Patent Publication Number: US-11032115-B2

Title: Device and method for decoding bootstrap signal

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage Application of International Application No. PCT/KR2018/005891, filed on May 24, 2018, which claims the benefit under 35 USC 119(a) and 365(b) of Korean Patent Application No. 10-2017-0130140, filed on Oct. 11, 2017, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes. 
     TECHNICAL FIELD 
     The present invention relates generally to broadcast and communications technology, and more particularly, to technology for more accurately decoding a received bootstrap signal. 
     BACKGROUND ART 
     In the frame of a broadcast signal, a bootstrap is placed at the head of the frame and provides the entry point thereof. Also, the bootstrap includes signaling information that is necessary in order to decode a preamble. The bootstrap signal may be configured with multiple symbols. For example, the first symbol may be used to estimate the initial synchronization time of the frame, a frequency offset, and a channel. The remaining symbols may include signaling information that is required for decoding a preamble. 
     A bootstrap signal is generated by multiplying a Zadoff-Chu sequence by a pseudo-noise (PN) sequence. Here, the root of the Zadoff-Chu sequence represents the major version of the bootstrap signal, and the seed of the PN sequence represents the minor version thereof. The generated sequence is mapped to 1498 subcarriers based on a DC subcarrier. The mapped signal in the frequency domain is transformed into a signal in the time domain through Inverse Fast Fourier Transform (IFFT). 
     For example, the signaling information required for decoding the preamble may be represented as the cyclic shift of remaining symbols, excluding the first bootstrap symbol, in the time domain. The cyclic shift may include a relative cyclic shift and an absolute cyclic shift. The relative cyclic shift represents the cyclic shift for the current symbol relative to the cyclic shift for the previous symbol, and the signaling information may be represented as the relative cyclic shift. The absolute cyclic shift represents the cyclic shift for the current symbol relative to the first symbol, and the signals cyclically shifted through the absolute cyclic shift may be finally transmitted. 
     Meanwhile, Korean Patent Application Publication No. 10-2017-0080495, titled “Apparatus for transmitting broadcast signal using transmitter identification and method using the same”, discloses an apparatus and method for transmitting broadcast signals in which a transmitter is identified using a transmitter identification (TxID) signal in a broadcast system. 
     DISCLOSURE 
     Technical Problem 
     The present invention intends to provide maximum-likelihood decoding in order to decode a bootstrap signal. 
     Also, the present invention intends to improve the accuracy of a channel gain estimate, which is necessary for maximum-likelihood decoding. 
     Also, the present invention intends to provide accurate decoding of a bootstrap signal by performing iterative maximum-likelihood decoding using a more accurate channel gain estimate. 
     Technical Solution 
     In order to accomplish the above objects, an apparatus for decoding a bootstrap signal according to an embodiment of the present invention includes an operation unit for calculating the relative cyclic shift and the channel gain estimate of a received bootstrap signal and correcting the channel gain estimate using the relative cyclic shift, and a decoding unit for decoding the bootstrap signal using the corrected channel gain estimate. 
     Here, the operation unit may calculate the relative cyclic shift using the absolute cyclic shifts of two successive symbols in the bootstrap signal. 
     Here, the operation unit may calculate the relative cyclic shift depending on the condition in which the channel gain values of the two successive symbols in the bootstrap signal are equivalent to each other. 
     Here, the operation unit may calculate the relative cyclic shift by applying an IFFT operation method and the condition in which the channel gain values are equivalent to each other in a maximum-likelihood decision rule for the absolute cyclic shift. 
     Here, the operation unit may calculate the channel gain estimate by multiplying the signal sequence of a symbol by a complex conjugate sequence before the cyclic shift of the symbol in the bootstrap signal. 
     Here, for multiple successive symbols in the bootstrap signal, the operation unit may correct the channel gain estimates of the symbols in order from the first symbol to the last symbol and again correct the channel gain estimates of the symbols in reverse order from the last symbol to the first symbol. 
     Here, the operation unit may correct the channel gain estimate of an N-th symbol (N being an integer that is equal to or greater than 2) using the average of the channel gain estimate of the N-th symbol and the channel gain estimate of an N−1-th symbol, among the multiple successive symbols in the bootstrap signal. 
