ES2904701T3 - Procedure for transmitting and receiving preambles in a digital video broadcasting system - Google Patents

Abstract

A method performed by a transmitter to transmit a preamble in a Digital Video Broadcasting, DVB, system, the method comprising: generating (803) a modulation signaling sequence, MSS, using a plurality of sequences; modulating (805) the generated MSS using differential modulation to generate a first sequence; generate a coding sequence using a binary pseudorandom sequence, PRBS; scrambling (809) the first sequence bitwise by multiplying the first sequence by the scrambling sequence to generate a second sequence; assigning (811) the second sequence to a plurality of subcarriers; converting (813) the second sequence in the preamble onto a time domain; and transmit of the preamble.

Description

DESCRIPTION

Procedure for transmitting and receiving preambles in a digital video broadcasting system

1. Field of the invention

The present invention generally relates to a Digital Video Broadcasting (DVB) system. More particularly, the present invention relates to an apparatus and method for transmitting and receiving preambles between components of a frame in a DVB system.

2. Background of the invention

In general, the term "digital broadcasting system" indicates a broadcasting system using a digital transmission technology, such as Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), and Digital Multimedia Broadcasting (DMB).

Among others, the DVB system, a European digital broadcasting technology, is a transmission standard to support not only existing digital broadcasting but also mobile/portable digital multimedia services. The DVB system can multiplex broadcast data based on Moving Picture Experts Group 2 (MPEG 2 TS) Transport Stream, and transmit IP-based data streams simultaneously. In the DVB system, various services can be transmitted after being multiplexed into an IP stream. And, after receiving data from the transmitted IP stream, a terminal can demultiplex it back into individual services, demodulate the services, and output them through a display 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 each of the services contains.

Figure 1 is a diagram illustrating a frame structure of a physical channel in a conventional DVB system.

Referring to Figure 1, the frame structure can be roughly divided into preamble parts P1 and P2, and Body parts BODY. The preamble parts P1 and P2 are used to transmit signaling information of the frame, while the body parts consist of the parts used to transmit data or payload.

The ends of the preamble P1 in Figure 1 are as follows. First, the P1 preamble is used to scan an initial signal of a frame at a receiver. Second, the P1 preamble is used to detect a frequency offset and adjust the center frequency at the receiver. Third, the P1 preamble is used to transmit frame identification information, as well as transmit the Fast Fourier Transform (FFT) size and other transmission information. Finally, the preamble P1 is used to detect and correct frequency and time synchronization in the receiver.

With respect to the structure of the preamble P1 in Figure 1, a part A, in which information is transmitted, is set to 1K Orthogonal Frequency Division Multiplexing (OFDM) symbols regardless of an FFT size of a payload where data is transmitted, and is 112 ms long. When the other parts B and C each consist of a 1/2 guard interval, they are added to both sides of the 1K symbols, with a length of 56 ms. As shown in Figure 1, the total length of the preamble P1 is 224 |is.

Figure 2 is a diagram illustrating carrier locations on which a preamble sequence is transmitted in the conventional art.

The drawing of Figure 2 is provided for a description of an internal structure of the 1K OFDM symbols shown in Figure 1. As illustrated in Figure 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.

Figure 3 is a block diagram illustrating a transmitter for transmitting a preamble in a conventional DVB system.

The locations of the carriers used for transmission of a preamble sequence among the 853 carriers can be predetermined. In Figure 3, carrier locations are predetermined and stored in a Carrier Distribution Sequence (CDS) table 300 .

An operation of a Modulation Signaling Sequence (MSS) processor 310 is as follows. MSS processor 310 receives a first sequence (hereinafter 'S1') and a second sequence (hereinafter 'S2') and generates Complementary Sequence Sets (CSS). The S1 and S2 include 3-bit information and 4-bit information, respectively. The CSSs generated by S1 and S2 have combinations 8 and 16, respectively, and CSSs1 and CSSs2 generated by S1 and S2 have a length of 64 and 256, respectively. Such CSS are characterized in that they are low in peak-to-average power ratio (PAPR) and orthogonal to each other. The signals of the S1 and S2 can be expressed as shown in Table 1, where they are expressed in hexadecimal.

Table 1

A series of procedures in which the sequences S1 and S2 are output as a modulated sequence by the MSS processor 310 through a phase shift processor 325 are as follows.

Equation (1) represents a sequence generated by a combination of S1 and S2 in MSS processor 310, and the sequence is indicated by MSS_SEQ.

