EP2122958A1

EP2122958A1 - Apparatus and method for pilot insertion and arrangement for hierarchical modulation in ofdm transmission system

Info

Publication number: EP2122958A1
Application number: EP08704919A
Authority: EP
Inventors: Jae-Hyun Seo; Ju-Yeun Kim; Heung-Mook Kim; Seo-Mee Choi; Young-Su Kim; Jong-Soo Lim; Soo-In Lee; Chie-Teuk Ahn
Original assignee: Electronics and Telecommunications Research Institute ETRI
Current assignee: Electronics and Telecommunications Research Institute ETRI
Priority date: 2007-01-23
Filing date: 2008-01-22
Publication date: 2009-11-25
Also published as: KR20080069495A; EP2122958A4; WO2008091102A1

Abstract

Provided is a hierarchical modulation apparatus capable of improving transmission performance of an OFDM transmission system through pilot insertion and a pilot array structure. In the OFDM transmission system having a base layer channel encoder, an enhancement layer channel encoder, and hierarchical modulator, the hierarchical modulation apparatus includes: a pilot insertion unit inserting pilots into an encoded enhancement layer signal sequence output from the enhancement layer encoder, the pilots having a correlation with a base layer signal sequence corresponding to the same sub-carriers as those of the encoded enhancement layer signal sequence; and a pilot size controller controlling sizes of the pilots received from the hierarchical modulator. Accordingly, by applying the hierarchical modulation to an existing DMB system, it is possible to minimize influence of channels to an existing service and increase a data transmission rate.

Description

APPARATUS AND METHOD FOR PILOT INSERTION AND ARRANGEMENT FOR HIERARCHICAL MODULATION IN OFDM

TRANSMISSION SYSTEM

Technical Field

[1] The present invention relates to an orthogonal frequency division multiplexing

(OFDM) system, and more particularly, to a hierarchical modulation apparatus and a transceiver apparatus capable of improving transmission performance of an OFDM transmission system by using pilot insertion and a pilot array structure in hierarchical modulation of the OFDM transmission system.

[2] This work was supported by the IT R&D program of MIC/IITA [2006-S-017-01, Development of advanced transmission technology for the terrestrial DMB system] Background Art

[3] In hierarchical modulation, at least two modulated signals that are separately modulated in different modulation schemes are synchronously modulated so as to transmit a multiplexed signal of the signals.

[4] In the hierarchical modulation, a base layer signal is a signal transmitted in an existing system, and an enhancement layer signal is a signal for providing a service added to the base layer signal.

[5] When transmitting and receiving hierarchically-modulated signals, signal reception performance of the base layer is lower than signal transmission performance of the enhancement layer. Therefore, in order to improve the signal transmission performance of the enhancement layer, additional pilot signals need to be inserted into the enhancement layer signals. In addition, a specific pilot arrangement pattern is needed. Disclosure of Invention Technical Problem

[6] The present invention provides a hierarchical modulation apparatus, in which pilots are inserted into only an enhancement layer signal without influencing a base layer signal when the pilots according to a protocol between a transmitter and a receiver are required for maintaining performance of reception and performance of in-phase demodulation of a hierarchically-modulated signal.

[7] The present invention also provides a hierarchical modulation apparatus capable of maintaining backward compatibility with an existing transmission standard when pilots are inserted into an enhancement layer signal in a pilot array structure according to a protocol between a transmitter and a receiver in hierarchical modulation. Technical Solution [8] According to an aspect of the present invention, there is provided a transmitting apparatus outputting a hierarchically-modulated signal in an OFDM (orthogonal frequency division multiplexing) system, comprising: a first channel encoder encoding a base layer signal sequence; a second channel encoder encoding an enhancement layer signal sequence; a pilot insertion unit inserting pilots into the enhancement layer signal sequence, the pilots having a correlation with the base layer signal sequence corresponding to the same sub-carriers as those of the encoded enhancement layer signal sequence output from the second channel encoder; and a hierarchical modulator modulating the encoded base layer signal sequence and the encoded enhancement layer signal sequence comprising the pilots output from the first channel encoder and the pilot insertion unit, respectively, and multiplexing the modulated signal sequences.

[9] According to another aspect of the present invention, there is provided a hierarchical modulation apparatus in an OFDM transmission system having a base layer channel encoder, an enhancement layer channel encoder, and hierarchical modulator, comprising: a pilot insertion unit inserting pilots into an encoded enhancement layer signal sequence output from the enhancement layer encoder, the pilots having a correlation with a base layer signal sequence corresponding to the same sub-carriers as those of the encoded enhancement layer signal sequence; and a pilot size controller controlling sizes of the pilots received from the hierarchical modulator.

[10] According to another aspect of the present invention, there is provided a receiver apparatus comprising: a hierarchical separator which receives a multiplexed signal of an encoded base layer signal sequence and a signal having pilots inserted into an encoded enhancement layer signal sequence and separates the encoded base layer signal sequence from the signal having the pilots inserted into the encoded enhancement layer signal sequence; a first channel decoder which demodulates the encoded base layer signal sequence separated by the hierarchical separator to transform the encoded base layer signal sequence into a base layer data; a channel estimation/ equalization unit which estimates channels of the sub-carriers from the signal having the pilots inserted into the encoded enhancement layer signal sequence by using pilot size and position information and equalizes the channels over the entire sub-carriers; and a second channel decoder which demodulates the encoded enhancement layer signal sequence transmitted from the channel estimation/equalization unit to transform the enhancement layer signal sequence into an enhancement layer data.

[11] According to another aspect of the present invention, there is provided an OFDM transmission system having a transmitter and a receiver, wherein the transmitter comprises: a first channel encoder encoding a base layer signal sequence; a second channel encoder encoding an enhancement layer signal sequence; a pilot insertion unit inserting pilots into the enhancement layer signal sequence, the pilots having a correlation with the base layer signal sequence corresponding to the same sub-carriers as those of the encoded enhancement layer signal sequence output from the second channel encoder; and a hierarchical modulator modulating the signal sequences output from the first channel encoder and the pilot insertion unit and multiplexing the modulated signal sequences, and wherein the receiver comprises: a hierarchical separator which receives a multiplexed signal of the encoded base layer signal sequence and the signal having pilots inserted into the encoded enhancement layer signal sequence and separates the base layer signal sequence from the signal having the pilots inserted into the enhancement layer signal sequence; a first channel decoder which demodulates the encoded base layer signal sequence separated by the hierarchical separator to transform the encoded base layer signal sequence into a base layer data; a channel estimation/equalization unit which estimates channels of the sub- carriers from the signal having the pilots inserted into the enhancement layer signal sequence by using pilot size and position information and equalizes the channels over the entire sub-carriers; and a second channel decoder which demodulates the enhancement layer signal sequence transmitted from the channel estimation/equalization unit to transform the enhancement layer signal sequence into an enhancement layer data.

[12] According to another aspect of the present invention, there is provided a transmitting method of outputting hierarchically-modulated signals in an OFDM transmission system, comprising: (a) encoding a base layer signal sequence; (b) encoding an en hancement layer signal sequence; (c) inserting pilots into the enhancement layer signal sequence, the pilots having a correlation with the base layer signal sequence corresponding to the same sub-carriers as those of the encoded enhancement layer signal sequence encoded in (b); and (d) modulating the signal sequences output in (a) and (c) and multiplexing the modulated signal sequences.

