WO2008147156A1

WO2008147156A1 - Method of transmitting and receiving a signal and apparatus for transmitting and receiving a signal

Info

Publication number: WO2008147156A1
Application number: PCT/KR2008/003082
Authority: WO
Inventors: Woo Suk Ko; Sang Chul Moon
Original assignee: Lg Electronics Inc.
Priority date: 2007-06-01
Filing date: 2008-06-02
Publication date: 2008-12-04
Also published as: KR20080105883A

Abstract

A method of transmitting/receiving a signal and an apparatus for transmitting/receiving a signal are disclosed. A modulation frame is built by a pilot symbol interval including first pilot symbols and a data symbol interval including data symbols and second pilot symbols and a signal is transmitted/received. A transmission parameter signal of the modulation frame may include at least one of an index of the modulation frame corresponding to an error correction encoding frame, the number of error correction encoding blocks included in the error correction encoding frame, and the number of modulation frames corresponding to the error correction encoding frame. By this configuration, it is possible to efficiently build frames and realize frame synchronization by the receiving apparatus although a separate operation is not performed.

Description

METHOD OF TRANSMITTING AND RECEIVING A SIGNAL AND APPARATUS FOR TRANSMITTING AND RECEIVING A

SIGNAL

Technical Field

[1] The present invention relates to a method of transmitting/receiving a signal and an apparatus for transmitting/receiving a signal, and more particularly to a method of transmitting/receiving a signal and an apparatus for transmitting/receiving a signal, which are capable of increasing a data transfer rate. Background Art

[2] As a digital broadcasting technology has been developed, users have received a broadcasting signal including a high definition (HD) moving image and high-quality digital sound. With continuous development of a compression algorithm and high performance of hardware, a better environment will be provided to the users in the future. A digital television (DTV) system can receive a digital broadcasting signal and provide a variety of supplementary services to users as well as a video signal and an audio signal.

[3] As a method of transmitting the digital broadcasting signal, an orthogonal frequency division multiplexing (OFDM) method may be used. In the OFDM method, frames suitable for the OFDM method are built using input data, are carried in a plurality of subcarriers having an orthogonal relationship, and are multiplexed and transmitted. Disclosure of Invention Technical Problem

[4] However, in the existing transmission frame structure, since it is difficult to estimate a channel in a variable channel environment and the size of data to be transmitted is not matched with that of a transmission frame, it is impossible to efficiently build frames.

[5] An object of the present invention devised to solve the problem lies on a method of transmitting/receiving a signal and an apparatus for transmitting/receiving a signal, which are capable of improving channel estimation performance and efficiently build frames. Technical Solution

[6] The object of the present invention can be achieved by providing an apparatus for transmitting a signal, the apparatus including, an error correction encoder which error- correction-encodes data, a symbol mapper which maps the error-correction-encoded data to data symbols, a frame builder which builds a modulation frame in which a pilot symbol interval including first pilot symbols and a data symbol interval including the data symbols and second pilot symbols are periodically repeated, and a transmitter which modulates the built modulation frame according to an orthogonal frequency division multiplexing (OFDM) method and transmits the modulated frame, and a method of transmitting a signal in the apparatus.

[7] In another aspect of the present invention, provided herein is an apparatus for receiving a signal, the apparatus including a demodulator which demodulates the received signal according to an orthogonal frequency division multiplexing (OFDM) method and obtains a modulation frame in which a pilot symbol interval including first pilot symbols and a data symbol interval including data symbols and second pilot symbols are periodically repeated, a frame parser which parses the demodulated frame, a demapper which demaps the data symbols included in the frame, and an error correction decoder which error-correction-decodes the demapped data, and a method of receiving a signal in the apparatus.

[8] The error-correction-encoded data may be distinguished in an error correction encoding block unit and at least one error correction encoding block unit may build an error correction encoding frame.

[9] The modulation frame may include a transmission parameter signal, and the transmission parameter signal may include at least one of the number of error correction encoding blocks encoded according to one error correction encoding mode, the number of modulation frames corresponding to an error correction encoding frame including at least one of the error correction encoding blocks, and an index of the modulation frame included in the error correction encoding frame.

[10] The second pilot symbols may be arranged in units of 24 symbols in the modulation frame and the modulation frame may have six arrangement patterns of the second pilot symbols according to a time.

Advantageous Effects

[11] According to a method of transmitting/receiving a signal and an apparatus for transmitting/receiving a signal of the present invention, it is possible to improve channel estimation performance. In addition, it is possible to efficiently build frames and realize frame synchronization by a receiving apparatus although a separate operation is not performed. Brief Description of the Drawings

[12] FIG. 1 is a schematic block diagram showing an apparatus for transmitting a signal according to an embodiment of the present invention.

