KR100920722B1 - Multi-carrier transmission system capable of improving the performance of receiving and a method proessing signal thereof - Google Patents

Abstract

The multi-carrier transmission system includes a FEC unit for encoding data in a frequency domain for detecting and correcting an error at a receiving side, a mapping unit for mapping data in a coded frequency domain by a predetermined mapping method, and mapped data. A serial / parallel converter which collects N pieces and outputs the parallel data; An inverse discrete Fourier transform unit for outputting an inverse discrete Fourier transform and outputting the OFDM signal in the time domain, a guard interval insertion unit for inserting a guard interval in the OFDM signal in the time domain, and an OFDM signal in the time domain in which the guard interval is inserted; And a second synchronous information inserting section for inserting two synchronous information. Therefore, by inserting the PN sequence into the data in the frequency domain, it is possible to improve the reception performance over the conventional multi-carrier transmission system.

Multicarrier, PN sequence, parallel data, spreader, reception performance improvement

Description

Multi-carrier transmission system capable of improving the performance of receiving and a method proessing signal

1 is a schematic block diagram of a typical TDS-OFDM transmission system;

2 is a schematic block diagram of a DMB-T transmission system using a TDS-OFDM scheme according to an embodiment of the present invention;

3 is a detailed block diagram of the first synchronization information insertion unit 230 of FIG.

4 is a flowchart illustrating a signal processing method according to a TDS-OFDM transmission system according to the present invention;

FIG. 5 is a detailed flowchart of the step S40 of inserting first synchronization information of FIG. 4; and

6A to 6E are conceptual views illustrating in more detail the step S40 of inserting the first synchronization information of FIG. 5.

Explanation of symbols on the main parts of the drawings

100 channel encoding unit 200 OFDM modulation unit

110: scrambler 120: FEC part

210: mapping unit 220: serial / parallel conversion unit                 

230: first synchronization information insertion unit 231: diffusion unit

233: multiplication unit 235: buffer

240: 3780-point IDFT unit 250: parallel / serial conversion unit

260: protection section insertion unit 270: second synchronous information insertion unit

280: molded filter part 290: RF part

The present invention relates to a digital broadcasting system, and more particularly, to provide a multi-carrier transmission system having improved reception performance.

Orthogonal Frequency Division Multiplexing (OFDM), which is a type of multicarrier modulation, has excellent performance in multipath and mobile reception environments.

The OFDM method improves frequency utilization efficiency by using a plurality of carriers having mutual orthogonality, and is a method suitable for high-speed data transmission using a multi-carrier in a wired or wireless channel. In the case of a high-speed data transmission with a short symbol period in a wireless communication channel having multipath fading, when the single carrier method is used, the inter-symbol interference becomes more severe, whereas the complexity of the receiver is greatly increased. Since the symbol period in each subcarrier can be extended by the number of subcarriers while maintaining the data rate, a simple equalizer with one tap can cope with severe frequency selective fading channels by multipath.

In the OFDM method, the frequency utilization efficiency is increased by using a plurality of carriers having mutual orthogonality, and the process of modulating and demodulating the plurality of carriers at the transmitting and receiving end can be implemented at high speed by using the resultant IFFT and FFT. Can be.

TDS-OFDM (Time Domain Synchronous-Orthogonal Frequence Division Multiplexing), one of the OFDM schemes, is a synchronization information for obtaining synchronization between a transmitter and a receiver in a time domain, for example, characterized in that a PN (Pseudo Noise) sequence is inserted. That's the way it is.

FIG. 1 is a schematic block diagram of a digital broadcasting system employing TDS-OFDM (Time Domain Synchronous-Orthogonal Frequency Division Multiplexing) scheme.