     Here, the operation unit may compensate for the phase difference of the channel gain estimate of the N−1-th symbol by multiplying the relative cyclic shift of the N-th symbol by the channel gain estimate of the N−1-th symbol, among the two successive symbols. 
     Here, the operation unit may compensate for the phase difference of the channel gain estimate of the N-th symbol by multiplying the channel gain estimate of the N-th symbol, the accuracy of which is improved, by the relative cyclic shift that was used to compensate for the phase difference of the N−1-th symbol. 
     Here, the operation unit may correct the channel gain estimate of the N−1-th symbol using the average of the channel gain estimate of the N-th symbol, of which the phase difference is compensated for, and the channel gain estimate of the N−1-th symbol, of which the phase difference is compensated for. 
     Also, in order to accomplish the above objects, a method for decoding a bootstrap signal, in which an apparatus for decoding a bootstrap signal is used, according to an embodiment of the present invention includes calculating the relative cyclic shift and the channel gain estimate of a received bootstrap signal; correcting the channel gain estimate using the relative cyclic shift; and decoding the bootstrap signal using the corrected channel gain estimate. 
     Here, calculating the relative cyclic shift and the channel gain estimate may be configured to calculate the relative cyclic shift using the absolute cyclic shifts of two successive symbols in the bootstrap signal. 
     Here, calculating the relative cyclic shift and the channel gain estimate may be configured to calculate the relative cyclic shift depending on the condition in which the channel gain values of the two successive symbols in the bootstrap signal are equivalent to each other. 
     Here, calculating the relative cyclic shift and the channel gain estimate may be configured to calculate the relative cyclic shift by applying an IFFT operation method and the condition in which the channel gain values are equivalent to each other in a maximum-likelihood decision rule for the absolute cyclic shift. 
     Here, calculating the relative cyclic shift and the channel gain estimate may be configured to calculate the channel gain estimate by multiplying the signal sequence of a symbol by a complex conjugate sequence before the cyclic shift of the symbol in the bootstrap signal. 
     Here, correcting the channel gain estimate may be configured to correct the channel gain estimates of symbols in order from the first symbol to the last symbol and to again correct the channel gain estimates of the symbols in reverse order from the last symbol to the first symbol for the multiple successive symbols in the bootstrap signal. 
     Here, correcting the channel gain estimate may be configured to correct the channel gain estimate of an N-th symbol (N being an integer that is equal to or greater than 2) using the average of the channel gain estimate of the N-th symbol and the channel gain estimate of an N−1-th symbol, among the multiple successive symbols in the bootstrap signal. 
     Here, correcting the channel gain estimate may be configured to compensate for the phase difference of the channel gain estimate of the N−1-th symbol by multiplying the relative cyclic shift of the N-th symbol by the channel gain estimate of the N−1-th symbol, among the two successive symbols. 
     Here, correcting the channel gain estimate may be configured to compensate for the phase difference of the channel gain estimate of the N-th symbol by multiplying the channel gain estimate of the N-th symbol, the accuracy of which is improved, by the relative cyclic shift that was used to compensate for the phase difference of the N−1-th symbol. 
     Here, correcting the channel gain estimate may be configured to correct the channel gain estimate of the N−1-th symbol using the average of the channel gain estimate of the N-th symbol, of which the phase difference is compensated for, and the channel gain estimate of the N−1-th symbol, of which the phase difference is compensated for. 
     Advantageous Effects 
     The present inventions may provide maximum-likelihood decoding in order to decode a bootstrap signal. 
     Also, the present invention may improve the accuracy of a channel gain estimate, which is necessary for maximum-likelihood decoding. 
     Also, the present invention may enable accurate decoding of a bootstrap signal by performing iterative maximum-likelihood decoding using a more accurate channel gain estimate. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram that shows an apparatus for decoding a bootstrap signal according to an embodiment of the present invention; 
         FIG. 2  is a flowchart that shows a method for decoding a bootstrap signal according to an embodiment of the present invention; 
         FIG. 3  is a flowchart that specifically shows an example of the step of correcting a channel gain estimate, illustrated in  FIG. 2 ; and 
         FIG. 4  is a block diagram that shows a computer system according to an embodiment of the present invention. 
     
