KR20100007468A - Method and apparatus for handling an error on data during channel decoding - Google Patents

Abstract

The present invention relates to error processing in channel decoding, and more particularly, to a method and apparatus for processing an error in channel decoding when the size of a channel coded data and a packet size are different. An error processing method for data when decoding a channel of the present invention includes decoding a frame including at least one constant size packet using a predetermined decoding code, checking whether an error exists in the decoded frame; Setting a value indicating an error occurrence in the decoded frame when the error exists, and transmitting a decoded packet for all packets among the at least one packet included in the frame to a packetizer. And, among the at least one packet includes a process of storing the decoded packets for all the packets in the buffer.

Description

Method and apparatus for error handling in channel decoding {Method and Apparatus for handling an error on data during channel decoding}

The present invention relates to error processing in channel decoding, and more particularly, to a method and apparatus for processing an error in channel decoding when the size of a channel coded data and a packet size are different.

In a digital communication system, in order to improve the efficiency of data transmission, a transmitter performs source coding and channel coding and then transmits data. Source coding is a technique for improving transmission efficiency by converting an analog signal into a digital signal and compressing and encoding the signal to overcome channel capacity limitations in data transmission, and channel coding eliminates errors that may occur during data transmission. It is a technique of inserting an additional code to increase reliability by correcting. The receiving side receiving the source coded and channel coded data restores the original data by performing channel decoding and source decoding on the received data as opposed to the transmitting side.

The receiving side corrects an error caused by channel noise or the like during data transmission by channel decoding the channel coded data. However, there is a case that can not be corrected even by channel decoding. If such an error is present, error processing for informing that an error has occurred can reduce resource waste for later data processing. For example, in case of data for digital broadcasting, a packet (Moving Picture Experts Group2 Transport Stream, hereinafter referred to as 'MPEG2 TS') as a data format (hereinafter referred to as 'MPEG2 TS packet)' 'Reed' may be used, and a Reed-Solomon code (hereinafter, referred to as an 'RS code') may be used as a code for channel coding. The packet size of the MPEG2 TS is 188 bytes, and the size of data coded by the RS code is also performed in units of 188 bytes. In this case, since the packet size and the channel coded data have the same size, when an uncorrected error exists in one packet during channel decoding, an error may be indicated in the channel decoded packet. By doing so, the error marked data does not perform unnecessary processing on the error marked data in the process after channel decoding.

On the other hand, the Low Density Parity Check (LDPC) code proposed by Gallagher in the early 1960s as a channel coding code has recently come to the attention again due to advantages such as simple decoding and low frame error rate. I am getting it. However, unlike the above-described RS code, the LDPC code does not perform channel coded data in units of 188 bytes. That is, the packet size and the channel coded data are not the same. In this case, one frame to be channel decoded may include one or more packets. If there is an error that cannot be corrected, there is no way to handle the error. Therefore, there is a need for a method of handling an error in the presence of an uncorrectable error when the size of the packet is different from the size of the channel coded data or the channel coding is not performed by an integer multiple of the packet size.

Accordingly, the present invention provides a method and apparatus for handling an error in channel decoding.

In addition, the present invention provides a method and apparatus for handling an error when the size of a packet and the size of data to be channel coded are different or channel coding is not performed by an integer multiple of the packet size.

According to an aspect of the preferred embodiment of the present invention, an error processing method for data when decoding a channel of the present invention includes decoding a frame including at least one constant size packet using a predetermined decoding code, and decoding Checking whether there is an error in the decoded frame, setting a value indicating an error occurrence in the decoded frame when the error exists, and all of the packets among the at least one packet included in the frame. And transmitting the decoded packet to the packetizer.

According to another aspect of the preferred embodiment of the present invention, an error processing apparatus for data when decoding a channel of the present invention performs decoding using a predetermined decoding code on a frame including at least one constant size packet, and the frame A decoder for transmitting a decoded packet to all packets among the at least one packet included in a packet; and checking whether an error exists in the decoded frame, and if the error exists, an error in the decoded frame. And a controller configured to set a value indicating occurrence, and a buffer to store a packet in which decoding is not completed for all packets among the at least one packet.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that those skilled in the art may better understand it from the following detailed description of the invention. In addition to these features and advantages, further features and advantages of the present invention which form the subject of the claims of the present invention will be better understood from the following detailed description of the invention.