[13] According to another aspect of the present invention, there is provided a hierarchically modulating method in an OFDM transmission system having a base layer channel encoder, an enhancement layer channel encoder, and hierarchical modulator, comprising: (a) inserting pilots into an encoded enhancement layer signal sequence output from the enhancement layer encoder, the pilots having a correlation with a base layer signal sequence corresponding to the same sub-carriers as those of the encoded enhancement layer signal sequence; and (b) controlling sizes of the pilots received from the hierarchical modulator.

[14] According to another aspect of the present invention, there is provided a receiving method of outputting a hierarchical data from a hierarchically-demodulated signal in an OFDM transmission system, comprising: (a) receiving a multiplexed signal of an encoded base layer signal sequence and a signal having pilots inserted into an encoded enhancement layer signal sequence and separating the base layer signal sequence from the signal having the pilots inserted into the enhancement layer signal sequence; (b) demodulating the separated encoded base layer signal sequence to transform the encoded base layer signal sequence into a base layer data; (c) estimating channels of the sub-carriers from the signal having the pilots inserted into the enhancement layer signal sequence by using pilot size and position information and equalizing the channels over the entire sub-carriers; and (d) demodulating the enhancement layer signal sequence transmitted from (c) to transform the enhancement layer signal sequence into an enhancement layer data.

[15] According to another aspect of the present invention, there is provided an OFDM transmitting method comprising: (a) encoding a base layer signal sequence; (b) encoding an enhancement layer signal sequence; (c) inserting pilots into the enhancement layer signal sequence, the pilots having a correlation with the base layer signal sequence corresponding to the same sub-carriers as those of the encoded enhancement layer signal sequence encoded in (b); (d) modulating the signal sequences output in (a) and (c) and multiplexing the modulated signal sequences; (e) receiving a multiplexed signal of the encoded base layer signal sequence and the signal having pilots inserted into the encoded enhancement layer signal sequence and separating the base layer signal sequence from the signal having the pilots inserted into the enhancement layer signal sequence; (f) demodulating the separated encoded base layer signal sequence to transform the encoded base layer signal sequence into a base layer data; (g) estimating channels of the sub-carriers from the signal having the pilots inserted into the enhancement layer signal sequence by using pilot size and position information and equalizing the channels over the entire sub-carriers; and (h) demodulating the enhancement layer signal sequence transmitted from (g) to transform the enhancement layer signal sequence into an enhancement layer data. Advantageous Effects

[16] According to the present invention, it is possible to maintain compatibility of an

OFDM communication or broadcasting system employing hierarchical modulation with an existing system and to improve performance of reception by transmitting pilots through only an enhancement layer signal.

[17] In addition, by using a pilot insertion apparatus and a pilot array method for improving the performance of reception and applying the hierarchical modulation to an existing DMB system, it is possible to minimize the influence of channels on an existing service and increase a data transmission rate.

[18] In addition, when an enhancement layer signal existing in a hierarchically-modulated signal is received by the receiver, the pilots can be used for frequency synchronization, symbol timing synchronization, channel estimation, and channel equalization, and thus reception performance can be improved. Description of Drawings

[19] The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:

[20] FIG. 1 is a block diagram illustrating a transmitter stage for hierarchical modulation in a digital audio broadcasting (DAB) or digital multimedia broadcasting (DMB) system, according to an embodiment of the present invention;

[21] FIG. 2 is a block diagram illustrating a transmitter stage in an orthogonal frequency division multiplexing (OFDM) transmission system, according to an embodiment of the present invention;

[22] FIG. 3 is a block diagram illustrating a receiver stage for hierarchical modulation in a

DAB or DMB system, according to an embodiment of the present invention;

[23] FIG. 4 is a block diagram illustrating a receiver stage in an OFDM transmission system, according to an embodiment of the present invention;

[24] FIG. 5 is a constellation diagram illustrating a π/4-DQPSK signal in a conventional

OFDM transmission system;

[25] FIG. 6 is a constellation diagram illustrating transmission of pilots inserted into an enhancement layer signal sequence in a hierarchically-modulated π/4-DQPSK signal according to an embodiment of the present invention;

[26] FIG. 7 is a constellation diagram illustrating transmission of a power-increased pilot inserted into an enhancement layer signal sequence in a hierarchically-modulated π/ 4-DQPSK signal according to an embodiment of the present invention;

[27] FIG. 8 is a view illustrating a 10x2 array structure of pilots inserted into an enhancement layer signal sequence according to an embodiment of the present invention;

[28] FIG. 9 is a view illustrating a 10x5 array structure of pilots inserted into an enhancement layer signal sequence according to an embodiment of the present invention;

[29] FIG. 10 is a view illustrating a 12x3 array structure of pilots inserted into an enhancement layer signal sequence according to an embodiment of the present invention;

[30] FIG. 11 is a view illustrating a 12x4 array structure of pilots inserted into an enhancement layer signal sequence according to an embodiment of the present invention;

[31] FIG. 12 is a flowchart illustrating a transmission method of outputting a hierarchically-modulated signal, according to an embodiment of the present invention;

[32] FIG. 13 is a flowchart illustrating a hierarchical modulation method according to an embodiment of the present invention;

[33] FIG. 14 is a flowchart illustrating a reception method of outputting a hierarchical data from a hierarchically-modulated signal, according to an embodiment of the present invention; and [34] FIG. 15 is a flowchart illustrating an OFDM transmission method according to an embodiment of the present invention. Best Mode

[35]

[36] According to an aspect of the present invention, there is provided a transmitting apparatus outputting a hierarchically-modulated signal in an OFDM (orthogonal frequency division multiplexing) system, comprising: a first channel encoder encoding a base layer signal sequence; a second channel encoder encoding an enhancement layer signal sequence; a pilot insertion unit inserting pilots into the enhancement layer signal sequence, the pilots having a correlation with the base layer signal sequence corresponding to the same sub-carriers as those of the encoded enhancement layer signal sequence output from the second channel encoder; and a hierarchical modulator modulating the encoded base layer signal sequence and the encoded enhancement layer signal sequence comprising the pilots output from the first channel encoder and the pilot insertion unit, respectively, and multiplexing the modulated signal sequences.

[37] In the above aspect of the present invention, the first channel encoder includes an RS encoder, a convolution interleaver, an energy dispersal scrambler, a convolution encoder, a Time interleaver, a Symbol mapper, and a frequency interleaver.

[38] In addition, the second channel encoder includes a channel encoder, a time interleaver, a symbol mapper, and a frequency interleaver.

[39] In addition, signal strength of the pilots may be equal to or larger than that of the enhancement layer signal sequence.

[40] In addition, the transmitting apparatus may further comprise a pilot size controller controlling the sizes of the pilots received from the hierarchical modulator.

[41] In addition, the pilot controller may control the signal strength of the pilots so as to be equal to or larger than that of the enhancement layer signal sequence.

