KR101373646B1 - OFDM transmitting/receiving device for transmitting/receiving OFDM symbols comprising LDPC coded data, and methods thereof - Google Patents

Abstract

An OFDM transmitter for transmitting an OFDM symbol classified into a predetermined transmission unit is disclosed. The OFDM transmission apparatus comprises: an OFDM transmission processor for encoding symbols having a hierarchical priority by coding a stream to be transmitted using at least one coding scheme including a low density parity check (LDPC) coding scheme, and constructing an OFDM symbol by using symbols At the same time, an LDPC block composed of a plurality of symbols coded by the LDPC code is arranged to have a natural number arranged in a transmission unit, and a transmission unit for converting and outputting OFDM symbols configured at the mux unit. Accordingly, hierarchical OFDM symbol transmission is possible using up to LDPC coding.

OFDM symbol, priority, LDPC

Description

OPM transmission and reception apparatus for transmitting and receiving OFM symbols containing LDCPC coded data, and a method thereof.

1 is a schematic diagram illustrating a process of symbol mapping a hierarchical data bit in a conventional OFDM system;

2 and 3 are block diagrams illustrating a configuration of an OFDM transmitting apparatus according to various embodiments of the present disclosure;

4 is a block diagram illustrating an example of a configuration of an OFDM transmission processor or an OFDM transmission processing module that can be applied to the OFDM transmission apparatus of FIGS. 2 and 3;

5 is a block diagram showing a configuration of an OFDM transmitting apparatus according to another embodiment of the present invention;

6 to 9 are schematic views for explaining various examples of hierarchically coded OFDM symbol patterns;

10 is a schematic diagram illustrating one OFDM symbol configuration including symbols having different priorities;

11 is a flowchart illustrating an OFDM transmission method according to an embodiment of the present invention.

12 is a flowchart for describing a symbol generation process in the OFDM transmission method of FIG. 11 in detail;

13 and 14 are block diagrams illustrating a configuration of an OFDM receiver according to various embodiments of the present disclosure;

FIG. 15 is a block diagram illustrating an example of a configuration of an OFDM receiving processor or an OFDM receiving processing module applicable to the OFDM receiving apparatus of FIGS. 13 and 14.

16 is a block diagram showing a configuration of an OFDM receiver according to another embodiment of the present invention;

17 is a flowchart for explaining an OFDM reception method according to an embodiment of the present invention;

FIG. 18 is a flowchart for describing a data stream recovery processing process in the OFDM reception method of FIG. 17 in detail.

[Description of Drawings]

110: OFDM transmission processing unit 120: mux unit

130: transmitter 231: symbol interleaver

232: IFT 233: GI insert

234: Up Converter

The present invention relates to an OFDM transceiver and method, and more particularly, to an OFDM transceiver and method for transmitting and receiving OFDM symbols including symbols hierarchically coded according to at least one coding scheme, including LDPC coding scheme. It is about.

 Due to the development of electronic and communication technologies, various standards for digital broadcasting have been introduced in the field of broadcasting system by introducing digital technology. Specifically, there are the ATSC VSB standard, which is a standard for the United States, and the DVB-T standard, which is a European standard. Although the two standards differ in terms of voice compression method and channel bandwidth, the most significant point is that the ATSC VSB standard is a single carrier scheme and the DVB-T standard is a multi-carrier scheme.

The multi-carrier scheme adopted in the DVB-T standard is the OFDM scheme. Orthogonal Frequency Division Multiplexing (OFDM) is a technology adopted by the IEEE 802.11a and ETSI BRAN'S HYPERLAN2 standards, European digital TV broadcasting DAB and DVB-T standards. The conventional single-carrier transmission system in which information is carried on one carrier has a problem that the inter-symbol interference increases and distortion increases. Therefore, the complexity of the equalizer of the receiving end must also increase. An OFDM scheme has been introduced to solve the problems of the single carrier transmission scheme.

The OFDM scheme refers to a technique of transmitting data using multi-carriers. The OFDM scheme refers to a technique of converting serially input data symbols in parallel, modulating each of them into a plurality of tone signals having mutual orthogonality, and transmitting the same.

OFDM is widely applied to digital transmission technologies such as digital audio broadcasting (DAB), digital television, wireless local area network (WLAN), and wireless asynchronous transfer mode (WATM) . Particularly, compared with the conventional multi-carrier method, since orthogonality is maintained between the surrounding tone signals, it is possible to obtain optimum transmission efficiency at the time of high-speed data transmission, (multi-path fading).

According to the OFDM scheme, OFDM symbols are transmitted and received in various transmission units, for example, a frame or a super frame. Each OFDM symbol consists of a plurality of symbols. The symbols may each represent at least one or more data bits.

Meanwhile, the existing DVB-T system supports a hierarchical transmission method. That is, the data bits constituting the transport stream may be coded at various coding rates and then mapped in a mapping scheme such as QPSK, 64QAM, 16QAM, and the like to generate one symbol. In this case, data coded at different coding rates or different coding schemes differs in their robustness. Thus, there is a priority between the data bits mapped to each symbol. As described above, a batch transmission of data having different priorities is generally called a hierarchical transmission method.

According to a conventional DVB-T system, data having a high priority (HP) and a low priority (LP) in one symbol is mixed and transmitted. HP and LP are classified according to the positions of the bits allocated at the time of mapping. Specifically, when mapped in the 64QAM scheme, 6 bits per symbol are mapped. Among them, HP is allocated with the first 2 bits to determine the positions of the first, second, third, and fourth planes on the mapping constellation diagram. HP is allocated to the remaining 4 bits. Accordingly, the ratio of HP to LP becomes 1: 2.

1 shows a constellation plot of symbols mapped in a 64QAM scheme. According to FIG. 1, 16 symbols are generated in the first, second, third and fourth quadrants, and each symbol is composed of six bits. Unlike in FIG. 1, when mapped in the 16QAM scheme, 4 bits are mapped per symbol. Therefore, the ratio of HP to LP is 1: 1. On the other hand, in the QPSK method, since two bits are used per symbol, hierarchical transmission is not possible.

As described above, in order to transmit HP and LP together in the conventional DVB-T system, there is a difficulty in using only a limited mapping scheme such as 16QAM or 64QAM. In addition, the priority can not only be divided into two types, such as high or low, but also has a difficulty in that the user cannot adjust the ratio because the ratio of HP: LP is fixed to 1: 1 or 1: 2.

