# Patent

## Title
Apparatus for transmitting and receiving a signal and method for transmitting and receiving a signal

## Abstract

A method for transmitting and receiving a signal and an apparatus for transmitting and receiving a signal are disclosed. The method includes receiving the signal from a first frequency band in a signal frame including at least one frequency band, demodulating the received signal by an orthogonal frequency division multiplexing (OFDM) method and parsing the signal frame, acquiring a symbol stream of a service stream from the at least one frequency band included in the parsed signal frame, demapping symbols included in the symbol stream and outputting the demapped symbols to sub streams, multiplexing the output sub streams and outputting one bit stream, and deinterleaving and error-correction-decoding the output bit stream.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a 371 U.S. national stage application of international application PCT/KR2008/005732, filed on Sep. 29, 2008, which claims priority to U.S. provisional applications 60/976,410, filed on Sep. 28, 2007, 60/978,725, filed on Oct. 9, 2007, and 60/980,799, filed on Oct. 18, 2007, the contents of which are hereby incorporated by reference herein in their entirety.


TECHNICAL FIELD
The present invention relates to a method for transmitting and receiving a signal and an apparatus for transmitting and receiving a signal, and more particularly, to a method for transmitting and receiving a signal and an apparatus for transmitting and receiving a signal, which are capable of improving data transmission efficiency.
BACKGROUND ART
As a digital broadcasting technology has been developed, users have received a high definition (HD) moving image. 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.
With the development of the digital broadcasting technology, a requirement for a service such as a video signal and an audio signal is increased and the size of data desired by a user or the number of broadcasting channels is gradually increased.
DISCLOSURE OF INVENTION
Technical Problem
Accordingly, the present invention is directed to a method for transmitting and receiving a signal and an apparatus for transmitting and receiving a signal that substantially obviate one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method for transmitting and receiving a signal and an apparatus for transmitting and receiving a signal, which are capable of improving data transmission efficiency.
Another object of the present invention is to provide a method for transmitting and receiving a signal and an apparatus for transmitting and receiving a signal, which are capable of improving error correction capability of bits configuring a service.
Technical Solution
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a method for transmitting a signal includes error-correction-coding a service stream and interleaving a bit stream in the error-correction-coded service stream, demultiplexing the interleaved bit stream and outputting sub streams by the demultiplexing, selecting bits included in the demultiplexed sub streams and mapping the selected bits to symbols, building a signal frame in which the mapped symbols are divided and arranged in at least one frequency band and temporally-divided slots of the at least one frequency band and modulating the signal frame by an orthogonal frequency division multiplexing (OFDM) method and transmitting the modulated signal.
In the demultiplexing of the interleaved bit stream, the demultiplexing may change the order of the selected bits. The order of the bits mapped to the symbols may be changed according to a code rate of the error correction coding or/and a symbol mapping method.
In another aspect of the present invention, a method for receiving a signal includes receiving the signal from a first frequency band in a signal frame including at least one frequency band, demodulating the received signal by an orthogonal frequency division multiplexing (OFDM) method and parsing the signal frame, acquiring a symbol stream of a service stream from the at least one frequency band included in the parsed signal frame, demapping symbols included in the symbol stream and outputting demapped symbols to sub streams, multiplexing the output sub streams and outputting one bit stream by using the multiplexed sub streams and deinterleaving and error-correction-decoding the output bit stream.
The outputting of the bit stream may include selecting bits included in the sub streams and outputting one bit stream. The order of selecting the bits may be changed according to a code rate of error correction coding corresponding to the error correction decoding or/and a symbol demapping method.
In another aspect of the present invention, an apparatus for transmitting a signal includes an error-correction coder for error-correction-coding a service stream, a bit interleaver interleaving for a bit stream in the error-correction-coded service stream, a symbol mapper for demultiplexing interleaved bit stream, for outputting sub streams by the demultiplexing, for selecting bits included in the demultiplexed sub streams, and for mapping the selected bits to symbols, a signal frame builder for building a signal frame in which the mapped symbols are divided and arranged in at least one frequency band and temporally-divided slots of the at least one frequency band, a modulator for modulating the signal frame by an orthogonal frequency division multiplexing (OFDM) method and a transmitter for transmitting the modulated signal.
The bit interleaver is arranged to interleave the bit stream by storing and reading the error-correction-coded bits in and from a memory in different directions.
The symbol mapper may include a demultiplexer for demultiplexing the interleaved bit stream to the sub streams according to a code rate of the error correction coding or and a symbol mapping method and a mapper for mapping the demultiplexed sub streams to the symbols.
In another aspect of the present invention, an apparatus for receiving a signal includes a receiver receiving the signal from a first frequency band in a signal frame including a receiver for receiving the signal from a first frequency band in a signal frame including at least one frequency band, a demodulator for demodulating the received signal by an orthogonal frequency division multiplexing (OFDM) method, a signal frame parser for parsing the signal frame from the demodulated signal and for outputting a symbol stream of a service stream from the at least one frequency band, a symbol demapper for demapping symbols included in the symbol stream, for outputting the demapped symbols to sub streams, for multiplexing the output sub streams, and outputting one bit stream by using the multiplexed sub streams, a bit deinterleaver for deinterleaving the output bit stream and an error correction decoder for error-correction-decoding the deinterleaved bit stream.
The symbol demapper may include a demapper for demapping the symbols to the sub streams and a multiplexer for multiplexing the sub streams according to a code rate of error correction coding corresponding to the error correction decoding or/and a symbol demapping method.
Advantageous Effects
According to the apparatus for transmitting and receiving the signal and the method for transmitting and receiving the signal of the present invention, it is possible to readily detect and restore the transmitted signal. In addition, it is possible to improve the signal transmission/reception performance of the transmitting/receiving system.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view showing a signal frame for transmitting a service;
FIG. 2 is a view showing the structure of a first pilot signal P1 of the signal frame;
FIG. 3 is a view showing a signaling window;
FIG. 4 is a schematic view showing an embodiment of an apparatus for transmitting a signal;
FIG. 5 is a view showing an example of an input processor 110;
FIG. 6 is a view showing an embodiment of a coding and modulation unit;
FIG. 7 is a view showing an embodiment of a frame builder;
FIG. 8 is a view showing a first example of a ratio of symbols when mappers 131a and 131b perform hybrid symbol mapping;
FIG. 9 is a view showing a second example of a ratio of symbols when the mappers 131a and 131b perform hybrid symbol mapping;
FIG. 10 is a view showing an embodiment of each of the symbol mappers 131a and 131b shown in FIG. 7;
FIG. 11 is a view showing another embodiment of the symbol mapper;
FIG. 12 is a view showing the concept of interleaving of bits by bit interleavers 1312a and 1312b of FIG. 11;
FIG. 13 is a view showing a first example of the number of rows and columns of memories of the bit interleavers 1312a and 1312b according to the types of symbol mappers 1315a and 1315b; 
FIG. 14 is a view showing a second example of the number of rows and columns of the memories of the bit interleavers 1312a and 1312b according to the types of the symbol mappers 1315a and 1315b; 
FIG. 15 is a view showing the concept of demultiplexing of input bits of demuxs 1313a and 1313b; 
FIG. 16 is a view showing an embodiment of demultiplexing an input stream by the demux
FIG. 17 is a view showing an example of a demultiplexing type according to a symbol mapping method;
FIG. 18 is a view showing an embodiment of demultiplexing an input bit stream according to a demultiplexing type;
FIG. 19 is a view showing a demultiplexing type which is determined according to a code rate of an error correction coding and a symbol mapping method;
FIG. 20 is a view showing an example of expressing the demultiplexing method by an equation;
FIG. 21 is a view showing an example of mapping a symbol by a symbol mapper;
FIG. 22 is a view showing an example of a multi-path signal coder;
FIG. 23 is a view showing an embodiment of a modulator;
FIG. 24 is a view showing an embodiment of an analog processor 160;
FIG. 25 is a view showing an embodiment of a signal receiving apparatus capable of receiving a signal frame;
FIG. 26 is a view showing an embodiment of a signal receiver;
FIG. 27 is a view showing an embodiment of a demodulator;
FIG. 28 is a view showing a multi-path signal decoder;
FIG. 29 is a view showing an embodiment of a frame parser;
FIG. 30 is a view showing an embodiment of each of symbol demappers 247a and 247p; 
FIG. 31 is a view showing another embodiment of each of the symbol demappers 247a and 247p; 
FIG. 32 is a view showing an embodiment of multiplexing a demultiplexed sub stream;
FIG. 33 is a view showing an example of a decoding and demodulation unit
FIG. 34 is a view showing an embodiment of an output processor;
FIG. 35 is a view showing another embodiment of a signal transmitting apparatus for transmitting a signal frame;
FIG. 36 is a view showing another embodiment of a signal receiving apparatus for receiving a signal frame;
FIG. 37 is a view showing an embodiment of a method for transmitting a signal; and
FIG. 38 is a view showing an embodiment of a method for receiving a signal.



