KR100927142B1 - Multicarrier transmission system and its method for improving transmission efficiency - Google Patents

Abstract

The multi-carrier transmission system according to the present invention is a multi-carrier transmission system in which pseudo-noise sequence information, which is synchronization information for synchronization between a transmitting side and a receiving side, is added to a transmission signal to transmit the OFDM signal in the input frequency domain. An IFFT unit for inverse fast Fourier transform into an OFDM signal of a region, a Walsh code generator for generating Walsh code, which is additional information for the transmitter, and a Walsh code and pseudo noise string information generated by the Walsh code generator And a guard interval insertion section for adding the signal coupled by the logic combining section and the OFDM signal converted by the IFFT section. Thus, the multi-carrier transmission system can improve the transmission efficiency of the entire system by transmitting the additional information using the Walsh code.

Description

Multi-carrier transmission system capable of improving transmission efficiency and a method thereof

1 is a schematic block diagram of a multi-carrier transmission system according to the DVB-T standard method and the SMCC method;

2 is a diagram illustrating a frame structure of a transmission signal according to an SMCC scheme;

3 is a schematic block diagram of a multicarrier transmission system according to the present invention;

4 is a flowchart illustrating a multicarrier transmission method according to FIG. 3; and

FIG. 5 is a diagram illustrating an example of a Walsh code shown in FIG. 3.

Explanation of symbols on the main parts of the drawings

10, 110: FEC part 20, 120: mapping part

30, 130: frame forming portion 40, 140: IFFT portion

60, 151: PN generator 153: Walsh code generator

155: logic coupling section 50, 160: protection section insertion section

The present invention relates to a multi-carrier transmission system and a transmission method thereof, and more particularly, to a multi-carrier transmission system and a transmission method that can improve the transmission rate of the entire system.

As communication, computers, and broadcasting converge to become multimedia, countries around the world are digitizing existing analog broadcasting. Digital broadcasting refers to a broadcasting system in which all signals from a source to a transmission are digitized. Of course, in analog broadcasting, digital equipment was partially used in the production process in recent years, but digital broadcasting means that the radio waves transmitted in addition to production are also digitally modulated. Advantages of digitally transmitting broadcast signals are as follows.

-In case of analog, the image quality is lower when the distance from the transmitting antenna is far. However, when transmitting digitally, there is little effect of signal attenuation, so there is no deterioration of image quality in the reception area. .

-Due to the digital signal characteristics, the transmission output may be smaller than that of analog broadcasting.

Unlike analog, where high-energy video / audio / color carriers interfere a lot on the same or adjacent channels, digital transmission has less inter-channel interference because energy is distributed evenly over the entire frequency band.

Recent advances in digital signal compression technology, error correction technology, and rapid advances in LSI technology have resulted in a significant reduction in the cost of receivers and a significant reduction in transmission costs. Some broadcasts are conducted. In addition, developed countries have developed standard methods for digital broadcasting, and these standard methods are configured slightly differently.

Standard methods for digital broadcasting are roughly classified into the US Advanced Television Systems Committee (ATSC) method, the European Digital Video Broadcasting-Terrestiral (DVB-T) method, and the Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) method in Japan. do.

The ATSC standard supports a variety of video formats, including high definition television (HDTV) and standard definition television (SDTV), interlaced and progressive scan, and 16: 9 and 4: 3 aspect ratios. Video encoding employs the MP @ HL of the MPEG-2 standard, audio encoding follows the Dolby AC-3 standard, service multiplexing, and the transport layer follows the MPEG-2 system standard. Channel coding uses Reed-Solomon coding, interleaving and Trellis coding, and modulation uses a single carrier 8-VSB (Vestigial Sideband) modulation. In addition, the ATSC standard shows a transmission rate of 19.39 Mbps over a bandwidth of 6 MHz, which is higher than DVB-T. ATSC standard method is designed to be strong against co-channel interference even in analog broadcasting environment with simulcast environment, and the hardware configuration is simpler than other methods to enable low-cost receiver configuration, and peak-to-average power. Ratio is better. However, there is no characteristic of single frequency network (SFN) or mobile reception of DVB-T.