[42] In addition, the pilot insertion unit may divide positions of the sub-carriers corresponding to the enhancement layer signal sequence in units of a predetermined interval and periodically insert the pilots into the enhancement layer signal sequence in the interval in units of an arbitrary number of OFDM signals.

[43] In addition, the pilot insertion unit may obtain a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted by dividing an OFDM symbol index 1 by 2 to calculate a remainder, adding five times the remainder and ten times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value and insert the pilot into the position indicated by the pilot sub-carrier index K.

[44] In addition, the pilot insertion unit may obtain a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted by dividing an OFDM symbol index 1 by 5 to calculate a remainder, adding two times the remainder and ten times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value and insert the pilot into the position indicated by the pilot sub-carrier index K.

[45] In addition, the pilot insertion unit may obtain a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted by dividing an OFDM symbol index 1 by 3 to calculate a remainder, adding four times the remainder and twelve times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value and insert the pilot into the position indicated by the pilot sub- carrier index K.

[46] In addition, the pilot insertion unit may obtain a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted by dividing an OFDM symbol index 1 by 4 to calculate a remainder, adding three times the remainder and twelve times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value and insert the pilot into the position indicated by the pilot sub- carrier index K.

[47] According to another aspect of the present invention, there is provided a hierarchical modulation apparatus in an OFDM transmission system having a base layer channel encoder, an enhancement layer channel encoder, and hierarchical modulator, comprising: a pilot insertion unit inserting pilots into an encoded enhancement layer signal sequence output from the enhancement layer encoder, the pilots having a correlation with a base layer signal sequence corresponding to the same sub-carriers as those of the encoded enhancement layer signal sequence; and a pilot size controller controlling sizes of the pilots received from the hierarchical modulator.

[48] In the above aspect of the present invention, sizes of the pilots may be equal to or larger than that of the enhancement layer signal sequence.

[49] In addition, the pilot size controller may control the sizes of the pilots so as to be equal to or larger than that of the enhancement layer signal sequence.

[50] In addition, the pilot insertion unit may divide positions of the sub-carriers corresponding to the enhancement layer signal sequence in units of a predetermined interval and periodically insert the pilots into the enhancement layer signal sequence in the interval in units of an arbitrary number of OFDM signals.

[51] In addition, the pilot insertion unit may obtain a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted by dividing an OFDM symbol index 1 by 2 to calculate a remainder, adding five times the remainder and ten times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value and insert the pilot into the position indicated by the pilot sub-carrier index K. [52] In addition, the pilot insertion unit may obtain a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted by dividing an OFDM symbol index 1 by 5 to calculate a remainder, adding two times the remainder and ten times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value and insert the pilot into the position indicated by the pilot sub-carrier index K.

[53] In addition, the pilot insertion unit may obtain a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted by dividing an OFDM symbol index 1 by 3 to calculate a remainder, adding four times the remainder and twelve times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value and insert the pilot into the position indicated by the pilot sub- carrier index K.

[54] In addition, the pilot insertion unit may obtain a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted by dividing an OFDM symbol index 1 by 4 to calculate a remainder, adding three times the remainder and twelve times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value and insert the pilot into the position indicated by the pilot sub- carrier index K.

[55] According to another aspect of the present invention, there is provided a receiver apparatus comprising: a hierarchical separator which receives a multiplexed signal of an encoded base layer signal sequence and a signal having pilots inserted into an encoded enhancement layer signal sequence and separates the encoded base layer signal sequence from the signal having the pilots inserted into the encoded enhancement layer signal sequence; a first channel decoder which demodulates the encoded base layer signal sequence separated by the hierarchical separator to transform the encoded base layer signal sequence into a base layer data; a channel estimation/ equalization unit which estimates channels of the sub-carriers from the signal having the pilots inserted into the encoded enhancement layer signal sequence by using pilot size and position information and equalizes the channels over the entire sub-carriers; and a second channel decoder which demodulates the encoded enhancement layer signal sequence transmitted from the channel estimation/equalization unit to transform the enhancement layer signal sequence into an enhancement layer data.

[56] In the above aspect of the present invention, the first channel decoder includes a convolution de-interleaver and an RS decoder.

[57] In addition, the second channel decoder includes a layered symbol de-mapper, a time de-interleaver, a channel decoder, and an energy dispersal de-scrambler.

[58] In addition, the channel estimation/equalization unit may compare signals corresponding to pilot positions in the signals having the pilots inserted into the en- hancement layer signal sequence by using signal strength of the pilot size and position information so as to estimate channels of the sub-carriers and equalize the channels over the entire sub-carriers by using values of the estimated channel signals, thereby removing influence of the channels.

[59] According to another aspect of the present invention, there is provided an OFDM transmission system having a transmitter and a receiver, wherein the transmitter comprises: a first channel encoder encoding a base layer signal sequence; a second channel encoder encoding an enhancement layer signal sequence; a pilot insertion unit inserting pilots into the enhancement layer signal sequence, the pilots having a correlation with the base layer signal sequence corresponding to the same sub-carriers as those of the encoded enhancement layer signal sequence output from the second channel encoder; and a hierarchical modulator modulating the signal sequences output from the first channel encoder and the pilot insertion unit and multiplexing the modulated signal sequences, and wherein the receiver comprises: a hierarchical separator which receives a multiplexed signal of the encoded base layer signal sequence and the signal having pilots inserted into the encoded enhancement layer signal sequence and separates the base layer signal sequence from the signal having the pilots inserted into the enhancement layer signal sequence; a first channel decoder which demodulates the encoded base layer signal sequence separated by the hierarchical separator to transform the encoded base layer signal sequence into a base layer data; a channel estimation/equalization unit which estimates channels of the sub- carriers from the signal having the pilots inserted into the enhancement layer signal sequence by using pilot size and position information and equalizes the channels over the entire sub-carriers; and a second channel decoder which demodulates the enhancement layer signal sequence transmitted from the channel estimation/equalization unit to transform the enhancement layer signal sequence into an enhancement layer data.

[60] According to another aspect of the present invention, there is provided a transmitting method of outputting hierarchically-modulated signals in an OFDM transmission system, comprising: (a) encoding a base layer signal sequence; (b) encoding an enhancement layer signal sequence; (c) inserting pilots into the enhancement layer signal sequence, the pilots having a correlation with the base layer signal sequence corresponding to the same sub-carriers as those of the encoded enhancement layer signal sequence encoded in (b); and (d) modulating the signal sequences output in (a) and (c) and multiplexing the modulated signal sequences.

[61] In the above aspect of the present invention, signal strength of the pilots may be equal to or larger than that of the enhancement layer signal sequence.

[62] In addition, the transmitting method may further comprise (e) controlling the signal strength of the pilots received from (d).

[63] In addition, in (e), the signal strength of the pilots may be controlled to be equal to or larger than that of the enhancement layer signal sequence.

[64] In addition, in (c), positions of the sub-carriers corresponding to the enhancement layer signal sequence may be divided in units of a predetermined interval, and the pilots may be periodically inserted into the enhancement layer signal sequence in the interval in units of an arbitrary number of OFDM signals.

[65] In addition, in (c), a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted may be obtained by dividing an OFDM symbol index 1 by 2 to calculate a remainder, adding five times the according remainder and ten times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value, and the pilot may be inserted into the position indicated by the pilot sub-carrier index K.