BEST MODE FOR CARRYING OUT THE INVENTION
In the following description, the term “service” is indicative of either broadcast contents which can be transmitted/received by the signal transmission/reception-apparatus, or content provision.
Prior to the description of an apparatus for transmitting and receiving a signal according to an embodiment of the present invention, a signal frame which is transmitted and received by the apparatus for transmitting and receiving the signal according to the embodiment of the present invention will be described.
FIG. 1 shows a signal frame for transmitting a service according to the present invention.
The signal frame shown in FIG. 1 shows an exemplary signal frame for transmitting a broadcast service including audio/video (A/V) streams. In this case, a single service is multiplexed in time- and frequency-channels, and the multiplexed service is transmitted. The above-mentioned signal transmission scheme is called a time-frequency slicing (TFS) scheme. Compared with the case in which a single service is transmitted to only one radio frequency (RF) band, the signal transmission apparatus according to the present invention transmits the signal service via at least one RF band (possibly several RF bands), such that it can acquire a statistical multiplexing gain capable of transmitting many more services. The signal transmission/reception apparatus transmits/receives a single service over several RF channels, such that it can acquire a frequency diversity gain.
First to third services (Services 1 ̃3) are transmitted to four RF bands (RF1 ̃RF4). However, this number of RF bands and this number of services have been disclosed for only illustrative purposes, such that other numbers may also be used as necessary. Two reference signals (i.e., a first pilot signal (P1) and a second pilot signal (P2)) are located at the beginning part of the signal frame. For example, in the case of the RF1 band, the first pilot signal (P1) and the second pilot signal (P2) are located at the beginning part of the signal frame. The RF1 band includes three slots associated with the Service 1, two slots associated with the Service 2, and a single slot associated with the Service 3. Slots associated with other services may also be located in other slots (Slots 4 ̃17) located after the single slot associated with the Service 3.
The RF2 band includes a first pilot signal (P1), a second pilot signal (P2), and other slots 13 ̃17. In addition, the RF2 band includes three slots associated with the Service 1, two slots associated with the Service 2, and a single slot associated with the Service 3.
The Services 1 ̃3 are multiplexed, and are then transmitted to the RF3 and RF4 bands according to the time-frequency slicing (TFS) scheme. The modulation scheme for signal transmission may be based on an orthogonal frequency division multiplexing (OFDM) scheme.
In the signal frame, individual services are shifted to the RF bands (in the case that there are a plurality of the RF bands in the signal frame) and a time axis.
If signal frames equal to the above signal frame are successively arranged in time, a super-frame can be composed of several signal frames. A future extension frame may also be located among the several signal frames. If the future extension frame is located among the several signal frames, the super-frame may be terminated at the future extension frame.
FIG. 2 shows a first pilot signal (P1) contained in the signal frame of FIG. 1 according to the present invention.
The first pilot signal P1 and the second pilot signal P2 are located at the beginning part of the signal frame. The first pilot signal P1 is modulated by a 2K FFT mode, and may be transmitted simultaneously while including a 1⁄4 guard interval. In FIG. 2, a band of 7.61 Mhz of the first pilot signal P1 includes a band of 6.82992 Mhz. The first pilot signal uses 256 carriers from among 1705 active carriers. A single active carrier is used for every 6 carriers on average. Data-carrier intervals may be irregularly arranged in the order of 3, 6, and 9. In FIG. 2, a solid line indicates the location of a used carrier, a thin dotted line indicates the location of an unused carrier, and a chain line indicates a center location of the unused carrier. In the first pilot signal, the used carrier can be symbol-mapped by a binary phase shift keying (BPSK), and a pseudo-random bit sequence (PRBS) can be modulated. The size of a FFT used for the second pilot signal can be indicated by several PRBSs.
The signal reception apparatus detects a structure of a pilot signal, and recognizes a time-frequency slicing (TFS) using the detected structure. The signal reception apparatus acquires the FFT size of the second pilot signal, compensates for a coarse frequency offset of a reception signal, and acquires time synchronization.
In the first pilot signal, a signal transmission type and a transmission parameter may be set.
The second pilot signal P2 may be transmitted with a FFT size and a guard interval equal to those of the data symbol. In the second pilot signal, a single carrier is used as a pilot carrier at intervals of three carriers. The signal reception apparatus compensates for a fine frequency synchronization offset using the second pilot signal, and performs fine time synchronization. The second pilot signal transmits information of a first layer (L1) from among Open Systems Interconnection (OSI) layers. For example, the second pilot signal may include a physical parameter and frame construction information. The second pilot signal transmits a parameter value by which a receiver can access a Physical Layer Pipe (PLP) service stream.
L1 (Layer 1) information contained in the second pilot signal P2 is as follows.
The Layer-1 (L1) information includes a length indicator indicating the length of data including the L1 information, such that it can easily use the signaling channels of Layers 1 and 2 (L1 and L2). The Layer-1 (L1) information includes a frequency indicator, a guard-interval length, a maximum number of FEC (Forward Error Correction) blocks for each frame in association with individual physical channels, and the number of actual FEC blocks to be contained in the FEC block buffer associated with a current/previous frame in each physical channel. In this case, the frequency indicator indicates frequency information corresponding to the RF channel.
The Layer-1 (L1) information may include a variety of information in association with individual slots. For example, the Layer-1 (L1) information includes the number of frames associated with a service, a start address of a slot having the accuracy of an OFDM carrier contained in an OFDM symbol, a length of the slot, slots corresponding to the OFDM carrier, the number of bits padded in the last OFDM carrier, service modulation information, service mode rate information, and Multi-Input-Multi-Output (MIMO) scheme information.
The Layer-1 (L1) information may include a cell ID, a flag for service like notification message service (e.g., an emergency message), the number of current frames, and the number of additional bits for future use. In this case, the cell ID indicates a broadcast area transmitted by a broadcast transmitter
The second pilot signal P2 is adapted to perform channel estimation for decoding a symbol contained in the P2 signal. The second pilot signal P2 can be used as an initial value for channel estimation for the next data symbol. The second pilot signal P2 may also transmit Layer-2 (L2) information. For example, the second pilot signal is able to describe information associated with the transmission service in Layer-2 (L2) information. The signal transmission apparatus decodes the second pilot signal, such that it can acquire service information contained in the time-frequency slicing (TFS) frame and can effectively perform the channel scanning. Meanwhile, this Layer-2 (L2) information may be included in a specific PLP of the TFS frame. According to another instance, L2 information can be included in a specific PLP, and the service description information also can be transmitted in the specific PLP.
For example, the second pilot signal may include two OFDM symbols of the 8 k FFT mode. Generally, the second pilot signal may be any one of a single OFDM symbol of the 32K FFT mode, a single OFDM symbol of the 16 k FFT mode, two OFDM symbols of the 8 k FFT mode, four OFDM symbols of the 4 k FFT mode, and eight OFDM symbols of the 2 k FFT mode.
In other words, a single OFDM symbol having the size of a large FFT or several OFDM symbols, each of which has the size of a small FFT, may be contained in the second pilot signal P2, such that capacity capable of being transmitted to the pilot can be maintained.
If information to be transmitted to the second pilot signal exceeds capacity of the OFDM symbol of the second pilot signal, OFDM symbols after the second pilot signal can be further used. L1 (Layer1) and L2 (Layer2) information contained in the second pilot signal is error-correction-coded and is then interleaved, such that data recovery is carried out although an impulse noise occurs.
As described the above, L2 information can also be included in a specific PLP conveying the service description information.
FIG. 3 shows a signaling window according to the present invention. The time-frequency slicing (TFS) frame shows an offset concept of the signaling information. Layer-1 (L1) information contained in the second pilot signal includes frame construction information and physical layer information required by the signal reception apparatus decoding the data symbol. Therefore, if information of the following data symbols located after the second pilot signal, is contained in the second pilot signal, and the resultant second pilot signal is transmitted, the signal reception apparatus may be unable to immediately decode the above following data symbols due to a decoding time of the second pilot signal.
Therefore, as shown in FIG. 3, the L1 information contained in the second pilot signal (P2) includes information of a single time-frequency slicing (TFS) frame size, and includes information contained in the signaling window at a location spaced apart from the second pilot signal by the signaling window offset.
In the meantime, in order to perform channel estimation of a data symbol constructing the service, the data symbol may include a scatter pilot and a continual pilot.
The signal transmission/reception system capable of transmitting/receiving signal frames shown in FIGS. 1 ̃3 will hereinafter be described. Individual services can be transmitted and received over several RF channels. A path for transmitting each of the services or a stream transmitted via this path is called a PLP. The PLP may be distributed among the timely-divided slots in several RF channels or a single RF band. This signal frame can convey the timely-divided PLP in at least one RF channel. In other word, a single PLP can be transferred through at least one RF channel with timely-divided regions. Hereinafter the signal transmission/reception systems transmitting/receiving a signal frame via at least one RF band will be disclosed.
FIG. 4 is a block diagram illustrating an apparatus for transmitting a signal according to one embodiment of the present invention. Referring to FIG. 4, the signal transmission apparatus includes an input processor 110, a coding and modulation unit 120, a frame builder 130, a MIMO/MISO encoder 140, a plurality of modulators (150a, . . . , 150r) of the MIMO/MISO encoder 140, and a plurality of analog processors (160a, . . . , 160r).
The input processor 110 receives streams equipped with several services, generates P number of baseband frames (P is a natural number) which includes modulation- and coding-information corresponding to transmission paths of the individual services, and outputs the P number of baseband frames.
The coding and modulation unit 120 receives baseband frames from the input processor 110, performs the channel coding and interleaving on each of the baseband frames, and outputs the channel coding and interleaving result.
