Abstract:
An apparatus and method for transmitting a preamble in a Digital Video Broadcasting (DVB) system are provided. The apparatus includes a first processor for generating a Modulation Signaling Sequence (MSS) using a plurality of received sequences, and for outputting a modulated sequence by differentially modulating the MSS. The apparatus also includes a scrambler for scrambling the modulated sequence by multiplying the modulated sequence by a scrambling sequence. A second processor receives the scrambled sequence through each allocated subcarrier, converts the received sequence into a time-domain signal, and generates and transmits the preamble.

Description:
PRIORITY 
       [0001]    This application claims the benefit under 35 U.S.C. §119(a) of a Korean Patent Application filed in the Korean Intellectual Property Office on Jan. 29, 2008 and assigned Serial No. 10-2008-0009295, a Korean Patent Application filed in the Korean Intellectual Property Office on Jan. 31, 2008 and assigned Serial No. 10-2008-0010415, and a Korean Patent Application filed in the Korean Intellectual Property Office on Feb. 29, 2008 and assigned Serial No. 10-2008-0019388, the entire disclosures of all of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to a Digital Video Broadcasting (DVB) system. More particularly, the present invention relates to an apparatus and method for transmitting and receiving preambles among components of a frame in a DVB system. 
         [0004]    2. Description of the Related Art 
         [0005]    Generally, the term “digital broadcasting system” denotes a broadcasting system using a digital transmission technology, such as Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB) and Digital Multimedia Broadcasting (DMB). 
         [0006]    Among others, the DVB system, a European digital broadcasting technology, is a transmission standard for supporting not only the existing digital broadcasting but also mobile/portable digital multimedia services. 
         [0007]    The DVB system can multiplex Moving Picture Experts Group 2 Transport Stream (MPEG 2 TS)-based broadcast data, and transmit IP-based data streams simultaneously. In the DVB system, various services can be transmitted after being multiplexed to one IP stream. And, after receiving data of the transmitted IP stream, a terminal can demultiplex it back into individual services, demodulate the services, and output them through a screen of the user terminal. At this point, the user terminal needs information indicating types of the various services provided by the DVB system and the details that each of the services contains. 
         [0008]      FIG. 1  is a diagram illustrating a frame structure of a physical channel in a conventional DVB system. 
         [0009]    Referring to  FIG. 1 , the frame structure can be roughly divided into preamble parts P 1  and P 2 , and body parts BODY. The preamble parts P 1  and P 2  are used for transmitting signaling information of the frame, while the body parts consist of the parts used for transmitting data or payload. 
         [0010]    The purposes of the preamble P 1  in  FIG. 1  are as follows. First, the preamble P 1  is used for scanning an initial signal of a frame at a receiver. Second, the preamble P 1  is used for detecting a frequency offset and tuning the center frequency at the receiver. Third, the preamble P 1  is used for transmitting identification information of the frame as well as transmitting Fast Fourier Transform (FFT) size and other transmission information. Finally, the preamble P 1  is used for detecting and correcting frequency and time synchronization at the receiver. 
         [0011]    Regarding the structure of the preamble P 1  in  FIG. 1 , a part A, in which information is transmitted, is fixed to 1K Orthogonal Frequency Division Multiplexing (OFDM) symbols regardless of an FFT size of a payload where data is transmitted, and has a length of 112 μs. When the other parts B and C each consist of a ½ guard interval, they are added to both sides of the 1K symbols, with a length of 56 μs. As shown in  FIG. 1 , the total length of the preamble P 1  is 224 μs. 
         [0012]      FIG. 2  is a diagram illustrating locations of carriers on which a preamble sequence is transmitted in the conventional art. 
         [0013]    The drawing of  FIG. 2  is given for a description of an internal structure of the 1K OFDM symbols shown in  FIG. 1 . As illustrated in  FIG. 2 , the 1K OFDM symbols include 853 carriers. Among the 853 carriers constituting the 1K OFDM symbols, only 384 carriers are used for transmission of a preamble sequence. 
         [0014]      FIG. 3  is a block diagram illustrating a transmitter for transmitting a preamble in a conventional DVB system. 
         [0015]    Locations of the carriers used for transmission of a preamble sequence among the 853 carriers can be predetermined. In  FIG. 3 , carrier locations are predetermined and stored in a Carrier Distribution Sequence (CDS) table  300 . 
         [0016]    An operation of a Modulation Signaling Sequence (MSS) processor  310  is as follows. The MSS processor  310  receives a first sequence (hereinafter ‘S 1 ’) and a second sequence (hereinafter ‘S 2 ’) and generates Complementary Sets of Sequences (CSSs). The S 1  and S 2  include 3-bit information and 4-bit information, respectively. The CSSs generated by the S 1  and S 2  have 8 and 16 combinations, respectively and CSS S1  and CSS S2  generated by the S 1  and S 2  have a length of 64 and 256, respectively. Such CSSs are characterized in that they are low in a Peak-to-Average Power Ratio (PAPR) and orthogonal with each other. 
         [0017]    Signals of the S 1  and S 2  can be expressed as shown in Table 1, where they are expressed in hexadecimal. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Field 
                 Val 
                 Sequence (Hexadecimal notation) 
               
               
                   
               
             
             
               
                 S1 
                 000 
                 124721741D482E7B 
               
               
                   
                 001 
                 47127421481D7B2E 
               
               
                   
                 010 
                 217412472E7B1D48 
               
               
                   
                 011 
                 742147127B2E481D 
               
               
                   
                 100 
                 1D482E7B12472174 
               
               
                   
                 101 
                 481D7B2E47127421 
               
               
                   
                 110 
                 2E7B1D4821741247 
               
               
                   
                 111 
                 7B2E481D74214712 
               
               
                 S2 
                 0000 
                 121D4748212E747B1D1248472E217B7412E247B721D174841DED48B82EDE7B8B 
               
               
                   
                 0001 
                 4748121D747B212E48471D127B742E2147B712E2748421D148B81DED7B8B2EDE 
               
               
                   
                 0010 
                 212E747B121D47482E217B741D12484721D1748412E247B72EDE7B8B1DED48B8 
               
               
                   