The TDS-OFDM transmission system includes a forward error correction (FEC) unit 10 that performs encoding for detecting and correcting an error at a receiving end, and a mapping unit 20 which maps coded data to QPSK, 16QAM, 64QAM, or the like. And an Invertes Discrete Fourier Transform (IDFT) unit 30 which modulates the OFDM signal in the frequency domain into the OFDM signal in the time domain, and the end of the OFDM signal modulated to prevent inter syambol interference (ISI) in a multipath environment. A guard section inserting section 40 for copying a section and inserting the section as a guard section at the front of the OFDM signal, a sync information inserting section 50 for inserting a sync signal in a time domain characteristic of the TDS-OFDM scheme, and the inserted sync section It has a shaping filter unit 60 for filtering for pulse shaping of information, and an RF unit 70 for carrying a signal in a frequency band to send an OFDM signal.

As described above, in a transmission system employing the TDS-OFDM scheme, a synchronization signal is inserted into the time domain, and the reception side performs synchronization and time equalization of the time domain and the frequency domain using only a sync segment of the time domain. As a result, the reception performance is deteriorated.

SUMMARY OF THE INVENTION An object of the present invention for solving the above problems is to insert a PN sequence which is general synchronization information into each symbol which is an OFDM signal in the frequency domain, and a multi-carrier transmission system capable of further improving the reception performance of the receiving side and its It is to provide a signal processing method.

The multi-carrier transmission system according to the present invention for achieving the above object, the FEC unit for coding the data of the frequency domain to detect and correct the error at the receiving side, and the predetermined data mapping of the coded frequency domain A mapping unit for mapping by a method, a serial / parallel conversion unit for collecting N mapped data and outputting the mapped data as parallel data, and first synchronization information for inserting different first synchronization information of the same length into each of the parallel data. An inserter, an inverse discrete Fourier transformer for converting the N pieces of data into which the first synchronization information is inserted and an inverse discrete Fourier transform to output an OFDM signal in a time domain, and a protection for inserting a guard interval in the OFDM signal in the time domain And an interval insertion unit and a second synchronization information insertion unit for inserting the second synchronization information into the OFDM signal of the time domain into which the protection interval is inserted.

Preferably, in the case where N = K x M (N, K, M is a natural number), the parallel data output from the serial / parallel conversion unit is composed of K data, and the first The sync information inserter inserts the spreader to spread the length of the K data by the length of the first sync information, and inserts the first sync information into the K data whose length is spread by the length of the first sync information. And a multiplier for multiplying the first synchronization information, and a buffer for accumulating the K data multiplied by the first synchronization information for M times and outputting the N data.

The first synchronization information is a PN sequence having a length of 2 ⁿ −1 (n is a natural number), and the number K of the parallel data corresponds to the length of the PN sequence.

On the other hand, the signal processing method of the multi-carrier transmission system according to the present invention comprises the steps of: coding the data of the frequency domain to detect and correct the error at the receiving side; Mapping the coded data of the frequency domain by a predetermined mapping method; Collecting parallel data and outputting parallel data; Inserting different first synchronization information of the same length into the parallel data; An inverse discrete Fourier transform step of inverse discrete Fourier transforming the parallel data into which the first synchronous information is inserted and outputting an OFDM signal in a time domain; Inserting a guard interval into the OFDM signal in the time domain; And inserting the second synchronization information into the OFDM signal of the time domain in which the guard interval is inserted.

In the inverse discrete Fourier transform step, when inverse discrete Fourier transform is performed on N pieces of data, when N = K × M (N, K, M is a natural number), the parallel data consists of K pieces of data. .

The inserting of the first synchronization information may include spreading the length of the K data by the length of the first synchronization information; Multiplying the first pieces of synchronous information to insert the first pieces of synchronous information into the K data whose length is spread by the length of the first pieces of synchronous information; And accumulating the M pieces of K data multiplied by the first synchronization information M times and outputting the N pieces of data.

According to the present invention, the reception performance can be improved compared to the conventional multicarrier transmission system by inserting a PN sequence into a symbol in the frequency domain.

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

2 is a schematic block diagram of a DMB-T transmission system employing a TDS-OFDM scheme as a preferred embodiment of the present invention.

The DMB-T transmission system may be divided into a channel encoding unit 100 and an OFDM modulation unit 200 according to its operation.