The frame builder 130 forms frames which transmit baseband frames contained in P number of PLPs to R number of RF channels (where R is a natural number), splits the formed frames, and outputs the split frames to paths corresponding to the R number of RF channels. Several services may be multiplexed in a single RF channel in time. The signal frames generated from the frame builder 140 may include a time-frequency slicing (TFS) structure in which the service is multiplexed in time- and frequency-domains.
The MIMO/MISO encoder 140 encodes signals to be transmitted to the R number of RF channels, and outputs the coded signals to paths corresponding to A number of antennas (where A is a natural number). The MIMO/MISO encoder 140 outputs the coded signal in which a single to be transmitted to a single RF channel is encoded to the A number of antennas, such that a signal is transmitted/received to/from a MIMO (Multi-Input-Multi-Output) or MISO (Multi-Input-Single-Output) structure.
The modulators (150a, . . . , 150r) modulate frequency-domain signals entered via the path corresponding to each RF channel into time-domain signals. The modulators (150a, . . . , 150r) modulate the input signals according to an orthogonal frequency division multiplexing (OFDM) scheme, and outputs the modulated signals.
The analog processors (160a, . . . , 160r) converts the input signals into RF signals, such that the RF signals can be outputted to the RF channels.
The signal transmission apparatus according to this embodiment may include a predetermined number of modulators (150a, . . . 150r) corresponding to the number of RF channels and a predetermined number of analog processors (160a, . . . , 160r) corresponding to the number of RF channels. However, in the case of using the MIMO scheme, the number of analog processors must be equal to the product of R (i.e., the number of RF channels) and A (i.e., the number of antennas).
FIG. 5 is a block diagram illustrating an input processor 110 according to the present invention. Referring to FIG. 5, the input processor 110 includes the first stream multiplexer 111a, the first service splitter 113a, and a plurality of first baseband (BB) frame builders (115a, . . . , 115m). The input processor 110 includes a second stream multiplexer 111b, a second service splitter 113b, and a plurality of second baseband (BB) frame builders (115n, . . . , 115p).
For example, the first stream multiplexer 111a receives several MPEG-2 transport streams (TSs), multiplexes the received MPEG-2 TS streams, and outputs the multiplexed MPEG-2 TS streams. The first service splitter 113a receives the multiplexed streams, splits the input streams of individual services, and outputs the split streams. As described above, provided that the service transmitted via a physical-channel path is called a PLP, the first service splitter 113a splits the service to be transmitted to each PLP, and outputs the split service.
The first BB frame builders (115a, . . . , 115m) build data contained in a service to be transmitted to each PLP in the form of a specific frame, and output the specific-frame-formatted data. The first BB frame builders (115a, 115m) build a frame including a header and payload equipped with service data. The header of each frame may include mode information based on the modulation and encoding of the service data, and a counter value based on a clock rate of the modulator to synchronize input streams.
The second stream multiplexer 111b receives several streams, multiplexes input streams, and outputs the multiplexed streams. For example, the second stream multiplexer 111b may multiplex Internet Protocol (IP) streams instead of the MPEG-2 TS streams. These streams may be encapsulated by a generic stream encapsulation (GSE) scheme. The streams multiplexed by the second stream multiplexer 111b may be any one of streams. Therefore, the above-mentioned streams different from the MPEG-2 TS streams are called generic streams (GS streams).
The second service splitter 113b receives the multiplexed generic streams, splits the received generic streams according to individual services (i.e., PLP types), and outputs the split GS streams.
The second BB frame builders (115n, . . . , 115p) build service data to be transmitted to individual PLPs in the form of a specific frame used as a signal processing unit, and output the resultant service data. The frame format built by the second BB frame builders (115n, . . . , 115p) may be equal to that of the first BB frame builders (115a, . . . , 115m) as necessary. If required, another embodiment may also be proposed. In another embodiment, the frame format built by the second BB frame builders (115n, . . . , 115p) may be different from that of the first BB frame builders (115a, . . . , 115m). The MPEG-2 TS header further includes a Packet Syncword which is not contained in the GS stream, resulting in the occurrence of different headers.
FIG. 6 is a block diagram illustrating a coding and modulation unit according to the present invention. The coding and modulation unit includes a first interleaver 123, a second encoder 125, and a second interleaver 127.
The first encoder 121 acts as an outer coder of the input baseband frame, and is able to perform the error correction encoding. The first encoder 121 performs the error correction encoding of the input baseband frame using a Bose-Chaudhuri-Hoc-quenghem (BCH) scheme. The first interleaver 123 performs interleaving of the encoded data, such that it prevents a burst error from being generated in a transmission signal. The first interleaver 123 may not be contained in the above-mentioned embodiment.
The second encoder 125 acts as an inner coder of either the output data of the first encoder 121 or the output data of the first interleaver 123, and is able to perform the error correction encoding. A low density parity bit (LDPC) scheme may be used as an error correction encoding scheme. The second interleaver 127 mixes the error-correction-encoded data generated from the second encoder 125, and outputs the mixed data. The first interleaver 123 and the second interleaver 127 are able to perform interleaving of data in units of a bit.
The coding and modulation unit 120 relates to a single PLP stream. The PLP stream is error-correction-encoded and modulated by the coding and modulation unit 120, and is then transmitted to the frame builder 130.
FIG. 7 is a block diagram illustrating a frame builder according to the present invention. Referring to FIG. 7, the frame builder 130 receives streams of several paths from the coding and modulation unit 120, and arranges the received streams in a single signal frame. For example, the frame builder may include a first mapper 131a and a first time interleaver 132a in a first path, and may include a second mapper 131b and a second time interleaver 132b in a second path. The number of input paths is equal to the number of PLPs for service transmission or the number of streams transmitted via each PLP.
The first mapper 131a performs mapping of data contained in the input stream according to the first symbol mapping scheme. For example, the first mapper 131a may perform mapping of the input data using a QAM scheme (e.g., 16 QAM, 64 QAM, and 256 QAM).
If the first mapper 131a performs mapping of the symbol, the input data may be mapped to several kinds of symbols according to several symbol mapping schemes. For example, the first mapper 131a classifies the input data into a baseband-frame unit and a baseband-frame sub-unit. Individual classified data may be hybrid-symbol-mapped by at least two QAM schemes (e.g., 16 QAM and 64 QAM). Therefore, data contained in a single service may be mapped to symbols based on different symbol mapping schemes in individual intervals.
The first time interleaver 132a receives a symbol sequence mapped by the first mapper 131a, and is able to perform the interleaving in a time domain. The first mapper 131a maps data, which is contained in the error-corrected frame unit received from the coding and modulation unit 120, into symbols. The first time interleaver 132a receives the symbol sequence mapped by the first mapper 131a, and interleaves the received symbol sequence in units of the error-corrected frame.
In this way, the p-th mapper 131p or the p-th time interleaver 132p receives service data to be transmitted to the p-th PLP, maps the service data into symbols according to the p-th symbol mapping scheme. The mapped symbols can be interleaved in a time domain. It should be noted that this symbol mapping scheme and this interleaving scheme are equal to those of the first time interleaver 132a and the first mapper 131a. 
The symbol mapping scheme of the first mapper 131a may be equal to or different from that of the p-th mapper 131p. The first mapper 131a and the p-th mapper 131p are able to map input data to individual symbols using the same or different hybrid symbol mapping schemes.
Data of the time interleavers located at individual paths (i.e., service data interleaved by the first time interleaver 132a and service data to be transmitted to R number of RF channels by the p-th time interleaver 132p) is interleaved, such that the physical channel allows the above data to be interleaved over several RF channels.
In association with streams received in as many paths as the number of PLPs, the TFS frame builder 133 builds the TFS signal frame such as the above-mentioned signal frame, such that the service is time-shifted according to RF channels. The TFS frame builder 133 splits service data received in any one of paths, and outputs the service data split into data of the R number of RF bands according to a signal scheduling scheme.
The TFS frame builder 133 receives the first pilot signal and the second pilot signal from the signaling information unit (denoted by Ref/PL signal) 135, arranges the first and second pilot signals in the signal frame, and inserts the signaling signal (L1 and L2) of the above-mentioned physical layer in the second pilot signal. In this case, the first and second pilot signals are used as the beginning signals of the signal frame contained in each RF channel from among the TFS signal frame received from the signaling information unit (Ref/PL signal) 135. As shown in FIG. 2, the first pilot signal may include a transmission type and basic transmission parameters, and the second pilot signal may include a physical parameter and frame construction information. Also, the second pilot signal includes a L1 (Layer 1) signaling signal and a L2 (Layer 2) signaling signal.
The R number of frequency interleavers (137a, . . . , 137r) interleave service data, to be transmitted to corresponding RF channels of the TFS signal frame, in a frequency domain. The frequency interleavers (137a, . . . , 137r) can interleave the service data at a level of data cells contained in an OFDM symbol.
Therefore, service data to be transmitted to each RF channel in the TFS signal frame is frequency-selective-fading-processed, such that it may not be lost in a specific frequency domain.
FIG. 8 is a view showing a first example of a ratio of symbols when the mappers 131a and 131b perform hybrid symbol mapping. This Figure shows the number of bits transmitted by one sub carrier (cell) if error correction coding is performed by the coding and modulation unit in a normal mode (the length of the error-correction-coded code is 64800 bits) of LDPC error correction coding mode.
For example, if the mappers 131a and 131b perform symbol mapping using 256 QAM, 64800 bits are mapped to 8100 symbols. If the mappers 131a and 131b perform hybrid symbol mapping (Hyb 128-QAM) using 256 QAM and 64 QAM with a ratio of 3:2, the number of symbols mapped by 256 QAM is 4860 and the number of symbols mapped by 64 QAM is 4320. The number of transmitted bits per sub carrier (cell) is 7.0588.
If a symbol mapping method of 64 QAM is used, input data may be mapped to 10800 symbols and six bits per cell may be transmitted. If data is mapped to the symbols by a hybrid symbol mapping method of 64 QAM and 16 QAM (64 QAM:16 QAM=3:2, Hyb32-QAM), five bits may be transmitted by one sub carrier (cell).
If data is mapped to symbols by the 16 QAM method, the data is mapped to 16200 symbols, each of which is used to transmit four bits.