                 0011 
                 747B212E4748121D7B742E2148471D12748471D147B712E27B8B2EDE48B81DED 
               
               
                   
                 0100 
                 1D1248472E217B74121D4748212E747B1DED48B82EDE7B8B12E247B721D17484 
               
               
                   
                 0101 
                 48471D127B742E214748121D747B212E48B81DED7B8B2EDE47B712E2748421D1 
               
               
                   
                 0110 
                 2E217B741D124847212E747B121D47482EDE7B8B1DED48B821D1748412E247B7 
               
               
                   
                 0111 
                 7B742E2148471D12747B212E4748121D7B8B2EDE48B81DED748421D147B712E2 
               
               
                   
                 1000 
                 12E247B721D174841DED48B82EDE7B8B121D4748212E747B1D1248472E217B74 
               
               
                   
                 1001 
                 47B712E2748421D148B81DED7B8B2EDE4748121D747B212E48471D127B742E21 
               
               
                   
                 1010 
                 21D1748412E247B72EDE7B8B1DED48B8212E747B121D47482E217B741D124847 
               
               
                   
                 1011 
                 748421D147B712E27B8B2EDE48B81DED747B212E4748121D7B742E2148471D12 
               
               
                   
                 1100 
                 1DED48B82EDE7B8B12E247B721D174841D1248472E217B74121D4748212E747B 
               
               
                   
                 1101 
                 48B81DED7B8B2EDE47B712E2748421D148471D127B742E214748121D747B212E 
               
               
                   
                 1110 
                 2EDE7B8B1DED48B821D1748412E247B72E217B741D124847212E747B121D4748 
               
               
                   
                 1111 
                 7B8B2EDE48B81DED748421D147B712E27B742E2148471D12747B212E4748121D 
               
               
                   
               
             
          
         
       
     
         [0018]    A series of processes in which the sequences S 1  and S 2  are output as a modulated sequence by means of the MSS processor  310  through a phase offset processor  325  is as follows. 
         [0019]    Equation (1) represents a sequence generated by a combination of S 1  and S 2  in the MSS processor  310 , and the sequence is denoted by MSS_SEQ. 
         [0000]      MSS_SEQ={CSS S1 , CSS S2 , CSS S1 }  (1) 
         [0020]    MSS_SEQ in Equation (1) is modulated by Differential BPSK (DBPSK) in a DBPSK modulator (or DBPSK mapper)  320 . Equation (2) represents the DBPSK-modulated sequence, which is denoted by MSS_DIFF. 
         [0000]      MSS_DIFF=DBPSK(MSS_SEQ)   (2) 
         [0021]    The phase offset processor  325  outputs the finally modulated sequence by applying a 180° phase offset to 64 Most Significant Bit (MSB) bits (or cells) in the modulated sequence. The phase offset processor  325  does not apply the phase offset to the remaining bits except for the 64 MSB bits. Since the 64 MSB bits all have the same offset value, the phase offset value will not affect a demodulation process of a DBPSK demodulator in a receiver. Hence, there is no need for a reverse process of the phase offset process at the receiver. Finally, an output of the phase offset processor  325  is defined as Equation (3). 
         [0000]      MSS={−MSS_DIFF 383, 382, . . . , 320 , MSS_DIFF 319, 318, . . . , 0 }  (3) 
         [0022]    The sequence being output through the MSS processor  310 , DBPSK modulator  320  and phase offset processor  325 , i.e. the modulated sequence, is allocated to 384 active carriers for P 1  by the carrier allocator  330 . 
         [0023]    In structure, 2 guard intervals are added to improve robustness of symbols for P 1 , and operations of an Inverse Fast Fourier Transform (IFFT) processor  340  and a preamble generator  350  are substantially the same as that in  FIG. 1 . 
         [0024]      FIG. 4  is a block diagram illustrating a receiver for receiving a preamble in a conventional DVB system. 
         [0025]    Referring to  FIG. 4 , a preamble detector  400  in the receiver detects a preamble and inputs it to an FFT processor  410 . The FFT processor  410  performs FFT on the detected preamble and outputs the results to a demultiplexer (DEMUX)  420 . Next, the DEMUX  420  demultiplexes data on active carriers through which a preamble is transmitted, and outputs the demultiplexed data to a DBPSK demodulator  430 . The DBPSK demodulator  430  performs a reverse process of the phase offset processor  325 , i.e. performs DBPSK demodulation that inversely phase-shifts MSB signals of the preamble by a length of 64 at the receiver, and then outputs the results to a signaling detector  440 . The signaling detector  440  outputs desired information by detecting S 1  and S 2  from the demodulated sequence. 
         [0026]      FIG. 5  is a flowchart illustrating a reception method for receiving a preamble in a conventional DVB system. 