The channel encoding unit 100 includes a scrambler 110 and a forward error correction unit (FEC) 120, and the OFDM modulation unit 200 includes a mapping unit 210, a serial / parallel conversion unit 220, and a first synchronizer. Information insertion unit 230, 3780-point IDFT unit 240, inter-protective interposition unit 250, parallel / serial conversion unit 260, second synchronous information insertion unit 270, shaping filter unit 280 and It has an RF unit 290.

The channel encoding unit 100 includes a scrambler 110 that randomizes data transmitted to prevent data loss during synchronous data transmission, and a forward error correction (FEC) unit that performs encoding to detect and correct errors at a receiving end. Have 120.

The channel encoding, that is, the encoding of the forward error correction (FEC) unit 120 is divided into a TV mode and a multimedia mode, and is applied differently.

First, FEC (Forward error correction) for the TV transmission mode is as follows.

Stepwise coding consisting of 2/3 trellis codes, convolutional interleaved codes, and reed-solomon (RS) codes are used as forward error correction (FEC) of TV broadcast programs.

A convolutional interleaved code is inserted between the inner code and the outer code of the DMB-T transmitting system to eliminate the effects of continuous error codes caused by burst impulse interference. .

Meanwhile, the forward error correction (FEC) for the multimedia transmission mode is as follows. Multi-level block product code (BPC) is employed for forward error correction (FEC) for multimedia integrated data traffic services. Multilevel BPC is a system code composed of block codes, and is a code made up of portions of two Dimensional Product Codes (DPCs).

The OFDM modulator 200 applies the TDS-OFDM scheme.                     

The mapping unit 210 maps the error coded data to symbol constellations such as QPSK, 16QAM, and 64QAM. The constellation of a typical DMB-T transmission system uses 64QAM.

The symbol constellation is also applied differently for each mode by the channel encoding method applied differently according to the TV transmission mode and the multimedia transmission mode. That is, in the DMB-T transmission system using forward error correction (FEC) of the TV transmission mode, the coordinates of the projection of I and Q are (-7, -5, -3, -1,1,3,5,7). It has a regularly distributed symbol constellation. The DMB-T transmission system using forward error correction (FEC) of the multimedia integrated data traffic service has the coordinates of the projections of I and Q (-9, -7, -4, -2,2,4,7,9). Have irregularly distributed symbol constellations.

The serial / parallel conversion unit 220 collects predetermined symbols that are mapped and output in serial form and outputs the parallel symbols. The number of data of the parallel data corresponds to the length of the PN sequence inserted by the first synchronous information insertion unit 230. For example, when the length of the PN sequence is 63 (2 ⁿ -1), the parallel data in the serial / parallel conversion unit 220 has 63 serial data. In this case, the data is in symbol units, and a PN sequence having a length of 63 is equal to 63 data, that is, 63 symbol lengths.

For example, the first synchronization information insertion unit 230 inserts a PN sequence, which is synchronization information, into 3780 pieces of data input to the IDFT unit 240. Hereinafter, a PN sequence is inserted into 3780 pieces of data with reference to FIG. 3.

The first synchronization information insertion unit 230 has a diffusion unit 231, a multiplication unit 233, and a buffer 235.

The spreader 231 spreads the length of each of the 63 pieces of data from the serial / parallel converter 220 by 63, which is the length of the PN sequence multiplied by the multiplier 233.

The multiplier 233 inserts the PN sequences into the 63 pieces of data by multiplying 63 pieces of 63 times the lengths of the data by 63 different lengths of PN sequences.

As described above, in order to input 63 data multiplied by the PN sequence to the 3780-point IDFT unit 240, 60 pieces are collected in the buffer 235 and 3780 data (63 × 60 = 3780) are output.

In this case, the number of data output from the serial / parallel conversion unit 220 and the length of the PN sequence to be multiplied with each data are equally implemented, and the size of the buffer 235 is determined to correspond to the length of the PN sequence.