Similarly, if data is mapped to symbols by a hybrid symbol mapping method of 16 QAM and QPSK (16 QAM:QPSK=2:3,Hyb8-QAM), three bits may be transmitted by one sub carrier (cell).
If data is mapped to symbols by a QPSK method, the data may be mapped to 32400 symbols, each of which is used to transmit two bits.
FIG. 9 shows symbol mapping methods of error-corrected data by LDPC error correction coding method of a short mode (the length of the error-correction-coded code is 16200 bits), which are equal to the symbol mapping methods of FIG. 8, and the numbers of bits per sub carrier according to the symbol mapping methods.
The numbers of bits transmitted by the sub carrier is equal to those of the normal mode (64800 bits) according to the symbol mapping methods such as 256 QAM, Hyb 128-QAM, 64-QAM, Hyb 32-QAM, 16 QAM, Hyb8-QAM and QPSK, but the total numbers of symbols transmitted are different from those of the normal mode. For example, 16200 bits are transmitted by 2025 symbols in 256 QAM, 16200 bits are transmitted by 1215 symbols according to 256 QAM and 1080 symbols according to 64 QAM (total 2295 symbols) in Hyb 128-QAM.
Accordingly, a data transmission rate per sub carrier (cell) for each PLP may be adjusted according to a hybrid symbol mapping method or a single symbol mapping method.
FIG. 10 is a view showing an example of each of the symbol mappers 131a and 131b shown in FIG. 7. Each of the symbol mappers 131a and 131b includes a first order mapper 1315a, a second order mapper 131b, a symbol merger 1317 and an error correction block merger 1318.
The bit stream parser 1311 receives the PLP service stream from the coding and modulation unit and splits the received service stream.
The first order symbol mapper 1315a maps the bits of the service stream split by a higher order symbol mapping method to symbols. The second order symbol mapper 1315b maps the bits of the service stream split by a lower order symbol mapping method to symbols. For example, in the above example, the first order symbol mapper 1315a may map the bit stream to symbols according to 256 QAM and the second order symbol mapper 1315b may map the bit stream to symbols according to 64 QAM.
The symbol merger 1317 merges the symbols output from the symbol mappers 1315a and 1315b to one symbol stream and outputs the symbol stream. The symbol merger 1317 may output the symbol stream included in one PLP.
The error correction block merger 1318 may output one symbol stream merged by the symbol merger 1317 in the error-correction-coded code block unit. The error correction block merger 1318 may output a symbol block such that the error-correction-coded code blocks are uniformly allocated to at least one RF band of the TFS signal frame. The error correction block merger 1318 may output the symbol block such that the length of the symbol block of the error-correction-coded block of a normal mode is equal to that of the symbol block of the error-correction-coded block of a short mode. For example, four symbol blocks of the error-correction-coded block of the short mode may be merged to one symbol block.
The error correction block merger 1318 may split the symbol stream according to a common multiple of the number of RF bands such that signal frame builder uniformly arranges the symbols to the RF bands. If the maximum number of RF bands in the signal frame is 6, the error correction block merger 1318 outputs the symbol block such that the total number of symbols can be divided by 60 which is a common multiple of 1, 2, 3, 4, 5 and 6.
The symbols included in the output symbol block may be arranged to be uniformly allocated to the six RF bands. Accordingly, although an error correction mode according to a code rate and a symbol mapping method are combined, the symbols configuring the PLP are uniformly allocated to the RF bands.
FIG. 11 is a view showing another embodiment of the symbol mapper. In the embodiment of this Figure, the symbol mapper includes the second encoder 125 and the second interleaver 127 included in the coding and modulation unit. That is, if this embodiment is used, the coding and modulation unit may include only the first encoder 121, the first interleaver 123 and the second encoder 125.
The embodiment of the symbol mapper includes a bit stream parser 1311, a first order bit interleaver 1312a, a second order bit interleaver 1312b, a first order demux 1313a, a second order demux 1313b, a first order symbol mapper 1315a, a second order symbol mapper 1315b and a symbol merger 1317.
When the second encoder 125 performs LDPC error correction coding, the length of the error-correction-coded block (e.g., the length of 64800 bits and the length of 16200 bits) may vary according to an LDPC mode. If the bits included in the error-correction-coded block are mapped to the symbols, the error correction capabilities of the bits included in a cell word configuring the symbol may vary according to the locations of the bits. For example, the cell word which is the symbol may be determined according to the code rate of the error correction coding and the symbol mapping method (whether the symbol mapping method is the higher order symbol mapping method or the lower order symbol mapping method). If the error-correction-code is the LDPC, the error correction capabilities of the bits vary according to the locations of the bits in the error-correction-coded block. For example, the reliabilities of the bits coded according to the characteristics of the H-matrix used in the irregular LDPC error correction coding method may vary according to the locations of the bits. Accordingly, the order of the bits configuring the cell word mapped to the symbol is changed such that the error correction capabilities of the bits which are weak against the error correction in the error-correction-coded block are adjusted and the robustness against the error in the bit level can be adjusted.
First, the second encoder 125, for example, performs the error correction coding with respect to the stream included in one PLP by the LDPC error correction coding method.
The bit stream parser 1311 receives the service stream according to the PLP and splits the received service stream.
The first order bit interleaver 1312a interleaves the bits included in a first bit stream of the split service streams. Similarly, the second order bit interleaver 1312b interleaves the bits included in a second bit stream of the split service streams.
The first order bit interleaver 1312a and the second order bit interleaver 1312b may correspond to the second interleaver 127 used as an inner interleaver. The interleaving method of the first order bit interleaver 1312a and the second order bit interleaver 1312b will be described later.
The first order demux 1313a and the second order demux 1313b demultiplex the bits of the bit streams interleaved by the first order bit interleaver 1312a and the second order bit interleaver 1312b. The demuxs 1313a and 1313b divide the input bit stream into sub bit streams which will be mapped to a real axis and an imaginary axis of a constellation and output the sub bit streams. The symbol mappers 1315a and 1315b map the sub bit streams demultiplexed by the demuxs 1313a and 1313b to the corresponding symbols.
The bit interleavers 1312a and 1312b and the demuxs 1313a and 1313b may combine the characteristics of the LDPC codeword and the characteristics of the constellation reliability of the symbol mapping according to the constellation. The detailed embodiment of the first order demuxs 1313a and 1313b will be described later.
The first order symbol mapper 1315a performs first order symbol mapping, for example, higher order symbol mapping, and the second order symbol mapper 1315b performs second order symbol mapping, for example, lower order symbol mapping. The first order symbol mapper 1315a maps the sub bit streams output from the first order demux 1313 to the symbols and the second order symbol mapper 1315b maps the sub bit streams output from the second order demux 1313b to the symbols.
The symbol merger 1317 merges the symbols mapped by the first order symbol mapper 1315a and the second order symbol mapper 1315b to one symbol stream and outputs the symbol stream.
As described above, in the LDPC, the error correction capabilities of the bits may be changed according to the locations of the bits in the error-correction-coded block. Accordingly, if the bit interleaver and the demux are controlled according to the characteristics of the LDPC encoder 125 so as to change the order of the bits configuring the cell word, the error correction capability in the bit level can be maximized.
FIG. 12 is a view showing the concept of interleaving of bits by the bit interleavers 1312a and 1312b of FIG. 11.
For example, input bits are stored in and read from a matrix-formed memory having a predetermined number of rows and columns. When the input bits are stored, first, the bits are stored in a first column in row direction, and, if the first column is filled up, the bits are stored in another column in row direction. When the stored bits are read, the bits are read in column direction and, if all the bits stored in a first row are read, the bits in another row are read in column direction. In other word, when the bits are stored, the bits are stored row-wise such that the columns are filled up serially. And when the stored bits are read, the stored bits are read column-wise from the first row to last row serially. In this Figure, MSB means a most significant bit and LSB means a least significant bit.
In order to map the LDPC-error-correction-coded bits to the symbols in the same length of error correction block unit at various code rates, the bit interleavers 1312a and 1312b may change the number of rows and columns of the memory according to the types of the symbol mappers 1315a and 1315b. 
FIG. 13 is a view showing an example of the number of rows and columns of memories of the bit interleavers 1312a and 1312b according to the types of symbol mappers 1315a and 1315b, if the LDPC mode is the normal mode.
For example, if the symbol mapper 1315a maps the bits to 256 QAM symbols, the first order interleaver 1312a interleaves the bits by a memory having 8100 rows and 8 columns. If the symbols are mapped by 64 QAM, the first order interleaver 1312a interleaves the bits by a memory having 10800 rows and 6 columns. If the symbols are mapped by 16 QAM, the first order interleaver 1312a interleaves the bits by a memory having 16200 rows and 4 columns.
For example, if the symbol mappers 1315a and 1315b map the bits to Hyb128-QAM symbols, the first order interleaver 1312a interleaves the bits using a memory having 4860 rows and 8 columns, and the second order interleaver 1312b interleaves the bits using a memory having 4320 rows and 6 columns.
Similarly, if the symbol mappers 1315a and 1315b map the symbols by Hyb32-QAM, the first order interleaver 1312a interleaves the bits using a memory having 6480 rows and 6 columns, and the second order interleaver 1312b interleaves the bits using a memory having 6480 rows and 4 columns.
FIG. 14 is a view showing an example of the number of rows and columns of the memories of the bit interleavers 1312a and 1312b according to the types of the symbol mappers 1315a and 1315b, if the LDPC mode is the short mode.
For example, if the symbol mapper 1315a maps the bits to 256 QAM symbols, the first order interleaver 1312a interleaves the bits by a memory having 2025 rows and 8 columns. If the symbol mappers 1315a and 1315b map the symbols by Hyb128-QAM, the first order interleaver 1312a interleaves the bits using a memory having 1215 rows and 8 columns, and the second order interleaver 1312b interleaves the bits using a memory having 1080 rows and 6 columns.
If the bit interleaving is performed with respect to the error-correction-coded block, the locations of the bits in the error-correction-coded block may be changed.
FIG. 15 is a view showing the concept of multiplexing of input bits of the demuxs 1313a and 1313b. 
The bit interleavers 1312a and 1312b interleave the input bits x0, x1, and xn-1 and output the interleaved bits. The interleaving method is already described above.