[13] FIG. 2 is a schematic block diagram showing an apparatus for receiving a signal according to an embodiment of the present invention. [14] FIG. 3 is a view showing the structure of a transmission frame according to an embodiment of the present invention. [15] FIG. 4 is a view showing the number of tracking pilots in a frame according to an embodiment of the present invention. [16] FIG. 5 is a view showing a frame including tracking pilots according to an embodiment of the present invention. [17] FIG. 6 is a view showing margins of the frame of FIG. 5 according to an embodiment of the present invention. [18] FIG. 7 is a view showing another frame including tracking pilots according to an embodiment of the present invention. [19] FIG. 8 is a view showing margins of the frame of FIG. 7 according to an embodiment of the present invention. [20] FIG. 9 is a view showing the number of symbols included in a low density parity check (LDPC) block according to an embodiment of the present invention. [21] FIG. 10 is a view showing the number of LDPC blocks included in an LDPC frame according to an embodiment of the present invention. [22] FIG. 11 is a view showing the number of OFDM blocks included in an LDPC frame according to an embodiment of the present invention. [23] FIG. 12 is a view showing the number of LDPC blocks included in an LDPC frame of another mode according to an embodiment of the present invention. [24] FIG. 13 is a view showing the number of OFDM blocks included in an LDPC frame of another mode according to an embodiment of the present invention. [25] FIG. 14 is a view showing the structure of an LDPC frame according to an embodiment of the present invention. [26] FIG. 15 is a view showing the structure of a transmission parameter signal (TPS) according to an embodiment of the present invention. [27] FIG. 16 is a view showing constellation information according to an embodiment of the present invention. [28] FIG. 17 is a view showing LDPC mode information according to an embodiment of the present invention. [29] FIG. 18 is a view showing the structure of an extended TPS according to an embodiment of the present invention. [30] FIG. 19 is a view showing OFDM block index information according to an embodiment of the present invention.

[31] FIG. 20 is a view showing the structure of a TPS including OFDM block index information according to an embodiment of the present invention. [32] FIG. 21 is a view showing LDPC block information according to an embodiment of the present invention.

[33] FIG. 22 is a view showing OFDM block information according to an embodiment of the present invention.

[34] FIG. 23 is a view showing the structure of a TPS including suggested information according to an embodiment of the present invention.

[35] FIG. 24 is a view showing the structure of an extended TPS including suggested information according to an embodiment of the present invention.

[36] FIG. 25 is a flowchart illustrating a method of transmitting/receiving data according to an embodiment of the present invention. Best Mode for Carrying Out the Invention

[37] A method of transmitting/receiving data according to the present invention and the operation of a frame structure will be described in detail with reference to the accompanying drawings.

[38] FIG. 1 is a schematic block diagram showing an apparatus for transmitting a signal according to an embodiment of the present invention. For example, the embodiment of the signal transmitting apparatus may be a signal transmitting system for transmitting video data such as a broadcasting signal, for example, a signal transmitting system according to a digital video broadcasting (DVB) system. The signal transmitting system according to the embodiment of the present invention now will be described with reference to FIG. 1.

[39] The embodiment of FIG. 1 includes an outer encoder 100, an inner encoder 110, a first interleaver 120, a symbol mapper 130, a linear pre-coder 140, a second interleaver 150, a frame builder 160, a modulator 170 and a transmitter 180.

[40] The outer encoder 100 and the inner encoder 110 encode respective input signals and output the encoded signals such that an error generated in transmitted data is detected and corrected by a receiving apparatus. That is, the outer encoder 100 and the inner encoder 110 configure a forward error correcting (FEC) encoder.

[41] The outer encoder 100 encodes the input data in order to prevent a transmission error of the input signal, that is, improve transmission performance of the input signal, and the inner encoder 110 encodes the signal to be transmitted again in order to prevent an error from occurring in the transmitted signal. The types of the encoders vary according to the coding methods used in the signal transmission system.

[42] For example, as the encoding method, a convolution coding method, a Reed-

Solomon (RS) coding method, a low density parity check (LDPC) coding method, a turbo coding method or the like may be used.

[43] The first interleaver 120 shuffles the data stream to random positions so as to become robust against a burst error which may occur in the data when the signal output from the inner encoder 110 is transmitted. For example, the first interleaver 120 may use a convolution interleaving method or a block interleaving method. The type of the first interleaver 120 may be changed according to the method used in the signal transmitting system.

[44] The symbol mapper 130 maps the data interleaved by the first interleaver 120 to symbols according to the transmitting method. As the mapping method, a quadrature amplitude modulation (QAM), a quadrature phase shift keying (QPSK), an amplitude phase shift keying (APSK), a pulse amplitude modulation (PAM) or an optimal constellation may be used.

[45] The linear pre-coder 140 disperses input symbol data into several pieces of output symbol data so as to decrease a probability that all information is lost due to fading when experiencing frequency- selective fading of a channel.

[46] The second interleaver 150 interleaves the symbol data output from the linear pre- coder 140 again such that the symbol data does not experience the same frequency- selective fading. The second interleaver 150 may use a convolution interleaving method or a block interleaving method.

[47] The frame builder 160 inserts a pilot signal into a data interval to build a frame such that the interleaved signal is modulated by an orthogonal frequency division multiplex (OFDM) method.