The DVB-T standard has enhanced compatibility by using common fundamental technologies for satellite broadcasting (DVB-S), cable television (DVB-C), and terrestrial broadcasting. In other words, video encoding uses MP @ ML of MPEG-2 standard, MPEG-2 (Layer II) for audio encoding, and MPEG-2 system for multiplexing. The channel encoding uses Reed Solomon code in common and is added depending on the transmission medium Error correction method was selected. The modulation scheme is Orthogonal Frequency Division Multiplexing (OFDM) using a multi-carrier, and the modulation of each carrier uses a Quadrature Amplitude Modulation (QAM) modulation scheme. The number of carriers has two modes, 2K and 8K. The DVB-T standard shows a transmission rate of 4.98 to 31.7 Mbps in terms of code rate, guard interval, etc., at a bandwidth of 8 MHz. By using the guard interval in OFDM modulation, data transmission efficiency is reduced, but it is resistant to ghost, SFN is possible, so that frequency can be efficiently used, and mobile reception service for vehicles is possible. In addition, the use of two-level hierarchical modulation enables robust reception or extended service in harsh environmental conditions.

ISDB-T standard video coding and multiplexing is the same as DVB-T. Audio coding is MPEG-2 (ACC) and Band Segemented Transmission-Orthogonal Frequency Division Multiplexing (BST-OFDM), which is similar to the basic skeleton of OFDM in modulation. Modulation method is used. This transmission method is to support digital audio broadcasting and digital TV broadcasting in common, and implements services such as audio broadcasting, data broadcasting, SDTV, and HDTV by combining as many frequency segments with 100 kHz bandwidth as necessary. A segment consists of multiple carriers spaced about 4kHz apart. By changing the number of segments, the occupied bandwidth can be adjusted, providing flexibility in terms of frequency, thereby increasing the efficiency of spectrum use. This is due to the fact that the frequency bands are very crowded and full in Japan. The ISDB-T standard method is easy to implement mobile reception and SFN like the DVB-T method by using the OFDM method in modulation. However, the receiver configuration is complicated and there is an overhead in data rate due to the use of guard intervals.

Recently, China's Chengdu University of Science and Technology applied the original Synchronized Multi-Carrier-CDMA (SMCC) digital broadcasting standard that applies Terrestrial Digital Audio Broadcasting (DVB-T) of the European digital broadcasting standard for digital broadcasting in China. Suggested. The main feature of the digital broadcasting system according to the SMCC digital broadcasting standard is to adopt 4K multicarrier transmission mode with optimal parameters, and in the synchronization method, CDMA (digital data) is digitized and then spread over the entire available bandwidth. code-division multiple access (Code Division Multiple Access) technology is used. In addition, the digital broadcasting system according to the SMCC digital broadcasting standard uses binary phase-shift keying (BPSK), QPSK, 16QAM, 32QAM, 64QAM, 128QAM, and 256QAM as a modulation method of subcarriers. Here, the BPSK is also referred to as a binary phase shift method, and is a PSK method in which a phase difference of 180 degrees is provided to each carrier when one bit of signal 0 and one.

1 is a schematic block diagram of a multicarrier transmission system according to the DVB-T standard method and the SMCC method. In the multi-carrier transmission system according to the DVB-T standard method, the FEC unit 10, the mapping unit 20, the frame forming unit 30, the IFFT unit 40, the guard section inserting unit 50, and the PN inserting unit 60 ), And an RF unit 60. Here, the protective section inserting portion 50 includes a first protective section inserting portion 51 and a second protective section inserting portion 53.                         

The FEC unit 10 performs coding for detecting and correcting an error at a receiving end. In general, the FEC unit 10 uses Reed-Solomon (RS) coding and convolutional coding. RS coding is part of the Forward Error Correction (FEC) structure added to the input data stream. FEC refers to a technique for correcting bit errors that occur during transmission.