[66] In addition, in (c), a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted is obtained by dividing an OFDM symbol index 1 by 5 to calculate a remainder, adding two times the according remainder and ten times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value, and the pilot may be inserted into the position indicated by the pilot sub-carrier index K.

[67] In addition, in (c), a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted is obtained by dividing an OFDM symbol index 1 by

3 to calculate a remainder, adding four times the according remainder and twelve times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value, and the pilot may be inserted into the position indicated by the pilot sub- carrier index K.

[68] In addition, in (c), a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted is obtained by dividing an OFDM symbol index 1 by

4 to calculate a remainder, adding three times the according remainder and twelve times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value, and the pilot may be inserted into the position indicated by the pilot sub-carrier index K.

[69] According to another aspect of the present invention, there is provided a hierarchically modulating method in an OFDM transmission system having a base layer channel encoder, an enhancement layer channel encoder, and hierarchical modulator, comprising: (a) inserting pilots into an encoded enhancement layer signal sequence output from the enhancement layer encoder, the pilots having a correlation with a base layer signal sequence corresponding to the same sub-carriers as those of the encoded enhancement layer signal sequence; and (b) controlling sizes of the pilots received from the hierarchical modulator.

[70] In the above aspect of the present invention, sizes of the pilots may be equal to or larger than that of the enhancement layer signal sequence.

[71] In addition, in (a), positions of the sub-carriers corresponding to the enhancement layer signal sequence may be divided in units of a predetermined interval, and the pilots may be periodically inserted into the enhancement layer signal sequence in the interval in units of an arbitrary number of OFDM signals.

[72] In addition, in (b), the sizes of the pilots may be controlled to be equal to or larger than that of the enhancement layer signal sequence.

[73] In addition, in (a), a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted may be obtained by dividing an OFDM symbol index 1 by 2 to calculate a remainder, adding five times the according remainder and ten times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value, and the pilot may be inserted into the position indicated by the pilot sub-carrier index K.

[74] In addition, in (a), a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted is obtained by dividing an OFDM symbol index 1 by 5 to calculate a remainder, adding two times the according remainder and ten times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value, and the pilot may be inserted into the position indicated by the pilot sub-carrier index K.

[75] In addition, in (a), a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted is obtained by dividing an OFDM symbol index 1 by

[76] In addition, in (a), a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted is obtained by dividing an OFDM symbol index 1 by

[77] According to another aspect of the present invention, there is provided a receiving method of outputting a hierarchical data from a hierarchically-demodulated signal in an OFDM transmission system, comprising: (a) receiving a multiplexed signal of an encoded base layer signal sequence and a signal having pilots inserted into an encoded enhancement layer signal sequence and separating the base layer signal sequence from the signal having the pilots inserted into the enhancement layer signal sequence; (b) demodulating the separated encoded base layer signal sequence to transform the encoded base layer signal sequence into a base layer data; (c) estimating channels of the sub-carriers from the signal having the pilots inserted into the enhancement layer signal sequence by using pilot size and position information and equalizing the channels over the entire sub-carriers; and (d) demodulating the enhancement layer signal sequence transmitted from (c) to transform the enhancement layer signal sequence into an enhancement layer data.

[78] In the above aspect of the present invention, in (c), signals corresponding to pilot positions in the signals having the pilots inserted into the enhancement layer signal sequence may be compared by using the pilot size and position information so as to estimate channels of the sub-carriers, and the channels may be equalized over the entire sub-carriers by using values of the estimated channel signals, thereby removing influence of the channels.

[79] According to another aspect of the present invention, there is provided an OFDM transmitting method comprising: (a) encoding a base layer signal sequence; (b) encoding an enhancement layer signal sequence; (c) inserting pilots into the enhancement layer signal sequence, the pilots having a correlation with the base layer signal sequence corresponding to the same sub-carriers as those of the encoded enhancement layer signal sequence encoded in (b); (d) modulating the signal sequences output in (a) and (c) and multiplexing the modulated signal sequences; (e) receiving a multiplexed signal of the encoded base layer signal sequence and the signal having pilots inserted into the encoded enhancement layer signal sequence and separating the base layer signal sequence from the signal having the pilots inserted into the enhancement layer signal sequence; (f) demodulating the separated encoded base layer signal sequence to transform the encoded base layer signal sequence into a base layer data; (g) estimating channels of the sub-carriers from the signal having the pilots inserted into the enhancement layer signal sequence by using pilot size and position information and equalizing the channels over the entire sub-carriers; and (h) demodulating the enhancement layer signal sequence transmitted from (g) to transform the enhancement layer signal sequence into an enhancement layer data. Mode for Invention

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

[81] FIG. 1 is a block diagram illustrating a transmitter stage for hierarchical modulation in a digital audio broadcasting (DAB) or digital multimedia broadcasting (DMB) system, according to an embodiment of the present invention.

[82] FIG. 1 is used as a reference diagram for explaining FIG. 2, and the following de- scrip tion is made with reference to FIGS. 1 and 2.

[83] FIG. 2 is a block diagram illustrating a transmitter stage in an orthogonal frequency division multiplexing (OFDM) transmission system, according to an embodiment of the present invention. Referring to FIG. 2, the transmitter stage includes a base layer channel encoder 200, an enhancement layer channel encoder 210, a pilot insertion unit 220, a pilot size controller 230, and a hierarchical modulator 240.

[84] The base layer channel encoder 200 encodes base layer signal sequences. The enhancement layer channel encoder 210 encodes enhancement layer signal sequences.

[85] The base layer signal sequences and enhancement layer signal sequences may be encoded using convolution encoding, lattice encoding, turbo encoding, low density parity check (LDPC) encoding, or concatenated encoding that is a concatenation of the aforementioned encoding methods.

[86] The pilot insertion unit 220 inserts pilots into the modulated enhancement layer signal sequences output from the enhancement layer channel encoder 210 in a pilot array structure.

[87] The pilot array method will be described later in detail with reference to Equations 1 to 4.

[88] The hierarchical modulator 240 modulates signals output from the base layer channel encoder 200 and the pilot insertion unit 220 and performs mapping of the signals into corresponding signal spaces.

[89] In FIG. 2, each of the base layer signal sequences corresponds to an output signal of a TS MUX 140 for a base layer 100 of FIG. 1, and each of the enhancement layer signal sequences corresponds to an output signal of a TS MUX 150 for an enhancement layer 110 of FIG. 1.

[90] Referring to Fig. 1, an RS encoder, a convolution interleaver, an energy dispersal scrambler, a convolution encoder, a time interleaver, a symbol mapper, and frequency interleaver of the base layer 100 correspond to the base layer channel encoder 200 of F IG. 2.

[91] A channel encoder, a time interleaver, a symbol mapper, and a frequency interleaver of the enhancement layer 110 of FIG. 1 correspond to the enhancement layer channel encoder 210 of FIG. 2.

[92] The detailed configurations of the base layer 100 and the enhancement layer 110 of

FIG. 1 are one embodiment of the present invention. Therefore, the base layer channel encoder 200 and the enhancement layer channel encoder 210 may have configurations different from those of the base layer 100 and the enhancement layer 110 of FIG. 1.