[48] The modulator 170 inserts a guard interval into the data output from the frame builder 160 and modulates the inserted data in a time domain such that the data is transmitted in a state of being carried in OFDM subcarriers. The transmitter 180 converts the digital signal having the guard interval and the data interval, which is output from the modulator 170, into an analog signal and transmits the converted analog signal.

[49] The signal transmitting apparatus of FIG. 1 is exemplary and an unnecessary block may be used according to the signal transmitting method. Alternatively, if a multi- input multi-output (MIMO) method, a multi-input single-output (MISO) method, or a single- input multi-output (SIMO) method is used, the symbol data output from the second deinterleaver 150 may be multi- input/output encoded and output to the frame builder 160.

[50] FIG. 2 is a schematic block diagram showing an apparatus for receiving a signal according to an embodiment of the present invention. The embodiment of FIG. 2 may be included in a DVB receiving apparatus.

[51] The embodiment of FIG. 2 includes a receiver 200, a synchronizer 210, a demodulator 220, a frame parser 230, a first deinterleaver 240, a linear pre-coding decoder 250, a symbol demapper 260, a second deinterleaver 270, an inner decoder 280 and an outer decoder 290. [52] The receiver 200 down-converts the frequency band of a received RF signal, converts the signal into a digital signal, and outputs the digital signal. The synchronizer 210 acquires synchronization of the received signal output from the receiver 200 in a frequency domain and a time domain and outputs the synchronization. The synchronizer 210 may use an offset result of the data output from the demodulator 220 in the frequency domain, for acquiring the synchronization of the signal in the frequency domain.

[53] The demodulator 220 demodulates the received data output from the synchronizer

210 and removes the guard interval. The demodulator 220 may convert the received data into the frequency domain and decode data values dispersed into the subcarriers to the values allocated to subcarriers. The frame parser 230 may output symbol data of the data symbol interval excluding the pilot symbol according the frame structure of the signal demodulated by the demodulator 220.

[54] The first deinterleaver 240 deinterleaves the data stream output from the frame parser

230 and restores the data into the sequence of the data before interleaving. The first deinterleaver 240 deinterleaves the data stream according to a method corresponding to the interleaving method of the second interleaver 150 shown in FIG. 1 and restores the sequence of the data stream.

[55] The linear pre-coding decoder 250 performs an inverse process of the process of dispersing the data in the signal transmitting apparatus and restores original data dispersed in the data input to the linear pre-coding decoder 250.

[56] The symbol demapper 260 may restore the symbol data restored by the linear pre- coding decoder 250 into a bitstream. As the demapping method of the symbol dempper 260, a method corresponding to the mapping method used by the symbol mapper 130 included in the signal transmitting apparatus shown in FIG. 1 is used.

[57] The second deinterleaver 270 performs the inverse process of the interleaving process of the bit data stream demapped by the symbol demapper 260. The second deinterleaver 270 performs the deinterleaving process corresponding to the first interleaver 120 of FIG. 1. The inner decoder 280 may decode the deinterleaved data and correct the error included in the data. The outer decoder 290 performs an error correction decoding process with respect to the bit data decoded by the inner decoder 280 and outputs the decoded bit data. The inner decoder 280 and the outer decoder 290 decode the data according to the decoding methods corresponding to the inner encoder 110 and the outer encoder 100 of FIG. 1.

[58] Similarly, the signal receiving apparatus of FIG. 2 is exemplary and an unnecessary block may be used according to the signal transmitting/receiving method. Alternatively, if encoded data is received according to the multi-input/output method, the symbol data output from the frame parser 230 may be multi-input/output decoded and output to the first deinterleaver 240.

[59] FIG. 3 is a view showing the structure of a transmission frame according to an embodiment of the present invention. The frame builder 160 of FIG. 1 builds and outputs transmission frame data having the structure shown in FIG. 3.

[60] The transmission frame of FIG. 3 includes a pilot symbol interval including pilot carrier information and a data symbol interval including data information and tracking pilot information. In FIG. 3, one frame includes M intervals, which are divided into M- 1 data symbol intervals and one pilot symbol interval which is used as a preamble. The frame having the above-described structure is repeated. The number of intervals included in one frame may vary according to implementation examples.

[61] In each symbol interval, carrier information is included by the number of subcarriers of the OFDM method. The pilot carrier information of the pilot symbol interval is composed of random data in order to decrease a peak to average power ratio (PAPR). The auto-correlation of the pilot carrier information has an impulse shape in a frequency domain.

[62] In the data symbol interval, tracking pilot information and data information to be transmitted are included. In the case where the frame having the structure shown in FIG. 3 is transmitted, the receiving apparatus performs channel estimation of the frame using the pilot carrier information located at the pilot symbol interval.

[63] However, in the case where a channel state is changed, it is difficult to accurately perform the channel estimation using only the pilot carrier information located at the pilot symbol interval by the receiving apparatus. Accordingly, the channel estimation of the interval including the tracking pilot can be accurately performed using the tracking pilot included in the data symbol interval in addition to the pilot carrier information located at the pilot symbol interval. The tracking pilot is inserted (or mapped) in a scattered pilot form.

