention.

* Explanation of symbols for main parts of the drawings

40 ... MCU (headend) 41,48 ... remaining processing block

42 ... RS Encoder 43 ... Convolution Interleaver

44 ... FEC Encoder & Modulator 45 ... FEC Decoder & Demodulator

46 ... Convolutional Deinterleaver 47 ... RS Decoder

49 ... MCU (Terminal) 51 ... Threshold Generator

53 ... Comparator 55 ... Multiplexer

57 ... transmission

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 shows a part of an FEC decoder in a general digital communication system, for example, cable, satellite, or digital terrestrial broadcasting, and shows a convolutional deinterleaver 31 and a Reed Solomon (RS) decoder 33. Include. Here, a Viterbi decoder (not shown) for the cable / satellite broadcasting receiver and a trellis decoder (not shown) for the terrestrial broadcasting / satellite broadcasting receiver may exist at the rear end of the convolutional deinterleaver 31.

In Fig. 3, the RS decoder 33 finds an error position and an error value by using the parity present in the received signal and corrects the error present in the received signal. However, the following limitations exist in the error correction capability of the RS decoder 33. If an RS encoder (not shown) in the transmitter forms a codeword by adding 2N parity to each RS block, that is, a data unit encoded in the RS code, the receiver transmits N codewords. You can correct up to errors, but if you exceed N, you can't correct any more. However, if the number of errors occurred is less than 2N, the number of errors can be obtained from the order of the error position polynomial obtained in the error correction process. This is possible because the order of error of the highest order term of the error location polynomial is generated. Therefore, if there are N errors or less in the input signal, the correction is made. If (N + 1) to 2N errors occur, correction is impossible but it is possible to know how many errors have occurred.

4 is a conceptual diagram illustrating an FEC method according to the present invention in a bidirectional communication system, in which a transmitting side includes a MCU 40, a remaining processing block 41, an RS encoder 42, a convolution interleaver 43, and an FEC of a headend. An encoder & modulator 44, and the receiving side includes an FEC decoder & demodulator 45, a convolutional deinterleaver 46, an RS decoder 47, a remaining processing block 48, and a MCU 49 of the terminal. .

FIG. 5 is a block diagram illustrating an FEC apparatus according to the present invention, which is included in the MCU (49 of FIG. 4) of a terminal, and includes a threshold generator 51 generating a predetermined threshold, an error number that cannot be corrected, A comparator 53 for comparing thresholds, a multiplexer 55 for selecting and outputting one of an 'OK' message and a 'NOK' message according to a comparison result of the comparator 53, and a selective output from the multiplexer 55 It consists of a transmission unit 57 for transmitting the message to the head end MCU (40 in FIG. 4).

Next, the FEC method and apparatus thereof according to the present invention will be described with reference to FIGS. 3 to 5.

First, a signal is sent from the headend or the base station to the terminal. In this case, the RS encoder 42 of the transmitter adds 2N parity to each RS block.

If there are less than N errors generated by the RS decoder 47 at the receiving end, error correction is performed to send the error corrected data to the convolutional deinterleaver 46, and zero (0) is set to an uncorrectable error number. To the MCU 49. The comparator 53 of the MCU 49 compares zero, which is an uncorrectable error count value output from the RS decoder 47, with a threshold value output from the threshold generator 51, in this case, N, and in the RS decoder 47. If there are less than N errors, a selection control signal for selecting an 'OK' message is output.

The multiplexer 55 selects and outputs an 'OK' message or a 'NOK' message according to the selection control signal output from the comparator 53. In this case, since the number of input uncorrectable errors is zero, the head end or base station direction is output. When there is a chance to send data, select 'OK' message as error status information. The MCU 40 of the headend side receiving the same maintains the current depth of the convolutional interleaver 43 because the error state is normal.

On the other hand, when the error generated by the RS decoder 47 on the receiving side exceeds the predetermined frequency and is between (N + 1) and 2N, the MCU 49 of the terminal transmits data toward the headend or base station. When there is a chance to do this, select 'NOK' message as the error status information and send it. The MCU 40 of the headend broadcasts to all terminals that the interleaving depth of the convolutional interleaver 43 is increased when the frequency of occurrence of the 'NOK' message in the error state information received from a plurality of terminals exceeds a predetermined limit. Next, the interleaving depth of the convolution interleaver 43 is immediately increased by a predetermined amount.

In another embodiment of the present invention, it is possible to use not only the Reed Solomon decoder but also other FEC decoders such as the Viterbi decoder or the trellis decoder.

According to the above configuration, in the bidirectional communication system, more reliable communication is possible by adjusting the interleaving depth of the downlink communication channel based on the number of uncorrectable errors calculated by the Reed Solomon decoder on the terminal side.

Claims (5)

In the bidirectional communication system having a transmitting end including a forward error correction encoding unit (42 ~ 44) and a receiving end including a forward error correction decoding unit (45 ~ 47), Determining whether an error generated by the forward error correction decoding unit deviates from a set error correction capability; Maintaining the interleaving depth in the forward error correction encoder when the generated error does not depart from the error correction capability; And And adjusting the interleaving depth in the forward error correction encoder according to an uncorrectable frequency of error from each receiver when the generated error is out of the error correction capability in the determining step. Error correction method. A forward error correction encoding unit 42 to 44 which performs forward error correction encoding on a signal to be transmitted; A forward error correction decoding unit 45 to 47 for performing forward error correction decoding on a signal received through a channel; A threshold value generator 51 for generating a predetermined threshold value according to the number of parity inserted by the forward error correction encoder; A comparator (53) for comparing the number of uncorrectable errors generated by the forward error correction decoding unit with the threshold to determine whether the error correction capability is out of the set error correction capability; And MCU 49 of the receiving end including a multiplexer 55 for supplying the corresponding error state information according to the determination result of the comparator; And Forward error in the bidirectional communication system characterized in that it comprises a MCU (40) of the transmitting end for adjusting the interleaving depth in the forward error correction encoder according to the content and frequency of the error state information output from the MCU of the receiving end Correction device. The apparatus of claim 2, wherein the forward error correction decoding unit comprises a Reed Solomon decoder, and supplies the number of uncorrectable errors generated in the Reed Solomon decoder to the comparator. The method of claim 2, wherein the forward error correction decoding unit includes a trellis decoder, and forward error correction in the bidirectional communication system, characterized in that for supplying the number of uncorrectable errors generated in the trellis decoder to the comparator. Device. The apparatus of claim 2, wherein the forward error correction decoding unit comprises a Viterbi decoder, and supplies an uncorrectable number of errors generated in the Viterbi decoder to the comparator.