Meanwhile, with the start of the third generation mobile communication service, a discussion about the shape of the fourth generation mobile communication service has been spreading, and the necessity of standardization work for this purpose is emerging.

Low Density Parity Check (LDPC) codes offer better error correction than turbo codes used as the channel coding standard for third-generation mobile communication services and can be implemented with simpler hardware. It has

In consideration of these advantages, the Digital Video Broadcasting over Satellite 2 (DVB-S2) standard uses BCH and LDPC codes as a standard to improve the performance of DVB-S.

Therefore, there is a need for a method of performing hierarchical transmission using an LDPC code.

An object of the present invention is to provide an OFDM transmission apparatus and method for transmitting an OFDM symbol including symbols hierarchically coded according to at least one coding scheme including an LDPC coding scheme.

Another object of the present invention is to provide an OFDM receiver and a method for receiving an OFDM symbol including symbols hierarchically coded according to at least one coding scheme including an LDPC coding scheme.

According to an embodiment of the present invention for achieving the above object, an OFDM transmission apparatus for transmitting an OFDM symbol divided into a predetermined transmission unit, at least one stream including a low density parity check (LDPC) coding scheme to transmit An OFDM transmission processor configured to output symbols having a hierarchical priority by coding by using a coding scheme of the at least one LDPC block comprising the plurality of symbols coded with the LDPC code while configuring the OFDM symbol using the symbols A mux part arranged to have as many natural numbers therein and a transmitting part for converting and outputting OFDM symbols configured in the mux part.

Here, the OFDM transmission processor outputs a plurality of symbols having different priorities for each group, and the MUX unit configures the OFDM symbols such that symbols having the same priority among the plurality of symbols are arranged in OFDM symbol units. Meanwhile, when the number of symbols having the same priority is not a natural number unit of the size of one OFDM symbol, symbols of different priority may be arranged together in one OFDM symbol.

Alternatively, the OFDM transmission processor may output a plurality of symbols having different priorities for each group, and the MUX unit may be configured to output the LDPC block if the size of the LDPC block is not a natural number multiple of the OFDM symbol size. The remaining part in the OFDM symbol in which some symbols of P may be arranged may be arranged as symbols having a priority different from that of the LDPC coded symbol.

Meanwhile, the OFDM transmission processor may include a plurality of OFDM transmission processing modules that code and output the stream at different coding rates.

In this case, at least one of the plurality of OFDM transmission processing modules may include: a scrambler for randomizing the stream to be transmitted, an FEC encoder for forward error correction (FEC) coding the randomized stream, and a mapper for symbol mapping the coded stream. It may include.

The FEC encoder may include an outer coder for coding the randomized stream, an interleaver for interleaving the coded stream, and an inner coder for coding the interleaved stream with the LDPC code.

Alternatively, the OFDM transmission processor itself may include a scrambler for randomizing the stream to be transmitted, an FEC encoder for FEC coding the randomized stream, and a mapper for symbol mapping the coded stream. . In this case, the FEC encoder may include an outer coder for coding the randomized stream and an inner coder for coding the coded stream into the LDPC code.

In this case, the FEC encoder may further include an interleaver for interleaving the stream coded by the outer coder and providing the inner code.

Also preferably, the OFDM transmission apparatus may further include an OFDM symbol processing module for coding and outputting data bits having different priorities to be mapped to one symbol. In this case, the MUX unit may mux the symbols output from the OFDM transmission processor and the symbols output from the OFDM symbol processing module to configure the OFDM symbol.

On the other hand, in the above embodiments, the MUX unit, when the natural number of LDPC blocks are arranged in the one transmission unit, if the remaining region size in the one transmission unit is less than one LDPC block size, The remaining area can be left as a null area.

Meanwhile, according to an embodiment of the present invention, an OFDM transmission method for transmitting OFDM symbols divided into predetermined transmission units is performed by coding at least one coding scheme including a Low Density Parity Check (LDPC) coding scheme. Outputting symbols having a hierarchical priority, configuring the OFDM symbol such that an LDPC block including a plurality of LDPC coded symbols is arranged in natural numbers in the transmission unit, and configuring the configured OFDM symbol Converting and outputting.

In the configuring of the OFDM symbol, the OFDM symbol is configured such that symbols having the same priority among the plurality of coding symbols are arranged in OFDM symbol units, and the number of symbols having the same priority is the one. In the case of not being a natural number multiple of the OFDM symbol size, the symbols of different priorities may be arranged together in one OFDM symbol.

Alternatively, in the configuring of the OFDM symbol, when the size of the LDPC block is not a natural number multiple of the OFDM symbol size, the remaining part in the OFDM symbol in which some symbols constituting the LDPC block are arranged It may be arranged in symbols having a priority different from that of the LDPC coded symbol.

The outputting of the symbols having hierarchical priority may include randomizing the stream to be transmitted, an outer coding step of coding the randomized stream, an inner coding step of coding the stream into the LDPC code, and Symbol mapping the coded stream to output the plurality of symbols.

Alternatively, outputting the hierarchical symbols may include: randomizing the stream to be transmitted, outer coding the randomized stream, interleaving the coded stream, and interleaving the stream. The method may include an inner coding step of coding the LDPC code, and outputting the plurality of symbols by symbol mapping the coded stream.

Preferably, the method may further include mapping data bits having different priorities to one symbol and outputting the same.

In this case, the configuring of the OFDM symbol may configure the OFDM symbol by muxing the symbols to which the data bits having different priorities are mapped and the symbols having the hierarchical priority.

Also preferably, in the outputting of the symbols having the hierarchical priority, in the state where the natural number of LDPC blocks are arranged in the one transmission unit, the remaining region size of the one transmission unit is one LDPC. If less than the block size, the remaining region may be left as a null region.

On the other hand, the OFDM receiver according to an embodiment of the present invention, an OFDM symbol consisting of symbols having a hierarchical priority coded by at least one coding scheme including a low density parity check (LDPC) coding scheme And a receiving unit for receiving, a demux for demuxing the received OFDM symbol, and an OFDM receiving processing unit for processing the demuxed symbols in the demux, and restoring a data stream. In this case, the OFDM symbols may be arranged as many as natural numbers within one transmission unit in which the LDPC block divides the OFDM symbols.

Here, the demux unit may provide only the symbols belonging to a predetermined priority group among the symbols constituting the OFDM symbol to the OFDM receiving processor. Accordingly, the OFDM receiving processor may perform symbol coding of the provided symbols. The provided symbols may be decoded by a decoding method corresponding to the method.