The demuxs 1313a and 1313b demultiplex the interleaved bit streams. The demultiplexing method may vary according to the code rate of the error correction coding method and the symbol mapping method of the symbol mapper. If the symbol method of the symbol mapper is QPSK, the input bits, for example, are interleaved to two sub streams and the symbol mapper maps the two sub streams to the symbols so as to correspond to the real axis and the imaginary axis of the constellation. For example, a first bit y0 of the demultiplexed first sub stream corresponds to the real axis and a first bit y1 of the demultiplexed second sub stream corresponds to the imaginary axis.
If the symbol method of the symbol mapper is 16 QAM, the input bits, for example, are demultiplexed to four sub frames. The symbol mapper selects the bits included in the four sub streams and maps the selected bits to the symbols so as to correspond to the real axis and the imaginary axis of the constellation.
For example, the bits y0 and y2 of the demultiplexed first and third sub streams correspond to the real axis and the bits y1 and y3 of the demultiplexed second and fourth sub streams correspond to the imaginary axis.
Similarly, if the symbol method of the symbol mapper is 64 QAM, the input bits may be demultiplexed to six bit streams. The symbol mapper maps the six sub streams to the symbols so as to correspond to the real axis and the imaginary axis of the constellation. For example, the demultiplexed first, third and fifth sub stream bits y0, y2 and y4 correspond to the real axis and the demultiplexed second, fourth and sixth sub stream bits y1, y3 and y6 correspond to the imaginary axis.
Similarly, if the symbol method of the symbol mapper is 256 QAM, the input bits may be demultiplexed to eight bit streams. The symbol mapper maps the eight sub streams to the symbols so as to correspond to the real axis and the imaginary axis of the constellation. For example, first, the demultiplexed first, third fifth and seventh sub stream bits y0, y2, y4 and y6 correspond to the real axis and the demultiplexed second, fourth, sixth and eighth sub stream bits y1, y3, y6 and y7 correspond to the imaginary axis.
If the symbol mapper maps the symbols, the sub streams demultiplexed by the demux may be mapped to the bit streams of the real axis and the imaginary axis of the constellation.
The above-described bit interleaving method, demultiplexing method and symbol mapping method are exemplary and various methods may be used as the method of selecting the bits in the sub streams such that the sub streams demultiplexed by the demux may correspond to the real axis and the imaginary axis of the constellation.
The cell word mapped to the symbols may vary according to any one of the error-corrected bit streams according to the code rate, the method of interleaving the bit streams, the demultiplexing method and the symbol mapping method. The MSB of the cell word is higher than the LSB of the cell word in the reliability of the error correction decoding. Although the reliability of the bit of a specific location of the error-correction-coded block is low, the reliability of the bit can be improved by the symbol demapping process if the bit of the cell word is arranged on the MSB or close to the MSB.
Accordingly, although the reliability of the bit coded according to the characteristics of the H-matrix used in the irregular LDPC error correction coding method is changed, the bit can be robustly transmitted/received by the symbol mapping and demapping process and the system performance can be adjusted.
FIG. 16 is a view showing an embodiment of demultiplexing an input stream by the demux.
If the symbol mapping method is QPSK, two bits are mapped to one symbol and the two bits of one symbol unit are demultiplexed in order of the bit indexes (indexes 0 and 1 of b).
If the symbol mapping method is 16 QAM, 4 bits are mapped to one symbol and the four bits of one symbol unit are demultiplexed according to the calculating result of the modulo-4 of bit indexes (indexes 0, 1, 2 and 3 of b).
If the symbol mapping method is 64 QAM, 6 bits are mapped to one symbol and the six bits of one symbol unit are demultiplexed according to the calculating result of the modulo-6 of bit indexes (indexes 0, 1, 2, 3, 4 and 5 of b).
If the symbol mapping method is 256 QAM, 8 bits are mapped to one symbol and the eight bits of one symbol unit are demultiplexed according to the calculating result of the modulo-8 of bit indexes (indexes 0, 1, 2, 3, 4, 5, 6 and 7 of b).
The demultiplexing order of the sub streams is exemplary and may be modified.
FIG. 17 is a view showing an example of a demultiplexing type according to a symbol mapping method. The symbol mapping method includes QPSK, 16 QAM, 64 QAM and 256 QAM, and the demultiplexing type includes a first type to a sixth type.
The first type is an example in which the input bits sequentially correspond to even-numbered indexes (0, 2, 4, 8) (or the real axis of the constellation) and sequentially correspond to odd-numbered indexes (1, 3, 5, 7) (or the imaginary axis of the constellation). Hereinafter, the bit demultiplexing of the first type may be represented by a demultiplexing identifier 10 (a binary number of 1010; the location of 1 is the location of the MSB corresponding to the real axis and the imaginary axis of the constellation).
The second type is an example in which the demultiplexing is performed in reverse order of the first type, that is, the LSB of the input bits sequentially correspond to even-numbered indexes (6, 4, 2, 0) (or the real axis of the constellation) and odd-numbered indexes (1, 3, 5, 7) (or the imaginary axis of the constellation). Hereinafter, the bit demultiplexing of the second type may be represented by a demultiplexing identifier 5 (a binary number of 0101).
The third type is an example in which the input bits are arranged such that the bits of the both ends of the codeword become the MSB. The input bits are rearranged so as to fill the code word from the both ends of the code word. Hereinafter, the bit demultiplexing of the third type may be represented by a demultiplexing identifier 9 (a binary number of 1001).
The fourth type is an example in which the input bits are arranged such that a middle bit of the code word becomes the MSB. A bit of the input bits is first filled in the middle location of the code word and the remaining bits are then rearranged toward the both ends of the code word in order of the input bits. Hereinafter, the bit demultiplexing of the fourth type may be represented by a demultiplexing identifier 6 (a binary number of 0110).
The fifth type is an example in which the bits are demultiplexed such that a last bit of the code word becomes the MSB and a first bit thereof becomes the LSB, and the sixth type is an example in which the bits are rearranged such that the first bit of the code word becomes the MSB and the last bit thereof becomes the LSB. Hereinafter, the bit demultiplexing of the fifth type may be represented by a demultiplexing identifier 3 (a binary number of 0011), and the bit demultiplexing of the sixth type may be represented by a demultiplexing identifier 12 (a binary number of 1100).
As described above, the demultiplexing type may vary according to the symbol mapping method or the code rate of the error correction coding method. That is, a different demultiplexing type may be used if the symbol mapping method or the code rate is changed.
FIG. 18 is a view showing an embodiment of demultiplexing an input bit stream according to a demultiplexing type. This embodiment may include bit interleavers 1312a and 1312b, demuxs 1313a and 1313b and mappers 1315a and 1315b. 
The bit interleavers 1312a and 1312b interleave the error-correction-coded PLP service streams. For example, the bit interleavers 1312a and 1312b may perform the bit interleaving in the error correction coding units according to the error correction coding mode. The bit interleaving method is already described above.
The demuxs 1313a and 1313b may include first type demuxs 1313a1 and 1313b1, and nth type demuxs 1313a2 and 1313b2. Here, n is an integer. The methods of demultiplexing the bits by the n types of demuxs follow the types shown in FIG. 17. For example, the first type demuxs may correspond to the first type bit demultiplexing (1100) and the second type demux (not shown) may correspond to the second type bit demultiplexing (0011). The nth type demux 1313b demultiplexes the input bit stream according to the nth type bit multiplexing (e.g., the demultiplexing identifier 1100) and outputs the demultiplexed bit stream. Selectors 1313a3 and 1313b3 receive a demux selection signal of the demultiplexing type suitable for the input bits and output the demultiplexed bit stream according to any one of the first type to the nth type and the demux selection signal. The demux selection signal may vary according to the code rate of the error correction coding and the symbol mapping method of the constellation. Accordingly, the demultiplexing type may be determined according to the code rate of the error correction coding method or/and the symbol mapping method of the constellation. The detailed example according to the symbols mapped to the constellation or/and the code rate of the error correction coding according to the demux selection signal will be described later.
The mappers 1315a and 1315b may map the demultiplexed sub bit streams to the symbols according to the demux selection signal and output the mapped symbols.
FIG. 19 is a view showing a demultiplexing type which is determined according to a code rate of the error correction coding and the symbol mapping method.
In the 4 QAM symbol mapping method, even when the code rate cr of the LDPC error correction coding method is any one of 1⁄4, 1⁄3, 2⁄5, 1⁄2, 3⁄5, 2⁄3, 3⁄4, 4⁄5, 5⁄6, 8/9 and 9/10, the bit stream can be demultiplexed according to all the demultiplexing types (denoted by all).
In the 16 QAM symbol mapping method, if the code rate of the LDPC error correction coding method is 1⁄4, 1⁄3, 2⁄5 and 1⁄2, the symbols can be mapped without performing the bit interleaving and the bit demultiplexing (denoted by No-Int and No-Demux). If the code rate of the error correction coding is 3⁄5, the bit can be demultiplexed according to any one of the demultiplexing identifiers 9, 10 and 12. If the code rate of the error correction coding is 2⁄3, 3⁄4, 4⁄5, 5⁄6, 8/9 and 9/10, the input bit stream can be demultiplexed according to the demultiplexing identifier 6.
In the 64 QAM symbol mapping method, if the code rate of the LDPC error correction coding is 1⁄4, 1⁄3, 2⁄5 and 1⁄2, the symbols can be mapped without performing the bit interleaving and the bit demultiplexing. If the code rate is 3⁄5, the bits can be demultiplexed according to any one of the demultiplexing identifiers 9 and 10. If the code rate is 2⁄3, 3⁄4, 4⁄5, 5⁄6, 8/9 and 9/10, the bits can be demultiplexed according to the demultiplexing identifier 6.
In the 256 QAM symbol mapping method, if the code rate of the LDPC error correction coding is 1⁄4, 1⁄3, 2⁄5 and 1⁄2, the symbols can be mapped without performing the bit interleaving and the bit demultiplexing. If the code rate is 3⁄5, the bits can be demultiplexed according to the demultiplexing identifier 9. If the code rate is 2⁄3, 3⁄4, 4⁄5, 5⁄6, 8/9 and 9/10, the bits can be demultiplexed according to the demultiplexing identifier 6.
As described above, the bit demultiplexing type may vary according to the code rate used for the error correction coding and the symbol mapping method. Accordingly, the error correction capability of a bit located on a specific location of the error-correction-coded block may be adjusted by mapping the demultiplexed sub streams to the symbols. Accordingly it is possible to optimize the robustness in the bit level.
FIG. 20 is a view showing an example of expressing the demultiplexing method by an equation. For example, if the symbol mapping method is QPSK, the input bits (xi, xN/2+i) correspond to the demultiplexed bits y0 and y1. If the symbol mapping method is 16 QAM, the input bits