         [0027]    Referring to  FIG. 5 , the receiver performs initialization in step  500 , and performs tuning on a preamble in step  505 . The receiver performs Guard Interval-Correlation (GIC) on a received signal in step  510 , and determines in step  515  whether it has detected a preamble P 1 . When the receiver has failed to detect the preamble P 1  in step  515 , the receiver returns to step  510 . Otherwise, when the receiver has detected the preamble P 1 , the receiver performs coarse time adjustment and fine frequency offset adjustment in step  520 . Next, in step  525 , the receiver performs power correlation to estimate power of active carriers, and determines again in step  530  whether it has detected the preamble P 1 . Upon failure to detect the preamble P 1 , the receiver returns back to step  510 , and when the receiver successfully detects the preamble P 1 , the receiver performs coarse frequency offset adjustment in step  535 . Thereafter, the receiver performs DBPSK demodulation, which is a reverse process of the differential modulation scheme at the transmitter, in step  540 , calculates a correlation value between preambles in step  545 , and detects signals of S 1  and S 2  in step  550 . 
         [0028]    As the above-stated conventional preamble structure uses the differential modulation (i.e. DBPSK), non-coherent reception is possible. However, a characteristic of the complementary sequences changes due to the execution of the differential modulation, causing an increase in the PAPR. Accordingly, there is a need for an improved apparatus and method for transmitting and receiving preambles among components of a frame in a DVB system. 
       SUMMARY OF THE INVENTION 
       [0029]    An aspect of the present invention is to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide an apparatus and method capable of reducing a PAPR of a preamble by scrambling. 
         [0030]    In accordance with an aspect of the present invention, an apparatus for transmitting a preamble in a Digital Video Broadcasting (DVB) system is provided. The transmission apparatus includes a first processor for generating a Modulation Signaling Sequence (MSS) using a plurality of received sequences, and for outputting a modulated sequence by differentially modulating the MSS, a scrambler for scrambling the modulated sequence by multiplying the modulated sequence by a scrambling sequence and a second processor for receiving the scrambled sequence through each of a plurality of allocated subcarriers, for converting the received sequence into a time-domain signal, and for generating and transmitting the preamble. 
         [0031]    In accordance with another aspect of the present invention, a method for transmitting a preamble in a Digital Video Broadcasting (DVB) system is provided. The transmission method includes generating a Modulation Signaling Sequence (MSS) using a plurality of received sequences, outputting a modulated sequence by differentially modulating the MSS, scrambling the modulated sequence by multiplying the modulated sequence by a scrambling sequence, receiving the scrambled sequence through each of a plurality of allocated subcarriers, converting the received sequence into a time-domain signal, and generating and transmitting the preamble. 
         [0032]    In accordance with still another aspect of the present invention, an apparatus for receiving a preamble in a Digital Video Broadcasting (DVB) system is provided. The reception apparatus includes a first processor for detecting a preamble from a received signal, for converting the detected preamble into a frequency-domain signal, and for demultiplexing the frequency-domain signal, a descrambler for descrambling the demultiplexed sequence by multiplying the demultiplexed sequence by a descrambling sequence and a second processor for differentially demodulating the descrambled sequence and for detecting a plurality of sequences from the demodulated sequence. 
         [0033]    In accordance with yet another aspect of the present invention, a method for receiving a preamble in a Digital Video Broadcasting (DVB) system is provided. The reception method includes detecting a preamble from a received signal, converting the detected preamble into a frequency-domain signal, demultiplexing the frequency-domain signal, descrambling the demultiplexed sequence by multiplying the demultiplexed sequence by a descrambling sequence, differentially demodulating the descrambled sequence and detecting a plurality of sequences from the demodulated sequence. 
         [0034]    Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]    The above and other aspects, features and advantages of certain exemplary embodiments of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings in which: 
           [0036]      FIG. 1  is a diagram illustrating a frame structure of a physical channel in a conventional DVB system; 
           [0037]      FIG. 2  is a diagram illustrating locations of carriers on which a preamble sequence is transmitted in the conventional art; 
           [0038]      FIG. 3  is a block diagram illustrating a transmitter for transmitting a preamble in a conventional DVB system; 
           [0039]      FIG. 4  is a block diagram illustrating a receiver for receiving a preamble in a conventional DVB system; 
           [0040]      FIG. 5  is a flowchart illustrating a reception method for receiving a preamble in a conventional DVB system; 
           [0041]      FIG. 6  is a block diagram illustrating a transmitter for transmitting a preamble in a DVB system according to an exemplary embodiment of the present invention; 
           [0042]      FIG. 7  is a diagram illustrating an example of a PRBS encoder for Equation (5); 
           [0043]      FIG. 8  is a flowchart illustrating a transmission method for transmitting a preamble in a DVB system according to an exemplary embodiment of the present invention; 
           [0044]      FIG. 9  is a block diagram illustrating a receiver for receiving a preamble in a DVB system according to an exemplary embodiment of the present invention; and 
           [0045]      FIG. 10  is a flowchart illustrating a reception method for receiving a preamble in a DVB system according to an exemplary embodiment of the present invention. 
       