Meanwhile, the OFDM receiving processor includes a plurality of OFDM receiving processing modules which receive the demuxed symbols and decode each of them by a decoding method corresponding to a symbol coding method of the provided symbols. In this case, the demux may demux the symbols constituting the OFDM symbol, classify the symbols having the same priority, and provide each classified symbol to the plurality of OFDM receiving processing modules, respectively.

Also preferably, the OFDM reception processing unit may further include: a demapper for demapping the symbols into data bits, an FEC decoder for decoding the demapped data bits in forward error correction (FEC), and inversely randomizing the FEC decoded data bits It may include a descrambler for restoring the data stream.

In this case, the FEC decoder may include an inner decoder for LDPC decoding the data bits, and an outer decoder for decoding the data bits.

Also preferably, the FEC decoder may further include a deinterleaver for deinterleaving the LDPC decoded data bits.

More preferably, the OFDM receiving apparatus may further include an OFDM received symbol processing module for reconstructing a data stream by processing an OFDM symbol in which data bits having different priorities are mapped to one symbol.

In this case, the demux unit provides symbols to which data bits having the same priority among the plurality of symbols are mapped to the OFDM receiving processor, and symbols to which data bits having different priorities are mapped to the OFDM receiving unit. It can be provided as a symbol processing module.

On the other hand, the OFDM reception method according to an embodiment of the present invention, the step of receiving an OFDM symbol consisting of symbols having a hierarchical priority coded by at least one coding scheme including a Low Density Parity Check (LDPC) coding scheme Demuxing the received OFDM symbols, and processing the demuxed symbols to recover a data stream. Here, the OFDM symbol may be a number of natural LDPC blocks arranged in the LDPC coding scheme are arranged within one transmission unit for separating the OFDM symbols.

Here, the demuxing may classify only symbols belonging to a predetermined priority group among symbols constituting the OFDM symbol. In this case, reconstructing the data stream by processing the demuxed symbols may decode the provided symbols in a decoding scheme corresponding to a symbol coding scheme of the classified symbols.

Alternatively, in the demuxing, the symbols constituting the OFDM symbol may be demuxed to classify symbols having the same priority. In this case, reconstructing the data stream by processing the demuxed symbols may receive the demuxed symbols and decode the decoding schemes corresponding to the symbol coding schemes of the provided symbols.

In addition, reconstructing the data stream by processing the demuxed symbols may include demapping the symbols into data bits, FEC decoding FEC decoding the demapped data bits, and the FEC decoded data bits. Derandomizing the data streams to restore the data stream.

Meanwhile, the FEC decoding step may include an inner decoding step of LDPC decoding the data bits and an outer decoding step of decoding the data bits.

Advantageously, said FEC decoding step may further comprise a deinterleaving step of deinterleaving said LDPC decoded data bits.

Further, preferably, the demuxing may classify symbols to which data bits having the same priority are mapped among the plurality of symbols, and symbols to which data bits having different priorities are mapped. . In this case, restoring a data stream by processing the demuxed symbols may include processing symbols mapped with data bits having the same priority and symbols mapped with data bits having different priorities. It is also possible to restore each data stream.

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

2 is a block diagram illustrating a configuration of an OFDM transmitting apparatus according to an embodiment of the present invention. According to FIG. 2, the present OFDM transmitter 100 includes an OFDM transmission processor 110, a mux unit 120, and a transmitter 130.

The OFDM transmission processor 110 symbol-codes and outputs a stream to be transmitted into at least one code (eg, a convolutional code, a turbo code, etc.) including a low density parity check (LDPC) code. The symbols output from the OFDM transmission processor 110 may have various types of priorities.

The priority may be set differently based on the importance of the data, the mapping scheme, the coding rate, the coding scheme, and the like. Specifically, when a mapping scheme, a coding scheme, or the like is differently applied to the streams to be transmitted, a high priority may be set for a symbol having a stronger coding degree.

Meanwhile, in order to code the streams using various coding schemes, the OFDM transmission processor 110 must be implemented in plural numbers. Such an embodiment will be described in detail with reference to FIG. 3.

The above priority is not simply divided into two types of high and low, and a middle priority (MP) may be added. Or, the priority may be set by dividing into even more diverse groups such as P1, P2, ... PN.

The mux unit 120 configures OFDM symbols by arranging the symbols output from the OFDM transmission processing unit 110. In this case, the mux unit 120 considers the order of priority of each symbol, and arranges appropriately in the transmission unit. Here, the transmission unit refers to a unit capable of distinguishing OFDM symbols transmitted by the OFDM transmission apparatus 100. Specifically, the frame may be a frame or a super frame, but other units may be applied.

The mux unit 120 arranges the symbols having the same priority to form one OFDM symbol. For example, assuming that there are two priority groups such as HP and LP, the mux unit 120 may configure an OFDM symbol composed only of HP and an OFDM symbol composed only of LP. In this case, the position of each OFDM symbol can be appropriately arranged to adjust the ratio of HP: LP.

Specifically, the MUX unit 120 configures OFDM symbols such that symbols having the same priority among the plurality of symbols are arranged in OFDM symbol units, and the number of symbols having the same priority is a natural number of one OFDM symbol size. In case of not a double unit, symbols having different priorities may be arranged together in one OFDM symbol.

Alternatively, when the size of the LDPC block is not a natural number unit of the OFDM symbol size, the mux unit 120 may have a different portion in the OFDM symbol in which some symbols of the LDPC block are disposed than the LDPC coded symbol. It may be filled with symbols having priority. That is, when the number of HP or LP symbols is less than one OFDM symbol unit, it is also possible to configure and use the OFDM symbols of the HP and LP symbols mixed form. The OFDM symbol configuration will be described in detail later.

On the other hand, the symbols coded by the LDPC code operates in units of blocks. Therefore, the mux unit 120 should arrange the symbols coded with the LDPC code together in block units. In this case, the LDPC block generally has a large size.

The size of the LDPC block coded by the LDPC coding scheme can be described through the following table.

LDPC code BCH uncoded block BCH coded block BCH t-error correction LDPC Coded Block 1/4 16008 16200 12 64800 1/3 21408 21600 12 64800 2/5 25728 25920 12 64800 1/2 32208 32400 12 64800 3/5 38688 38880 12 64800 2/3 43040 43200 10 64800 3/4 48408 48600 12 64800 4/5 51648 51840 12 64800 5/6 53840 54000 10 64800 8/9 57472 57600 8 64800 9/10 58192 58320 8 64800

Table 1 shows coding parameters used in DVB-S2.