Atmospheric noise, multipath propagation, signal fading, and nonlinearity of the transmitter all contribute to bit error, and RS coding adds 20 bytes to the trailing 187 bytes for MPEG-II transport streams. The 20 additional bytes are called Reed Solomon Parity Bytes. The receiver compares the received 187 bytes with 20 parity bytes to determine accuracy. If an error is detected by the accuracy determination, the receiver locates the error and corrects the distorted byte to recover the original signal. In this way up to 10 bytes of error per stream can be recovered. Any further error is not recoverable, and if not recoverable, the entire stream is discarded. Convolutional coding is a code whose output bits are affected by past input bits as well as the current input and are effective for correcting random errors.

The mapping unit 20 maps the coded data to Quadrature Phase Shift Keying (QPSK), Quadrature Amplitude Modulation (16QAM), 64QAM, and the like. Phase shift keying (PSK) is a method of changing a phase according to a digital value. A method of associating four values, that is, two bits, in one symbol with a phase shift interval of 90 degrees among the PSK is called a QPSK. In the QAM method, a phase change interval of 90 degrees corresponds to 4 symbols, or 2 bits, in one symbol.                         

The frame forming unit 30 pilot inserts and forms a frame in the transmission mode. The inserted pilot inserts a distributed pilot and a continuous pilot for transmission acquisition and channel equalization at the receiver, and a transmission parameter signal (TPS). TPS transmits six pieces of information: pattern information of QAM constellation, hierarchy information, length of protection interval, inner code rate, transmission mode of 2K or 8K, and frame number.

Inverse Fast Fourier Transform (IFFT) unit 40 performs an inverse fast Fourier transform of the OFDM signal in the frequency domain into an OFDM signal in the time domain.

The guard interval inserter 50 inserts the end of the modulated OFDM signal as a guard interval in front of the OFDM signal in order to prevent inter syambol interference (ISI) in a multipath environment.

The PN inserting unit 60 inserts Pseudo Noise Sequence (PN) information into the OSDM symbol in which the protection interval is inserted.

2 is a diagram illustrating a frame structure of a transmission signal according to the SMCC scheme. Referring to the drawings, a transmission signal according to the SMCC scheme forms a frame by combining a frame for an OFDM symbol and a frame for a CDMA symbol. That is, the frame for the OFDM symbol and the frame for the CDMA symbol are formed in parallel processing. The first guard interval inserting unit 51 copies the rear part of the OFDM symbol output from the IFFT unit 40 and inserts it in front of the OFDM symbol. In addition, the second protection section insertion unit 53 copies the signal from the PN insertion unit 60, that is, the rear part of the CDMA symbol, and inserts it in front of the CDMA symbol. The guard interval inserter 50 combines each signal into which a part of the OFDM symbol and a part of the CDMA symbol are inserted.

The RF unit 70 loads a signal in a frequency band to which an OFDM signal is to be transmitted and transmits the signal over a wireless channel.

In general, pseudo-noise sequence information inserted in the SMCC scheme is used only for frequency synchronization or symbol timing synchronization. However, in a system using multiple carriers, a lot of additional information is required for the FEC to operate. Examples of such additional information include a modulation method of each subcarrier in OFDM, a code rate of an inner code, a type of an inner code, a type of an outer code, and the like. When the additional information is inserted into the OFDM symbol and transmitted, it takes a long time to perform the FEC operation, thereby reducing the transmission efficiency of the multicarrier transmission system.

The present invention was devised to solve the above problems, and in the multi-carrier transmission system of the SMCC method, multi-carrier transmission which can improve the transmission efficiency of the entire system by transmitting additional information using a Walsh code. It is an object of the present invention to provide a system and a method thereof.