    
    
       [0046]    Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features and structures. 
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0047]    The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness. 
         [0048]    The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. 
         [0049]    It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces. 
         [0050]    By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide. 
         [0051]    The present invention relates to a preamble where signaling information is transmitted, and in particular, to a preamble P 1  through which initial information is transmitted. Exemplary embodiments of the present invention provide a method for addressing the above-stated problem that a Peak-to-Average Power Ratio (PAPR) of complementary sequences for a preamble increases due to the use of the differential modulation. 
         [0052]    A description of exemplary embodiments of the present invention will now be given below. 
         [0053]    Table 2 shows the PAPRs of preambles for a case in which the differential modulation scheme is not applied in the preamble P 1 . When 128 preamble signals are generated by combinations of S 1  and S 2 , the maximum PAPR is 10.29 dB, the minimum PAPR is 6.72 dB, and an average PAPR is 8.21 dB. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 S1 
                 S2 
                 PAPR 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 0 
                 0 
                 8.05 
               
               
                 0 
                 1 
                 7.76 
               
               
                 0 
                 2 
                 8.38 
               
               
                 0 
                 3 
                 8.84 
               
               
                 0 
                 4 
                 7.93 
               
               
                 0 
                 5 
                 8.45 
               
               
                 0 
                 6 
                 8.60 
               
               
                 0 
                 7 
                 7.41 
               
               
                 0 
                 8 
                 7.42 
               
               
                 0 
                 9 
                 8.55 
               
               
                 0 
                 10 
                 8.58 
               
               
                 0 
                 11 
                 9.44 
               
               
                 0 
                 12 
                 8.87 
               
               
                 0 
                 13 
                 8.87 
               
               
                 0 
                 14 
                 6.87 
               
               
                 0 
                 15 
                 7.58 
               
               
                 1 
                 0 
                 8.48 
               
               
                 1 
                 1 
                 8.19 
               
               
                 1 
                 2 
                 9.61 
               
               
                 1 
                 3 
                 6.78 
               
               
                 1 
                 4 
                 7.94 
               
               
                 1 
                 5 
                 7.96 
               
               
                 1 
                 6 
                 8.61 
               
               
                 1 
                 7 
                 8.43 
               
               
                 1 
                 8 
                 7.54 
               
               
                 1 
                 9 
                 9.21 
               
               
                 1 
                 10 
                 7.63 
               
               
                 1 
                 11 
                 7.94 
               
               
                 1 
                 12 
                 9.22 
               
               
                 1 
                 13 
                 8.82 
               
               
                 1 
                 14 
                 8.26 
               
               
                 1 
                 15 
                 7.09 
               
               
                 2 
                 0 
                 6.72 
               
               
                 2 
                 1 
                 8.94 
               
               
                 2 
                 2 
                 9.20 
               
               
                 2 
                 3 
                 8.88 
               
               
                 2 
                 4 
                 8.60 
               
               
                 2 
                 5 
                 8.00 
               
               
                 2 
                 6 
                 8.07 
               
               
                 2 
                 7 
                 8.81 
               
               
                 2 
                 8 
                 7.06 
               
               
                 2 
                 9 
                 8.24 
               
               
                 2 
                 10 
                 7.35 
               
               
                 2 
                 11 
                 8.16 
               
               
                 2 
                 12 
                 7.83 
               
               
                 2 
                 13 
                 6.86 
               
               
                 2 
                 14 
                 8.79 
               
               
                 2 
                 15 
                 7.65 
               
               
                 3 
                 0 
                 8.32 
               
               
                 3 
                 1 
                 8.60 
               
               
                 3 
                 2 
                 7.90 
               
               
                 3 
                 3 
                 7.38 
               
               
                 3 
                 4 
                 9.02 
               
               
                 3 
                 5 
                 6.73 
               
               
                 3 
                 6 
                 8.05 
               
               
                 3 
                 7 
                 6.98 
               
               
                 3 
                 8 
                 8.05 
               
               
                 3 
                 9 
                 7.63 
               
               
                 3 
                 10 
                 7.37 
               
               
                 3 
                 11 
                 8.55 
               
               
                 3 
                 12 
                 7.28 
               
               
                 3 
                 13 
                 7.48 
               
               
                 3 
                 14 
                 7.56 
               
               
                 3 
                 15 
                 8.87 
               
               
                 4 
                 0 
                 8.52 
               
               
                 4 
                 1 
                 8.62 
               
               
                 4 
                 2 
                 9.11 
               
               
                 4 
                 3 
                 8.77 
               
               
                 4 
                 4 
                 7.18 
               
               
                 4 
                 5 
                 10.22 
               
               
                 4 
                 6 
                 8.16 
               
               
                 4 
                 7 
                 7.42 
               
               
                 4 
                 8 
                 8.32 
               
               
                 4 
                 9 
                 8.49 
               
               
                 4 
                 10 
                 7.56 
               
               
                 4 
                 11 
                 8.60 
               
               
                 4 
                 12 
                 8.64 
               
               
                 4 
                 13 
                 7.62 
               
               
                 4 
                 14 
                 8.34 
               
               
                 4 
                 15 
                 9.72 
               
               
                 5 
                 0 
                 8.85 
               
               
                 5 
                 1 
                 9.23 
               
               
                 5 
                 2 
                 7.39 
               
               
                 5 
                 3 
                 7.54 
               
               
                 5 
                 4 
                 9.27 
               
               
                 5 
                 5 
                 10.07 
               
               
                 5 
                 6 
                 8.11 
               
               
                 5 
                 7 
                 7.90 
               
               
                 5 
                 8 
                 8.74 
               
               
                 5 
                 9 
                 10.29 
               
               
                 5 
                 10 
                 7.99 
               
               
                 5 
                 11 
                 7.91 
               
               
                 5 
                 12 
                 8.64 
               
               
                 5 
                 13 
                 8.68 
               
               
                 5 
                 14 
                 7.76 
               
               
                 5 
                 15 
                 8.48 
               
               
                 7 
                 0 
                 7.87 
               
               
                 7 
                 1 
                 8.78 
               
               
                 7 
                 2 
                 8.62 
               
               
                 7 
                 3 
                 7.52 
               
               
                 7 
                 4 
                 8.67 
               
               
                 7 
                 5 
                 8.65 
               
               
                 7 
                 6 
                 8.16 
               
               
                 7 
                 7 
                 7.61 
               
               
                 7 
                 8 
                 7.26 
               
               
                 7 
                 9 
                 7.68 
               
               
                 7 
                 10 
                 7.49 
               
               
                 7 
                 11 
                 8.64 
               
               
                 7 
                 12 
                 7.54 
               
               
                 7 
                 13 
                 8.01 
               
               
                 7 
                 14 
                 7.98 
               
               
                 7 
                 15 
                 7.04 
               
               
                 8 
                 0 
                 8.49 
               
               
                 8 
                 1 
                 8.15 
               
               
                 8 
                 2 
                 7.09 
               
               
                 8 
                 3 
                 7.27 
               
               
                 8 
                 4 
                 7.27 
               
               
                 8 
                 5 
                 7.14 
               
               
                 8 
                 6 
                 7.22 
               
               
                 8 
                 7 
                 6.99 
               
               
                 8 
                 8 
                 7.47 
               
               
                 8 
                 9 
                 8.72 
               
               
                 8 
                 10 
                 7.92 
               
               
                 8 
                 11 
                 7.66 
               
               
                 8 
                 12 
                 9.32 
               
               
                 8 
                 13 
                 8.13 
               
               
                 8 
                 14 
                 7.72 
               
               
                 8 
                 15 
                 8.48 
               
               
                   
               
             
          
         
       
     
         [0054]    However, Table 3 shows the PAPRs of preambles for a case in which the differential modulation scheme is applied. In this case, the maximum PAPR of the preambles is 10.50 dB, the minimum PAPR is 7.14 dB, and an average PAPR is 7.14 dB. As stated above, it can be seen from a comparison between Table 2 and Table 3 that the PAPR increases as characteristics of the complementary sequences are discrepant from each other due to the use of the differential modulation scheme. From Table 2 and Table 3, it can be appreciated that the average PAPR increases by 0.42 dB due to an influence of the differential modulation. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 S1 
                 S2 
                 PAPR 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 0 
                 0 
                 8.34 
               