    
    
     BEST MODE 
     The present invention will be described in detail below with reference to the accompanying drawings. Repeated descriptions and descriptions of known functions and configurations which have been deemed to unnecessarily obscure the gist of the present invention will be omitted below. The embodiments of the present invention are intended to fully describe the present invention to a person having ordinary knowledge in the art to which the present invention pertains. Accordingly, the shapes, sizes, etc. of components in the drawings may be exaggerated in order to make the description clearer. 
     Throughout this specification, the terms “comprises” and/or “comprising” and “includes” and/or “including” specify the presence of stated elements but do not preclude the presence or addition of one or more other elements unless otherwise specified. 
     Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a block diagram that shows an apparatus for decoding a bootstrap signal according to an embodiment of the present invention. 
     Referring to  FIG. 1 , the apparatus for decoding a bootstrap signal according to an embodiment of the present invention may include a reception unit  110 , an operation unit  120 , and a decoding unit  130 . 
     The reception unit  110  may receive a broadcast signal. 
     Here, the reception unit  110  may acquire a bootstrap signal, which is the initial frame, from the broadcast signal. 
     The operation unit  120  may calculate the relative cyclic shift and the channel gain estimate of the received bootstrap signal. 
     Here, the operation unit  120  may correct the channel gain estimate using the relative cyclic shift. 
     Here, the operation unit  120  may receive a bootstrap signal from a broadcast signal reception device that originally receives the signal. In this case, the apparatus for decoding a bootstrap signal may not include the reception unit  110 . 
     That is, the apparatus for receiving a bootstrap signal according to an embodiment of the present invention may directly receive a broadcast signal and acquire a bootstrap signal therefrom, or the apparatus may be connected with a broadcast signal reception device for receiving broadcast signals, or may be included in the broadcast signal reception device as a module thereof. 
     In the apparatus for receiving a bootstrap signal according to an embodiment of the present invention, if a broadcast signal transmission device and a broadcast signal reception device are perfectly synchronized with each other, the received signal in the frequency domain may be represented as shown in Equation 1. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           
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                             n 
                           
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                             ( 
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                         = 
                           
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                                 ( 
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                                     ⁢ 
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                                     ⁢ 
                                     
                                         
                                     
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                                     k 
                                     ⁢ 
                                     
                                         
                                     
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                                       M 
                                       n 
                                     
                                   
                                   
                                     N 
                                     FFT 
                                   
                                 
                               
                             
                           
                           + 
                           
                             
                               W 
                               n 
                             
                             ⁡ 
                             
                               ( 
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                               ) 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             
                               
                                 H 
                                 
                                   e 
                                   , 
                                   n 
                                 
                               
                               ⁡ 
                               
                                 ( 
                                 k 
                                 ) 
                               
                             
                             ⁢ 
                             
                               
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                                 n 
                               
                               ⁡ 
                               
                                 ( 
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                                 ) 
                               
                             
                           
                           + 
                           
                             
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                               n 
                             
                             ⁡ 
                             
                               ( 
                               k 
                               ) 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     Here, H n (k) denotes the channel gain of the k-th subcarrier for the n-th symbol, S n (k) denotes a sequence acquired by multiplying a Zadoff-Chu sequence for the n-th symbol by a pseudo-noise sequence, and W n (k) denotes the Additive White Gaussian Noise (AWGN) of the k-th subcarrier for the n-th symbol. 
     H e,n (k) may be 
                   H   n     ⁡     (   k   )       ⁢     e     j   ⁢       2   ⁢           ⁢   π   ⁢           ⁢   k   ⁢           ⁢     M   n         N   FFT             ,         
and N FFT  may be the size of FFT.
 
     Here, when the broadcast signal reception device has complete information about a channel, a maximum likelihood decision rule for an absolute cyclic shift M may be represented as shown in Equation 2. 
                     M   n     =     arg   ⁢           ⁢       min       m   n     ⁢   ϵ   ⁢           ⁢     x   a         ⁢       ∑     k   =   0         N   FFT     -   1       ⁢                R   n     ⁡     (   k   )       -         H   n     ⁡     (   k   )       ⁢       S   n     ⁡     (   k   )       ⁢     e     j   ⁢       2   ⁢           ⁢   π   ⁢           ⁢   k   ⁢           ⁢     m   n         N   FFT                    2                   [     Equation   ⁢           ⁢   2     ]               
Here, x a  may represent all possible absolute cyclic shifts.
 
     Here, in a static or slow fading channel, the symbol duration of a bootstrap signal may be shorter than that of a single data OFDM symbol. 
     Here, the channel gain values of two successive symbols may be consistent. 
     Accordingly, the channel gain values of the two successive symbols and the absolute cyclic shift may be represented as shown in Equation 3.
 