[64] FIG. 4 is a view showing the number of tracking pilots in a frame according to an embodiment of the present invention. In the OFDM method, symbols may be transmitted in a state of being carried in subcarriers using Fourier Transform.

[65] FIG. 4 shows the number of available subcarriers, the number of tracking pilots and the number of pieces of symbol data according to a Fast Fourier Transform (FFT) mode in the case where the symbols are transmitted using the FFT. The number of available subcarriers denotes a value obtained by subtracting the number of subcarriers for a transmission parameter signal (TPS) from the total number of subcarriers, and the number of tracking pilots denotes the number of tracking pilots inserted into the data symbol interval. The number of pieces of symbol data denotes a value obtained by subtracting the number of tracking pilots from the number of available subcarriers, that is, the number of subcarriers which can transmit the symbol data. For example, in a 2k mode, among 1688 available subcarriers, 68 subcarriers are used for transmitting the tracking pilots and the remaining 1620 subcarriers are used for transmitting the symbol data.

[66] FIG. 5 is a view showing a frame including tracking pilots according to an embodiment of the present invention. FIG. 5 shows a state in which the tracking pilots are inserted into one data symbol interval according to the 2k mode among transmission modes of FIG. 4.

[67] In FIG. 5, among 1688 subcarriers excluding the subcarriers for the TPS from 1710

(0 to 1709 ) subcarriers, 68 subcarriers are used for transmitting the tracking pilot information and 1620 subcarriers are used for transmitting the symbol data.

[68] The tracking pilots have five patterns (pattern 0 to pattern 4) according to a time and are inserted in the scattered pilot form. The symbol distance between the tracking pilots of one pattern and another pattern is 5 and the symbol distance between the tracking pilots of one pattern is 25.

[69] FIG. 6 is a view showing margins of the frame of FIG. 5 according to an embodiment of the present invention. In the case where the tracking pilots are inserted in the form shown in FIG. 5, a left margin is a symbol distance of 4 and a right margin is a symbol distance of 5. In a region in which the margin is generated, since the channel estimation cannot be performed using the tracking pilots, the margin should be reduced in order to accurately perform the channel estimation.

[70] FIG. 6 shows the number of tracking pilots, the left margin and the right margin according to the FFT modes with respect to the frame shown in FIG. 5. For example, in the 2k mode, the left margin and the right margin are symbol distances of 4 and 5, respectively. In an 8k mode, the left margin and the right margin are symbol distances of 48 and 58, respectively. That is, it can be seen that, as the length of the symbol is increased according to the FFT mode, the margin region is increased.

[71] FIG. 7 is a view showing another frame including tracking pilots according to an embodiment of the present invention. FIG. 7 shows another state in which the tracking pilots are inserted into one data symbol interval according to the 2k mode among transmission modes of FIG. 4.

[72] In FIG. 7, among 1688 subcarriers excluding the subcarriers for the TPS from 1710

(0 to 1709 ) subcarriers, 71 subcarriers are used for transmitting the tracking pilot information and 1617 subcarriers are used for transmitting the symbol data.

[73] The tracking pilots have six patterns (pattern 0 to pattern 5) and are inserted in the scattered pilot form. The symbol distance between the tracking pilots of one pattern and another pattern is 4 and the symbol distance between the tracking pilots of one pattern is 24.

[74] FIG. 8 is a view showing margins of the frame of FIG. 7 according to an embodiment of the present invention. In the case where the tracking pilots are inserted in the form shown in FIG. 7, a left margin is a symbol distance of 2 and a right margin is a symbol distance of 2.

[75] FIG. 8 shows the number of tracking pilots, the left margin and the right margin according to the FFT modes with respect to the frame shown in FIG. 7. For example, in the modes (2k, 4k and 8k modes), the left margin and the right margin are symbol distances of 2 and 2, respectively. 71 tracking pilots, 142 tracking pilots and 284 tracking pilots are inserted in the 2k, 4k and 8k modes, respectively. That is, in the frame shown in FIG. 7, the number of tracking pilots is increased, but the margin region is reduced. Accordingly, the channel can be accurately estimated.

[76] FIG. 9 is a view showing the number of symbols included in a low density parity check (LDPC) block according to an embodiment of the present invention. In the case where an LDPC encoder is used as the inner encoder 110 of FIG. 1, a Bose- Chaudhuri-Hocqenghem (BCH) encoder may be used as the outer encoder 100 in order to prevent an error floor. If the LDPC encoder which can ignore the error floor is used, the BCH encoder may not be used. Alternatively, another encoder may be used as the outer encoder, instead of the BCH encoder.

[77] In the case where data is encoded and output according to the LDPC mode, since the size of the LDPC frame is different from that of the OFDM frame, the receiver needs to perform a separate process of synchronizing the LDPC frame. Accordingly, it is possible to readily realize the synchronization of the LDPC frame, by efficiently building the OFDM frame.