               
                 0 
                 1 
                 9.17 
               
               
                 0 
                 2 
                 7.96 
               
               
                 0 
                 3 
                 9.36 
               
               
                 0 
                 4 
                 10.15 
               
               
                 0 
                 5 
                 9.68 
               
               
                 0 
                 6 
                 8.59 
               
               
                 0 
                 7 
                 9.33 
               
               
                 0 
                 8 
                 8.85 
               
               
                 0 
                 9 
                 8.83 
               
               
                 0 
                 10 
                 8.53 
               
               
                 0 
                 11 
                 7.70 
               
               
                 0 
                 12 
                 9.21 
               
               
                 0 
                 13 
                 7.64 
               
               
                 0 
                 14 
                 7.99 
               
               
                 0 
                 15 
                 7.81 
               
               
                 1 
                 0 
                 8.93 
               
               
                 1 
                 1 
                 10.21 
               
               
                 1 
                 2 
                 8.42 
               
               
                 1 
                 3 
                 10.50 
               
               
                 1 
                 4 
                 9.36 
               
               
                 1 
                 5 
                 10.41 
               
               
                 1 
                 6 
                 9.25 
               
               
                 1 
                 7 
                 8.92 
               
               
                 1 
                 8 
                 9.48 
               
               
                 1 
                 9 
                 9.20 
               
               
                 1 
                 10 
                 8.36 
               
               
                 1 
                 11 
                 9.28 
               
               
                 1 
                 12 
                 9.79 
               
               
                 1 
                 13 
                 9.59 
               
               
                 1 
                 14 
                 8.00 
               
               
                 1 
                 15 
                 9.58 
               
               
                 2 
                 0 
                 8.56 
               
               
                 2 
                 1 
                 9.69 
               
               
                 2 
                 2 
                 9.65 
               
               
                 2 
                 3 
                 10.04 
               
               
                 2 
                 4 
                 8.89 
               
               
                 2 
                 5 
                 9.84 
               
               
                 2 
                 6 
                 8.72 
               
               
                 2 
                 7 
                 8.66 
               
               
                 2 
                 8 
                 8.90 
               
               
                 2 
                 9 
                 9.30 
               
               
                 2 
                 10 
                 8.14 
               
               
                 2 
                 11 
                 7.89 
               
               
                 2 
                 12 
                 9.31 
               
               
                 2 
                 13 
                 8.92 
               
               
                 2 
                 14 
                 8.81 
               
               
                 2 
                 15 
                 8.89 
               
               
                 3 
                 0 
                 8.81 
               
               
                 3 
                 1 
                 9.50 
               
               
                 3 
                 2 
                 8.18 
               
               
                 3 
                 3 
                 9.16 
               
               
                 3 
                 4 
                 10.45 
               
               
                 3 
                 5 
                 9.57 
               
               
                 3 
                 6 
                 9.32 
               
               
                 3 
                 7 
                 9.82 
               
               
                 3 
                 8 
                 9.50 
               
               
                 3 
                 9 
                 7.96 
               
               
                 3 
                 10 
                 8.64 
               
               
                 3 
                 11 
                 7.14 
               
               
                 3 
                 12 
                 9.76 
               
               
                 3 
                 13 
                 7.98 
               
               
                 3 
                 14 
                 8.18 
               
               
                 3 
                 15 
                 8.32 
               
               
                 4 
                 0 
                 7.68 
               
               
                 4 
                 1 
                 8.10 
               
               
                 4 
                 2 
                 8.41 
               
               
                 4 
                 3 
                 9.10 
               
               
                 4 
                 4 
                 8.41 
               
               
                 4 
                 5 
                 9.16 
               
               
                 4 
                 6 
                 8.65 
               
               
                 4 
                 7 
                 9.29 
               
               
                 4 
                 8 
                 9.40 
               
               
                 4 
                 9 
                 7.59 
               
               
                 4 
                 10 
                 8.87 
               
               
                 4 
                 11 
                 8.48 
               
               
                 4 
                 12 
                 8.38 
               
               
                 4 
                 13 
                 8.48 
               
               
                 4 
                 14 
                 7.55 
               
               
                 4 
                 15 
                 8.32 
               
               
                 5 
                 0 
                 8.31 
               
               
                 5 
                 1 
                 9.12 
               
               
                 5 
                 2 
                 8.33 
               
               
                 5 
                 3 
                 9.44 
               
               
                 5 
                 4 
                 8.79 
               
               
                 5 
                 5 
                 9.36 
               
               
                 5 
                 6 
                 8.24 
               
               
                 5 
                 7 
                 8.84 
               
               
                 5 
                 8 
                 8.38 
               
               
                 5 
                 9 
                 8.00 
               
               
                 5 
                 10 
                 8.23 
               
               
                 5 
                 11 
                 10.39 
               
               
                 5 
                 12 
                 8.70 
               
               
                 5 
                 13 
                 8.44 
               
               
                 5 
                 14 
                 8.15 
               
               
                 5 
                 15 
                 8.44 
               
               
                 7 
                 0 
                 7.54 
               
               
                 7 
                 1 
                 8.51 
               
               
                 7 
                 2 
                 8.87 
               
               
                 7 
                 3 
                 8.92 
               
               
                 7 
                 4 
                 8.16 
               
               
                 7 
                 5 
                 8.70 
               
               
                 7 
                 6 
                 8.85 
               
               
                 7 
                 7 
                 8.25 
               
               
                 7 
                 8 
                 7.69 
               
               
                 7 
                 9 
                 7.65 
               
               
                 7 
                 10 
                 9.14 
               
               
                 7 
                 11 
                 9.27 
               
               
                 7 
                 12 
                 8.14 
               
               
                 7 
                 13 
                 7.64 
               
               
                 7 
                 14 
                 8.53 
               
               
                 7 
                 15 
                 7.96 
               
               
                 8 
                 0 
                 7.52 
               
               
                 8 
                 1 
                 7.75 
               
               
                 8 
                 2 
                 8.48 
               
               
                 8 
                 3 
                 8.85 
               
               
                 8 
                 4 
                 8.83 
               
               
                 8 
                 5 
                 8.70 
               
               
                 8 
                 6 
                 7.47 
               
               
                 8 
                 7 
                 8.69 
               
               
                 8 
                 8 
                 8.75 
               
               
                 8 
                 9 
                 7.19 
               
               
                 8 
                 10 
                 8.88 
               
               
                 8 
                 11 
                 8.57 
               
               
                 8 
                 12 
                 8.81 
               
               
                 8 
                 13 
                 7.67 
               
               
                 8 
                 14 
                 7.32 
               
               
                 8 
                 15 
                 8.94 
               
               
                   