 H   n ( k )≈ H   n-1 ( k )
 
 M   n   =M   n-1   +{tilde over (M)}   n   [Equation 3]
 
     Here, the operation unit  120  may calculate a relative cyclic shift using the absolute cyclic shifts of two successive symbols in the bootstrap signal, as shown in Equation 3. 
     That is, the operation unit  120  may calculate the relative cyclic shift depending on the condition in which the channel gain values of the two successive symbols in the bootstrap signal are equivalent to each other. 
     Here, the ML decision rule for the relative cyclic shift may be derived using Equation 3, as shown in Equation 4. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           M 
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                         = 
                           
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                                   - 
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                               ⁢ 
                               
                                 
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                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     4 
                   
                   ] 
                 
               
             
           
         
       
     
     In Equation 4, maximum-likelihood decoding may be performed through an IFFT operation. 
     Here, x r  may be all possible relative cyclic shifts, and IFFT{·} may represent an IFFT operation. 
     That is, the operation unit  120  may calculate the relative cyclic shifts of multiple symbols using Equation 4. 
     Here, the operation unit  120  may calculate the relative cyclic shift by applying the IFFT operation method and the condition in which the channel gain values are equivalent to each other in the ML decision rule for the absolute cyclic shift. 
     For example, the operation unit  120  may calculate the channel gain estimate {tilde over (H)} e,n-1 (k) by multiplying the signal sequence of the symbol by a complex conjugate sequence before the cyclic shift of the symbol in the bootstrap signal, as shown in Equation 5. 
     
       
         
           
             
               
                 
                   
                     
                       
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                       ⁡ 
                       
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                     ⁢ 
                     
                       
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                   = 
                   
                     
                       
                         
                           
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                             ⁢ 
                             
                               
                                 2 
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                                 ⁢ 
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                                 ⁢ 
                                 
                                     
                                 
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                                 n 
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                                   0 
                                 
                               
                               
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                                 FFT 
                               
                             
                           
                         
                       
                       + 
                       
                         
                           
                             W 
                             0 
                           
                           ⁡ 
                           
                             ( 
                             k 
                             ) 
                           
                         
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                             0 
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                             ( 
                             k 
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                     = 
                     
                       
                         
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                           ~ 
                         
                         
                           e 
                           , 
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                       ⁡ 
                       
                         ( 
                         k 
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                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     5 
                   
                   ] 
                 
               
             
           
         
       
     
     Because the detection performance of the ML decision rule is based on the result of channel gain estimation, excellent detection performance may be realized when a channel gain estimate is very reliable. 
     Here, in order to improve the reliability of a channel gain estimate, the operation unit  120  averages the channel gain estimate of a previous symbol and the channel gain estimate of a current symbol using a forward decoding algorithm, thereby improving accuracy. 
     Here, the operation unit  120  may calculate the first relative cyclic shift {tilde over (M)} 1  using Equation 4. 
     Here, the operation unit  120  may calculate the channel gain estimates of the multiple successive symbols using Equation 5. 
     For example, the operation unit  120  may calculate the channel gain estimates of symbol 0 and symbol 1 using Equation 5. 
     Also, the operation unit  120  may correct the channel gain estimate of the N-th symbol (N being an integer that is equal to or greater than 2) using the average of the channel gain estimate of the N-th symbol and the channel gain estimate of the N−1-th symbol, among the multiple successive symbols in the bootstrap signal. 
     For example, in order to calculate the second relative cyclic shift, the operation unit  120  may estimate the channel of symbol 1 and then calculate the average of the estimated channel of symbol 1 and the channel gain estimate of symbol 0, which is {tilde over (H)} e,0 (k). 
     Here, because the symbol value before the cyclic shift is used for the channel gain estimate, the phase rotation by the cyclic shift of the symbol may be reflected to the estimated channel value. Accordingly, a phase difference corresponding to the relative cyclic shift is generated between the channel gain estimates for two successive symbols, and it is required to compensate for the phase difference when the channel gain estimates are averaged. 
     That is, the operation unit  120  multiplies the relative cyclic shift of the N-th symbol by the channel gain estimate of the N−1-th symbol, among the two successive symbols, thereby compensating for the phase difference of the channel gain estimate of the N−1-th symbol. 
     For example, in order to improve the reliability of the channel gain estimate of symbol 1, the operation unit  120  calculates the average of the channel gain estimate {tilde over (H)} e,1 (k), acquired using the received signal corresponding to symbol 1, and the channel gain estimate 
                     H   ~       e   ,   0       ⁡     (   k   )       ⁢     e     j   ⁢       2   ⁢           ⁢   π   ⁢           ⁢   k   ⁢           ⁢       M   ~     1         N   FFT             ,         
acquired by rotating the phase of the channel gain estimate of symbol 0, {tilde over (H)} e,0 (k), by the relative cyclic shift {tilde over (M)} 1 , thereby calculating a more accurate channel gain estimate of symbol 1, as shown in Equation 6.
 