The 3780-point IDFT unit 240 outputs 3780 pieces of data to which the PN sequence is output from the first synchronization inserting unit 230 as OFDM symbols in the time domain. Here, the OFDM symbol is 3780 sample data.

The parallel / serial converter 250 converts the parallel OFDM symbol into a serial OFDM symbol and outputs the converted OFDM symbol.

The guard interval insertion unit 260 inserts sample data of a portion of the end of the OFDM symbol in the guard interval GI in front of the OFDM symbol in order to prevent inter symbol interference (ISI) in a multipath environment. The guard intervals GI are 1/6, 1/9, 1/12, 1/20, 1/30 of 3780.                     

The second synchronization information insertion unit 270 inserts synchronization information, such as a PN sequence, in front of the guard interval GI in the time domain according to the TDS-OFDM method, and is used for time and frequency synchronization acquisition and channel equalization at the receiving end by using the same. do.

The shaping filter unit 280 shaping filters the PN sequence with respect to the OFDM symbol covered with the PN sequence, and transmits the shaping filter to the wireless channel through the RF unit 290.

As such, a PN sequence is added to each data in the frequency domain before the data in the frequency domain is modulated with the data in the time domain. As a result, the reception side can further improve reception reliability by using PN correlation.

4 is a flowchart illustrating a process of processing a signal by a TDS-OFDM transmission system according to an embodiment of the present invention.

The FEC unit 120 for detecting and correcting an error in the receiving apparatus encodes the corresponding mode according to each mode, that is, the TV transmission mode and the multimedia transmission mode (S10).

The mapping unit 210 maps the OFDM signal encoded according to each mode to symbol constellations such as QPSK, 16 QAM, and 64 QAM (S20).

The serial / parallel conversion unit 220 collects a predetermined number of mapped symbols and outputs them in parallel (S30). Here, it is assumed that the number of parallel symbols is 63 (PN sequence length).

For example, the first synchronization information insertion unit 230 inserts a PN sequence, which is synchronization information, into 3780 symbols input to the IDFT unit 240 (S40). FIG. 5 is a detailed flowchart of adding a PN sequence as first synchronization information to 3780 symbols (S40). Referring to FIGS. 6A to 6E, FIG. 5 is a diagram illustrating 3780 symbols D1, D2,... A method of inserting PN sequences (PN1, PN2, ...) as one synchronization information will be described.

The spreader 231 spreads the length of the parallel data output from the serial / parallel converter 220 by the length of the PN sequence (S41). As shown in FIG. 6A, the serial / parallel conversion unit 220 collects 63 symbols D1, D2,..., Which are serial data output from the mapping unit 210, in parallel, as shown in FIG. 6A. Output as data (D1, D2, ...). The spreader 231 spreads the length of 63 symbols by the length 63 of the PN sequence, as shown in FIG. 6C. That is, the number of parallel data output from the serial / parallel converter 220 is set equal to the length of the PN sequence.

The multiplier 233 multiplies the 63 symbols D1, D2, ..., whose lengths are spread by the length 63 of the PN sequence, respectively, with different PN sequences PN1, PN2, ..., respectively (S43). . As shown in FIG. 6D, 63 different PN sequences PN1, PN2,... Are multiplied by 63 symbols output from the spreader 231 in the multiplier 233. The 63 symbols multiplied by the PN sequence are as shown in Fig. 6E.

In this way, in order to input 63 symbols D1, D2, ... multiplied by the PN sequence (PN1, PN2, ...) to the 3780-point IDFT unit 240, 60 buffers 235 are collected. 3780 symbols (63 x 60 = 3780) are output (S45).

The 3780 symbols in which the PN sequence is inserted by the first synchronization information inserting unit 230 are modulated into OFDM symbols (3780 sample data) in the time domain by the 3780-point IDFT unit 240 (S50).                     

The parallel / serial converter 250 converts the OFDM symbols into a serial form and outputs the serial symbols (S60).