In the multi-carrier transmission system according to the present invention for achieving the above object, in the multi-carrier transmission system for adding and transmitting pseudo-noise string information, which is synchronization information for synchronization of the transmitting side and the receiving side to the transmission signal, An IFFT unit for inverse fast Fourier transform of an OFDM signal in a frequency domain into an OFDM signal in a time domain, a Walsh code generator for generating a Walsh code as additional information for the transmitting side, and the Walsh code generated by the Walsh code generator And a logic combining unit for logically combining the pseudo-noise string information, a guard interval inserting unit for adding the signal combined by the logic combining unit and the OFDM signal converted by the IFFT unit, and the pseudo-noise string information. It characterized in that it comprises a generating PN generation unit. Here, the PN generation unit generates the pseudo noise string information in a CDMA manner. In addition, the IFFT unit, the Walsh code generator, the logical coupling unit, the guard section insertion unit, and the PN generator is implemented to be applicable to the SMCC standard of the Chinese multi-carrier method. The logic combiner may be implemented to exotherm the pseudo noise string information and the Walsh code. The Walsh code is composed of a set of bit strings of the same size. In this case, the bit string may be implemented such that the number of bits is 2 ^N (N is a natural number).

On the other hand, according to the multi-carrier transmission system according to the present invention, in the multi-carrier transmission method for transmitting the pseudo-noise sequence information, which is synchronization information for synchronization between the transmitting side and the receiving side to the transmission signal, OFDM in the input frequency domain Inverse fast Fourier transforming a signal into an OFDM signal in a time domain, generating a Walsh code as additional information for the transmitting side, and logically storing the Walsh code and the pseudo noise sequence information generated by the Walsh code generator A method of multicarrier transmission is provided, comprising: combining and summing the signal combined by the logical combining step and the OFDM signal converted by the converting step.                     

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

3 is a schematic block diagram of a multicarrier transmission system according to the present invention, and FIG. 4 is a flowchart illustrating a multicarrier transmission method according to FIG. 3. Referring to the drawings, the multi-carrier transmission system is the FEC unit 110, the mapping unit 120, the frame forming unit 130, IFFT unit 140, PN inserting unit 151, Walsh code generating unit 153, The logic coupling unit 155, the protective section insertion unit 160, and the RF unit 170 are provided. In addition, the protective section insertion unit 50 includes a first protective section insertion unit 161 and a second protective section insertion unit 163. Here, each component included in the multicarrier transmission system is preferably implemented to perform signal processing for digital broadcasting according to the SMCC method.

The FEC unit 110, the mapping unit 120, and the frame forming unit 130 have the same configuration and operation as those described above, and thus description thereof will be omitted.

The IFFT unit 140 inverses fast Fourier transforms the input OFDM signal in the frequency domain into the OFDM signal in the time domain (S401). The PN generation unit 151 generates pseudo noise string information on the OMD symbol in which the protection interval is inserted. The pseudo-noise string information is synchronization information for predicting synchronization and channel of the OMD signal received by the OMD receiver which receives the transmitted OMD signal. In the SMCC method, pseudo noise string information is implemented by the CDMA method. Here, the CDMA (Code Division Multiple Access) method uses a spread spectrum method and modulates a signal by assigning codes having low correlation to each subscriber channel within the same frequency band. It is a method to recover the signal only when used. Here, the transmitting side refers to a transmitting side having a digital broadcasting transmission system for transmitting digital broadcasting in a single carrier system, and the receiving side refers to a receiving side for receiving digital broadcasting transmitted in a single carrier system.

The Walsh code generator 153 generates a Walsh code that is additional information for the transmitting side (S403). Here, the additional information refers to information provided by the transmitting side so that the receiving side can quickly and easily decode the transmission signal. Examples of such additional information include identification information for the transmitting side, frame structure information for the transmission signal, data distribution information distributed by an interleaver (not shown) provided in the FEC unit 110, and modulation of each subcarrier of OFDM. Method, code rate of the inner code by an inner coding unit (not shown) provided in the FEC unit 11, types of inner codes, outer coding provided in the FEC unit 110 ( type of outer code performed by an outer coding unit (not shown). Therefore, the Walsh code includes identification information on the transmitting side, frame structure information on the transmission signal, data distribution information distributed by the interleaver, a modulation method of each subcarrier of OFDM, and an inner coding unit provided in the FEC unit 110. It can be implemented as information including at least one of the coding rate of the inner code, the type of inner code, the type of outer code performed by the outer coding unit provided in the FEC unit 110. In addition, the Walsh code is composed of a set of bit strings of the same size, and the bit string is implemented with 2 ^N bits (N is a natural number). An example of the Walsh code when the number of bits in the bit string is 16 (= 2 ⁴ ) is shown in FIG. 5.