[93] The present invention is characterized by a method of inserting pilots into the enhancement layer 110, but not detailed configurations of the base layer 100 and the enhancement layer 110. [94] Referring to FIG. 1, an alternate π/4 shifting unit 131 connected to the enhancement layer 110 of FIG. 1 and a base layer-based differential modulator 132, an adder 133, and an IFFT 134, and a guard interval inserter 135 connected to the base layer 100 of FIG. 1 correspond to the hierarchical modulator 240 of FIG. 2.

[95] The hierarchical modulator 240 processes an output signal of the alternate π/4 shifting unit 131 of the enhancement layer 110 of FIG. 1 by using sizes of the pilots received from the pilot size controller 230 of FIG. 2.

[96] The size of the pilots may be equal to or larger than a size of data loaded on the enhancement layer 110. For example, in a good propagation environment, the size of pilots needs to be larger than that of data. In a poor propagation environment, the size of pilots may be equal to that of data.

[97] The hierarchical modulator 240 demodulates signals output from the base layer channel encoder 200 and the pilot insertion unit 220 so as to perform mapping of the signals into corresponding signal spaces.

[98] For example, the base layer 100 may be a signal space for π/4-differential quadrature phase-shift keying (DQPSK) modulated signals, and the enhancement layer 110 may be a signal space of QPSK modulated signals.

[99] In addition, the enhancement layer 110 may be a signal space for signals modulated according to one of 2- ASK, 4- ASK, and 16-QAM modulation schemes. Various modulation schemes may be applied to the enhancement layer 110 according to propagation environment, data transmission rate, and the like.

[100] FIG. 3 is a block diagram illustrating a receiver stage for hierarchical modulation in a DAB or DMB system, according to an embodiment of the present invention.

[101] FIG. 4 is used as a reference diagram for explaining FIG. 3, and the following description is made with reference to FIGS. 3 and 4.

[102] FIG. 4 is a block diagram illustrating a receiver stage in an OFDM transmission system, according to an embodiment of the present invention. Referring to FIG. 4, the receiver stage includes a hierarchical separator 400, a channel estimation/equalization unit 410, a base layer demodulator 420, an enhancement layer demodulator 430, a base layer channel decoder 440, and an enhancement layer channel decoder 450.

[103] The hierarchical separator 400 receives a multiplexed signal transmitted from the hierarchical modulator 240 of FIG. 2 and separates the multiplexed signal into a base layer signal and an enhancement layer signal.

[104] The base layer demodulator 420 performs the same process as an existing demodulating process for DAB or DMB signals. Due to the same process as that of an existing DAB or DMB receiver stage, backward compatibility can be maintained.

[105] The channel estimation/equalization unit 410 is disposed before the enhancement layer demodulator 430. In order to remove influence of the channel to the received signal, the channel estimation/equalization unit 410 compares signals corresponding to pilot positions in the received signal by using the pilot size and position information 411 so as to estimate channels of the sub-carriers. The channel estimation/equalization unit 410 equalizes the channels over the entire sub-carriers by using values of the estimated channel signals.

[106] The enhancement layer demodulator 430 demodulates the enhancement layer signal from the signal output from the channel estimation/equalization unit 410.

[107] The pilot size and position information 411 is transmitted from the transmitter stage . The pilot size and position information 411 is in accordance with a protocol between the transmitter stage and the receiver stage.

[108] When the pilots are inserted, the signals corresponding to constellation positions of the base layer signal are transmitted to positions of sub-carriers according to the protocol. Therefore, the receiver stage uses information stored in an internal memory of the receiver stage, but not information which is obtained externally.

[109] The base layer channel decoder 440 performs inverse transformation on the encoded signal output from the base layer channel encoder of FIG. 2. That is, the base layer channel decoder 400 decodes the base layer signal sequence to transform the base layer signal sequence into base layer data.

[110] The enhancement layer channel decoder 450 performs inverse transformation on the encoded signal output from the enhancement layer channel encoder 210 of FIG. 2. That is, the enhancement layer channel decoder 450 decodes the enhancement layer signal sequence to transform the enhancement layer signal sequence into enhancement layer data.

[I l l] FIG. 5 is a constellation diagram illustrating a π/4-DQPSK signal in a conventional OFDM transmission system.

[112] FIG. 5 illustrates an example of constellation of a π/4-DQPSK transmission-scheme DMB or DMB transmission system.

[113] In FIG. 5, squares indicate sub-carrier signals of odd-numbered OFDM symbols from the firstly-transmitted phase reference symbol (PRS) in a DAB or DMB transmission frame.

[114] Circles indicate sub-carrier signals of even-numbered OFDM symbols from the PRS. In a conventional DAB or DMB transmission system, any pilot symbol is not included in the OFDM symbol.

[115] FIG. 6 is a constellation diagram illustrating transmission of pilots inserted into an enhancement layer signal sequence in a hierarchically-modulated π/4-DQPSK signal according to an embodiment of the present invention.

[116] More specifically, FIG. 6 is an example of a constellation diagram illustrating sub- carriers of the enhancement layer signal sequence and the pilots inserted into the en- hancement layer signal sequence in the case of applying hierarchical modulation to an existing DAB or DMB transmission system.

[117] In FIG. 6, OFDM symbol indices applied to the array structure of pilots are applied to only the OFDM symbols of a fast information channel and a main service channel of a frame structure of the DAB or DMB transmission system. Namely, a synchronization channel constructed with the PRSs is excluded.

[118] Similarly to FIG. 5, in FIG. 6, squares indicate sub-carrier signals of odd-numbered OFDM symbols from the firstly-transmitted phase reference symbol (PRS) in a DAB or DMB transmission frame.

[119] Circles indicate sub-carrier signals of even-numbered OFDM symbols from the PRS.

[120] Black squares or circles indicate pilot signals.

[121] The pilot signals are required for channel estimation and equalization for in-phase demodulation corresponding to the hierarchical modulation.

[122] In order to support compatibility with an existing system, in the hierarchical modulation, the π/4-DQPSK signal of the base layer is not modulated, but only the enhancement layer signal is modulated. Therefore, the pilot signals are inserted into only the enhancement layer signal.

[123] In this case, unlike most communication or broadcasting systems, the pilot signals are random data for which a protocol between the transmitter and the receiver is not established, and a power of the pilot signals is lower than that of the base layer signal.

[124] Accordingly, it is preferable that the pilot signals inserted into the enhancement layer signal has a correlation with the base layer signal corresponding to the sub-carrier of the pilot signal. The correlation between the pilot signal and the base layer signal is represented by the squares 510 and 610 of FIGS. 5 and 6.

[125] Namely, in a case where the base layer signal corresponding to a sub-carrier through which a pilot is transmitted in an even-number OFDM symbol interval which is even- numbered from the PRS is located at a position indicated by the squares 510 in an enhancement layer quadrant of FIG. 5, a signal corresponding to a constellation point indicated by the squares 610 in the enhancement layer quadrant of FIG. 6 is transmitted as a pilot signal, so that transmission power of the base layer signal can be increased. As a result, determination error of the base layer signal can be reduced.