According to the present invention, when the size of the source coded packet and the size of the channel coded data are different, there is an advantage in that an error for the packet can be processed in the presence of an error after channel decoding. If the decoding of all parts of the packet is not completed after the channel decoding, the packet is stored in the buffer and the decoded packets of all parts of the packet are transferred to the next step, so that the size of the packet and the size of the channel decoded data In other cases, error handling of packets is possible. In the case of including an uncorrectable error for a frame in which an error occurs due to a channel environment, error handling may be performed on all TS packets, thereby preventing a problem that may occur in later systems.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this case, it should be noted that like elements are denoted by like reference numerals as much as possible. In addition, detailed descriptions of well-known functions and configurations that may blur the gist of the present invention will be omitted.

A system used as a standard for transmitting or transmitting a video bit stream and an audio bit stream together is a moving picture expert group (hereinafter referred to as a 'MPEG') system. There are various MPEG systems depending on the field of use. Among MPEG systems, a transport stream (hereinafter referred to as 'MPEG2 TS' (Transport Stream)) of an MPEG2 system is used to multiplex and transmit a plurality of programs in an error channel environment of a wide range of applications such as broadcasting, communication, and storage media. It is used a lot. In particular, since MPEG2 TS is multiplexed into a single bit string in a channel environment in which an error occurs, an MPEG2 TS has an advantage in transmitting data in a multimedia service, for example, a digital broadcasting service. Hereinafter, the present invention will be described taking an MPEG2 TS packet encoded in an MPEG2 TS format in which data has the above advantages. However, the present invention is not only limited to the MPEG2 TS packet but can also be applied to packets encoded by other methods.

1 is a diagram illustrating an MPEG2 TS packet structure according to an embodiment of the present invention.

Referring to FIG. 1, one MPEG2 TS packet 100 is 188 bytes in size, and a 4-byte header 101 including information about the packet and a 184 byte payload including actual data are included. 102. The header 101 specifically includes an 8-bit Synchronization byte field for packet synchronization, a 3-bit flag field for indicating a method of processing a payload, and a 13-bit program for identification. Program Identification (PID) field containing information, a 2-bit transport scrambling control field containing information for accessing the payload of an encrypted TS packet, and 2-bit indicating whether the field is used or not. Is composed of an adaptation field control and a 4-bit continuity counter. The three-bit flag fields are in detail a transport error indicator field indicating a 1-bit transmission error, a payload unit start indicator field indicating a start time of a 1-bit payload, 1 It consists of a transport priority flag field (Transport priority) indicating the transmission priority of the bit. The present invention sets the transmission error indicator field value to '1' to indicate if an error exists after channel decoding. The setting of the transmission error indicator field value may vary depending on the set state. However, if the transmission error indicator flag is set to '0' as the initial value and is determined to be an error packet after channel decoding, the flag ' Can be set to 1 '. In the present invention, the transmission error indicator field is set to '0' as an initial value for convenience of explanation, and the transmission error indicator field value is set to '1' when an error occurs after channel decoding is performed. It explains by doing. However, the present invention is not limited only to the above-described case, and the transmission error indicator field value may be set in another manner to indicate that an error has occurred.

Encoders to correct errors caused by channel environment, such as signal attenuation, attenuation distortion, delay distortion, and noise, may be performed on the MPEG2 TS packet. have. This encoding is called channel coding. The channel coding scheme may be divided into a channel coding scheme having a size equal to 188 bytes, which is the size of an MPEG2 TS packet, and a channel coding scheme having a size different from that of the 188 bytes. An example of a channel coding scheme having a size different from that of the 188 byte includes a low density parity check, which is a channel coding scheme used in a terrestrial-mobile multimedia broadcasting (T-MMB) system, which is one of the standards of a digital multimedia broadcasting system. (Hereinafter referred to as 'LDPC') is a method of encoding using. The channel coding method using the LDPC code is a method of encoding in units of frames having a size different from that of 188 bytes. Specifically, the LDPC code, which was proposed by Gallagher in the early 1960s and rediscovered after 1996, is defined as a code having a significantly smaller number of non-zero elements in the parity check matrix than the length of the code. It is an error correcting code with the advantage that the complexity does not increase significantly even though iterative decoding is used.