     
       
         
           
             
               
                 
                   
                     
                       
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                         ~ 
                       
                       
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                         , 
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                       ′ 
                     
                     ⁡ 
                     
                       ( 
                       k 
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                   = 
                   
                     
                       1 
                       2 
                     
                     ⁢ 
                     
                       ( 
                       
                         
                           
                             
                               
                                 H 
                                 ~ 
                               
                               
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                                 , 
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                             ⁡ 
                             
                               ( 
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                           ⁢ 
                           
                             e 
                             
                               j 
                               ⁢ 
                               
                                 
                                   2 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   π 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   k 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     
                                       M 
                                       ~ 
                                     
                                     1 
                                   
                                 
                                 
                                   N 
                                   FFT 
                                 
                               
                             
                           
                         
                         + 
                         
                           
                             
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                               ~ 
                             
                             
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                           ⁡ 
                           
                             ( 
                             k 
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                       ) 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     6 
                   
                   ] 
                 
               
             
           
         
       
     
     Also, in order to calculate the third relative cyclic shift, the operation unit  120  may estimate the channel gain estimate of symbol 2 and then calculate the average of the channel gain estimate of symbol 2 and the more accurate channel gain estimate {tilde over (H)} e,1 ′(k), which is calculated above using the average. 
     Here, because the phases of the channel gain estimates differ from each other, the operation unit  120  may correct {tilde over (H)} e,1 ′(k) using the second relative cyclic shift {tilde over (M)} 2 , as shown in Equation 7. 
     
       
         
           
             
               
                 
                   
                     
                       
                         H 
                         ~ 
                       
                       
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                         , 
                         2 
                       
                       ′ 
                     
                     ⁡ 
                     
                       ( 
                       k 
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                   = 
                   
                     
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                       ( 
                       
                         
                           
                             
                               
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                             ( 
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                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     7 
                   
                   ] 
                 
               
             
           
         
       
     
     Also, the operation unit  120  may execute a backward decoding algorithm, in which averages are again calculated in the order reverse to the order in which the averages are calculated using the above-described forward decoding algorithm, in order to improve channel gain estimation performance. The ML decision rule for backward decoding may be represented as shown in Equation 8. 
     That is, the operation unit  120  multiplies the channel gain estimate of the N-th symbol, the accuracy of which is improved, by the relative cyclic shift that was used to compensate for the phase difference of the N−1-th symbol, thereby compensating for the phase difference of the channel gain estimate of the N-th symbol. 
     Here, the operation unit  120  may correct the channel gain estimate of the N−1-th symbol using the average of the channel gain estimate of the N-th symbol, of which the phase difference is compensated for, and the channel gain estimate of the N−1-th symbol, of which the phase difference is compensated for. 
     
       
         
           
             
               
                 
                   
                     
                       M 
                       ~ 
                     
                     
                       n 
                       + 
                       1 
                     
                   
                   = 
                   
                     arg 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       
                         max 
                         
                           
                             
                               M 
                               ~ 
                             
                             
                               n 
                               + 
                               1 
                             
                           
                           ∈ 
                           
                             x 
                             r 
                           
                         
                       
                       ⁢ 
                       
                         Re 
                         ⁢ 
                         
                           { 
                           
                             IFFT 
                             ⁢ 
                             
                               { 
                               
                                 
                                   
                                     R 
                                     n 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     k 
                                     ) 
                                   
                                 
                                 ⁢ 
                                 
                                   
                                     H 
                                     
                                       e 
                                       , 
                                       
                                         n 
                                         + 
                                         1 
                                       
                                     
                                     * 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     k 
                                     ) 
                                   
                                 
                                 ⁢ 
                                 
                                   
                                     S 
                                     n 
                                     * 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     k 
                                     ) 
                                   
                                 
                               
                               } 
                             
                           
                           } 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     8 
                   
                   ] 
                 
               
             
           
         
       
     
     For example, in order to calculate the third relative cyclic shift having improved accuracy, the operation unit  120  may estimate the channel gain estimate of symbol 3 and then calculate the average of the channel gain estimate of symbol 3 and the channel gain estimate of symbol 2, the accuracy of which is improved, {tilde over (H)} e,2 ′(k), as shown in Equation 9. 
     Here, because the phases of the channel gain estimates differ from each other, the operation unit  120  may correct {tilde over (H)} e,2 ′(k) using the third relative cyclic shift {tilde over (M)} 3 , as shown in Equation 9. 
     