The guard interval inserting unit 260 inserts sample data of a part of the end of the OFDM symbol composed of 3780 sample data into the guard interval GI at the front end of the OFDM symbol (S70).

The second synchronization information insertion unit 270 inserts second synchronization information such as a PN sequence before the guard period GI (S80).

The shaping filter 280 performs shaping filtering on the second synchronization information (PN sequence) inserted in front of the protection section, and transmits the shaping filter through the RF unit 290 to the wireless channel (S90).

 In this way, a PN sequence of a predetermined length is added to each symbol in the frequency domain. Therefore, by adding a PN sequence as synchronization information to a plurality of symbols in the frequency domain, it is possible to improve reception performance such as synchronization acquisition and channel equalization performed at the receiving side.

According to the present invention, the reception performance can be improved compared to the conventional TDS-OFDM transmission system by inserting a PN sequence into a plurality of symbols in the frequency domain.

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 skilled in the art can make various modifications, as well as such modifications are within the scope of the claims.

Claims (10)

An FEC unit for coding data in a frequency domain to detect and correct an error at a receiving side; A mapping unit for mapping the coded data of the frequency domain by a predetermined mapping method; A serial / parallel conversion unit for collecting the mapped data by N and outputting the parallel data as N data; A first synchronization information insertion unit for inserting different first synchronization information of the same length into each of the parallel data; An inverse discrete Fourier transformer for inversely discrete Fourier transforming the N data into which the first synchronization information is inserted and outputting the inverse discrete Fourier transform; A guard interval insertion unit inserting a guard interval into the OFDM signal in the time domain; And And a second synchronization information insertion unit for inserting second synchronization information into the OFDM signal of the time domain into which the protection interval is inserted. The method of claim 1, The N is, when N = K × M (N, K, M is a natural number), the parallel data output from the serial / parallel conversion section is composed of K data, The first synchronous information inserting unit, A spreader configured to spread the lengths of the K data by the length of the first synchronization information; A multiplier that multiplies the first synchronous information to insert the first synchronous information into the K data whose length is spread by the length of the first synchronous information; And And a buffer for accumulating the K data multiplied by the first synchronization information M times and outputting the N data. The method of claim 2, The first synchronization information is characterized in that the PN sequence, The number K of the parallel data corresponds to the length of the PN sequence. The method of claim 2, The length of the PN sequence is 2 ⁿ -1 (n is a natural number), and K is 2 ⁿ -1 characterized in that the multi-carrier transmission system. The method of claim 2, N is 3780, K is 63, and M is 60, characterized in that the multi-carrier transmission system. Coding data in the frequency domain to detect and correct errors at the receiving end; Mapping the coded data of the frequency domain by a predetermined mapping method; Collecting parallel data and outputting parallel data; Inserting different first synchronization information of the same length into the parallel data; An inverse discrete Fourier transform step of inverse discrete Fourier transforming the parallel data into which the first synchronous information is inserted and outputting an OFDM signal in a time domain; Inserting a guard interval into the OFDM signal in the time domain; And And inserting second synchronization information into the OFDM signal of the time domain into which the guard interval is inserted. The method of claim 6, In the inverse discrete Fourier transform step, when inverse discrete Fourier transform is performed on N pieces of data, When N = K × M (N, K, M is a natural number), the parallel data is composed of K data, Inserting the first synchronization information, Spreading the lengths of the K data by the length of the first synchronization information; Multiplying the first pieces of synchronous information to insert the first pieces of synchronous information into the K data whose length is spread by the length of the first pieces of synchronous information; And And accumulating the M pieces of K data multiplied by the first synchronization information M times and outputting the N pieces of data. The method of claim 6, The first synchronization information is characterized in that the PN sequence, The number K of the parallel data corresponds to the length of the PN sequence. The method of claim 6, The length of the PN sequence is 2 ⁿ -1 (n is a natural number), and K is 2 ⁿ -1, the signal processing method of the multi-carrier transmission system. The method of claim 6, N is 3780, K is 63, and M is 60, the signal processing method of the multi-carrier transmission system.

Images