[78] FIG. 9 shows the number of symbols corresponding to one LDPC block according to a symbol mapping mode and the LDPC mode. The LDPC mode includes the cases where the length of the LDPC codeword is 64800 bits and 16200 bits and the symbol mapping mode includes 256-quadrature amplitude modulation (256QAM), 64QAM, 16QAM and 4QAM. That is, the data LDPC-encoded by the inner encoder 110 of FIG. 1 is mapped to the symbols by the symbol mapper 130 according to the 256QAM, 64QAM, 16QAM and 4QAM.

[79] In FIG. 9, in the case where the length of the LDPC codeword is 64800, the data is mapped to the symbols by the 256QAM, 8 bits per symbol can be transmitted and thus the number of symbols corresponding to one LDPC block is 64800/8=8100. If the data is mapped to the symbols by the 64QAM, 6 bits per symbol can be transmitted and thus the number of symbols corresponding to one LDPC block is 64800/6=10800.

[80] FIG. 10 is a view showing the number of LDPC blocks included in an LDPC frame according to an embodiment of the present invention. FIG. 10 shows the number of LDPC blocks necessary for building one LDPC frame according to the symbol mapping mode and the FFT mode if the length of the LDPC codeword is 64800. [81] If the data is mapped to the symbols by the 256QAM as shown in FIG. 10, four

LDPC blocks are included in the case of the 8k FFT mode and one LDPC block is included in the case of the 2k FFT mode.

[82] The symbols to which the LDPC codeword is mapped by symbol mapping according to the LDPC mode form one LDPC block, and the LDPC blocks are collected by the number shown in FIG. 10 so as to generate one LDPC frame.

[83] FIG. 11 is a view showing the number of OFDM blocks included in an LDPC frame according to an embodiment of the present invention. FIG. 11 shows the number of OFDM blocks necessary for building one LDPC frame according to the symbol mapping mode and the FFT mode if the length of the LDPC codeword is 64800.

[84] If the data is mapped to the symbols by the 256QAM as shown in FIG. 11, five

OFDM blocks are included in the case of the 8k FFT mode and five OFDM blocks are included in the case of the 2k FFT mode.

[85] FIG. 12 is a view showing the number of LDPC blocks included in an LDPC frame of another mode according to an embodiment of the present invention. FIG. 13 is a view showing the number of OFDM blocks included in an LDPC frame of another mode according to an embodiment of the present invention. FIGs. 12 and 13 show the case where the length of the LDPC codeword is 16200.

[86] The values of FIGs. 10 to 13 are obtained by calculation and, for convenience of description, the method of the calculating values will be omitted.

[87] FIG. 14 is a view showing the structure of an LDPC frame according to an embodiment of the present invention. FIG. 14 shows a relationship among an LDPC frame, LDPC blocks and OFDM blocks.

[88] In FIG. 14, the length of the LDPC codeword is 64800, the symbol mapping mode is

256QAM, and the FFT mode is 8k. One LDPC frame includes four LDPC blocks and corresponds to five OFDM blocks. Under the above-described condition, it can be seen that the number of LDPC blocks included in one LDPC frame is 4 in FIG. 10 and the number of OFDM blocks included in one LDPC frame is 5 in FIG. 11.

[89] In FIG. 14, it can be seen that the start point of the LDPC block is not matched with that of the OFDM block. Accordingly, the frame parser of the receiving apparatus requires a synchronization process of detecting the start point of the LDPC block in order to build the LDPC block from the received OFDM blocks again.

[90] For synchronization, a method using the TPS structure which is used in the DVM system or a method of transmitting an OFDM block index used for building one LDPC frame may be used. Hereinafter, these methods will be described.

[91] First, the method using the TPS structure used in the DVM system will be described.

FIG. 15 is a view showing the structure of a TPS according to an embodiment of the present invention. [92] The TPS is transmitted one bit by one bit in each of the OFDM blocks and one TPS frame includes total 68 bits. Accordingly, one TPS frame is transmitted via 68 OFDM blocks. FIG. 15 shows 68 bit numbers included in one TPS frame. The bit numbers are matched with OFDM block numbers for transmitting the bits.

[93] The information shown in the right column of FIG. 15 may be transmitted using the

68 bits included in one TPS frame. For example, initialization information may be transmitted using a 0 bit, and constellation information, that is, mapping method, may be transmitted using 25 and 26 bits. 38 and 39 bits may transmit transmission mode information.

[94] FIG. 16 is a view showing constellation information according to an embodiment of the present invention. Among the TPS bits of FIG. 15, the constellation information may be transmitted using the 25 and 26 bits. FIG. 16 shows the constellation information identified using the two bits.

[95] That is, symbol data mapped by the QPSK method is transmitted if the 25 and 26 bits are "00" (the 25 bit is "0" and the 26 bit is "0"), symbol data mapped by the 16QAM method is transmitted if the 25 and 26 bits are "01", symbol data mapped by a 64QAM is transmitted if the 25 and 26 bits are " 10", and symbol data mapped by the 256QAM method is transmitted if the 25^th and 26^th bits are "11".