       
         
           
             
               
                 
                   
                     
                       
                         H 
                         ~ 
                       
                       
                         e 
                         , 
                         3 
                       
                       ′ 
                     
                     ⁡ 
                     
                       ( 
                       k 
                       ) 
                     
                   
                   = 
                   
                     
                       1 
                       2 
                     
                     ⁢ 
                     
                       ( 
                       
                         
                           
                             
                               
                                 H 
                                 ~ 
                               
                               
                                 e 
                                 , 
                                 2 
                               
                               ′ 
                             
                             ⁡ 
                             
                               ( 
                               k 
                               ) 
                             
                           
                           ⁢ 
                           
                             e 
                             
                               j 
                               ⁢ 
                               
                                 
                                   2 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   π 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   k 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     
                                       M 
                                       ~ 
                                     
                                     3 
                                   
                                 
                                 
                                   N 
                                   FFT 
                                 
                               
                             
                           
                         
                         + 
                         
                           
                             
                               H 
                               ~ 
                             
                             
                               e 
                               , 
                               3 
                             
                           
                           ⁡ 
                           
                             ( 
                             k 
                             ) 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     9 
                   
                   ] 
                 
               
             
           
         
       
     
     Also, in order to calculate the second relative cyclic shift having improved accuracy using a backward decoding algorithm, the operation unit  120  may calculate the average of the channel gain estimate of symbol 3, {tilde over (H)} e,3 ′(k), which is calculated above using the average, and the channel gain estimate of symbol 2, {tilde over (H)} e,2 (k), as shown in Equation 10. 
     Here, because the phases of the channel gain estimates differ from each other, the operation unit  120  may correct {tilde over (H)} e,3 ′(k) using {tilde over (M)} 3 , which is the recently calculated third relative cyclic shift, as shown in Equation 10. 
     
       
         
           
             
               
                 
                   
                     
                       
                         H 
                         ~ 
                       
                       
                         e 
                         , 
                         2 
                       
                       ″ 
                     
                     ⁡ 
                     
                       ( 
                       k 
                       ) 
                     
                   
                   = 
                   
                     
                       1 
                       2 
                     
                     ⁢ 
                     
                       ( 
                       
                         
                           
                             
                               
                                 H 
                                 ~ 
                               
                               
                                 e 
                                 , 
                                 3 
                               
                               ′ 
                             
                             ⁡ 
                             
                               ( 
                               k 
                               ) 
                             
                           
                           ⁢ 
                           
                             e 
                             
                               j 
                               ⁢ 
                               
                                 
                                   2 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   π 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     k 
                                     ⁡ 
                                     
                                       ( 
                                       
                                         - 
                                         
                                           
                                             M 
                                             ~ 
                                           
                                           3 
                                         
                                       
                                       ) 
                                     
                                   
                                 
                                 
                                   N 
                                   FFT 
                                 
                               
                             
                           
                         
                         + 
                         
                           
                             
                               H 
                               ~ 
                             
                             
                               e 
                               , 
                               2 
                             
                           
                           ⁡ 
                           
                             ( 
                             k 
                             ) 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     10 
                   
                   ] 
                 
               
             
           
         
       
     
     Also, in order to calculate the first relative cyclic shift having improved accuracy, the operation unit  120  may calculate the average of the channel gain estimate of symbol 2, {tilde over (H)} e,2 ″(k), which is calculated above using the average, and the channel gain estimate of symbol 1, {tilde over (H)} e,1 (k), as shown in Equation 11. 
     Here, because the phases of the channel gain estimates differ from each other, the operation unit  120  may correct {tilde over (H)} e,2 ″(k) using {tilde over (M)} 2 , which is the recently calculated second relative cyclic shift, as shown in Equation 11. 
     