               
             
          
         
       
     
         [0055]    As a method for addressing the problem of increasing PAPR caused by the differential modulation, i.e. for PAPR reduction, the DVB system can apply scrambling. 
         [0056]      FIG. 6  is a block diagram illustrating a transmitter for transmitting a preamble in a DVB system according to an exemplary embodiment of the present invention. 
         [0057]    Referring to  FIG. 6 , the transmitter includes a CDS table  600 , an MSS processor  610 , a DBPSK modulator  620 , a phase offset processor  630 , a scrambler  635 , a carrier allocator  640 , an IFFT processor  650 , and a preamble generator  660 . Since the CDS table  600 , the MSS processor  610 , the DBPSK modulator  620 , the phase offset processor  630 , the carrier allocator  640 , the IFFT processor  650  and the preamble generator  660  are substantially equal in operation to the CDS table  300 , the MSS processor  310 , the DBPSK modulator  320 , the phase offset processor  325 , the carrier allocator  330 , the IFFT processor  340  and the preamble generator  350  in the conventional transmitter of  FIG. 3 , a detailed description thereof will be omitted. 
         [0058]    The scrambler  635 , according to an exemplary embodiment of the present invention, can prevent a Complementary Set of Sequence (CSS) generated by the MSS processor  610  from increasing in a PAPR by the DBPSK modulator  620  and the phase offset processor  630 . In other words, in an exemplary implementation, the scrambler  635  generates a new sequence by multiplying a modulated sequence output from the phase offset processor  630  by a scrambling sequence. The scrambler  635  can operate with any arbitrary sequence when an operation of changing the signal from the MSS processor  610  to an arbitrary form is performed. 
         [0059]    An output MSS_SCR of the scrambler  635  is expressed as Equation (4). 
         [0000]      MSS_SCR=SCR(MSS)   (4) 
         [0060]    In Equation (4), the term “SCR” denotes a scrambling operation of the scrambler  635 . A new sequence is generated by multiplying the modulated sequence input to the scrambler  635  by a scrambling sequence. For example, when a length-K BSPK sequence is input as a modulated sequence, i.e. when {1 0 , −1 1 , −1 2 , 1 3 , . . . , 1 K-1 } is input as a modulated sequence, even the scrambling sequence can be generated with a length-K arbitrary BPSK sequence. When a scrambling sequence is {−1 0 , 1 1 , −1 2 , −1 3 , . . . , −1 K-1 }, the scrambler  635  generates {−1 0 , −1 1 , 1 2 , −1 3 , . . . , −1 K-1 } as a new length-K BPSK sequence by multiplying the modulated sequence of {1 0 , −1 1 , −1 2 , 1 3 , . . . , 1 K-1 } by the scrambling sequence of {−1 0 , 1 1 , −1 2 , −1 3 , . . . , 1 K-1 }. That is, the scrambler  635  generates a new sequence MSS_SCR by multiplying the sequence modulated using Equation (4) by the scrambling sequence. 
         [0061]    The scrambler  635  performs scrambling by multiplying the sequence modulated in the DBPSK modulator  620  and the phase offset processor  630 , i.e. a length—384 modulated sequence expressed in 1 or −1, by a length—384 scrambling sequence used in the scrambler  635 . The scrambling sequence will be described in more detail in the following exemplary embodiment. 
         [0062]    The scrambler  635  generates a scrambling sequence for reducing a PAPR of a preamble P 1 . In a DVB system, a Pseudo Random Binary Sequence (PRBS) defined as Equation (5) is used, and the scrambler  635  can generate a scrambling sequence using the existing PRBS. 
         [0000]      1+X 14 +X 15    (5) 
         [0063]      FIG. 7  is a diagram illustrating an example of a PRBS encoder for Equation (5). 
         [0064]    Referring to  FIG. 7 , a PRBS register  710  receives an initial value sequence (100010111100101), and generates a PRBS sequence (1110100011100100011100100 . . . ). The initial value and the length—384 PAPR scrambling sequence are shown in Table 4. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
             
             
               
                 Initial value sequence 
               
             
          
           
               
                 1 
                 0 
                 0 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 0 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 0 
                 1 
               
             
          
           
               
                 PRBS (Scrambling sequence) 
               
             
          
           
               
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 0 
                 0 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 0 
                 0 
                 0 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 0 
                 0 
                 1 
                 0 
                 1 
                 1 
                 0 
                 0  1 
               
               
                 0 
                 0 
                 1 
                 0 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1  0 
               
               
                 0 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 0 
                 0 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1  1 
               
               
                 0 
                 0 
                 0 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 0 
                 0 
                 0 
                 0 
                 0 
                 1 
                 0 
                 0 
                 0 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 0 
                 0 
                 0 
                 0 
                 1 
                 1 
                 0  0 
               
               
                 1 
                 0 
                 0 
                 1 
                 0 
                 1 
                 1 
                 0 
                 0 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1  1 
               
               
                 0 
                 0 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 0 
                 0 
                 0 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                 0 
                 0 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1  1 
               
               
                 0 
                 1 
                 0 
                 0 
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                 0 
                 0 
                 0 
                 0 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 0 
                 1 
                 0 
                 0 
                 1 
                 0 
                 0 
                 0 
                 1 
                 0 
                 0  1 
               
               
                 1 
                 0 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 0  1 
               
               
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 0 
                 0 
                 0 
                 1 
                 0 
                 0 
                 1 
                 0 
                 0 
                 0 
                 0  0 
               
               
                 1 
                 0 
                 0 
                 0 
                 0 
                 1 
                 1 
                 0 
                 1 
                 1 
                 0 
                 0 
                 0 
                 0 
                 1 
                 1 
                 0 
                 0 
                 0 
                 1 
                 0 
                 1 
                 1 
                 0 
                 1 
                 0 
                 0 
                 0 
                 1 
                 0 
                 1  0 
               
               
                 0 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 0 
                 1 
                 1 
                 0 
                 0 
                 1 
                 0 
                 1 
                 0 
                 0 
                 0 
                 1 
                 1 
                 1  0 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 0 
                 1 
                 0 
                 1 
                 1 
                 0 
                 1 
                 0 
                 0 
                 0  0 
               