  
    
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correspond to the demultiplexed bits y0, y1, y2, y3, y4, y5, y6 and y7.

Here, N denotes the number of bits mapped to the symbols with respect to the input of the bit interleaver.
FIG. 21 is a view showing an example of mapping a symbol by a symbol mapper. For example, in the QPSK symbol mapping method, the symbols on the constellation correspond to the value of the bit y0 of the demultiplexed first sub stream and the value of the bit y1 of the demultiplexed second sub stream.
In the 16 QAM, the real axis of the symbols on the constellation corresponds to the bits of the demultiplexed first and third sub streams (bits separated from the location of the MSB by 0 and 2) and the imaginary axis thereof corresponds to the bits of the demultiplexed second and fourth sub streams (bits separated from the location of the MSB by 1 and 3).
In the 64 QAM, the real axis of the symbols on the constellation corresponds to the bits of the demultiplexed first, third, and fifth sub streams (bits separated from the location of the MSB by 0, 2 and 4) and the imaginary axis thereof corresponds to the bits of the demultiplexed second, fourth and sixth sub streams (bits separated from the location of the MSB by 1, 3 and 5).
Accordingly, the bits configuring the symbol may be mapped to the cell word in the demultiplexing order. If the bits configuring the cell word are demultiplexed, the MSB and the LSB of the cell word are changed and the robustness of the bits can be adjusted although the reliabilities of the LDPC error-correction-coded bits vary according to the locations.
FIG. 22 is a block diagram illustrating a MIMO/MISO encoder according to the present invention. Referring to FIG. 22, the MIMO/MISO encoder encodes the input data using the MIMO/MISO encoding scheme, and outputs the encoded data to several paths. If a signal reception end receives the signal transmitted to the several paths from one or more paths, it is able to acquire a gain (also called a diversity gain, a payload gain, or a multiplexing gain).
The MIMO/MISO encoder 140 encodes service data of each path generated from the frame builder 130, and outputs the encoded data to the A number of paths corresponding to the number of output antennas.
FIG. 23 is a block diagram illustrating a modulator according to the present invention. Referring to FIG. 23, the modulator includes a first power controller (PAPR Reduce1) 151, a time-domain transform unit (IFFT) 153, a second power controller (PAPR Reduce2) 157, and a guard-interval inserter 159.
The first power controller 151 reduces a PAPR (Peak-to-Average Power Ratio) of data transmitted to the R number of signal paths in the frequency domain.
The time-domain transform (IFFT) unit 153 converts the received frequency-domain signals into time-domain signals. For example, the frequency-domain signals may be converted into the time-domain signals according to the IFFT algorithm. Therefore, the frequency-domain data may be modulated according to the OFDM scheme.
The second power controller (PAPR Reduce2) 157 reduces a PAPR (Peak-to-Average Power Ratio) of channel data transmitted to the R number of signal paths in the time domain. In this case, a tone reservation scheme, and an active constellation extension (ACE) scheme for extending symbol constellation can be used.
The guard-interval inserter 159 inserts the guard interval into the output OFDM symbol, and outputs the inserted result. As described above, the above-mentioned embodiment can be carried out in each signal of the R number of paths.
FIG. 24 is a block diagram illustrating an analog processor 160 according to the present invention. Referring to FIG. 24, the analog processor 160 includes a digital-to-analog converter (DAC) 161, an up-conversion unit 163, and an analog filter 165.
The DAC 161 converts the input data into an analog signal, and outputs the analog signal. The up-conversion unit 163 converts a frequency domain of the analog signal into an RF area. The analog filter 165 filters the RF-area signal, and outputs the filtered RF signal.
FIG. 25 is a block diagram illustrating an apparatus for receiving a signal according to the present invention. Referring to FIG. 25, the signal reception apparatus includes a first signal receiver 210a, an n-th signal receiver 210n, a first demodulator 220a, an n-th demodulator 220n, a MIMO/MISO decoder 230, a frame parser 240, and a decoding demodulator 250, and an output processor 260.
In the case of a reception signal according to the TFS signal frame structure, several services are multiplexed to R channels, and are then time-shifted, such that the time-shifted result is transmitted.
The receiver may include at least one signal receiver for receiving a service transmitted over at least one RF channel. The TFS signal frame transmitted to the R (where R is a natural number) number of RF channels can be transmitted to a multipath via the A number of antennas. The A antennas have been used for the R RF channels, such that a total number of antennas is R×A.
The first signal receiver 210a is able to receive service data transmitted via at least one path from among overall service data transmitted via several RF channels. For example, the first signal receiver 210a can receive the transmission signal processed by the MIMO/MISO scheme via several paths.
The first signal receiver 210a and the n-th signal receiver 210n can receive several service data units transmitted over n number of RF channels from among several RF channels, as a single PLP. Namely, this embodiment shows the signal reception-apparatus capable of simultaneously receiving data of the R number of RF channels. Therefore, if this embodiment receives a single RF channel, only the first receiver 210a is needed.
The first demodulator 220a and the n-th demodulator 220n demodulate signals received in the first and n-th signal receivers 210a and 210n according to the OFDM scheme, and output the demodulated signals.
The MIMO/MISO decoder 230 decodes service data received via several transmission paths according to the MIMO/MISO decoding scheme, and outputs the decoded service data to a single transmission path. If the number R of services transmitted over several transmission paths are received, the MIMO/MISO decoder 230 can output single PLP service data contained in each of R services corresponding to the number of R channels. If P number of services are transmitted via the R number of RF channels, and signals of individual RF channels are received via the A number of antennas, the receiver decodes the P number of services using a total of (R×A) reception antennas.
The frame parser 240 parses the TFS signal frame including several services, and outputs the parsed service data.
The decoding demodulator 250 performs the error correction decoding on the service data contained in the parsed frame, demaps the decoded symbol data into bit data, and outputs the demapping-processed result.
The output processor 260 decodes a stream including the demapped bit data, and outputs the decoded stream.
In the above-mentioned description, each of the frame parser 240, and the decoding demodulator 250, and the output processor 260 receives several service data units as many as the number of PLPs, and performs signal processing on the received service data.
FIG. 26 is a block diagram illustrating a signal receiver according to the present invention. Referring to FIG. 26, the signal receiver may include a tuner 211, a down-converter 213, and an analog-to-digital converter (ADC) 215.
The tuner 211 performs hopping of some RF channels capable of transmitting user-selected services in all RF channels when the PLP is included in several RF channels, and outputs the hopping result. The tuner 211 performs hopping of RF channels contained in the TFS signal frame according to input RF center frequencies, and at the same time tunes corresponding frequency signals, such that it outputs the tuned signals. If a signal is transmitted to A number of multi-paths, the tuner 211 performs the tuning to a corresponding RF channel, and receives reception signals via the A number of antennas.
The down converter 213 performs down conversion of the RF frequency of the signal tuned by the tuner 211, and outputs the down-conversion result. The ADC 215 converts an analog signal into a digital signal.
FIG. 27 is a block diagram illustrating a demodulator according to the present invention. Referring to FIG. 27, the demodulator includes a frame detector 221, a frame synchronization unit 222, a guard-interval remover 223, a frequency-domain transform unit (FFT) 224, a channel estimator 225, a channel equalizer 226, and a signaling-information extractor 227.
If the demodulator acquires service data transmitted to a single PLP stream, the following signal demodulation will be carried out. A detailed description thereof will hereinafter be described.
The frame detector 221 identifies a delivery system of a reception signal. For example, the frame detector 221 determines whether the reception signal is a DVB-TS signal or not. And, the frame detector 221 may also determine whether a reception signal is a TFS signal frame or not. The frame synchronization unit 222 acquires time- and frequency-domain synchronization of the TFS signal frame.
The guide interval controller 223 removes a guard interval located between OFDM symbols from the time domain. The frequency-domain converter (FFT) 224 converts a reception signal into a frequency-domain signal using the FFT algorithm, such that it acquires frequency-domain symbol data.
The channel estimator 225 performs channel estimation of a reception channel using a pilot symbol contained in symbol data of the frequency domain. The channel equalizer 226 performs channel equalization of reception data using channel information estimated by the channel estimator 225.
The signaling information extractor 227 can extract the signaling information of a physical layer established in the first and second pilot signals contained in channel-equalized reception data.
FIG. 28 is a block diagram illustrating a MIMO/MISO decoder according to the present invention. The signal receiver and the demodulator are designed to process a signal received in a single path. If the signal receiver and the demodulator receive PLP service data providing a single service via several paths of several antennas, and demodulate the PLP service data, the MIMO/MIMO decoder 230 outputs the signal received in several paths as service data transmitted to a single PLP. Therefore, the MIMO/MISO decoder 230 can acquire a diversity gain and a multiplexing gain from service data received in a corresponding PLP.
The MIMO/MISO decoder 230 receives a multi-path transmission signal from several antennas, and is able to decode a signal using a MIMO scheme capable of recovering each reception signal in the form of a single signal. Otherwise, the MIMO/MISO decoder 230 is able to recover a signal using a MIMO scheme which receives the multi-path transmission signal from a single antenna and recovers the received multi-path transmission signal.
Therefore, if the signal is transmitted via the R number of RF channels (where R is a natural number), the MIMO/MISO decoder 230 can decode signals received via the A number of antennas of individual RF channels. If the A value is equal to “1”, the signals can be decoded by the MISO scheme. If the A value is higher than “1”, the signals can be decoded by the MIMO scheme.
FIG. 29 is a block diagram illustrating a frame parser according to the present invention. Referring to FIG. 29, the frame parser includes a first frequency deinterleaver 241a, a r-th frequency de-interleaver 241r, a frame parser 243, a first time de-interleaver 245a, a p-th time de-interleaver 245p, a first symbol demapper 247a, and a p-th symbol demapper. The value of “r” can be decided by the number of RF channels, and the value of “p” can be decided by the number of streams transmitting PLP service data generated from the frame parser 243.
Therefore, if p number of services are transmitted to p number of PLP streams over R number of RF channels, the frame parser includes the r number of frequency deinterleavers, the p number of time de-interleavers, and the p number of symbol demappers.
In association with a first RF channel, the first frequency interleaver 241a performs de-interleaving of frequency-domain input data, and outputs the de-interleaving result.
The frame parser 243 parses the TFS signal frame transmitted to several RF channels using scheduling information of the TFS signal frame, and parses PLP service data contained in the slot of a specific RF channel including a desired service. The frame parser 243 parses the TFS signal frame to receive specific service data distributed to several RF channels according to the TFS signal frame structure, and outputs first-path PLP service data.
The first time de-interleaver 245a performs de-interleaving of the parsed first-path PLP service data in the time domain. The first symbol demapper 247a determines service data mapped to the symbol to be bit data, such that it can output a PLP stream associated with the first-path PLP service data.
Provided that symbol data is converted into bit data, and each symbol data includes symbols based on the hybrid symbol-mapping scheme, the p number of symbol demappers, each of which includes the first symbol demapper, can determine the symbol data to be bit data using different symbol-demapping schemes in individual intervals of the input symbol data.
FIG. 30 is a view showing an embodiment of each of symbol demappers 247a and 247p. The symbol demappers receive the streams corresponding to the PLPs from the time interleavers 245a and 245p respectively corresponding to the symbol demappers.
Each of the symbol demappers 247a and 247p may include an error correction block splitter 2471, a symbol splitter 2473, a first order demapper 2475a, a second order demapper 2475b and a bit stream merger 2478.
The error correction block splitter 2471 may split the PLP stream received from the corresponding one of the time interleavers 245a and 245p in the error correction block units. The error correction block splitter 2471 may split the service stream in the normal mode LDPC block unit. In this case, the service stream may be split in a state in which four blocks according to the short mode (the block having the length of 16200 bits) are treated as the error correction block of one block according to the normal mode (the block having the length of 64800 bits).
The symbol splitter 2473 may split the symbol stream in the split error correction block according to the symbol mapping method of the symbol stream.
For example, the first order demapper 2475a converts the symbols according to the higher order symbol mapping method into the bits. The second order demapper 2475b converts the symbols according to the lower order symbol mapping method into the bits.
The bit stream merger 2478 may receive the converted bits and output one bit stream.
FIG. 31 is a view showing another embodiment of each of the symbol demappers 247a and 247p. Each of the symbol demappers 247a and 247p may include a symbol splitter 2473, a first order demapper 2474a, a second order demapper 2474b, a first order mux 2475a, a second order mux 2475b, a first order bit deinterleaver 2476a, a second order bit deinterleaver 2476b and a bit stream merger 2478. By this embodiment, the embodiment of the decoding and demodulation unit of FIG. 33 includes a first decoder 253, a first deinterleaver 255 and a second decoder 257.
The symbol splitter 2473 may split the symbol stream of the PLP according to the method corresponding to the symbol mapping method.
The first order demapper 2474a and the second order demapper 2474b convert the split symbol streams into bits. For example, the first order demapper 2474a performs the symbol demapping of the higher order QAM and the second order demapper 2474b performs the symbol demapping of the lower order QAM. For example, the first order demapper 2474a may perform the symbol demapping of 256 QAM and the second order demapper 2474b may perform the symbol demapping of 64 QAM.
The first order mux 2475a and the second order mux 2475b multiplex the symbol-mapped bits. The multiplexing methods may correspond to the demultiplexing methods described with reference to FIGS. 15 to 18. Accordingly, the demultiplexed sub streams may be converted into one bit stream.
The first order bit deinterleaver 2476a deinterleaves the bit streams multiplexed by the first order mux 2475a. The second order bit deinterleaver 2476b deinterleaves the bits multiplexed by the first order mux 2475a. The deinterleaving method corresponds to the bit interleaving method. The bit interleaving method is shown in FIG. 12.