       
         
           
             
               
                 
                   
                     
                       
                         H 
                         ~ 
                       
                       
                         e 
                         , 
                         1 
                       
                       ″ 
                     
                     ⁡ 
                     
                       ( 
                       k 
                       ) 
                     
                   
                   = 
                   
                     
                       1 
                       2 
                     
                     ⁢ 
                     
                       ( 
                       
                         
                           
                             
                               
                                 H 
                                 ~ 
                               
                               
                                 e 
                                 , 
                                 2 
                               
                               ″ 
                             
                             ⁡ 
                             
                               ( 
                               k 
                               ) 
                             
                           
                           ⁢ 
                           
                             e 
                             
                               j 
                               ⁢ 
                               
                                 
                                   2 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   π 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     k 
                                     ⁡ 
                                     
                                       ( 
                                       
                                         - 
                                         
                                           
                                             M 
                                             ~ 
                                           
                                           2 
                                         
                                       
                                       ) 
                                     
                                   
                                 
                                 
                                   N 
                                   FFT 
                                 
                               
                             
                           
                         
                         + 
                         
                           
                             
                               H 
                               ~ 
                             
                             
                               e 
                               , 
                               1 
                             
                           
                           ⁡ 
                           
                             ( 
                             k 
                             ) 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     11 
                   
                   ] 
                 
               
             
           
         
       
     