According to Table 1, when the number of data bits before BCH external encoding is 16008, 16200 bits are output when BCH coding is performed, and when LDPC coding is performed at 1/4 coding rate, an LDPC block consisting of 64800 bits is output. Able to know. On the other hand, when mapping is performed using the 16QAM scheme, 6 bits are represented per symbol, so a total of 10800 symbols are required to represent one LDPC block.

Meanwhile, a total of 1704 symbols constitute one OFDM symbol in a 2K fast fourier transform (FFT) mode defined in the DVB-T standard, and a total of 6816 symbols constitute one OFDM symbol in an 8K FFT mode. Therefore, the size of one LDPC block becomes larger than one OFDM symbol. In this case, if the 8K FFT mode, approximately 1.6 OFDM symbols can represent one LDPC block.

Since the LDPC coded data operates in one block unit, if one LDPC block is transmitted divided into two or more transmission units, the LDPC block cannot be specified at the receiving side, which causes difficulty in decoding.

Accordingly, the mux unit 120 configures an OFDM symbol such that as many natural number n LDPC blocks are arranged in one transmission unit. That is, as described above, if 1.6 OFDM symbols can represent one LDPC block, a total of eight OFDM symbols can represent five LDPC blocks. If the transmission unit is a frame and one frame includes a total of 100 OFDM symbols, the equation of 8 * 12 + 4 = 100 is satisfied, so the mux unit 120 has only 5 * 12 = 60 LDPC blocks in one frame. Configure OFDM symbols to be placed within. The remaining four OFDM symbols place symbols of groups other than the data coded by the LDPC code or leave a null area at all.

For convenience of description, assuming that the size of one LDPC block is 2.5 times the size of one OFDM symbol, two LDPC blocks are arranged in five OFDM symbols. In this case, if the transmission unit is a frame and 64 OFDM symbols are arranged in one frame, the mux unit 120 may place 24 LDPC blocks in 60 of these OFDM symbols. Here, if the transmission unit is a super frame, four frames exist in one super frame, and each frame has 64 OFDM symbols, a total of 256 OFDM symbols exist. In this case, a total of 102 LDPC blocks may be arranged for 255 OFDM symbols.

When the OFDM symbol is configured in the MUX unit 120 as described above, the transmitter 130 converts the configured OFDM symbol and transmits the converted OFDM symbol through a wireless channel.

3 is a block diagram illustrating a configuration of an OFDM transmission apparatus according to another embodiment of the present invention. The OFDM transmission apparatus 200 of FIG. 3 is basically configured as the OFDM transmission processing unit 210, the mux unit 220, and the transmission unit 230, where the OFDM transmission processing unit 210 includes a plurality of OFDM transmission processing modules 211. , 212).

Each OFDM transmission processing module 211 and 212 receives a transport stream, codes each at a predetermined coding rate or coding scheme, and outputs symbols having different priorities. Specifically, each OFDM transmission processing module 211, 212 can be coded using an LDPC code, a convolution code, a turbo code, or the like. In this case, priority may be determined according to encoding performance of a coding scheme used.

Alternatively, when the OFDM transmission processing modules 211 and 212 use the same coding scheme (for example, LDPC coding scheme), coding using different coding rates may output symbols of different priorities. Can be. Although only two OFDM transmission processing modules 211 and 212 are illustrated in FIG. 3, three or more OFDM transmission processing modules may be used according to an embodiment. In this case, the priority group may also be classified into three or more types, not merely two types of high and low.

The first and second OFDM transmission processing modules 211 and 212 may be configured as shown in FIG.

According to FIG. 4, the OFDM transmission processing module may be implemented in a form including a scrambler 310, an FEC encoder 320, and a mapper 330. In addition, the FEC encoder 320 may include an outer coder 321, an interleaver 322, and an inner coder 323.

The scrambler 310 randomizes the stream to be transmitted.

The FEC encoder 300 error corrects the randomized stream. Specifically, the outer coder 321 externally encodes the randomized stream using a code such as Bose-Chaudhuri-Hocquenghem (BCH).

The interleaver 322 interleaves the externally encoded stream according to a predefined interleaving rule.

Next, an inner coder 323 performs internal encoding using an LDPC code.

In general, the LDPC code can detect most errors that are not corrected by a turbo code. The LDPC code not only has low decoding complexity, but also has excellent distance characteristics, so that an error floor does not appear. It is known to have the advantage of being possible.

The inner coder 323 for performing LDPC coding may perform LDPC coding in various ways such as a matrix multiplication method, a cyclic matrix method, a preprocessing method, a differential coding method, and the like. Among these, the preprocessing method proposed by Richardson and Urbanke is a technique that enables encoding using only the parity check matrix by reconstructing the parity check matrix without a generation matrix. The preprocessing method is applied to LDPC codes proposed by Samsung, Motorola and Nortel.

The mapper 330 symbol-maps the coded data output from the FEC encoder 320. In this case, various mapping rules such as QPSK, 16QAM, and 64QAM may be applied. Unlike the related art, the mapper 330 may use the QPSK scheme because hierarchical transmission is performed on a symbol basis.

On the other hand, the outer coder 321 may perform external encoding using a RS code (Reed-Solomon code) in addition to the BCH. The inner coder 323 may also perform internal encoding using a convolutional code, a turbo code, etc. in addition to the LDPC. That is, when one of the first and second OFDM transmission processing modules 211 and 212 codes using the LDPC coding method, the other is coded using a convolution code or a turbo code to output data having different priorities. Can be.

Alternatively, both the first and second OFDM transmission processing modules 211 and 212 may be implemented in an LDPC coding scheme so that the coding rates are different so that the priorities are different.

In FIG. 4, some of the components constituting the FEC encoder 320, for example, the interleaver 322, may be deleted according to an embodiment. In addition, an interleaver (not shown) may be further included at the rear end of the inner coder 323 to interleave LDPC coded data. In addition, the arrangement position of each component can also be changed.

4 may be applied to the OFDM transmission processor 110 of FIG. 2 as it is. In this case, the outer coder 321 performs an external call using the BCH, and the inner coder 323 performs an internal call using the LDPC. The mapper 330 may apply data while changing mapping rules such as QPSK, 16QAM, and 64QAM, and output data having different priorities.