MSS _ SEQ = {CSS sl, CSSS2, CSS sl} .................... ( 1 ) MSS_SEQ in Equation (1) is modulated by Differential BPSK (DBPSK ) into a DBPSK modulator (or DBPSK mapper) 320. Equation (2) represents the modulated DBPSK sequence, which is denoted by MSS_DIFF.

M SS _ D IFF = DBPSK ( M SS _ SEQ) ...................... ( 2 )

Phase shift processor 325 outputs the finally modulated sequence by applying a 180° phase shift to the 64 bits (or cells) of the Most Significant Bits (MSB) in the modulated sequence. The phase shift processor 325 does not phase shift 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 procedure of a DBPSK demodulator in a receiver. Therefore, there is no need for a reverse phase shift procedure at the receiver. Finally, an output of phase shift processor 325 is defined as Equation (3).

MSS = {-MSS _ DIFFmM2 .. m ,MSS _DIFFmJ¡¡g ... „}..................... ( 3 )

The stream that is output via MSS processor 310, DBPSK modulator 320, and phase shift processor 325, ie the modulated stream, is assigned to 384 active carriers for P1 by carrier allocator 330.

In the structure, 2 guard intervals are added to improve symbol robustness for P1, and the operations of an Inverse Fast Fourier Transform (IFFT) processor 340 and a preamble generator 350 are substantially the same as in Figure 1.

Figure 4 is a block diagram illustrating a receiver for receiving a preamble in a conventional DVB system.

Referring to Figure 4, a preamble detector 400 in the receiver detects a preamble and inputs it to an FFT processor 410. FFT processor 410 performs FFTs on the detected preamble and outputs the results to a demultiplexer (DEMUX) 420. DEMUX 420 then demultiplexes data onto active carriers on which a preamble is transmitted, and outputs the demultiplexed data to a DBPSK demodulator 430. DBPSK demodulator 430 performs a reverse of phase shift processor 325, i.e. performs DBPSK demodulation that reverse phase shifts preamble MSB signals by a length of 64 at the receiver, and then outputs the results to the receiver. a signaling detector 440. Signaling detector 440 outputs desired information by detecting S1 and S2 from the demodulated sequence.

Figure 5 is a flowchart illustrating a receiving procedure for receiving a preamble in a conventional DVB system.

Referring to Figure 5, the receiver performs initialization at step 500, and performs adjustment on a preamble at step 505. The receiver performs Guard Interval Correlation (GIC) on a received signal at step 510, and determines in step 515 whether it has detected a preamble P1. When the receiver has failed to detect the P1 preamble at step 515, the receiver returns to step 510. Otherwise, when the receiver has detected the P1 preamble, the receiver performs coarse time adjustment and fine frequency offset adjustment. at step 520. Next, at step 525, the receiver performs power correlation to estimate power of active carriers, and again determines at step 530 whether it has detected the P1 preamble. After the failure to detect the P1 preamble, the receiver returns back to step 510, and when the receiver successfully detects the P1 preamble, the receiver performs coarse frequency offset adjustment at step 535. Subsequently, the receiver performs frequency demodulation. DBPSK, which is an inverse procedure of the differential modulation scheme at the transmitter, at step 540, calculates an inter-preamble correlation value at step 545, and detects signals from S1 and S2 at step 550.

Since the above conventional preamble structure uses differential modulation (ie 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 between components of a frame in a DVB system.

ETSI: “Frame structure channel coding and modulation for a second generation digital terrestrial television broadcasting system (DVB-T2)”, DVB DOCUMENT A122r1 (01-01-2008) unveils a second generation baseline transmission system for broadcasting digital terrestrial television, which describes in detail the signal processing on the modulator side, while the processing on the receiver side is left open to different implementation solutions.

US 2007/206638 A1 discloses methods and apparatus for obtaining and demodulating a data stream transmitted in a communication system, finding a first 26 bits of a Unique Word (UW) associated with the data stream, finding a scrambling code that the UW uses. And using a decoding procedure to determine a modulation type and code rate used for desired signals within the data stream.

Summary of the invention

The invention is defined by the independent claims. Certain embodiments are intended to provide at least one of the advantages described below. Accordingly, one aspect of the invention provides a method capable of reducing a PARP from a preamble by encryption.

Other 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 accompanying drawings, discloses exemplary embodiments of the invention. Aspects of the present invention are provided in the independent claims. Preferred embodiments are provided in the dependent claims.