               
                   
               
             
          
         
       
     
         [0065]    The scrambling sequence of Table 4 is used as a scrambling sequence for a scrambler used for reducing a PAPR of a preamble P 1 . In the PRBS encoder of  FIG. 7 , a length—384 sequence generated with the initial value of Table 4 is converted from a value of 0 or 1 to a value of 1 or −1, and multiplied by a modulated sequence output from a phase offset processor in the scrambler  635 , thereby reducing a PAPR. 
         [0066]    Table 5 shows the PAPRs of 128 preambles P 1  in an exemplary embodiment of the present invention which uses scrambling for PAPR reduction. It can be noted that the maximum PAPR is 9.10 dB, the minimum PAPR is 6.71 dB, and an average PAPR is 8.01 dB. Compared with Table 3, a gain of 1.4 dB can be obtained at the maximum PAPR. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                 S1 
                 S2 
                 PAPR 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 0 
                 0 
                 7.42 
               
               
                 0 
                 1 
                 7.23 
               
               
                 0 
                 2 
                 7.71 
               
               
                 0 
                 3 
                 7.16 
               
               
                 0 
                 4 
                 8.00 
               
               
                 0 
                 5 
                 8.16 
               
               
                 0 
                 6 
                 7.87 
               
               
                 0 
                 7 
                 7.81 
               
               
                 0 
                 8 
                 8.30 
               
               
                 0 
                 9 
                 8.20 
               
               
                 0 
                 10 
                 8.11 
               
               
                 0 
                 11 
                 8.12 
               
               
                 0 
                 12 
                 8.91 
               
               
                 0 
                 13 
                 8.43 
               
               
                 0 
                 14 
                 7.88 
               
               
                 0 
                 15 
                 7.46 
               
               
                 1 
                 0 
                 7.18 
               
               
                 1 
                 1 
                 8.31 
               
               
                 1 
                 2 
                 7.76 
               
               
                 1 
                 3 
                 7.99 
               
               
                 1 
                 4 
                 8.78 
               
               
                 1 
                 5 
                 7.82 
               
               
                 1 
                 6 
                 7.78 
               
               
                 1 
                 7 
                 7.15 
               
               
                 1 
                 8 
                 7.96 
               
               
                 1 
                 9 
                 8.14 
               
               
                 1 
                 10 
                 7.76 
               
               
                 1 
                 11 
                 7.80 
               
               
                 1 
                 12 
                 7.19 
               
               
                 1 
                 13 
                 8.84 
               
               
                 1 
                 14 
                 8.78 
               
               
                 1 
                 15 
                 7.43 
               
               
                 2 
                 0 
                 8.21 
               
               
                 2 
                 1 
                 8.05 
               
               
                 2 
                 2 
                 7.67 
               
               
                 2 
                 3 
                 8.25 
               
               
                 2 
                 4 
                 8.86 
               
               
                 2 
                 5 
                 7.39 
               
               
                 2 
                 6 
                 7.04 
               
               
                 2 
                 7 
                 8.08 
               
               
                 2 
                 8 
                 8.18 
               
               
                 2 
                 9 
                 7.55 
               
               
                 2 
                 10 
                 8.20 
               
               
                 2 
                 11 
                 7.82 
               
               
                 2 
                 12 
                 7.64 
               
               
                 2 
                 13 
                 8.55 
               
               
                 2 
                 14 
                 8.05 
               
               
                 2 
                 15 
                 8.09 
               
               
                 3 
                 0 
                 8.32 
               
               
                 3 
                 1 
                 8.09 
               
               
                 3 
                 2 
                 7.38 
               
               
                 3 
                 3 
                 8.02 
               
               
                 3 
                 4 
                 8.13 
               
               
                 3 
                 5 
                 7.21 
               
               
                 3 
                 6 
                 8.04 
               
               
                 3 
                 7 
                 7.99 
               
               
                 3 
                 8 
                 7.55 
               
               
                 3 
                 9 
                 8.97 
               
               
                 3 
                 10 
                 8.37 
               
               
                 3 
                 11 
                 7.35 
               
               
                 3 
                 12 
                 8.13 
               
               
                 3 
                 13 
                 7.62 
               
               
                 3 
                 14 
                 7.93 
               
               
                 3 
                 15 
                 7.37 
               
               
                 4 
                 0 
                 6.71 
               
               
                 4 
                 1 
                 8.51 
               
               
                 4 
                 2 
                 7.39 
               
               
                 4 
                 3 
                 7.96 
               
               
                 4 
                 4 
                 7.66 
               
               
                 4 
                 5 
                 8.43 
               
               
                 4 
                 6 
                 8.48 
               
               
                 4 
                 7 
                 8.70 
               
               
                 4 
                 8 
                 8.01 
               
               
                 4 
                 9 
                 8.04 
               
               
                 4 
                 10 
                 7.78 
               
               
                 4 
                 11 
                 7.74 
               
               
                 4 
                 12 
                 9.10 
               
               
                 4 
                 13 
                 8.46 
               
               
                 4 
                 14 
                 7.47 
               
               
                 4 
                 15 
                 9.08 
               
               
                 5 
                 0 
                 7.13 
               
               
                 5 
                 1 
                 7.55 
               
               
                 5 
                 2 
                 9.01 
               
               
                 5 
                 3 
                 8.25 
               
               
                 5 
                 4 
                 7.90 
               
               
                 5 
                 5 
                 8.64 
               
               
                 5 
                 6 
                 8.92 
               
               
                 5 
                 7 
                 8.34 
               
               
                 5 