[126] FIG. 7 is a constellation diagram illustrating transmission of a power- increased pilot inserted into an enhancement layer signal sequence in a hierarchically-modulated π/ 4-DQPSK signal according to an embodiment of the present invention.

[127] Although the determination error of the base layer signal can be reduced by inserting the pilots into the enhancement layer signal by using the method described with refe rence to FIG. 6, the powers of the pilot signal and the data signal in the enhancement layer signal are not different from each other. [128] Therefore, in a case where the base layer signal is located at the position indicated by the squares 510 in the enhancement layer quadrant of FIG. 5, a signal corresponding to a constellation point indicated by squares 710 in the enhancement layer quadrant of FIG. 7 is transmitted as a pilot signal, so that the power of the pilot signal in the enhancement layer signal can be greater than that of the data signal. Accordingly, when receiving the enhancement layer signal, performance of frequency synchronization, symbol timing synchronization, channel estimation, and channel equalization using the pilot signal can be improved.

[129] In FIGS. 6 and 7, dotted squares or dotted rhombi are illustrated for comparison of powers of pilot signals and data signals in the enhancement layer signal.

[130] As shown in FIG. 7, the power of the pilot signal inserted into the enhancement layer signal is greater than an average power of the data signals of the enhancement layer signal.

[131] However, since most sub-carriers of the enhancement layer signal are filled with the data signals, only the sub-carriers into which the pilots are inserted are shown in the constellation diagram of FIG. 7.

[132] In FIG. 7, OFDM symbol indices applied to the array structure of pilots are applied to only the OFDM symbols of a fast information channel and a main service channel of a frame structure of the DAB or DMB transmission system. Namely, a synchronization channel constructed with the PRSs is excluded.

[133] FIGS. 8 to 11 are views illustrating examples of array structures of pilots inserted into an enhancement layer signal.

[134] In FIGS. 8 to 11, OFDM symbol indices applied to array structures of pilots are applied to only the OFDM symbols of a fast information channel and a main service channel of a frame structure of a DAB or DMB transmission system. Namely, a synchronization channel constructed with PRSs is excluded.

[135] In FIGS. 8 to 11, Symbol Index 0 indicates a first OFDM symbol of the fast information channel.

[136] FIG. 8 is a view illustrating a 10x2 array structure of pilots inserted into an enhancement layer signal sequence according to an embodiment of the present invention.

[137] FIG. 8 is a view illustrating an example of a 10x2 array structure of pilots inserted into an enhancement layer signal sequence. For the convenience of description, Transmission Mode 1 in an existing DAB or DMB transmission frame is exemplified.

[138] Total numbers K of sub-carriers in Transmission Modes 1 to 4 are 1536, 384, 192, and 768, respectively. In addition, the same positions of pilots are applied to the transmission modes as described later.

[139] In Transmission Mode 1, the total number of sub-carriers is in a range of -K/2 to +K/2, where K is 1536. [140] Pilot sub-carrier indices indicating pilot-insertion positions are obtained from

Equation 1.

[141] [Equation 1] [142] K = l+5*mod(l,2)+10*p [143] Here, K denotes the pilot sub-carrier index, 1 denotes the OFDM symbol index, and the p is an integer of 0 or more. The mod(A, B) is a remainder when A is divided by B. [144] The K is in a range of 1 to 1536, and the p is in a range of 0 to 153. [145] K = { 1 ~ 768} is mapped into K' = {-769 ~ -l }, and K = {769 - 1536} is mapped into K' = { 1 - 768}. [146] Namely, the K' is in a range of -768 to +768, and the data and the pilots are not inserted into the range of K'. [147] In FIG. 8, the sub-carrier indices are represented by using the K'. In FIG. 8, the positions of pilots inserted into the enhancement layer signal are indicated in black. [148] In one OFDM symbol, one of ten sub-carriers corresponds to one pilot, and the pilot is repeated in a two-symbol period.

[149] FIG. 9 is a view illustrating a 10x5 array structure of pilots inserted into an enhancement layer signal sequence according to an embodiment of the present invention. [150] FIG. 9 is a view illustrating an example of a 10x5 array structure of pilots inserted into an enhancement layer signal sequence. For convenience of description,

Transmission Mode 1 in an existing DAB or DMB transmission frame is exemplified. [151] Total numbers K of sub-carriers in Transmission Modes 1 to 4 are 1536, 384, 192, and 768, respectively. In addition, the same positions of pilots are applied to the transmission modes as described later. [152] In Transmission Mode 1, the total number of sub-carriers is in a range of -K/2 to

+K/2, where K is 1536. [153] Pilot sub-carrier indices indicating pilot-insertion positions are obtained using

Equation 2.

[154] [Equation 2] [155] K = l+2*mod(l,5)+10*p [156] Here, K denotes the pilot sub-carrier index, 1 denotes the OFDM symbol index, and the p is an integer of 0 or more. The mod(A, B) is a remainder when A is divided by B. [157] The K is in a range of 1 to 1536, and the p is in a range of 0 to 153. [158] K = { 1 ~ 768} is mapped into K' = {-769 ~ -l }, and K = {769 - 1536} is mapped into K' = { 1 - 768}. [159] Namely, the K' is in a range of -768 to +768, and, in a case where K' is 0, the data and the pilots are not inserted. [160] In FIG. 9, the sub-carrier indices are represented by using the K'. In FIG. 9, the positions of pilots inserted into the enhancement layer signal are indicated in black. [161] In one OFDM symbol, one of ten sub-carriers corresponds to one pilot, and the pilot is repeated in a five- symbol period.

[162] FIG. 10 is a view illustrating a 12x3 array structure of pilots inserted into an enhancement layer signal sequence according to an embodiment of the present invention. [163] FIG. 10 is a view illustrating an example of a 12x3 array structure of pilots inserted into an enhancement layer signal sequence. For the convenience of description,

Transmission Mode 1 in an existing DAB or DMB transmission frame is exemplified. [164] Total numbers K of sub-carriers in Transmission Modes 1 to 4 are 1536, 384, 192, and 768, respectively. In addition, the same positions of pilots are applied to the transmission modes as described later. [165] In Transmission Mode 1, the total number of sub-carriers is in a range of -K/3 to

+K/2, where K is 1536. [166] Pilot sub-carrier indices indicating pilot-insertion positions are obtained from

Equation 3.

[167] [Equation 3] [168] K = 1+4 mod(l,3)+12*p [169] Here, K denotes the pilot sub-carrier index, 1 denotes the OFDM symbol index, and the p is an integer of 0 or more. The mod(A, B) is a remainder when A is divided by B. [170] The K is in a range of 1 to 1536, and the p is in a range of 0 to 153. [171] K = { 1 ~ 768} is mapped into K' = {-769 ~ -l }, and K = {769 - 1536} is mapped into K' = { 1 - 768}. [172] Namely, the K' is in a range of -768 to +768, and, in a case where K' is 0, the data and the pilots are not inserted. [173] In FIG. 10, the sub-carrier indices are represented by using the K'. In FIG. 10, the positions of pilots inserted into the enhancement layer signal are indicated in black. [174] In one OFDM symbol, one of twelve sub-carriers corresponds to one pilot, and the pilot is repeated in three-symbol period.