3, the transmitter 230 includes an interleaver 231, an inverse discrete fourier transformer (IDFT) 232, a guard interval insertion unit 233, and an UP converter 234.

The interleaver 231 interleaves the OFDM symbols configured in the mux unit 220 in symbol units or subcarrier units.

The IDFT 232 performs a reverse discrete Fourier transform to convert an OFDM symbol in the frequency domain into an OFDM signal in the time domain. In this case, the IDFT 232 may be implemented as an inverse fast fourier transformer (IFFT).

The GI insertion unit 233 inserts a guard interval between symbols in order to reduce the influence of inter-symbol interference (ISI).

The UP converter 234 up-converts the signal output from the GI insertion unit 234 into a transmission band frequency signal and outputs it through a wireless channel.

Since the configuration of the transmitter 230 of FIG. 3 is well described in a predefined standard, the detailed description thereof will be omitted. The transmitter 230 of FIG. 3 may be applied to the transmitter 130 of FIG. 2 as it is.

5 is a block diagram illustrating a configuration of an OFDM transmission apparatus according to another embodiment of the present invention. According to FIG. 5, the OFDM transmitter 400 may include an OFDM transmitter 410, an OFDM symbol processor 420, a mux 430, and a transmitter 440.

Here, the OFDM transmission processing unit 410 may be implemented as an OFDM transmission processing module having the configuration of FIG. 4, or alternatively, may be implemented with a plurality of OFDM transmission processing modules having the configuration of FIG. 4. The configuration and operation of the MUX 430 and the transmitter 440 are the same as those described with reference to FIGS. 2 and 3, and thus, further description thereof will be omitted.

The OFDM symbol processing module 420 of FIG. 5 generates hierarchical data by coding input streams using a plurality of outer coders and a plurality of inner coders, respectively, and then maps them together so that data bits having different priorities are mapped. To be represented by a symbol. That is, as shown in Figure 1 by mapping in a mapping scheme such as 16QAM or 64QAM, a symbol is generated to include both HP and LP in one symbol.

The mux unit 430 may be symbols output from the OFDM transmission processor 410, that is, symbols representing data bits having one priority, and symbols output from the OFDM symbol processing module 420. The OFDM symbols may be configured by receiving symbols representing data bits having different priorities and muxing them together. That is, according to FIG. 5, the conventional hierarchical transmission scheme may be applied to the embodiments of FIGS. 2 and 3.

6 through 9 are schematic diagrams for describing an OFDM symbol configuration according to various embodiments of the present disclosure.

First, FIGS. 6 to 8 show an OFDM symbol pattern when a frame is used as a transmission unit. In FIG. 6, an HP symbol means an OFDM symbol composed of symbols having a relatively high priority, and an LP symbol refers to an OFDM symbol composed of symbols having a relatively low priority. HP and LP may be arranged alternately within one frame. Alternatively, an OFDM symbol composed of HP symbols may be placed first at a frame front end, followed by an OFDM symbol composed of LP symbols.

7 shows an OFDM symbol pattern when HP and LP are each LDPC coded. If the size of one HP LDPC block is 2.5 times the size of an OFDM symbol and the size of one LP LDPC block is 1.5 times the size of an OFDM symbol, some OFDM symbols, such as the third OFDM symbol, may be configured in the form of a mixture of HP and LP. . Accordingly, a total of four OFDM symbols are required to transmit one HP or LP LDPC block. For example, if one frame is composed of a total of 81 OFDM symbols, the OFDM transmitter transmits HP, LP LDPC blocks using 80 OFDM symbols, and the other OFDM symbol is left as a null region. As such, the OFDM symbol may be configured such that the LDPC block exists by a natural number of times in one transmission unit. Meanwhile, if only HP is LDPC coded in FIG. 7, the null region may be filled with LP.

8 is a schematic diagram showing another OFDM symbol pattern. According to FIG. 8, an HP / LP, which is an OFDM symbol in which HP and LP symbols are mixed, and an OFDM symbol composed of only LPs are alternately arranged in one frame, or after HP / LP is placed first, LPs are consecutive. It is shown in the form arranged.

9 is a schematic diagram illustrating a case where a super frame consisting of N frames is used as a transmission unit. In FIG. 9, assuming that the size of an LDPC block composed of HP symbols is 2N times one OFDM symbol, a portion of the LDPC block is arranged in two OFDM symbols for each of N frames, and within the entire super frame. It is possible to have as many as several natural LDPC blocks, that is, 2N.

In addition, if the LP is also coded by the LDPC coding scheme, the LP LDPC block may be disposed in the remaining region other than the HP LDPC block in each frame. In this case, the LP LDPC blocks are adjusted so that only m natural numbers are arranged. As a result, according to FIG. 9, the HP LDPC block exists by the natural number times in the super frame unit, and the LP LDPC block exists by the natural number times in the frame unit.

In general, HP data can be used in mobile transmission environments that require high reception performance, which can increase processing time. Therefore, when it is difficult to arrange the HP LDPC block by a natural number of times in one frame, it may be arranged in units of a super frame as shown in FIG.

Meanwhile, the HP / LP illustrated in FIGS. 7 and 8 may be configured by arranging HP symbols and LP symbols in various forms. 10 shows various examples of HP / LP patterns.

According to FIG. 10, HP / LP has a form in which an HP symbol is first placed in one OFDM symbol and then an LP symbol is disposed 10, a form in which LP symbols are arranged between HP symbols 20, LP, and HP. The symbol may be implemented in various forms, such as the form 30 in which the symbols are alternately arranged.

As described above, according to the present invention, the ratio between HP and LP can be adjusted in various forms, and in particular, the LDPC block to which LDPC coding is applied can be adjusted to exist as much as natural multiple times within one transmission unit. The decoding difficulty on the side can be prevented.

11 is a flowchart illustrating an OFDM transmission method according to an embodiment of the present invention. Referring to FIG. 11, first, a plurality of coding symbols are generated using at least one coding scheme including an LDPC coding scheme (S1110). Each coding symbol may be classified into two or more priority groups. The priority may be determined for each symbol by a mapping method, data importance, coding rate, coding method, and the like.

Next, OFDM symbols are formed by arranging each symbol (S1120). In this case, the LDPC block composed of symbols coded by the LDPC coding scheme among the generated symbols configures OFDM symbols such that as many as n natural numbers are disposed in one transmission unit.