                 8 
                 7.91 
               
               
                 5 
                 9 
                 7.02 
               
               
                 5 
                 10 
                 8.33 
               
               
                 5 
                 11 
                 7.84 
               
               
                 5 
                 12 
                 6.80 
               
               
                 5 
                 13 
                 7.42 
               
               
                 5 
                 14 
                 9.09 
               
               
                 5 
                 15 
                 7.01 
               
               
                 7 
                 0 
                 7.67 
               
               
                 7 
                 1 
                 7.45 
               
               
                 7 
                 2 
                 8.50 
               
               
                 7 
                 3 
                 8.57 
               
               
                 7 
                 4 
                 8.74 
               
               
                 7 
                 5 
                 8.06 
               
               
                 7 
                 6 
                 7.84 
               
               
                 7 
                 7 
                 8.11 
               
               
                 7 
                 8 
                 8.74 
               
               
                 7 
                 9 
                 8.10 
               
               
                 7 
                 10 
                 7.12 
               
               
                 7 
                 11 
                 7.10 
               
               
                 7 
                 12 
                 7.66 
               
               
                 7 
                 13 
                 8.14 
               
               
                 7 
                 14 
                 8.47 
               
               
                 7 
                 15 
                 7.89 
               
               
                 8 
                 0 
                 7.22 
               
               
                 8 
                 1 
                 8.34 
               
               
                 8 
                 2 
                 7.78 
               
               
                 8 
                 3 
                 8.07 
               
               
                 8 
                 4 
                 6.99 
               
               
                 8 
                 5 
                 8.90 
               
               
                 8 
                 6 
                 8.48 
               
               
                 8 
                 7 
                 8.16 
               
               
                 8 
                 8 
                 7.74 
               
               
                 8 
                 9 
                 8.43 
               
               
                 8 
                 10 
                 8.88 
               
               
                 8 
                 11 
                 8.16 
               
               
                 8 
                 12 
                 8.29 
               
               
                 8 
                 13 
                 7.49 
               
               
                 8 
                 14 
                 7.57 
               
               
                 8 
                 15 
                 8.03 
               
               
                   
               
             
          
         
       
     
         [0067]    In an exemplary implementation, a new sequence is generated by the above-stated scrambler  635 . Moreover, each scrambling sequence can be stored in a look-up table for future use, or can be determined when necessary. As an example, the output of the DBPSK modulator  620  in  FIG. 6  can be stored in the look-up table, the output of the scrambler  635  can be stored in the look-up table, or the outputs of all the blocks  600  to  635  can be stored in the look-up table for an operation of the scrambler  635 . 
         [0068]      FIG. 8  is a flowchart illustrating a transmission method for transmitting a preamble in a DVB system according to an exemplary embodiment of the present invention. 
         [0069]    Referring to  FIG. 8 , the transmitter receives S 1  and S 2  in step  801 , and generates an MSS by selecting a sequence corresponding to the S 1  and S 2  in step  803 . The transmitter differentially modulates the MSS in step  805 , and applies 180° phase offset to the 64 MSB bits in step  807 . In step  809 , the transmitter performs scrambling by multiplying the scrambling sequence generated by Equation (5) by the sequence modulated in step  807 . In step  811 , the transmitter receives the scrambled sequence through each allocated subcarrier. Next, in step  813 , the transmitter generates a time-domain signal by performing IFFT on the scrambled sequence received through the allocated subcarrier. Finally, in step  815 , the transmitter generates a preamble having a structure illustrated in  FIG. 1 . 
         [0070]    As the scrambling operation performed by the scrambler  635  is carried out after DBPSK modulation, exemplary embodiments of the present invention are more stable in the detection performance of S 1  and S 2 , as compared with when the scrambling operation is performed before the DBPSK modulation. In other words, exemplary embodiments of present invention are robust in detection performance of S 1  and S 2 . 
         [0071]      FIG. 9  is a block diagram illustrating a receiver for receiving a preamble in a DVB system according to an exemplary embodiment of the present invention. 
         [0072]    Referring to  FIG. 9 , the receiver includes a preamble detector  900 , an FFT processor  910 , a DEMUX  920 , a descrambler  930 , a DBPSK demodulator  940 , and a signaling detector  950 . Since the preamble detector  900 , the FFT processor  910 , the DEMUX  920 , the DBPSK demodulator  940  and the signaling detector  950  are substantially the same in operation as the preamble detector  400 , the FFT processor  410 , the DEMUX  420 , the DBPSK demodulator  430  and the signaling detector  440  illustrated in  FIG. 4 , a detailed description thereof will be omitted. 
         [0073]    The descrambler  930 , according to an exemplary embodiment of the present invention, performs a reverse process of the scrambler  635  on the sequence obtained by demultiplexing data on active carriers through which a preamble is transmitted. That is to say, the descrambler  930  performs descrambling by multiplying the demultiplexed sequence by the descrambling sequence. The descrambling sequence has the same length as that of the demultiplexed sequence. The descrambling sequence can be previously determined and stored in a look-up table, or can be generated using PRBS, in substantially the same way as for the above-stated scrambling sequence. 
         [0074]      FIG. 10  is a flowchart illustrating a reception method for receiving a preamble in a DVB system according to an exemplary embodiment of the present invention. 
         [0075]    Referring to  FIG. 10 , the receiver performs initialization in step  1000 , and performs tuning on a preamble in step  1005 . The receiver performs Guard Interval-Correlation (GIC) on the received signal in step  1010 , and determines in step  1015  whether it has detected a preamble P 1 . When the receiver has failed to detect the preamble P 1  in step  1015 , the receiver returns to step  1010 . However, when the receiver has detected the preamble P 1 , the receiver performs coarse time adjustment and fine frequency offset adjustment in step  1020 . Thereafter, the receiver performs power correlation to estimate power of active carriers in step  1025 , and then determines again in step  1030  whether it has detected the preamble P 1 . When the receiver has failed to detect the preamble P 1  in step  1030 , the receiver returns back to step  1010 , and when receiver has successfully received the preamble P 1 , the receiver performs coarse frequency offset adjustment in step  1035 . Next, the receiver performs descrambling using a descrambling sequence according to an exemplary embodiment of the present invention in step  1040 , and performs differential demodulation, which is a reverse process of the differential modulation scheme at the transmitter, in step  1045 . Thereafter, the receiver determines a correlation between preambles in step  1050 , and detects signals of S 1  and S 2  in step  1055 . 
         [0076]    As is apparent from the foregoing description, exemplary embodiments of the present invention use the differential modulation scheme in transmitting a preamble, one of physical channels, in the DVB system, thus reducing a PAPR of the preamble P 1  by solving the PAPR increase problem using scrambling. 
         [0077]    While the invention has been shown and described with reference to certain 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 and their equivalents.