The scope of the present invention is determined solely by the scope of the appended claims. Brief description of the drawings

The foregoing 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:

Figure 1 is a diagram illustrating a frame structure of a physical channel in a conventional DVB system;

Figure 2 is a diagram illustrating carrier locations on which a preamble sequence is transmitted in the conventional art;

Figure 3 is a block diagram illustrating a transmitter for transmitting a preamble in a conventional DVB system;

Figure 4 is a block diagram illustrating a receiver for receiving a preamble in a conventional DVB system;

Figure 5 is a flowchart illustrating a receiving procedure for receiving a preamble in a conventional DVB system;

Figure 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;

Figure 7 is a diagram illustrating an example of a PRBS encoder for Equation (5);

Figure 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;

Figure 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; Y

Figure 10 is a flowchart illustrating a reception procedure for receiving a preamble in a DVB system according to an exemplary embodiment of the present invention.

Throughout the drawings, it should be noted that similar reference numerals are used to represent the same or similar elements, features and structures.

Detailed Description of Exemplary Embodiments

The following description with reference to the accompanying drawings is provided to aid in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims. It includes various specific details to aid in that understanding, but these are to be considered exemplary only. Accordingly, those skilled in the art will recognize that the scope of the present invention is defined by the scope of the appended claims, descriptions of well-known functions and constructions being omitted for clarity and clarification.

The terms and words used in the following description and claims are not limited to literature meanings, but are used simply 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 is provided for purposes of illustration only and not for the purpose of limiting the invention as defined by the appended claims.

The singular forms “a”, “an” and “the”, the” are to be understood to include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a component surface" includes reference to one or more such surfaces.

By the term "substantially" it is intended that the stated characteristic, parameter, or value need not be exactly achieved, but that deviations or variations may occur, including, for example, tolerances, measurement error, measurement accuracy limitations, and other known factors. for those skilled in the art, in amounts that do not impede the effect of the characteristic that it was intended to provide.

The present invention relates to a preamble where signaling information is transmitted, and in particular to a preamble P1 through which initial information is transmitted. Exemplary embodiments of the present invention provide a method of dealing with the aforementioned problem that a peak-to-average power ratio (PAPR) of complementary sequences for a preamble is increased due to the use of differential modulation.

A description of exemplary embodiments of the present invention will now be provided below.

Table 2 shows the preamble PAPRs for a case where the differential modulation scheme is not applied in the P1 preamble. When 128 preamble signals are generated by combinations of S1 and S2, the maximum PAPR is 10.29 dB, the minimum PAPR is 6.72 dB, and an average pAp R is 8.21 dB.

Table 2

However, Table 3 shows the preamble PAPRs for a case where 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 indicated above, it can be seen from a comparison between Table 2 and Table 3 that the PAPR increases as the characteristics of the complementary sequences are discrepant with each other due to the use of the differential modulation scheme. From Table 2 and Table 3, it can be seen that the average PAPR increases by 0.42 dB due to an influence of differential modulation.

Table 3

As a method of dealing with the problem of increasing PAPR caused by differential modulation, ie, for PAPR reduction, the DVB system may apply scrambling.

Figure 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.

Referring to Figure 6, the transmitter includes a CDS table 600, an MSS processor 610, a DBPSK modulator 620, a phase shift processor 630, a scrambler 635, a carrier allocator 640, a carrier processor 650 IFFT, and a preamble generator 660. Since in CDS table 600, MSS processor 610, DBPSK modulator 620, phase shift processor 630, allocator Carrier 640, IFFT processor 650, and preamble generator 660 are substantially the same in operation as CDS table 300, MSS processor 310, DBPSK modulator 320, phase shift processor 325, allocator carrier 330, IFFT processor 340 and preamble generator 350 in the conventional transmitter of Fig. 3, a detailed description thereof will be omitted.

Scrambler 635, in accordance with an exemplary embodiment of the present invention, can prevent a Complementary Sequence Set (CSS) generated by MSS processor 610 from being increased by a PAPR by DBPSK modulator 620 and offset processor 630. phase. In other words, in an exemplary implementation, scrambler 635 generates a new sequence by multiplying a modulated sequence output from phase shift processor 630 by a scrambling sequence. The scrambler 635 can operate with any arbitrary sequence when performing an operation to change the signal from the MSS processor 610 to an arbitrary shape.

An MSS_SCR output of scrambler 635 is expressed as Equation (4).