Then, the converted OFDM symbol is converted and output through a wireless channel (S1130).

The OFDM transmission method illustrated in FIG. 11 may be implemented by the OFDM transmission apparatuses described with reference to FIGS. 2 to 5.

12 is a flowchart for describing in detail a step (S1110) of generating a symbol in the OFDM transmission method of FIG. 11. First, the data to be transmitted is randomized (S1210). As illustrated in FIG. 3, when the OFDM transmission processing unit 210 includes a plurality of OFDM transmission processing modules 211 and 212, different streams may be input to each OFDM transmission processing module 211 and 212. .

Then, the randomized data is BCH coded (S1220), and interleaved and then LDPC coded (S1230, S1240).

Then, symbol-mapping the LDPC coded data (S1250), and outputs a symbol.

The symbol generation step illustrated in FIGS. 11 and 12 may be performed by one OFDM symbol processor 110 as shown in FIG. 2. In this case, the mapping scheme may be sequentially applied differently in the mapping process S1250, and the priority of each symbol may be changed.

Alternatively, the symbol generation step illustrated in FIGS. 11 and 12 may be performed by at least one of the plurality of OFDM symbol processing modules 211 and 212 as illustrated in FIG. 3. In this case, the symbols generated by the OFDM symbol processing modules 211 and 212 have different priorities according to the applied coding rate, coding scheme, mapping scheme, and the like.

In addition, the symbol generation step illustrated in FIGS. 11 and 12 may be performed by the OFDM transmission processor 410 illustrated in FIG. 5.

13 is a block diagram illustrating an OFDM receiver according to an embodiment of the present invention. According to FIG. 13, the OFDM receiver includes a receiver 510, a demux 520, and an OFDM receiver 530.

Each of the OFDM transmitters described with reference to FIGS. 2 to 5 may be implemented as a broadcasting station for transmitting broadcast data in an OFDM scheme, while the OFDM receiver of FIG. 13 may be implemented as various broadcast receivers for receiving broadcast data. . Specifically, the present invention may be implemented in various devices such as a TV, a PDA, a mobile phone, and a set top box. Each OFDM transmitter described in FIGS. 2 to 5 transmits data having various priorities, while the OFDM receiver of FIG. 13 selectively implements only data having a priority corresponding to the OFDM receiver in FIG. 13. Can be restored In other words, when implemented with a device such as a mobile phone or PDA with high mobility, only HP data may be selectively restored, and when implemented with a device such as a TV or set-top box with low mobility, only LP data may be selectively restored. Can be. Even in this case, when a plurality of processing modules are provided, it is also possible to restore all data corresponding to various priority groups. This will be described later in the description with reference to FIG. 14.

The receiver 510 in FIG. 13 receives an OFDM symbol transmitted from an OFDM transmitter. Specifically, an OFDM symbol composed of a plurality of coding symbols divided into a plurality of priority groups and coded according to at least one coding scheme including a low density parity check (LDPC) code is received. The OFDM symbol received through the receiver 510 is configured by arranging as many as n natural number of LDPC blocks in one transmission unit, for example, a frame or a super frame.

The demux 520 demuxes the received OFDM symbols and provides only the OFDM symbols corresponding to the priority group corresponding to the present OFDM receiver to the OFDM receiving processor 530. Specifically, the demux unit 520 may detect an OFDM symbol at a location commonly known to the OFDM transmitter and provide the OFDM symbol to the OFDM receiving processor 530. In this case, the LDPC blocks are demuxed in blocks.

The OFDM reception processing unit 530 processes the symbols provided by the demux unit 520 to reconstruct the data stream. Specifically, decoding is performed in a decoding scheme corresponding to the symbol coding scheme applied to the provided symbols to restore the data stream.

14 is a block diagram illustrating an OFDM receiver according to another embodiment of the present invention. According to FIG. 14, the OFDM receiver includes a receiver 610, a demux 620, and an OFDM receiver 630, and the OFDM receiver 630 includes first and second OFDM receiver modules 631. , 632 may be implemented.

The receiver 610 may include an A / D converter 611, a down converter 612, a discrete fourier transformer 613, and an equalizer 614.

The A / D converter 611 analog-to-digital converts OFDM symbol data received through an antenna and outputs digital OFDM symbol data.

The down converter 612 down converts the symbol output from the A / D converter 611 into a baseband signal.

The DFT 613 performs a Fourier transform on the down-converted symbols and outputs OFDM symbols in the frequency domain. In this case, the DFT 613 may be implemented as a fast fourier transformer (FFT).

The equalizer 614 detects pilot symbols included in each OFDM symbol and performs channel equalization.

The configuration of the receiver 610 of FIG. 14 may be applied to the receiver 510 of FIG. 13 as it is. The configuration of the receiver 610 is described in detail in well-known standard documents, a detailed description thereof will be omitted.

The demux unit 620 demuxes the symbols constituting the OFDM symbol received by the receiving unit 610, classifies the symbols having the same priority, and classifies the classified symbols into the plurality of OFDM receiving processing modules 631. , 632). Specifically, when two types of priority exist, such as HP and LP, HP may provide the first OFDM reception processing module 631 and LP may provide the second OFDM reception processing module 632. .

Each OFDM reception processing module 631 and 632 receives the demuxed symbols, decodes each of them in a decoding scheme corresponding to the symbol coding scheme of the provided symbols, and restores the data stream. Each OFDM reception processing module 631 and 632 may have the same configuration as the OFDM reception processing unit 530 of FIG. 13.

In FIG. 14, only two OFDM reception processing modules 631 and 632 are illustrated, but three or more OFDM reception processing modules may be used according to an embodiment. For example, if an OFDM receiver is a type of apparatus capable of processing all kinds of data streams, demuxing symbols having various kinds of priorities such as HP, MP, and LP, and each corresponding OFDM receiver. The processing module may be used to decode and recover the data streams.

FIG. 15 illustrates a configuration that may be applied to the OFDM reception processing unit 530 of FIG. 13 or the OFDM reception processing modules 631 and 632 of FIG. 14.

According to FIG. 15, the OFDM reception processor includes a de-mapper 710, an FEC decoder 720, and a descrambler 730.

The demapper 710 demaps the provided symbols into data bits.

FEC decoder 720 performs forward error decoding on the demapped data bits. Specifically, the FEC decoder 720 includes an inner decoder 721, a deinterleaver 722, and an outer decoder 723.