The bit stream merger 2478 may merge the bit streams deinterleaved by the bit interleavers 2476a and 2476b to one bit stream.
The first decoder 253 of the decoding and demodulation unit may error correction decode the output bit stream according to the normal mode or the short mode and the code rate according to the modes.
FIG. 32 is a view showing an embodiment of multiplexing the demultiplexed sub stream. In this embodiment, the demappers 2474a and 2474b decide the cell words including the bits. The muxs 2475a and 2475b multiplex the decided cell words according to the mux selection signal. The demultiplexed cell words are input to any one of first muxs 2475a2 and 2475b2 to nth muxs 2475a3 and 2475b3.
The first muxs 2475a2 and 2475b2 to the nth muxs 2475a3 and 2475b3 change the order of the bits in the cell words input according to the mux selection signal. The mux selection signal may be changed according to the code rate of the error correction coding or the symbol mapping method. In order to generate one stream and the bit streams delivered to the muxs, the order of selecting the sub stream may be changed according to the mux selection signal.
The first demuxs 2475a1 and 2475b1 output the symbol-demapped bit streams to any one of the first muxs 2475a2 and 2475b2 to the nth muxs 2475a3 and 2475b3 according to the mux selection signal. The first sub muxs 2475a1 and 2475b1 may receive the sub streams multiplexed by the first muxs 2475a2 and 2475b2 to the nth muxs 2475a3 and 2475b3 and output one stream, according to the mux selection signal.
The cell words including the changed bits are input to the bit interleavers 2476a and 2476b, and the bit deinterleavers 2476a and 2476b deinterleave the input bits and output the deinterleaved bits.
FIG. 33 is a block diagram illustrating a decoding demodulator according to the present invention. Referring to FIG. 33, the decoding demodulator may include several function blocks corresponding to the coding and modulation unit. In this embodiment, the decoding demodulator of FIG. 16 may include a first de-interleaver 251, a first decoder 253, a second de-interleaver 255, and a second decoder 257. The second deinterleaver 255 can be selectively contained in the decoding demodulator.
The first de-interleaver 251 acts as an inner de-interleaver, and is able to perform deinterleaving of the p-th PLP stream generated from the frame parser.
The first decoder 253 acts as an inner decoder, can perform error correction of the de-interleaved data, and can use an error correction decoding algorithm based on the LDPC scheme.
The second de-interleaver 255 acts as an outer interleaver, and can perform deinterleaving of the error-correction-decoded data.
The second decoder 257 acts as an outer decoder. Data de-interleaved by the second de-interleaver 255 or error-corrected by the first decoder 253 is error-corrected again, such that the second decoder 257 outputs the re-error-corrected data. The second decoder 257 decodes data using the error correction decoding algorithm based on the BCH scheme, such that it outputs the decoded data.
The first de-interleaver 251 and the second de-interleaver 255 are able to convert the burst error generated in data contained in the PLP stream into a random error. The first decoder 253 and the second decoder 257 can correct errors contained in data.
The decoding demodulator shows operation processes associated with a single PLP stream. If the p number of streams exist, the p number of decoding demodulators are needed, or the decoding demodulator may repeatedly decode input data p times.
FIG. 34 is a block diagram illustrating an output processor according to the present invention. Referring to FIG. 34, the output processor may include p number of baseband (BB) frame parsers (251a, 261p), a first service merger 263a, a second service merger 263b, a first demultiplexer 265a, and a second demultiplexer 265b. 
The BB frame parsers (261a, 261p) remove BB frame headers from the first to p-th PLP streams according to the received PLP paths, and output the removed result. This embodiment shows that service data is transmitted to at least two streams. A first stream is an MPEG-2 TS stream, and a second stream is a GS stream.
The first service merger 263a calculates the sum of service data contained in payload of at least one BB frame, such that it outputs the sum of service data as a single service stream. The first demultiplexer 255a may demultiplex the service stream, and output the demultiplexed result.
In this way, the second service merger 263b calculates the sum of service data contained in payload of at least one BB frame, such that it can output another service stream. The second demultiplexer 255b may demultiplex the GS-format service stream, and output the demultiplexed service stream.
FIG. 35 is a block diagram illustrating an apparatus for transmitting a signal according to another embodiment of the present invention. Referring to FIG. 35, the signal transmission apparatus includes a service composer 310, a frequency splitter 320, and a transmitter 400. The transmitter 400 encodes or modulates a signal including a service stream to be transmitted to each RF band.
The service composer 310 receives several service streams, multiplexes several service streams to be transmitted to individual RF channels, and outputs the multiplexed service streams. The service composer 310 outputs scheduling information, such that it controls the transmitter 400 using the scheduling information, when the transmitter 400 transmits the PLP via several RF channels. By this scheduling information, the service composer 310 modulates several service frames to be transmitted to the several RF channels by the transmitter 400, and transmits the modulated service frames.
The frequency splitter 320 receives a service stream to be transmitted to each RF band, and splits each service stream into several sub-streams, such that the individual RF frequency bands can be allocated to the sub-streams.
The transmitter 400 processes the service streams to be transmitted to individual frequency bands, and outputs the processed resultant streams. For example, in association with a specific service stream to be transmitted to the first RF channel, the first mapper 410 maps the input service stream data into symbols. The first interleaver 420 interleaves the mapped symbols to prevent the burst error.
The first symbol inserter 430 can insert a signal frame equipped with a pilot signal (e.g., a scatter pilot signal or a continual pilot signal) into the modulated signal.
The first modulator 440 modulates the data interleaved by the signal modulation scheme. For example, the first modulator 440 can modulate signals using the OFDM scheme.
The first pilot symbol inserter 450 inserts the first pilot signal and the second pilot signal in the signal frame, and is able to transmit the TFS signal frame.
Service stream data transmitted to the second RF channel is transmitted to the TFS signal frame via several blocks 415, 425, 435, 445, and 455 of different paths shown in the transmitter of FIG. 18.
The number of signal processing paths transmitted from the transmitter 400 may be equal to the number of RF channels contained in the TFS signal frame.
The first mapper 410 and the second mapper may respectively include the demultiplexers 1313a and 1313b, and allow the locations of the MSB and the LSB to be changed in the symbol-mapped cell word.
FIG. 36 is a block diagram illustrating an apparatus for receiving a signal according to another embodiment of the present invention. Referring to FIG. 36, the signal reception apparatus may include a reception unit 510, a synchronization unit 520, a mode detector 530, an equalizer 540, a parameter detector 550, a de-interleaver 560, a demapper 570, and a service decoder 580.
The reception unit 500 is able to receive signals of a first RF channel selected by a user from among the signal frame. If the signal frame includes several RF channels, the reception unit 500 performs hopping of the several RF channels, and at the same time can receive a signal including the selected service frame.
The synchronization unit 510 acquires synchronization of a reception signal, and outputs the synchronized reception signal. The demodulator 520 is able to demodulate the synchronization-acquired signal. The mode detector 530 can acquire a FFT mode (e.g., 2 k, 4 k, 8 k FFT operation length) of the second pilot signal using the first pilot signal of the signal frame.
The demodulator 520 demodulates the reception signal under the FFT mode of the second pilot signal. The equalizer 540 performs channel estimation of the reception signal, and outputs the channel-estimation resultant signal. The de-interleaver 560 deinterleaves the channel-equalized reception signal. The demapper 570 demaps the interleaved symbol using the symbol demapping scheme corresponding to the transmission-signal symbol mapping scheme (e.g., QAM).
The parameter detector 550 acquires physical parameter information (e.g., Layer-1 (L1) information) contained in the second pilot signal from the output signal of the equalizer 540, and transmits the acquired physical parameter information to the reception unit 500 and the synchronization unit 510. The reception unit 500 is able to change the RF channel to another channel using network information detected by the parameter detector 550.
The parameter detector 550 outputs service-associated information, service decider 580 decodes service data of the reception signal according to the service-associated information from the parameter detector 550, and outputs the decoded service data.
The demapper 570 may include the muxs 2475a and 2475b and output the bit stream obtained by restoring the order of the bits of which the locations of the MSB and the LSB are changed according to the code rate of the error correction coding and the symbol mapping method.
FIG. 37 is a view showing an embodiment of a method for transmitting a signal.
The service stream is error-correction-coded (S110).
As the error correction coding method, an LDPC error correction coding scheme may be used or error correction coding may be performed at various code rates. The bits error-correction-coded according to a specific error code rate may be included in the error-correction-coded block according to the error correction coding mode. If the error correction coding method is the LDPC, the normal mode (64800 bits) and the short mode (16200 bits) may be used.
The error-correction-coded bits are interleaved (S120). The interleaving may be performed by storing and reading the bits included in the error-correction-coded block in and from the memory in different directions. The number of rows and the number of columns may be changed according to the error correction coding mode.
The interleaved bit stream is demultiplexed and the sub streams are output by the demultiplexing (S130). The demultiplexing method may be changed according to the code rate of the error correction coding or/and the symbol mapping method and various examples including FIG. 17 are already described above. The interleaved input bits may be converted into the sub streams by the demultiplexing methods which be changed according to the code rate of the error correction coding or/and the symbol mapping method. FIG. 18 shows an example of outputting the sub streams according to the demultiplexing methods. The number of output sub streams may be changed according to the demultiplexing methods. If the demultiplexing is performed, the locations of the bits in the cell word mapped to the symbols in the interleaved bit stream are changed and thus the MSB and the LSB may be changed. Therefore, although the reliability of the bit of a specific location in the error-correction-coded block according to the error correction coding mode is low, the locations of the bits may be changed such that the reliability of the bit is improved in the symbol mapping step.
The demultiplexed sub streams are sequentially selected and the bits included in the selected sub streams are mapped to the symbols (S140). There are methods of sequentially selecting the plurality of sub streams. The symbol-mapped cell word may be changed according to the order of selecting the sub streams.
At least one symbol mapping method may be used. For example, the higher order symbol mapping method and the lower order symbol mapping method may be used together.
A signal frame in which the mapped symbols are arranged in at least one frequency band and temporally-divided slots of the at least one frequency band is built (S150). A reference symbol and a pilot symbol may be inserted into the signal frame. The symbols of the plurality of service streams which are subjected to the steps S110 to S140 may be arranged in the signal frame in the step S150. The symbols of the plurality of service streams are distributed in the at least one frequency band, and the distributed symbols may be arranged at locations which are temporally shifted in the frequency band or between the frequency bands.
The signal frame is converted into the time domain according to the OFDM method and the guard interval is inserted into the OFDM symbols converted into the time domain (S160). The length of the guard interval may be changed according to the FFT mode used in the OFDM method.
The preamble for identifying the signal frame is inserted into the start portion of the signal frame of each RF band and the signal is transmitted (S170). The first pilot signal and the second pilot signal may be inserted into the preamble.
FIG. 38 is a view showing an embodiment of a method for receiving a signal.
The method of receiving the transmitted signal is as follows.
The signal is received from a specific frequency band included in the signal frame (S210). The signal frame may have a plurality of frequency bands. The signal may be received from the specific frequency band.
When the signal frame is detected from the received signal, the received signal is demodulated by the OFDM method and the signal frame corresponding to the frequency band is parsed from the demodulated signal (S220). The signal frame is parsed such that the number of frequency bands included in the signal frame and the service stream included in the frequency band may be identified, if the signal frame has several frequency bands. And if the frequency bands are hopped, the symbols of a desired service stream can be obtained.
The symbol demapping corresponding to the symbol mapping method is performed with respect to the symbol stream and the symbol-demapped sub streams are output (S230). The symbol demapping method corresponding to at least one symbol mapping method may be used. For example, the hybrid symbol mapping/demapping method may be used.
The plurality of sub streams are multiplexed according to the symbol mapping method or/and the code rate of the error correction coding and one bit stream is output (S240). The reliability of the specific bit of the error-correction-coded block may be low according to the symbol mapping method and the code rate of the error correction coding. Accordingly, the sub streams may be multiplexed such that the MSB and the LSB of the cell word mapped to the symbol are rearranged. The multiplexing method may correspond to the demultiplexing method of the step S130.
The output bit streams are bit-deinterleaved (S250). The deinterleaving method may correspond to the step S120.
The deinterleaved streams may be error-correction-decoded (S260).
The service is obtained from the error-correction-decoded service streams (S270).
According to the apparatus for transmitting and receiving the signal and the method for transmitting and receiving the signal of the present invention, it is possible to readily detect and restore the transmitted signal. In addition, it is possible to improve the signal transmission/reception performance of the transmitting/receiving system.
It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
MODE FOR THE INVENTION
The embodiments of the invention are described in the best mode of the invention.
INDUSTRIAL APPLICABILITY
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 for transmitting a signal, the method comprising:
error-correction-coding service data according to an error-correction coding method;
interleaving bits of the error-correction-coded service data, wherein the interleaving comprises:
writing the error-correction-coded service data column-wise into a memory; and
reading the written service data row-wise from the memory,
wherein a number of columns and a number of rows of the memory used for the writing and reading vary according to symbol mapping methods, wherein the symbol mapping methods include 16-QAM, 64-QAM, and 256-QAM;