[175] FIG. 11 is a view illustrating a 12x4 array structure of pilots inserted into an enhancement layer signal sequence according to an embodiment of the present invention. [176] FIG. 11 is a view illustrating an example of a 12x4 array structure of pilots inserted into an enhancement layer signal sequence. For the convenience of description,

Transmission Mode 1 in an existing DAB or DMB transmission frame is exemplified. [177] Total numbers K of sub-carriers in Transmission Modes 1 to 4 are 1536, 384, 192, and 768, respectively. In addition, the same positions of pilots are applied to the transmission modes as described later. [178] In Transmission Mode 1, the total number of sub-carriers is in a range of -K/2 to

+K/2, where K is 1536. [179] Pilot sub-carrier indices indicating pilot-insertion positions are obtained using Equation 4.

[180] [Equation 4]

[181] K = l+3*mod(l,4)+12*p

[182] Here, K denotes the pilot sub-carrier index, 1 denotes the OFDM symbol index, and the p is an integer of 0 or more. The mod(A, B) is a remainder when A is divided by B.

[183] The K is in a range of 1 to 1536, and the p is in a range of 0 to 153.

[184] K = { 1 ~ 768} is mapped into K' = {-769 ~ -l }, and K = {769 - 1536} is mapped into K' = { 1 - 768}.

[185] Namely, the K' is in a range of -768 to +768, and, in a case where K' is 0, the data and the pilots are not inserted.

[186] In FIG. 11, the sub-carrier indices are represented by using the K'. In FIG. 11, the positions of pilots inserted into the enhancement layer signal are indicated in black.

[187] In one OFDM symbol, one of twelve sub-carriers corresponds to one pilot, and the pilot is repeated in a four- symbol period.

[188] In FIG. 6, although power of the pilots inserted into the enhancement layer signal is greater than that of the base layer signal, the same level of power is inserted in terms of the enhancement layer signal. In FIG. 7, the pilots having high power are inserted into the enhancement layer signal in terms of the base layer signal as well as the enhancement layer signal.

[189] The positions of pilots inserted into each OFDM symbol in FIG. 6 or 7 are illustrated in FIGS. 8 to 11.

[190] The positions of the pilots in FIGS. 8 to 11 are in accordance with a protocol between the transmitter and the receiver. The pilots can be inserted into the enhancement layer signal at the positions according to the four cases of FIGS. 8 to 11.

[191] As an alternative embodiment of the present invention, data instead of the pilot signals can be transmitted.

[192] In the case of a good channel environment between the transmitter and the receiver, data can be transmitted at the positions into which the pilots are inserted. In the case of a poor channel environment, the pilots having correlation with the base layer signal are transmitted at four types of positions of pilots.

[193] An object of insertion of pilots into the enhancement layer is to improve performances of frequency synchronization, symbol timing synchronization, channel estimation, and channel equalization of a receiver. Therefore, in the case of a good channel environment, although only data are transmitted without insertion of pilots, a data transmission rate of the enhancement can be increased.

[194] Accordingly, in a case where the transmitter inserts the pilots, various levels of power of pilots and the pilot array can be selected if pilot information according to a protocol between the transmitter and the receiver is transmitted. [195] FIG. 12 is a flowchart illustrating a transmission method of outputting a hierarchically-modulated signal, according to an embodiment of the present invention.

[196] Referring to FIG. 12, first, a base layer signal sequence is encoded (S 1201), and an enhancement layer signal sequence is encoded (S 1202).

[197] Then, pilots having a correlation with the base layer signal sequence corresponding to the same sub-carriers as those of the encoded enhancement layer signal sequence are inserted into the enhancement layer signal sequence (S 1210).

[198] Finally, each output signal sequences are modulated, and the modulated signal sequences are multiplexed (S 1220).

[199] FIG. 13 is a flowchart illustrating a hierarchical modulation method according to an embodiment of the present invention.

[200] Referring to FIG. 13, in the hierarchical modulation method in an OFDM system including a base layer channel encoder, an enhancement layer channel encoder, and a hierarchical modulator, pilots having a correlation with a base layer signal sequence corresponding to the same sub-carriers as those of an encoded enhancement layer signal sequence output from the enhancement layer encoder are inserted into the enhancement layer signal sequence (S 1310).

[201] Then, the size of the pilots received from the hierarchical modulator is controlled (S 1320).

[202] FIG. 14 is a flowchart illustrating a reception method of outputting a hierarchical data from a hierarchically-modulated signal, according to an embodiment of the present invention.

[203] Referring to FIG. 14, a multiplexed signal of an encoded base layer signal sequence and a signal having pilots inserted into an encoded enhancement layer signal sequence is received, and the encoded base layer signal sequence and the signal having the pilots inserted into the enhancement layer signal sequence are separated from each other (S 1400).

[204] Next, the separated encoded base layer signal sequence is demodulated to be transformed into a base layer data (S 1410).

[205] Then, channels of sub-carriers are estimated from the signals having pilots inserted into the enhancement layer signal sequence by using pilot size and position information, and the channels are equalized over the entire sub-carrier signals (S 1420).

[206] Finally, the transmitted enhancement layer signal sequence is demodulated to be transformed into an enhancement layer data (S 1430).

[207] FIG. 15 is a flowchart illustrating an OFDM transmission method according to an embodiment of the present invention.

[208] First, a base layer signal sequence is encoded (S 1501), and an enhancement layer signal sequence is encoded (S 1502). [209] Then, pilots having a correlation with a base layer signal sequence corresponding to the same sub-carriers as those of an encoded enhancement layer signal sequence are inserted into the enhancement layer signal sequence (S 1510).

[210] Then, each output signal sequences are modulated, and the modulated signal sequences are multiplexed (S 1520).

[211] Next, a multiplexed signal of the encoded base layer signal sequence and the signal having the pilots inserted into the encoded enhancement layer signal sequence is received, and the encoded base layer signal sequence and the signal having the pilots inserted into the enhancement layer signal sequence are separated from each other (S1530).

[212] Then, the separated encoded base layer signal sequence is demodulated to be transformed into a base layer data (S 1540).

[213] Channels of sub-carriers are estimated from the signals having pilots inserted into the enhancement layer signal sequence by using pilot size and position information, and the channels are equalized over the entire sub-carrier signals (S 1550).

[214] The transmitted enhancement layer signal sequence is demodulated to be transformed into an enhancement layer data (S1560).

[215] The invention can also be embodied as computer readable codes on a computer readable recording medium. The computer readable recording medium is any data storage device that can store data which can be thereafter read by a computer system. Examples of the computer readable recording medium include read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storage devices, and carrier waves (such as data transmission through the Internet). The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

[216] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The exemplary embodiments should be considered in descriptive sense only and not for purposes of limitation. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention.

Claims

[1] A transmitting apparatus outputting a hierarchically-modulated signal in an

OFDM (orthogonal frequency division multiplexing) system, the apparatus comprising: a first channel encoder encoding a base layer signal sequence; a second channel encoder encoding an enhancement layer signal sequence; a pilot insertion unit inserting pilots into the enhancement layer signal sequence, the pilots having a correlation with the base layer signal sequence corresponding to the same sub-carriers as those of the encoded enhancement layer signal sequence output from the second channel encoder; and a hierarchical modulator modulating the encoded base layer signal sequence and the encoded enhancement layer signal sequence comprising the pilots output from the first channel encoder and the pilot insertion unit, respectively, and multiplexing the modulated signal sequences.