The logical combiner 153 logically combines the pseudo-noise string information generated by the PN information generator 151 and the Walsh code generated by the Walsh code generator 153 (S405). Here, the logic combiner 155 is preferably implemented to XOR the pseudo-noise string information and the Walsh code.

The first guard interval inserting unit 161 of the guard interval inserting unit 160 copies the rear part of the OFDM symbol transmitted from the IFFT unit 140 and inserts it in front of the OFDM symbol. In addition, the second protection section insertion unit 53 copies the signal from the PN insertion unit 60, that is, the rear part of the CDMA symbol, and inserts it in front of the CDMA symbol. The guard interval inserting unit 50 adds a signal in which a part of the OFDM symbol and a part of the CDMA symbol are inserted (S407).

The RF unit 70 loads a signal in a frequency band to which an OFDM signal is to be transmitted and transmits the signal over a wireless channel.

As a result, the multicarrier transmission system according to the present invention adds additional information to the time domain using Walsh codes, thereby eliminating the need for demodulating OFDM symbols on the receiving side to find information. As a result, FEC processing is performed quickly. The time taken to decode the transmission signal at the receiving side can be reduced.

According to the present invention, the multi-carrier transmission system can improve the transmission efficiency of the entire system by transmitting the additional information using the Walsh code.

Although the preferred embodiments of the present invention have been illustrated and described above, the present invention is not limited to the specific embodiments described above, and the present invention is not limited to the specific embodiments of the present invention without departing from the spirit of the present invention as claimed in the claims. Anyone of ordinary skill in the art can make various modifications, and such changes are within the scope of the claims.

Claims (12)

In a multi-carrier transmission system for transmitting pseudo-noise sequence information, which is synchronization information for synchronization between a transmitter and a receiver, by adding to a transmission signal, An IFFT unit for inverse fast Fourier transforming the input OFDM signal in the frequency domain into the OFDM signal in the time domain; A Walsh code generator for generating Walsh codes as additional information for the transmitter; A logic combiner configured to logically combine the Walsh code generated by the Walsh code generator and the pseudo-noise sequence information through a predetermined logical operation; And And a guard interval insertion unit for adding the signal coupled by the logical combining unit and the OFDM signal converted by the IFFT unit. The method of claim 1, Further comprising: a PN generator for generating the pseudo-noise sequence information, The PN generation unit generates the pseudo-noise string information by the CDMA method. The method of claim 2, And the IFFT unit, the Walsh code generator, the logical coupling unit, the guard interval insertion unit, and the PN generator are applicable to an SMCC standard. The method of claim 3, wherein And the logical combiner combines the pseudo-noise string information and the Walsh code by XOR-combining. The method of claim 4, wherein And the Walsh code comprises a set of bit strings of the same size. The method of claim 5, And the bit string has 2 ^N bits (N is a natural number). In the multi-carrier transmission method for transmitting pseudo-noise sequence information, which is synchronization information for synchronization between the transmitting side and the receiving side, is added to a transmission signal and transmitted. An inverse fast Fourier transform of the input OFDM signal in the frequency domain into the OFDM signal in the time domain; A Walsh code generation step of generating a Walsh code as additional information for the transmitting side; A logical combining step of logically combining the generated Walsh code and the pseudo-noise sequence information through a predetermined logical operation; And And adding the signal combined by the logical combining step and the OFDM signal converted by the converting step. The method of claim 7, wherein And generating pseudo noise column information for generating the pseudo noise column information. The pseudo-noise sequence information generating step comprises generating the pseudo-noise sequence information in a CDMA manner. The method of claim 8, Wherein said converting step, said Walsh code generating step, said logical combining step, said adding step, and said pseudo-noise sequence information generating step are applicable to SMCC standard. The method of claim 9, In the logical combining step, the pseudo-noise sequence information and the Walsh code are XOR-combined. The method of claim 10, And the Walsh code comprises a set of bit strings of the same size. The method of claim 11, And the bit string has 2 ^N bits (N is a natural number).

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