demultiplexing the interleaved bits according to a code rate of the error-correction coding method and one of the symbol mapping methods, wherein an order of outputting demultiplexed bits is different from an order of the interleaved bits when the symbol mapping method is one of 16-QAM, 64-QAM, or 256-QAM,
mapping the demultiplexed bits to a symbol;
building a signal frame including the mapped symbol;
modulating the signal frame according to an orthogonal frequency division multiplexing (OFDM) method; and
transmitting the signal including the modulated signal frame via at least one frequency band.

2. The method according to claim 1, wherein a least significant bit (LSB) or a most significant bit (MSB) of the bits mapped to the symbol is determined by the demultiplexing.

3. A method for receiving a signal, the method comprising:
receiving the signal including a signal frame via at least one frequency band, the signal frame including symbols for at least one service;
demodulating the signal frame in the received signal by an orthogonal frequency division multiplexing (OFDM) method;
acquiring the symbols of the at least one service from the signal frame;
de-mapping each of the acquired symbols into bits;
multiplexing the de-mapped bits according to a code rate of an error-correction coding method and a symbol mapping method, wherein the symbol mapping method is one of 16-QAM, 64-QAM, or 256-QAM, and wherein an order of multiplexed bits is different from an order of the de-mapped bits when the symbol mapping method is one of 16-QAM, 64-QAM, or 256-QAM;
deinterleaving the multiplexed bits; and
error-correction-decoding the de-interleaved bits according to the code rate of the error-correction coding method,
wherein:
the deinterleaving is performed by an inverse process of an interleaving process,
the interleaving process comprises:
writing error-correction-coded service data column-wise into a memory; and
reading the written service data row-wise from the memory, and

a number of columns and a number of rows of the memory used for the writing and reading vary according to the symbol mapping method.

4. An apparatus for transmitting a signal, the apparatus comprising:
an error-correction encoder for error-correction-coding service data according to an error-correction coding method;
a bit interleaver for interleaving bits of the error-correction-coded service data, wherein the bit interleaver is configured to:
write the error-correction-coded service data column-wise into a memory; and
read the written service data row-wise from the memory,
wherein a number of columns and a number of rows of the memory used for the writing and reading vary according to symbol mapping methods, wherein the symbol mapping methods include 16-QAM, 64-QAM, and 256-QAM;

a demultiplexer for demultiplexing the interleaved bits according to a code rate of the error-correction coding method and one of the symbol mapping methods, wherein an order of outputting demultiplexed bits is different from an order of the interleaved bits when the symbol mapping method is one of 16-QAM, 64-QAM, or 256-QAM;
a symbol mapper for mapping the demultiplexed bits to a symbol;
a signal frame builder for building a signal frame including the mapped symbol;
a modulator for modulating the signal frame according to an orthogonal frequency division multiplexing (OFDM) method; and
a transmitter for transmitting a signal including the modulated signal frame via at least one frequency band.

5. The apparatus according to claim 4, wherein a least significant bit (LSB) or a most significant bit (MSB) of the bits mapped to the symbol is determined by the demultiplexing.

6. An apparatus for receiving a signal, the apparatus comprising:
a receiver for receiving the signal including a signal frame via at least one frequency band, the signal frame including symbols for at least one service;
a demodulator for demodulating the signal frame included in the received signal according to an orthogonal frequency division multiplexing (OFDM) method;
a signal frame parser for acquiring the symbols of the at least one service from the signal frame;
a symbol de-mapper for de-mapping each of the acquired symbols into bits;
a multiplexer for multiplexing the de-mapped bits according to a code rate of an error-correction coding method and a symbol mapping method, wherein the symbol mapping method is one of 16-QAM, 64-QAM, or 256-QAM, and wherein an order of multiplexed bits is different from an order of the de-mapped bits when the symbol mapping method is one of 16-QAM, 64-QAM, or 256-QAM;
a bit deinterleaver for deinterleaving the multiplexed bits; and
an error correction decoder for error-correction-decoding the deinterleaved bits according to the code rate of the error-correction coding method,
wherein the bit deinterleaver performs an inverse process of an interleaver, and
wherein the interleaver is configured to:
write error-correction-coded service data column-wise into a memory; and
read the written service data row-wise from the memory, and
wherein a number of columns and a number of rows of the memory used for the writing and reading vary according to the symbol mapping method.