The inner decoder 721 LDPC decodes the received data bits. The inner decoder 721 may be implemented in a serial structure, a fully parallel structure, an anti-parallel structure, and the like according to an embodiment. The configuration of the inner decoder 721 for performing LDPC decoding has been described in detail through existing published papers, and thus, a detailed description thereof will be omitted.

Deinterleaver 722 deinterleaves LDPC decoded data bits.

The outer decoder 723 decodes the deinterleaved data bits by BCH (Bose-Chaudhuri-Hocquenghem).

Although FIG. 15 illustrates the configuration of the FEC decoder 720 including the inner decoder 721, the deinterleaver 722, and the outer decoder 723, some components including the deinterleaver 722 in the FEC decoder 720 are illustrated. The elements may be omitted, and the arrangement order of each component may also be changed according to embodiments.

The descrambler 730 derandomizes the FEC decoded data to recover the data stream.

16 is a block diagram illustrating a configuration of an OFDM receiver according to another embodiment of the present invention. The OFDM receiver 800 of FIG. 16 further includes an OFDM reception symbol processing module 840 in addition to the receiver 810, the demux 820, and the OFDM reception processor 830.

The OFDM received symbol processing module 840 processes an OFDM symbol in which data bits having different priorities are mapped to one symbol to restore a data stream. That is, as in the OFDM transmission apparatus shown in FIG. 5, when data bits having different priorities are mapped and transmitted to each symbol, the OFDM reception symbol processing module 840 decodes the symbol.

In this case, the demux unit 820 may provide symbols to which data bits having the same priority among the plurality of symbols are mapped to the OFDM reception processor 830, and the data bits having different priorities may be converted into the same symbol. When mapped, each symbol is provided to the OFDM received symbol processing module 840.

Accordingly, the hierarchical transmission scheme supported by the conventional OFDM transceiver can also be used together.

The OFDM symbol received by the OFDM receiver described with reference to FIGS. 13 through 16 may have the OFDM symbol pattern described with reference to FIGS. 6 through 10.

17 is a flowchart illustrating an OFDM reception method according to an embodiment of the present invention. According to FIG. 17, when an OFDM symbol is received (S1710), the received symbols are demuxed (S1720). In this case, the received OFDM symbols are divided into frames, super frames, and various transmission units, and are transmitted. Within each transmission unit, an LDPC block includes as many natural numbers as 1, 2, 3, ... n. The symbols included in the received OFDM symbol may be prioritized by data importance, mapping method, coding rate, coding method, and the like. In the demuxing operation S1720, demuxing is performed based on the priority.

Accordingly, each demuxed symbol is decoded by an appropriate decoding method to recover a data stream (S1730).

18 is a flowchart illustrating a decoding process of the OFDM reception method of FIG. 17 in more detail. According to FIG. 18, the demuxed symbols are demapped (S1810) and converted into data bits. Accordingly, the decoded data bits are decoded by the LDPC method (S1820), and then operations such as deinterleaving and BCH outer decoding are sequentially performed (S1820 and S1830). Thereafter, the outer decoded data is derandomized to restore the data stream (S1850).

In the case of having a plurality of OFDM receiving processing modules, some OFDM receiving processing modules may restore the data stream by a turbo decoding method in addition to the decoding method of FIG. 18.

As described above, according to the present invention, it is possible to transmit and receive symbol code hierarchically using an LDPC coding scheme. In particular, only a natural number of LDPC blocks may be arranged in one transmission unit to facilitate decoding on the receiving side. In addition, the ratio between priority groups can be arbitrarily freely adjusted, and the types of priorities are not limited to simply high and low, but can be implemented in larger numbers.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention.

Claims (31)