According to the present invention, in order to explain a method of error processing when a packet size and a channel coded data are different, a source coded using an MPEG2 TS and a channel coded using an LCPD code, as in the T-MMB system described above. Take for example. In other words, the error processing procedure of the present invention will be described using an MPEG2 TS packet source coded to a size of 188 bytes and an LDPC frame channel coded to a size different from the size of the MPEG2 TS packet. For convenience of explanation, it is assumed that the size of a frame coded using LDPC code is 288 bytes (2304 bits). A frame (hereinafter, referred to as an 'LDPC frame') encoded by the LDPC code with a size of 288 bytes may include two or more MPEG2 TS packets. This will be described in detail with reference to FIG. 2.

2 is a diagram illustrating a packet structure of data by an LDPC code and MPEG2 TS according to an embodiment of the present invention. The LDPC frame may include a plurality of MPEG2 TS packets. Since the size of the LDPC frame is assumed to be 288 bytes, one LDPC frame may include up to three MPEG2 TS packets. 2 shows an example in which an LDPC frame includes three MPEG2 TS packets, and only three LDPC frames and three MPEG2 TS packets are shown for convenience of description.

Referring to FIG. 2, assuming that K-1 th LDPC frame, K th LDPC frame, and K + 1 th LDPC frame, each of which is 288 bytes in size, the K th LDPC frame includes up to three MPEG2 TS packets having a size of 188 bytes. Can include up to. That is, the K-th LDPC frame may include an N-1 th MPEG2 TS packet, an N th MPEG2 TS packet, and an N + 1 th MPEG2 TS packet. Since the LDPC frame is assumed to be encoded by the LDPC code, decoding is performed on each LDPC frame using the LDPC code during channel decoding. The decoding process for the LDPC frame corrects errors caused by the channel environment. However, if an uncorrected error exists even after channel decoding, the original packet recovery is impossible, and error processing should be performed on the packet so as not to perform unnecessary processing in subsequent processing. For example, when an error exists in the K-th LDPC frame after decoding the K-th LDPC frame, a value indicating an error occurrence is set in the MPEG2 TS packets included in the K-th LDPC frame. As illustrated in FIG. 2, the MPEG-2 TS packets included in the K-th LDPC frame include an N-1 th MPEG2 TS packet, an N th MPEG2 TS packet, and an N + 1 th MPEG2 TS packet. Accordingly, it is not known which MPEG2 TS packet has an error among three MPEG2 TS packets included in the decoded LDPC frame. In this case, error processing is performed on all MPEG2 TS packets, that is, N-1 th MPEG2 TS packet, N th MPEG2 TS packet, and N + 1 th MPEG2 TS packet. In other words, a value indicating an error occurrence is set for all MPEG2 TS packets included in the decoded LDPC frame. In this case, the value setting indicating the error occurrence for the MPEG2 TS packet may be performed by setting the value of the transmission error indicator field of the header 101 to '1' as described with reference to FIG. 1.

On the other hand, as shown in Figure 2, the N + 1 st MPEG2 TS packet is included in the K th LDPC frame and K + 1 th LDPC frame. Therefore, channel decoding for the N + 1 th MPEG2 TS packet is completed only when the channel decoding for the K + 1 th LDPC frame as well as the K th LDPC frame is completed. The N + 1 th MPEG2 TS packet is stored in the buffer when the channel decoding for the K th LDPC frame is completed, and the block for the subsequent step, that is, the TS packetizer (packetizer) when the channel decoding for the K + 1 th LDPC frame is completed. Is sent). Detailed description thereof will be described later. In this way, when the size of the TS packet and the size of the channel coded data are different, the present invention processes an error generated during channel decoding so that unnecessary processing is not performed on packets having errors in subsequent processes.