     That is, for the multiple successive symbols in a bootstrap signal, the operation unit  130  may correct the channel gain estimates of the symbols in order from the first symbol to the last symbol, and may again correct the channel gain estimates in reverse order from the last symbol to the first symbol, as shown in Equations 6 to 11. 
     Here, the operation unit  130  repeatedly executes the forward decoding algorithm and the backward decoding algorithm, whereby performance in detection of the channel gain estimates may be further improved. 
     The decoding unit  130  may decode a bootstrap signal using corrected channel gain estimates. 
     That is, the decoding unit  130  performs decoding operations based on the ML decision rule shown in Equations 4 and 8 and selects the channel gain estimates calculated in Equations 6, 7 and 9 to 11, thereby decoding the bootstrap signal. 
       FIG. 2  is a flowchart that shows a method for decoding a bootstrap signal according to an embodiment of the present invention.  FIG. 3  is a flowchart that specifically shows the step of correcting the channel gain estimate, illustrated in  FIG. 2 . 
     Referring to  FIG. 2 , in the method for decoding a bootstrap signal according to an embodiment of the present invention, first, a bootstrap signal may be received at step S 210 . 
     That is, at step S 210 , a broadcast signal may be received. 
     Here, at step S 210 , a bootstrap signal, which is the initial frame, may be acquired from the broadcast signal. 
     Here, at step S 210 , alternatively, a bootstrap signal, received by a broadcast signal reception device, may be input. 
     Also, in the method for decoding a bootstrap signal according to an embodiment of the present invention, a relative cyclic shift and a channel gain estimate may be calculated at step S 220 . 
     That is, at step S 220 , the relative cyclic shift and the channel gain estimate of the received bootstrap signal may be calculated. 
     Here, at step S 220 , the relative cyclic shift may be calculated using the absolute cyclic shifts of two successive symbols in the bootstrap signal, as shown in Equation 3. 
     Here, at step S 220 , the relative cyclic shift may be calculated depending on the condition in which the channel gain values of two successive symbols in the bootstrap signal are equivalent to each other. 
     Also, at step S 220 , the relative cyclic shifts of the multiple symbols may be calculated using Equation 4. 
     Here, at step S 220 , the relative cyclic shift may be calculated by applying the IFFT operation method and the condition in which the channel gain values are equivalent to each other in the ML decision rule for the absolute cyclic shift. 
     Here, the operation unit  120  may calculate the channel gain estimates of the multiple successive symbols using Equation 5. 
     Also, in the method for decoding a bootstrap signal according to an embodiment of the present invention, the channel gain estimate may be corrected at step S 230 . 
     That is, at step S 230 , the channel gain estimate may be corrected using the relative cyclic shift. 
     Here, at step S 230 , a forward channel gain estimate may be corrected at step S 231 . 
     That is, at step S 231 , in order to improve the reliability of the channel gain estimate, the channel gain estimate of a previous symbol and that of a current symbol are averaged using a forward decoding algorithm, whereby accuracy may be improved. 
     Here, at step S 231 , the channel gain estimate of the N-th symbol (N being an integer that is equal to or greater than 2) may be corrected using the average of the channel gain estimate of the N-th symbol and the channel gain estimate of the N−1-th symbol, among the multiple successive symbols in the bootstrap signal. 
     Here, because the symbol value before the cyclic shift is used for the channel gain estimate, the phase rotation by the cyclic shift of the symbol may be reflected to the estimated channel value. Accordingly, a phase difference corresponding to the relative cyclic shift is generated between the channel gain estimates for two successive symbols, and it is required to compensate for the phase difference when the channel gain estimates are averaged. 
     That is, at step S 231 , the phase difference of the channel gain estimate of the N−1-th symbol may be compensated for by multiplying the relative cyclic shift of the N-th symbol by the channel gain estimate of the N−1-th symbol in the two successive symbols. 
     Also, at step S 230 , a backward channel gain estimate may be corrected at step S 232 . 
     That is, at step S 232 , a backward decoding algorithm, in which averages are again calculated in the order reverse to the order in which the averages are calculated using the above-described forward decoding algorithm, is performed in order to improve the channel gain estimation performance. 
     Here, at step S 232 , the channel gain estimate of the N-th symbol, the accuracy of which is improved, is multiplied by the relative cyclic shift that was used to compensate for the phase difference of the N−1-th symbol, whereby the phase difference of the channel gain estimate of the N-th symbol may be compensated for. 
     Here, at step S 232 , the channel gain estimate of the N−1-th symbol may be corrected using the average of the channel gain estimate of the N-th symbol, of which the phase difference is compensated for, and the channel gain estimate of the N−1-th symbol, of which the phase difference is compensated for. 
     Here, at step S 232 , for the multiple successive symbols of the bootstrap signal, the channel gain estimates of the first to last symbols are sequentially corrected, and the channel gain estimates may be corrected again in reverse order from the last symbol to the first symbol, as shown in Equations 6 to 11. 
     Also, at step S 230 , steps S 231  and  232  may be repeatedly performed. 
     That is, at step S 230 , performance in detection of the channel gain estimates may be further improved by repeatedly executing the forward decoding algorithm at step S 231  and the backward decoding algorithm at step S 232 . 
     Also, in the method for decoding a bootstrap signal according to an embodiment of the present invention, the bootstrap signal may be decoded at step S 240 . 
     That is, at step S 240 , the bootstrap signal may be decoded using the corrected channel gain estimates. 
     Here, at step S 240 , the decoding operations based on the ML decision rule, shown in Equations 4 and 8, are performed, and the channel gain estimates, calculated in Equations 6, 7 and 9 to 11, are selected, whereby the bootstrap signal may be decoded. 
       FIG. 4  is a block diagram that shows a computer system according to an embodiment of the present invention. 
     Referring to  FIG. 4 , the apparatus for decoding a bootstrap signal according to an embodiment of the present invention may be implemented in a computer system  1100  including a computer-readable recording medium. As illustrated in  FIG. 4 , the computer system  1100  may include one or more processors  1110 , memory  1130 , a user-interface input device  1140 , a user-interface output device  1150 , and storage  1160 , which communicate with each other via a bus  1120 . Also, the computer system  1100  may further include a network interface  1170  connected with a network  1180 . The processor may be a central processing unit or a semiconductor device for executing processing instructions stored in the memory  1130  or the storage  1160 . The memory  1130  and the storage  1160  may be various types of volatile or nonvolatile storage media. For example, the memory may include ROM  1131  or RAM  1132 . 
     As described above, the apparatus and method for decoding a bootstrap signal according to the present invention are not limitedly applied to the configurations and operations of the above-described embodiments, but all or some of the embodiments may be selectively combined and configured, so that the embodiments may be modified in various ways. 
     
       
         
           
               
             
               
                   
               
               
                 Description of Reference numerals 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 110: 
                 reception unit 
                 120: 
                 operation unit 
               
               
                 130: 
                 decoding unit 
               
               
                 1100: 
                 computer system 
                 1110: 
                 processor 
               
               
                 1120: 
                 bus 
                 1130: 
                 memory 
               
               
                 1131: 
                 ROM 
                 1132: 
                 RAM 
               
               
                 1140: 
                 user interface 
                 1150: 
                 user interface 
               
               
                   
                 input device 
                   
                 output device 
               
               
                 1160: 
                 storage 
                 1170: 
                 network interface 
               
               
                 1180: 
                 network