In an OFDM transmitter for transmitting an OFDM symbol divided into a predetermined transmission unit, An OFDM transmission processor for coding the stream to be transmitted using at least one coding scheme including a Low Density Parity Check (LDPC) coding scheme and outputting symbols having a hierarchical priority; A mux unit configured to configure the OFDM symbol by using the symbols, and to arrange as many natural number of LDPC blocks as possible within the transmission unit, the LDPC block including a plurality of symbols coded by the LDPC code; And And a transmitter for converting and outputting an OFDM symbol configured in the mux unit. The method of claim 1, The OFDM transmission processing unit, Outputs a plurality of symbols having different priorities for each group, The mux part, The OFDM symbols are configured such that symbols having the same priority among the plurality of symbols are arranged in OFDM symbol units, and the number of symbols having the same priority is a natural number unit of the size of one OFDM symbol. If not, OFDM transmission apparatus, characterized in that to place the symbols of different priority together in one OFDM symbol. The method of claim 1, The OFDM transmission processing unit, Outputs a plurality of symbols having different priorities for each group, The mux part, If the size of the LDPC block is not a natural number unit of the OFDM symbol size, the remaining part in the OFDM symbol in which some symbols of the LDPC block are disposed has a priority different from that of the LDPC coded symbol. OFDM transmission apparatus, characterized in that arranged in. The method according to any one of claims 1 to 3, The OFDM transmission processing unit, And a plurality of OFDM transmission processing modules for coding and outputting the streams at different coding rates, respectively. 5. The method of claim 4, At least one of the plurality of OFDM transmission processing modules, A scrambler for randomizing the stream to be transmitted; An FEC encoder for forwarding error correction (FEC) coding the randomized stream; And And a mapper for symbol mapping the coded streams. 6. The method of claim 5, The FEC encoder, An outer coder for coding the randomized stream; An interleaver for interleaving the coded stream; And And an inner coder for coding the interleaved stream into the LDPC code. The method according to any one of claims 1 to 3, The OFDM transmission processing unit, A scrambler for randomizing the stream to be transmitted; An FEC encoder for forwarding error correction (FEC) coding the randomized stream; And A mapper for symbol mapping the coded stream; The FEC encoder, And an outer coder for coding the randomized stream and an inner coder for coding the coded stream with the LDPC code. 8. The method of claim 7, The FEC encoder, And an interleaver for interleaving the stream coded by the outer coder and providing the inner code. The method according to any one of claims 1 to 3, And an OFDM symbol processing module for coding and outputting data bits having different priorities to be mapped to one symbol. The mux unit muxes the symbols output from the OFDM transmission processor and the symbols output from the OFDM symbol processing module to configure the OFDM symbol. The method according to any one of claims 1 to 3, The mux part, And transmitting the remaining area as a null area when the size of the remaining area in the transmission unit is less than one LDPC block in the state where the natural number of LDPC blocks is arranged in the transmission unit. . In the OFDM transmission method for transmitting an OFDM symbol divided into a predetermined transmission unit, Coding symbols to be transmitted using at least one coding scheme including a Low Density Parity Check (LDPC) coding scheme to output symbols having a hierarchical priority; Constructing the OFDM symbol such that an LDPC block including a plurality of LDPC coded symbols is arranged in natural numbers in the transmission unit; And And converting and outputting the configured OFDM symbol. 12. The method of claim 11, Comprising the OFDM symbol, The OFDM symbols are configured such that symbols having the same priority among the plurality of coding symbols are arranged in OFDM symbol units, and the number of symbols having the same priority is a natural number unit of the size of one OFDM symbol. If not, the OFDM transmission method, characterized in that the symbols of different priorities are arranged together in one OFDM symbol. 12. The method of claim 11, Comprising the OFDM symbol, When the size of the LDPC block is not a natural number unit of the OFDM symbol size, the remaining part in the OFDM symbol in which some symbols constituting the LDPC block are arranged has a priority different from that of the LDPC coded symbol. OFDM transmission method, characterized in that arranged in symbols. The method according to any one of claims 11 to 13, The outputting the symbols having the hierarchical priority may include: Randomizing the stream to be transmitted; An outer coding step of coding the randomized stream; Inner coding the stream into the LDPC code; And Symbol mapping the coded stream and outputting the plurality of symbols. The method according to any one of claims 11 to 13, The outputting the symbols having the hierarchical priority may include: Randomizing the stream to be transmitted; An outer coding step of coding the randomized stream; Interleaving the coded stream; Inner coding the interleaved stream into the LDPC code; And Symbol mapping the coded stream and outputting the plurality of symbols. The method according to any one of claims 11 to 13, And mapping the data bits having different priorities to one symbol and outputting the same. The configuring of the OFDM symbol may include: configuring the OFDM symbol by muxing the symbols to which data bits having different priorities are mapped and the symbols having the hierarchical priority. The method according to any one of claims 11 to 13, The outputting the symbols having the hierarchical priority may include: And the remaining area of the transmission unit is less than one LDPC block size in the state where the natural number of LDPC blocks is arranged in the transmission unit, leaving the remaining area as a null area. . In an OFDM receiver, A receiver configured to code an stream to be transmitted by at least one coding scheme including a low density parity check (LDPC) coding scheme to receive an OFDM symbol composed of symbols having a hierarchical priority; A demux unit for demuxing the received OFDM symbol; And And an OFDM reception processor configured to recover the data stream by processing the demuxed symbols in the demux unit. The OFDM symbol is an OFDM receiver, characterized in that the LDPC block consisting of a plurality of symbols coded by the LDPC code is arranged by a natural number within one transmission unit for distinguishing the OFDM symbol. 19. The method of claim 18, The demux unit, Provides only the symbols belonging to a predetermined priority group among the symbols constituting the OFDM symbol to the OFDM receiving processor, The OFDM reception processing unit, And decoding the provided symbols in a decoding scheme corresponding to a symbol coding scheme of the provided symbols. 19. The method of claim 18, The OFDM reception processing unit, And a plurality of OFDM reception processing modules which receive the demuxed symbols and decode each of them in a decoding scheme corresponding to a symbol coding scheme of the provided symbols. The demux unit, Demuxing the symbols constituting the OFDM symbol, classifying symbols having the same priority, and providing each classified symbol to the plurality of OFDM receiving processing modules, respectively. 19. The method of claim 18, The OFDM reception processing unit, A demapper for demapping the symbols into data bits; An FEC decoder for decoding the de-mapped data bits into forward error correction (FEC); And And a descrambler for inversely randomizing the FEC decoded data bits to recover the data stream. 22. The method of claim 21, The FEC decoder, An inner decoder for LDPC decoding the data bits; And an outer decoder for decoding the data bits. 23. The method of claim 22, The FEC decoder, And a deinterleaver for deinterleaving the LDPC decoded data bits. 19. The method of claim 18, And an OFDM received symbol processing module for reconstructing a data stream by processing an OFDM symbol in which data bits having different priorities are mapped to one symbol. The demux unit provides symbols to which data bits having the same priority among the symbols constituting the OFDM symbol are mapped to the OFDM receiving processor, and symbols to which data bits having different priorities are mapped to the OFDM receiving unit. OFDM receiving apparatus characterized in that provided to the symbol processing module. In the OFDM reception method, Receiving an OFDM symbol composed of symbols having hierarchical priorities coded with at least one coding scheme including a Low Density Parity Check (LDPC) coding scheme; Demuxing the received OFDM symbols; And Processing the demuxed symbols to recover a data stream; The OFDM symbol is characterized in that the LDPC block coded by the LDPC coding scheme is arranged by a natural number within one transmission unit for distinguishing the OFDM symbol. 26. The method of claim 25, The demuxing step, Only the symbols belonging to the predetermined priority group among the symbols constituting the OFDM symbol are classified, Reconstructing the data stream by processing the demuxed symbols, And decoding the provided symbols in a decoding scheme corresponding to a symbol coding scheme of the classified symbols. 26. The method of claim 25, The demuxing step, Demuxing the symbols constituting the OFDM symbol, classifying symbols having the same priority, Reconstructing the data stream by processing the demuxed symbols, And receiving the demuxed symbols and decoding the demuxed symbols in a decoding scheme corresponding to the symbol coding scheme of the provided symbols. 26. The method of claim 25, Reconstructing the data stream by processing the demuxed symbols, Demapping the symbols into data bits; An FEC decoding step of FEC decoding the de-mapped data bits; And Derandomizing the FEC decoded data bits to recover the data stream. 29. The method of claim 28, The FEC decoding step, An inner decoding step of LDPC decoding the data bits; And An outer decoding step of decoding the data bits; OFDM receiving method comprising a. 30. The method of claim 29, The FEC decoding step, And deinterleaving the interleaved LDPC decoded data bits. 26. The method of claim 25, The demuxing step, Among the symbols constituting the OFDM symbol, the data bits having the same priority are mapped to the symbols, and the data bits having the different priority are mapped to the symbols. Reconstructing the data stream by processing the demuxed symbols, And reconstructing each data stream by processing symbols mapped with data bits having the same priority and symbols mapped with data bits having different priorities.

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