[2] The transmitting apparatus of claim 1, wherein signal strength of the pilots are equal to or larger than that of the enhancement layer signal sequence.

[3] The transmitting apparatus of claim 1, further comprising a pilot controller controlling the signal strength of the pilots received from the hierarchical modulator.

[4] The transmitting apparatus of claim 3, wherein the pilot size controller controls the signal strength of the pilots to be equal to or larger than that of the enhancement layer signal sequence.

[5] The transmitting apparatus of claim 1, wherein the pilot insertion unit divides positions of the sub-carriers corresponding to the enhancement layer signal sequence in units of a predetermined interval and periodically inserts the pilots into the enhancement layer signal sequence in the interval in units of an arbitrary number of OFDM signals.

[6] The transmitting apparatus of claim 5, wherein the pilot insertion unit obtains a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted by dividing an OFDM symbol index 1 by 2 to calculate a remainder, adding five times the remainder and ten times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value and inserts the pilot into the position indicated by the pilot sub-carrier index K.

[7] The transmitting apparatus of claim 5, wherein the pilot insertion unit obtains a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted by dividing an OFDM symbol index 1 by 5 to calculate a remainder, adding two times the remainder and ten times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value and inserts the pilot into the position indicated by the pilot sub-carrier index K.

[8] The transmitting apparatus of claim 5, wherein the pilot insertion unit obtains a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted by dividing an OFDM symbol index 1 by 3 to calculate a remainder, adding four times the remainder and twelve times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value and inserts the pilot into the position indicated by the pilot sub-carrier index K.

[9] The transmitting apparatus of claim 5, wherein the pilot insertion unit obtains a pilot sub-carrier index K indicating a position of the sub-carrier into which the pilot is to inserted by dividing an OFDM symbol index 1 by 4 to calculate a remainder, adding three times the remainder and twelve times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value and inserts the pilot into the position indicated by the pilot sub-carrier index K.

[10] A receiver apparatus comprising: a hierarchical separator which receives a multiplexed signal of an encoded base layer signal sequence and a signal having pilots inserted into an encoded enhancement layer signal sequence and separates the encoded base layer signal sequence from the signal having the pilots inserted into the encoded enhancement layer signal sequence; a first channel decoder which demodulates the encoded base layer signal sequence separated by the hierarchical separator to transform the encoded base layer signal sequence into a base layer data; a channel estimation/equalization unit which estimates channels of the sub- carriers from the signal having the pilots inserted into the encoded enhancement layer signal sequence by using pilot size and position information and equalizes the channels over the entire sub-carriers; and a second channel decoder which demodulates the encoded enhancement layer signal sequence transmitted from the channel estimation/equalization unit to transform the enhancement layer signal sequence into an enhancement layer data.

[11] The receiver apparatus according to claim 10, wherein the channel estimati on/ equalization unit compares signals corresponding to pilot positions in the signals having the pilots inserted into the enhancement layer signal sequence by using signal strength of the pilot and position information so as to estimate channels of the sub-carriers and equalizes the channels over the entire sub-carriers by using values of the estimated channel signals, thereby removing influence of the channels.

[12] A transmitting method of outputting hierarchically-modulated signals in an

OFDM transmission system, the method comprising:

(a) encoding a base layer signal sequence;

(b) encoding an enhancement layer signal sequence;

(c) inserting pilots into the enhancement layer signal sequence, the pilots having a correlation with the base layer signal sequence corresponding to the same sub- carriers as those of the encoded enhancement layer signal sequence encoded in (b); and

(d) modulating the signal sequences output in (a) and (c) and multiplexing the modulated signal sequences.

[13] The transmitting method according to claim 12, wherein signal strength of the pilots are equal to or larger than that of the enhancement layer signal sequence.

[14] The transmitting method according to claim 12, further comprising (e) controlling the signal strength of the pilots received from (d).

[15] The transmitting method according to claim 14, wherein, in (e), the signal strength of the pilots are controlled to be equal to or larger than that of the enhancement layer signal sequence.

[16] The transmitting method according to claim 12, wherein, in (c), positions of the sub-carriers corresponding to the enhancement layer signal sequence are divided in units of a predetermined interval, and the pilots are periodically inserted into the enhancement layer signal sequence in the interval in units of an arbitrary number of OFDM signals.

[17] The transmitting method according to claim 16, wherein, in (c), a pilot sub- carrier index K indicating a position of the sub-carrier into which the pilot is to inserted is obtained by dividing an OFDM symbol index 1 by 2 to calculate a remainder, adding five times the according remainder and ten times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value, and the pilot is inserted into the position indicated by the pilot sub-carrier index K.

[18] The transmitting method according to claim 16, wherein, in (c), a pilot sub- carrier index K indicating a position of the sub-carrier into which the pilot is to inserted is obtained by dividing an OFDM symbol index 1 by 5 to calculate a remainder, adding two times the according remainder and ten times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value, and the pilot is inserted into the position indicated by the pilot sub-carrier index K.

[19] The transmitting method according to claim 16, wherein, in (c), a pilot sub- carrier index K indicating a position of the sub-carrier into which the pilot is to inserted is obtained by dividing an OFDM symbol index 1 by 3 to calculate a remainder, adding four times the according remainder and twelve times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value, and the pilot is inserted into the position indicated by the pilot sub- carrier index K.

[20] The transmitting method according to claim 16, wherein, in (c), a pilot sub- carrier index K indicating a position of the sub-carrier into which the pilot is to inserted is obtained by dividing an OFDM symbol index 1 by 4 to calculate a remainder, adding three times the according remainder and twelve times an arbitrary integer of 0 or more to calculate an added value, and adding 1 and the added value, and the pilot is inserted into the position indicated by the pilot sub- carrier index K.

[21] A receiving method of outputting a hierarchical data from a hierarchically-demodulated signal in an OFDM transmission system, the method comprising:

(a) receiving a multiplexed signal of an encoded base layer signal sequence and a signal having pilots inserted into an encoded enhancement layer signal sequence and separating the base layer signal sequence from the signal having the pilots inserted into the enhancement layer signal sequence;

(b) demodulating the separated encoded base layer signal sequence to transform the encoded base layer signal sequence into a base layer data;

(c) estimating channels of the sub-carriers from the signal having the pilots inserted into the enhancement layer signal sequence by using pilot size and position information and equalizing the channels over the entire sub-carriers; and

(d) demodulating the enhancement layer signal sequence transmitted from (c) to transform the enhancement layer signal sequence into an enhancement layer data.

[22] The receiving method according to claim 21, wherein, in (c), signals corresponding to pilot positions in the signals having the pilots inserted into the enhancement layer signal sequence are compared by using the pilot size and position information so as to estimate channels of the sub-carriers, and the channels are equalized over the entire sub-carriers by using values of the estimated channel signals, thereby removing influence of the channels.