[96] For synchronization for detecting the start point of the LDPC block by the receiving apparatus, LDPC mode information may be further included in the TPS in addition to the mapping information.

[97] FIG. 17 is a view showing LDPC mode information according to an embodiment of the present invention. The TPS mapping information shown in FIG. 15 may further include the LDPC mode information. For example, among the bit numbers 40 to 53, that is, the reserved bits, the LDPC mode information may be transmitted using a 40 bit and a 41^st bit. FIG. 17 shows the LDPC information identified using the two bits.

[98] That is, the used LDPC has a codeword length of 64800 if the 40^th and 41^st bits are

"00" and has a codeword length of 16200 if the 40^th and 41^st bits are "01". Since two modes of 64800 and 16200 are described in the above example, the two bits (40 and 41^st bits) are used. If the number of modes is increased, the number of bits may be increased according to the number of modes.

[99] FIG. 18 is a view showing the structure of an extended TPS according to an embodiment of the present invention. FIG. 18 shows the extended TPS structure including the information of FIGs. 16 and 17.

[100] The TPS of FIG. 18 may be extended for synchronization of the LDPC block and the length of one TPS frame may be 80 bits. That is, if the start point of the TPS frame is matched with that of the LDPC frame, the receiving apparatus does not need to perform a separate operation. [101] As can be seen from FIGs. 11 and 13, the least common multiple of the number of OFDM block necessary for building one LDPC frame is 20. Accordingly, if the length of the TPS frame is an integral multiple of 20, the synchronization between the TPS frame and the LDPC frame can be performed. Accordingly, FIG. 18 shows a TPS frame of 80 bits which are larger than 68 bits of the TPS frame shown in FIG. 15 and are an integral multiple of 20. The length of the TPS frame may be extended to 100 bits or 120 bits, but the 80-bit TPS frame is advantageous in that the length is small.

[102] At this time, if the BCH encoder is used as the outer encoder 100 of FIG. 1, a BCH error protection field becomes a protection field of the overall 80-bit TPS frame.

[103] The receiving apparatus can receive the TPS frame shown in FIG. 18 and obtain the constellation information, the LDPC mode information and the transmission mode information. Accordingly, the number of OFDM blocks and the number of LDPC blocks included in one LDPC frame can be checked using the constellation information, the LDPC mode information and the transmission mode information obtained from the TPS frame, and the information of FIGs. 10 to 13. In addition, the start point of the LDPC block can be checked using the number of blocks included in one LDPC frame.

[104] That is, the start point of the LDPC frame can be checked using the start point of the 80-bit extended TPS frame, and the start point of the LDPC block can be checked using the number of OFDM blocks and the number of LDPC blocks included in one LDPC frame.

[105] Second, the method of transmitting the OFDM block index used for building one LDPC frame will be described.

[106] FIG. 19 is a view showing OFDM block index information according to an embodiment of the present invention. Among the reserved bits of the TPS frame shown in FIG. 15, the OFDM block index information may be transmitted using 42° to 46 bits. FIG. 19 shows the OFDM block index information identified using the five bits.

[107] In the examples of FIGs. 11 and 13, one LDPC frame may include a maximum of 20 OFDM blocks. Accordingly, the TPS frame including the TPS frame OFDM block indexes for distinguishing between the 20 OFDM blocks is transmitted. The OFDM block indicated by the OFDM block index may become any block from a first OFDM block to a last OFDM block of the TPS frame. For example, the index may be an index indicating a first block among the 20 OFDM blocks or an index indicating a last block. This may vary according to implementation examples. The transmitting apparatus and the receiving apparatus transmit/receive the OFDM block index information according to the structure of the TPS frame so as to identify the OFDM blocks.

[108] In FIG. 19, the OFDM block index is 0 if the 42^nd to 46^th bits are "00000" and the

OFDM block index is 19 if the 42° to 46 bits are "10011". The remaining values are the reserved regions. Since the 20 blocks are identified in the above example, the five bits (the 42° to 46 bits) are used, but the number of bits used may be adjusted according to the maximum number of blocks.

[109] FIG. 20 is a view showing the structure of a TPS including OFDM block index information according to an embodiment of the present invention. The TPS frame includes the information described in FIGs. 16 and 17. In addition, the TPS frame may further include the OFDM block index information using the 42° to 46 bits.

[110] The receiving apparatus can receive the TPS frame shown in FIG. 20 and obtain the constellation information, the LDPC mode information, the transmission mode information, and the index information of a specific OFDM block included in one LDPC frame. Accordingly, the number of OFDM blocks and the number of LDPC blocks included in one LDPC frame can be obtained using the constellation mode, the LDPC mode information and the transmission mode information obtained from the TPS frame, and the information shown in FIGs. 10 to 13. In addition, the start point of the LDPC block can be obtained using the number of OFDM blocks and the number of LDPC blocks included in one LDPC frame and the index information of the specific OFDM block included in the LDPC frame.