3 is a block diagram illustrating a configuration of processing an error in channel decoding in a receiver according to an exemplary embodiment of the present invention.

Referring to FIG. 3, when the packet size and the size of channel coded data are different, the receiver 300 of the present invention which processes an error in channel decoding may have a radio frequency (hereinafter referred to as RF) unit 305. We have added a controller outside the modem, such as the Base-Band MODEM (MOdulator / DEModulator) (310) and the controller (320) (the inventor, the RF unit and the CPU that controls the baseband modem.) ). The receiver 300 may include other components in addition to the RF unit 305, the baseband modem 310, and the controller 320, but the description of the other components will be omitted for convenience of description. However, the receiver 300 may include additional components for performing other functions in addition to the function for error processing of the present invention.

The RF unit 305 receives data in the form of a received transport stream (TS). It is assumed that the TS is a transport stream encoded using MPEG2 TS and LDPC codes. The RF unit 305 may include a frequency receiver for low noise amplifying the received signal and down converting the frequency. The baseband modem 310 for demodulating and decoding the received TS includes a demodulator 312, an LDPC decoder 314, a buffer 316, and a TS packetizer 318. . The demodulator 312 performs demodulation to detect synchronization and convert it to a digital signal according to the synchronization signal included in the TS. The LDPC decoder 314 performs channel decoding on the demodulated TS in units of frames having a predetermined size using an LDPC code. In this case, channel decoding may be performed in units of 288 byte frames as described in FIG. 2, and one LDPC frame may include two or more 188 byte MPEG2 TS packets. The buffer 316 stores MPEG2 TS packets in which decoding of all 188-byte MPEG2 TS packets has not been performed after channel decoding and before being transmitted to the TS packetizer 318. The TS packetizer 318 depacketizes the MPEG2 TS packet packetized in the MPEG2 TS format. The baseband modem 310 is an equalizer for compensating for channel distortion due to multiple paths of channels in addition to the above-described demodulator 312, LDPC decoder 314, buffer 316, and TS packetizer 318. (Not shown), a demultiplexer (not shown) that demultiplexes into multiple packets, such as video and audio packets, or decoding to recover the source coded packet, such as MPEG2 TS packets, to the original data. Although it may further include components required to process data received through the RF unit 305, such as a coder (CODER / DECoder) (not shown) to be performed, only the components for error processing are described for convenience of description. do.

The controller 320 controls the overall operations of the receiver 300. In particular, the controller 320 of the present invention controls operations for error processing when the packet size and the size of channel coded data are different. In detail, the controller 320 controls the LDPC decoder 314 to set a value indicating an error occurrence in all MPEG2 TS packets included in the LDPC frame when an error exists after channel decoding for an arbitrary LDPC frame. In addition, the controller 320 checks whether decoding of all MPEG2 TS packets included in the decoded LDPC frame is completed. That is, the controller 320 controls and transmits the decoded packets for all portions of the MPEG2 TS packet among the MPEG2 TS packets included in the decoded LDPC frame to the TS packetizer 318. That is, when only a portion of any MPEG2 TS packet of the MPEG2 TS packets included in the decoded LDPC frame is channel decoded, the controller 320 includes only the portion included in the decoded LDPC frame except the decoded MPEG2 TS packet. The MPEG2 TS packets are transferred to the TS packetizer 318, and only a portion of the decoded MPEG2 TS packets are stored in the buffer 316. Herein, the MPEG2 TS packet stored in the buffer 316 is transferred to the TS packetizer 318 when the channel decoding is performed on the remaining part, that is, all the MPEG2 TS packets. Therefore, even if the size of the TS packet and the size of the channel coded data are different, if there is an error after channel coding for the LDPC frame, error processing for TS packets that are expected to occur may be possible.