M SS _ SCR = SCR ( MSS ) ......................( 4 )

In Equation (4), the term "SCR" indicates a scrambling operation of scrambler 635. A new sequence is generated by multiplying the modulated sequence input to scrambler 635 by a scrambling sequence. For example, when a BSPK sequence of length K is entered as a modulated sequence, i.e. when {10, -11, -12, 13, ..., 1K-1} is entered as a modulated sequence, even the sequence The scrambling sequence can be generated with an arbitrary BPSK sequence of length K. When a scrambling sequence is {-10, 11, -12, -13, ... , -1 K-1}, the 635 scrambler generates {-10 , -11, 12 , -13, ... , -1 K-1} as a new BPSK sequence of length K by multiplying the modulated sequence by {10, -11, -12, 13, ... , 1 K -1} by the randomization sequence of {-10, 11, -12, -13, ... , -1 K-1}. That is, scrambler 635 generates a new MSS_SCR sequence by multiplying the sequence modulated using Equation (4) by the scrambling sequence.

Scrambler 635 performs scrambling by multiplying the modulated sequence in DBPSK modulator 620 and phase shift processor 630, i.e. a modulated sequence of length 384 by 1 or -1, by a scrambling sequence of length 384 used in the scrambler. 635. The scrambling sequence will be described in more detail in the following exemplary embodiment.

Scrambler 635 generates a scramble sequence to reduce a PAPR from a preamble P1. 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.

1X14X15 ...................... (5)

Figure 7 is a diagram illustrating an example of a PRBS encoder for Equation (5).

Referring to Figure 7, a PRBS register 710 receives an initial value sequence (100010111100101), and generates a PRBS sequence (1110100011100100011100100...). The initial value and randomization sequence of PAPR of length 384 are shown in Table 4.

Table 4

continuation

The scrambling sequence of Table 4 is used as a scrambling sequence for a scrambler used to reduce a PAPR of a preamble P1. In the PRBS encoder of Figure 7, a sequence of length 384 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 an output modulated sequence from a phase shift processor in scrambler 635, thereby reducing a PAPR.

Table 5 shows the PAPRs of 128 P1 preambles in an exemplary embodiment of the present invention using randomization for PAPR reduction. It can be seen that the maximum PAPR is 9.10 dB, the minimum PAPR is 6.71 dB, and an average PAPR is 8.01 dB. Compared to Table 3, a gain of 1.4 dB at maximum ^p A ^p R can be obtained.

Table 5

In an exemplary implementation, a new sequence is generated by the aforementioned scrambler 635. Furthermore, each randomization sequence can be stored in a lookup table for future use, or can be determined as needed. As an example, the output of DBPSK modulator 620 in Figure 6 can be stored in the lookup table, the output of scrambler 635 can be stored in the lookup table, or the outputs of all blocks 600 to 635 can be stored in the lookup table. lookup table for a 635 scrambler operation.

Figure 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.

Referring to Figure 8, the transmitter receives S1 and S2 at step 801, and generates an MSS by selecting a sequence corresponding to S1 and S2 at step 803. The transmitter differentially modulates the MSS at step 805, and applies 180° phase shift to the 64 MSB bits at step 807. At step 809, the transmitter performs scrambling by multiplying the scrambling sequence generated by Equation (5) by the modulated sequence at step 807. step 811, the transmitter receives the scrambled sequence via each assigned subcarrier. Next, at step 813, the transmitter generates a time domain signal by performing IFFT on the received scrambled sequence via the assigned subcarrier. Finally, at step 815, the transmitter generates a preamble having a structure illustrated in Figure 1.

Since the scrambling operation performed by the scrambler 635 is performed after DBPSK modulation, the exemplary embodiments of the present invention are more stable in the detection performance of S1 and S2, compared to when the scrambling operation is performed before DBPSK modulation. In other words, exemplary embodiments of the present invention are robust in performing detection of S1 and S2.

Figure 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.

Referring to Figure 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 preamble detector 900, FFT processor 910, DEMUX 920, DBPSK demodulator 940, and signaling detector 950 are substantially the same in operation as preamble detector 400, FFT processor 410, DEMUX 420, DBPSK demodulator 430 and signaling detector 440 illustrated in Figure 4, a detailed description thereof will be omitted.

The descrambler 930, in accordance with an exemplary embodiment of the present invention, performs a reverse procedure of the scrambler 635 on the sequence obtained by demultiplexing data on active carriers on which a preamble is transmitted. That is, descrambler 930 performs descrambling by multiplying the demultiplexed sequence by the descrambling sequence. The descrambling sequence is the same length as the demultiplexed sequence. The descrambling sequence can be predetermined and stored in a lookup table, or generated using PRBS, in substantially the same way as for the scrambling sequence above.