[I l l] For example, it is assumed that the OFDM block index information indicates a third block of the OFDM blocks included in one LDPC frame. It can be seen that the number of OFDM blocks and the number of LDPC blocks included in one LDPC frame can be checked and the LDPC block and the OFDM block are started from the block which precedes the block indicated by the OFDM block index by two blocks.

[112] As described above, the receiving apparatus can check the start point of the LDPC block using the TPS frame information having the structure shown in FIG. 18 or FIG. 20.

[113] Hereinafter, a method of obtaining the start point of the LDPC block without using the information shown in FIGs. 10 to 13 will be described.

[114] FIG. 21 is a view showing LDPC block information according to an embodiment of the present invention. In FIG. 21, among the bits of the TPS frame shown in FIG. 15, information on the number of LDPC blocks included in one LDPC frame may be included in the bits of the reserved region.

[115] For example, the information on the number of LDPC blocks may be transmitted using 47 and 50 bits. As can be seen from FIGs. 10 and 12, the maximum number of LDPC blocks which may be included in one LDPC frame according to the LDPC modes is 16. In the embodiment of FIG. 21, the information on the number of LDPC blocks is transmitted using four bits.

[116] In FIG. 21 , the number of LDPC blocks included in one LDPC frame is 1 if the 47^th to 50^th bits are "0000" and is 16 if if the 47^th to 50^th bits are "0111". In Fig. 21, since the number of blocks used in FIGs. 10 and 12 is at most 8 (1, 2, 3, 4, 6, 8, 12 and 16), the values other than the eight values become the reserved region. Since a maximum of 16 blocks are distinguished in the above example, the four bits (the 47 to 50 bits) are used. However, the number of bits used may be adjusted according to the maximum number of blocks. The bit value corresponding to the number of blocks is exemplary and may vary according to implementation examples.

[117] FIG. 22 is a view showing OFDM block information according to an embodiment of the present invention. In FIG. 22, the information on the number of OFDM blocks included in one LDPC frame may be transmitted using the bits of the reserved region, which is not used, among the bits of the TPS frame of FIG. 15.

[118] For example, the information on the number of OFDM blocks is transmitted using 51 s^t to 53^r bits. As can be seen from FIGs. 11 and 13, the maximum number of OFDM blocks which may be included in one LDPC frame according to the LDPC modes is 20. However, three types of the number of blocks included are 5, 10 or 20. Accordingly, in FIG. 22, the information on the number of OFDM blocks is transmitted using 3 bits. Although the three bits are used in FIG. 22, only two bits may be used.

[119] In FIG. 22, the number of OFDM blocks included in one LDPC frame is 5 if the 51^st to 53^r bits are "000" and is 10 if the 51^st to 53^r bits are "001". The remaining values become the reserved regions. Although three types of the number of blocks should be distinguished and the three bits (the 51^st to 53^r bits) are used in the above example, the number of bits used may be adjusted according to the number of types of the number of blocks. The bit value corresponding to the number of blocks may vary according to implementation examples.

[120] FIG. 23 is a view showing the structure of a TPS including suggested information according to an embodiment of the present invention. FIG. 23 shows the structure including the information of FIGs. 21 and 22 in the structure of the TPS frame of FIG. 20. Accordingly, the receiving apparatus may receive the TPS frame having the structure shown in FIG. 23 and obtain the constellation information, the LDPC mode information, the transmission mode information, the index information of the specific OFDM block included in one LDPC frame, the number of LDPC blocks included in one LDPC frame, and the number of OFDM blocks included in the LDPC frame.

[121] The receiving apparatus can directly check the start point of the LDPC block using the information included in the received TPS frame without using the information of FIGs. 10 and 13.

[122] FIG. 24 is a view showing the structure of an extended TPS including suggested information according to an embodiment of the present invention. FIG. 24 shows the structure including the information of FIGs. 21 and 22 in the structure of the extended TPS frame of FIG. 18. Accordingly, the receiving apparatus may receive the TPS frame having the structure shown in FIG. 24 and obtain the constellation information, the LDPC mode information, the transmission mode information, the number of LDPC blocks included in one LDPC frame, and the number of OFDM blocks included in the LDPC frame. In FIG. 24, the index information of the specific OFDM block included in one LDPC frame may not be included.

[123] The receiving apparatus can directly check the start point of the LDPC block using the information included in the received TPS frame without using the information of FIGs. 10 and 13.

[124] FIG. 25 is a flowchart illustrating a method of transmitting/receiving data according to an embodiment of the present invention.

[125] The transmitting apparatus maps error-correction-encoded data to symbol data

(S2500). For example, the LDPC may be used as the error correction encoding method and the LDPC-encoded data includes at least one LDPC block in one LDPC frame.

[126] The mapped symbol data and a pilot are inserted such that a transmission frame is built according to the OFDM method (S2510). The transmission frame is composed of at least one block.

[127] At this time, the information on the OFDM block in which the start position of the error-correction-encoded data block is matched with the start position of the OFDM block is included in the transmission frame. Examples of information include the information described in FIGs. 16, 17, 19, 21 and 22. For example, if the signal transmitting/receiving system is the DVB system, the information may be included in the TPS frame.