For example, assume that the K-1 th LDPC frame of FIG. 2 is composed of three MPEG2 TS packets, that is, an N-3 th MPEG2 TS packet, an N-2 th MPEG2 TS packet, and an N-1 th MPEG2 TS packet. It is assumed that channel decoding is performed on the K−1 th LDPC frame. At this time, when the channel decoding is completed for the K-1 th LDPC frame, the N-3 th MPEG2 TS packet and the N-2 th MPEG2 TS packet, which have completed channel decoding for all parts of the MPEG2 TS packet, are transferred to the TS packetizer 318. Delivered. Even if the channel decoding for the K-1 th LDPC frame is completed, the N-1 th MPEG2 TS packet in which the channel decoding is not completed for all parts of the MPEG2 TS packet is not transferred to the TS packetizer 318, and the buffer 316 is not transmitted. Are stored in. The N-1 th MPEG2 TS packet is included in a K-1 th LDPC frame and a K th LDPC frame as shown in FIG. Accordingly, the N-1 th MPEG2 TS packet is delivered to the TS packetizer 318 when the channel decoding for the K th LDPC frame is completed. In this way, in the present invention, when error correction fails after channel decoding for a K-th LDPC frame, all the MPEG2 TS packets included in the K-th LDPC frame, that is, the N-1 th MPEG2 TS packet, the N th MPEG2 TS packet, and N + 1 Error processing may be performed on the first MPEG2 TS packet. Error processing here means setting a value indicating an error in the transmission error indicator field of the MPEG2 TS packet header. For example, a value indicating error occurrence is '1'.

Referring to the drawings, a process of processing an error in channel decoding when a packet size and a channel coded data are different is described in detail.

4 is a flowchart illustrating an error processing process in channel decoding according to an embodiment of the present invention.

Referring to FIG. 4, the demodulator 312 of FIG. 3 demodulates data received under the control of the controller 320 in step 405. In this case, the received data is data in the form of a transport stream (TS) received and transmitted through the RF receiver 305 of FIG. 3, and it is assumed that the data is composed of an MPEG2 TS packet and an LDPC frame. In step 410, under the control of the controller 320, the LDPC decoder 314 decodes the demodulated data in LDPC frame units by using an LDPC code. In step 415, the controller 320 checks whether there is an error that fails to correct the decoded LDPC frame. If an error exists, the controller 320 performs error processing on MPEG2 TS packets included in the LDPC frame decoded at step 420. In this case, the error processing may indicate that an error occurs by setting a transmission error indicator field value of all MPEG2 TS packets headers included in the decoded LDPC frame to '1' as described in FIG. 2. If no error exists, the controller 320 proceeds to step 425. In the present invention, for convenience of description, it is assumed that the transmission error field value is basically set to '0', so that an additional field value setting process is not performed when an error does not exist. However, depending on the configuration, it may be set to set a field value indicating that an error does not exist even when no error exists. In this case, a process of setting a field value indicating that a packet does not occur can be additionally performed. have.

In step 425, the controller 320 checks whether channel decoding is completed for all parts of all MPEG2 TS packets included in the decoded LDPC frame. In other words, it is checked whether decoding of all parts of the MPEG2 TS packet included in two LDPC frames, such as the N-1 th MPEG2 TS packet or the N + 1 th MPEG2 TS packet of FIG. 2, is completed. If the channel decoding is not completed for all parts of the MPEG2 TS packet, under the control of the controller 320, the LDPC decoder 314 may perform the TS packetization process on the TS packet having completed channel decoding for all parts of the MPEG2 TS packet in step 430. 318). In this case, the MPEG2 TS packet in which channel decoding is completed for all parts of the MPEG2 TS packet may be one or more MPEG2 TS packets according to the number of MPEG2 TS packets included in the decoded LDPC frame. Under the control of the controller 320, the LDPC decoder 314 stores the MPEG2 TS packet in which the channel decoding is not completed for all the parts in the buffer 316 in step 435. The MPEG2 TS packet stored in the buffer 316 is transferred to the TS packetizer 318 after decoding of the next LDPC frame is performed. In all MPEG2 TS packets included in the decoded LDPC frame, when channel decoding is completed for all portions of the MPEG2 TS packet, in step 440, the LDPC decoder 314 is included in the decoded LDPC frame under the control of the control unit 320. All MPEG2 TS packets are transferred to the TS packetizer 138.