Figure 10 is a flowchart illustrating a reception procedure for receiving a preamble in a DVB system according to an exemplary embodiment of the present invention.

Referring to Figure 10, the receiver performs initialization at step 1000, and performs adjustment on a preamble at step 1005. The receiver performs Guard Interval Correlation (GIC) on the received signal at step 1010, and determines at step 1015 if it has detected a preamble P1. When the receiver has failed to detect the P1 preamble at step 1015, the receiver returns to step 1010. However, when the receiver has detected the P1 preamble, the receiver performs coarse time adjustment and fine frequency offset adjustment in step 1020. Subsequently, 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 P1 preamble. When the receiver has failed to detect the P1 preamble at step 1030, the receiver returns back to step 1010, and when the receiver has successfully received the P1 preamble, the receiver performs coarse frequency offset adjustment at step 1035. The receiver then performs descrambling using a descrambling sequence in accordance with an exemplary embodiment of the present invention in step 1040, and performs differential modulation, which is a reverse procedure of the differential modulation scheme at the transmitter, in step 1045. Subsequently, the receiver determines a correlation between preambles in step 1050, and detects signals from S1 and S2 in step 1055.

As is evident from the above description, exemplary embodiments of the present invention use the differential modulation scheme when transmitting a preamble, one of the physical channels, in the DVB system, thereby reducing a PAPR of the P1 preamble by solving the PAPR boosting problem using randomization.

It will be appreciated that embodiments of the present invention may be embodied in hardware, software, or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device such as a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or in an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape or the like. It will be appreciated that the storage devices and storage media are machine-readable storage embodiments that are suitable for storing a program or programs comprising instructions that, when executed, implement the embodiments of the present invention. Accordingly, embodiments provide a program comprising code for implementing a system or method as claimed in any one of the claims of this specification and machine-readable storage that stores such a program. Still further, such programs may be carried electronically by any means such as a communication signal carried over a wired or wireless connection and the embodiments suitably encompass the same.

Throughout the description and claims of this specification, the words "comprise" and "contains" and variations of the words, for example "comprising" and "comprising", mean "including, but not limited to", and are not intended to (and do not) exclude other moieties, additives, components, integers, or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context requires otherwise. In particular, when the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties, or groups described in conjunction with a particular aspect, embodiment, or example of the invention are to be understood as applicable to any other aspect, embodiment, or example described herein unless that are incompatible with them.

It will also be appreciated that, throughout the description and claims of this specification, language in the general form of "X for Y" (where Y is some action, activity or step and X is some means of carrying out that action, activity or step) encompasses means X adapted or arranged specifically, but not exclusively, to do Y.

Claims (8)

1. A procedure performed by a transmitter to transmit a preamble in a Digital Video Broadcasting, DVB, system, the procedure comprising: generating (803) a modulation signaling sequence, MSS, using a plurality of sequences; modulating (805) the generated MSS using differential modulation to generate a first sequence; generate a coding sequence using a binary pseudorandom sequence, ^p R ^b S; scrambling (809) the first sequence bitwise by multiplying the first sequence by the scrambling sequence to generate a second sequence; assigning (811) the second sequence to a plurality of subcarriers; converting (813) the second sequence in the preamble onto a time domain; and transmit of the preamble. 2. The method of claim 1, wherein the encoding sequence is equal to the 384-length sequence converted from the initial 384 bits of the PRBS generator. 3. The method of claim 1, wherein the differential modulation is binary differential key phase shift keying, DBPSK. 4. The method of claim 1, wherein the modulated sequence and the encoding sequence are the same length. 5. A procedure performed by a receiver to receive a preamble in a Digital Video Broadcasting, DVB, system, the procedure comprising: obtain a preamble from a received signal; converting the obtained preamble into a frequency domain signal; demultiplexing the frequency domain signal to generate a demultiplexed sequence; generate a descrambling sequence using a binary pseudorandom sequence, PRBS; scrambling (1040) the demultiplexed sequence bit by bit by multiplying the demultiplexed sequence by the descrambling sequence to generate a descrambled sequence; demodulating (1045) the descrambled sequence using differential demodulation to generate a demodulated sequence; and obtaining a plurality of sequences from the demodulated sequence. 6. The method of claim 5, wherein the descrambling sequence is equal to the 384-length sequence converted from the initial 384 bits of the PRBS generator. The method of claim 5, wherein the differential demodulation is key phase shift binary differential demodulation, DBPSK. 8. The method of claim 5, wherein the demodulated sequence and the descrambling sequence are the same length.