[128] The transmitting apparatus transmits the frame including the information (S2520).

[129] The receiving apparatus receives the frame including the information, parses the received frame, and restores the symbol data (S2530). At this time, the OFDM symbol in which the error-correction-encoded data block is started can be checked using the information for allowing the receiver to check the OFDM block in which the start position of the error-correction-encoded data block is matched with the start position of the OFDM block.

[130] The restored symbol data is demapped according to a method corresponding to the mapping method of the transmitting and is error-correction-decoded (S2540).

[131] Although the LDPC frame is described in the above example, any signal transmitting/receiving method necessary for the synchronization of the frame is applicable.

[132] It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. Mode for the Invention

[133] The embodiments of the invention are described in the best mode of the invention. Industrial Applicability

[134] A method of transmitting/receiving a signal and an apparatus for transmitting/ receiving a signal of the present invention can be used in broadcast and communication fields.

Claims

[1] A method of transmitting a signal, the method comprising: error-correction-encoding data; mapping the error-correction-encoded data to data symbols; building a modulation frame in which a pilot symbol interval including first pilot symbols and a data symbol interval including the data symbols and second pilot symbols are periodically repeated; and modulating the built modulation frame according to an orthogonal frequency division multiplexing (OFDM) method and transmitting the modulated frame.

[2] The method according to claim 1, wherein the error-correction-encoded data is distinguished in an error correction encoding block unit and at least one error correction encoding block unit builds an error correction encoding frame.

[3] The method according to claim 1, wherein the modulation frame includes a transmission parameter signal, and the transmission parameter signal includes at least one of an index of the modulation frame corresponding to an error correction encoding frame, the number of error correction encoding blocks included in the error correction encoding frame, and the number of modulation frames corresponding to the error correction encoding frame.

[4] The method according to claim 1, wherein the second pilot symbols are arranged in units of 24 symbols in the modulation frame and the modulation frame has six arrangement patterns of the second pilot symbols according to a time.

[5] A method of receiving a signal, the method comprising: demodulating the received signal according to an orthogonal frequency division multiplexing (OFDM) method and obtaining a modulation frame in which a pilot symbol interval including first pilot symbols and a data symbol interval including data symbols and second pilot symbols are periodically repeated; parsing the demodulated frame; demapping the data symbols included in the frame; and error-correction-decoding the demapped data.

[6] The method according to claim 5, wherein the modulation frame includes a transmission parameter signal, and the transmission parameter signal includes at least one of the number of error correction encoding blocks encoded according to one error correction encoding mode, the number of modulation frames corresponding to an error correction encoding frame including at least one of the error correction encoding blocks, and an index of the modulation frame included in the error correction encoding frame.

[7] The method according to claim 5, wherein the second pilot symbols are arranged in units of 24 symbols in the modulation frame and the modulation frame has six arrangement patterns of the second pilot symbols according to a time.

[8] An apparatus for transmitting a signal, the apparatus comprising: an error correction encoder which error-correction-encodes data; a symbol mapper which maps the error-correction-encoded data to data symbols; a frame builder which builds a modulation frame in which a pilot symbol interval including first pilot symbols and a data symbol interval including the data symbols and second pilot symbols are periodically repeated; and a transmitter which modulates the built modulation frame according to an orthogonal frequency division multiplexing (OFDM) method and transmits the modulated frame.

[9] The apparatus according to claim 8, wherein the error-correction-encoded data is distinguished in an error correction encoding block unit and at least one error correction encoding block unit builds an error correction encoding frame.

[10] The apparatus according to claim 8, wherein the modulation frame includes a transmission parameter signal, and the transmission parameter signal includes at least one of the number of error correction encoding blocks encoded according to one error correction encoding mode, the number of modulation frames corresponding to an error correction encoding frame including at least one of the error correction encoding blocks, and an index of the modulation frame included in the error correction encoding frame.

[11] The apparatus according to claim 8, wherein the second pilot symbols are arranged in units of 24 symbols in the modulation frame and the modulation frame has six arrangement patterns of the second pilot symbols according to a time.

[12] An apparatus for receiving a signal, the apparatus comprising: a demodulator which demodulates the received signal according to an orthogonal frequency division multiplexing (OFDM) method and obtains a modulation frame in which a pilot symbol interval including first pilot symbols and a data symbol interval including data symbols and second pilot symbols are periodically repeated; a frame parser which parses the demodulated frame; a demapper which demaps the data symbols included in the frame; and an error correction decoder which error-correction-decodes the demapped data.

[13] The apparatus according to claim 12, wherein the modulation frame includes a transmission parameter signal, and the transmission parameter signal includes at least one of the number of error correction encoding blocks encoded according to one error correction encoding mode, the number of modulation frames cor- responding to an error correction encoding frame including at least one of the error correction encoding blocks, and an index of the modulation frame included in the error correction encoding frame.

[14] The apparatus according to claim 12, wherein the second pilot symbols are arranged in units of 24 symbols in the modulation frame and the modulation frame has six arrangement patterns of the second pilot symbols according to a time.