For example, assuming that the K-th LDPC frame is decoded in FIG. 2, the N-th MPEG2 TS packet, the N-th MPEG2 TS packet, and the N + 1-th MPEG2 TS packet included in the K-th LDPC frame will be described. The MPEG2 TS packet, which has been decoded for all parts of the MPEG2 TS packet, becomes an N-1 th MPEG2 TS packet and an N th MPEG2 TS packet. The MPEG2 TS packet, in which channel decoding is not completed for all parts of the MPEG2 TS packet, becomes an N + 1th MPEG2 TS packet. Accordingly, after decoding the K th LDPC frame, the LPDC decoder 314 transfers the N-1 th MPEG2 TS packet and the N th MPEG2 TS packet to the TS packetizer 318, and the N + 1 th MPEG2 TS. The packet is stored in the buffer 316. By doing so, the present invention can perform error processing on all MPEG2 TS packets included in the LDPC frame in the presence of an error after channel decoding for the LDPC frame even when the size of the source coded packet and the channel coded data are different. Can be.

On the other hand, the embodiments of the present invention disclosed in the specification and drawings are merely presented specific examples to easily explain the technical contents of the present invention and help the understanding of the present invention, and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that other modifications based on the technical idea of the present invention can be carried out in addition to the embodiments disclosed herein.

1 is a diagram illustrating an MPEG2 TS packet structure according to an embodiment of the present invention.

2 is a diagram showing a packet structure of data by LDPC code and MPEG2 TS according to an embodiment of the present invention;

3 is a block diagram illustrating a configuration of processing an error in channel decoding in a receiver according to a preferred embodiment of the present invention.

4 is a flowchart illustrating an error processing procedure in channel decoding according to an embodiment of the present invention.

Claims (19)

In the error processing method for the data when decoding the channel, Decoding a frame including at least one constant size packet using a predetermined decoding code, Checking whether an error exists in the decoded frame; Setting a value representing occurrence of an error in the decoded frame when the error exists; And transmitting the decoded packet to all the packets among the at least one packet included in the frame to a packetizer. The method of claim 1, The method of claim 1, further comprising storing a packet in which decoding is not completed for all of the at least one packet in a buffer. The method of claim 1, And a size of data decoded by the predetermined decoding code is different from a predetermined size of the packet. The method of claim 1, wherein the packet is composed of a header including information of the packet and a payload including data, And a value representing the occurrence of the error is included in a transport error indicator field of the header. The method of claim 4, wherein the setting of the value indicating occurrence of the error is And setting the transmission error indicator field value to '1'. The method of claim 1, wherein the packet is a packet encoded into a video expert group 2 transport stream (MPEG2 TS). The method of claim 1, wherein the predetermined size of the packet is 188 bytes. The method of claim 1, wherein the predetermined decoding code, Error processing method characterized in that the low density parity check (LDPC) code. The method of claim 8, wherein the frame, Error processing method characterized in that the LDPC frame having a size of 288 bytes. An error processing apparatus for data in channel decoding, A decoder which decodes a frame including at least one constant size packet using a predetermined decoding code, and transmits a decoded packet to all packets among the at least one packet included in the frame to a packetizer. Wow, And a controller which checks whether an error exists in the decoded frame and sets a value indicating an error occurrence in the decoded frame when the error exists. The method of claim 10, And a buffer for storing a decoded packet for all of the at least one packet. The method of claim 10, And a size of data decoded by the predetermined decoding code is different from a predetermined size of the packet. The method of claim 12, wherein the packet comprises a header including information of the packet and a payload including data, And a value representing the occurrence of the error is included in a transport error indicator field of the header. The method of claim 13, wherein the control unit, The transmission error indicator field value is set to '1' when an error exists in the decoded frame. The apparatus of claim 10, wherein the packet is a packet encoded into a video expert group 2 transport stream (MPEG2 TS). 11. The error processing apparatus of claim 10, wherein the predetermined size of the packet is 188 bytes. The method of claim 10, wherein the predetermined decoding code, Error processing device, characterized in that the low density parity check (LDPC) code. The method of claim 17, wherein the frame, Error processing device, characterized in that the LDPC frame having a size of 288 bytes. The method of claim 10, wherein the control unit, And determining whether decoding of all of the at least one packet included in the frame is completed.

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