KR20040035288A - 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 coding data in the frequency domain for detecting and correcting an error on the receiving side, a serial / parallel converter for collecting predetermined data in the frequency domain in parallel, and predetermined data, respectively. A synchronization information insertion unit for inserting different synchronization information of the same length into the frame; a frame forming unit for forming a predetermined frame including predetermined data and pilot data to which different synchronization information is added; An inverse fast Fourier transform unit for converting and modulating an OFDM signal in a time domain, and a guard interval insertion unit for inserting a guard interval in an OFDM signal in a time domain. 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.

Description

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

The present invention relates to a terrestrial digital broadcasting system, and more particularly, to a multi-carrier transmission system for improving 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 by 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.

The modulation scheme of DVB-T, a digital broadcasting standard currently adopted in Europe, adopts the OFDM scheme (Orthogonal Frequency Division Multiplexing) described above. OFDM is a method of transmitting a plurality of data at the same time by using a multi-carrier, the biggest feature is that it shows a very strong characteristics in a multi-path environment and can be received mobile.

1 is a schematic block diagram of a DVB-T transmission system employing a general COFDM scheme.

The DVB-T transmission system includes an FEC unit 10, a mapping unit 20, a frame forming unit 30, an IFFT unit 40, a guard section insertion unit 50, an RF unit 60, and the like.

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.

The mapping unit 20 maps the coded data to QPSK, 16QAM, 64QAM, and the like.

The frame forming unit 30 inserts a distributed pilot, a continuous pilot, and a transmission parameter signal (TPS) into a symbol mapped in a predetermined manner, and inserts a guard band to form a frame corresponding to the operation mode of the IFFT unit 40. Form. TPS transmits six kinds of information.

1) Pattern Information of QAM Constellation

2) hierarchy information

3) information on the length of the protective section;

4) inner code rate

5) 2K or 8K transmission mode

6) Frame Number

An Inverse Fast Fourier Transform (IFFT) unit 40 transforms an OFDM signal having a frame in the frequency domain into an inverse fast Fourier transform and converts the OFDM signal to an OFDM symbol which is an OFDM signal in a time domain.

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

The RF unit 60 loads a signal in a frequency band to which the OFDM signal processed as described above is transmitted and transmits the signal over a wireless channel.

In such a DVB-T transmission system, not only the synchronization of the time domain and the frequency domain but also channel equalization are performed using only the inserted pilot signal in the frequency domain, thereby reducing the limitations of the reception system and performance degradation. Have.

SUMMARY OF THE INVENTION An object of the present invention for solving the above problems is to provide a multi-carrier transmission system and a signal processing method thereof capable of improving reception performance by inserting a PN sequence as synchronization information into each symbol mapped in the frequency domain. will be.

1 is a schematic block diagram of a DVB-T transmission system using a general COFDM scheme;

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

3 is a detailed block diagram of the synchronization information insertion unit 330 of FIG.

4 is a flow chart showing a signal processing method by the BDB-T transmission system of FIG.

5 is a detailed flowchart of the step (S40) of adding a PN sequence which is 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: splitter 200: channel encoding unit

210: scrambler 220: external encoder

230: external interleaver 240: internal encoder

250: internal interleaver 300: OFDM modulator

310: mapping unit 320: serial / parallel conversion unit

330: synchronization information insertion unit 340: frame forming unit

350: IFFT unit 360: protective section insertion unit

370: parallel / serial converter

According to an aspect of the present invention, there is provided a multicarrier transmission system comprising: an FEC unit for coding data in a frequency domain to detect and correct an error at a receiving side; A serial / parallel converter configured to collect predetermined data of the frequency domain and output the parallel data; A synchronization information insertion unit for inserting different synchronization information of the same length into each of the predetermined data; A frame forming unit configured to form a predetermined frame including the predetermined data and pilot data to which the different synchronization information is added; An inverse fast Fourier transform unit which modulates the formed frame by inverse fast Fourier transform and modulates the OFDM signal in a time domain; And a guard interval inserter for inserting a guard interval into the OFDM signal of the time domain.

In this case, the inverse fast Fourier transform unit can support 2K, 4K, and 8K modes, and the predetermined number is the number of effective carriers in which the data in the frequency domain is loaded corresponding to the respective modes.

Preferably, the predetermined number is N approximations, and when N = K × M (N, K, M is a natural number), the data output from the serial / parallel conversion unit is composed of the K data. The synchronization information insertion unit may include: a diffusion unit configured to spread the length of the K data by the length of the synchronization information; A multiplier for multiplying the synchronization information to insert the synchronization information into the K data whose length is spread by the length of the synchronization information; And a buffer for accumulating the K data multiplied by the synchronization information M times and outputting the N data as the N data.

The synchronization information is a PN sequence having a length of 2 ⁿ -1 (n is a natural number), and the number of parallel data K 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; Collecting predetermined data of the frequency domain and outputting the parallel data; Inserting different synchronization information of the same length into each of the predetermined data; Forming a predetermined frame including the predetermined data and pilot data to which the different synchronization information is added; An inverse fast Fourier transform step of performing inverse fast Fourier transform on the formed frame to modulate an OFDM signal in a time domain; And inserting a guard interval into the OFDM signal of the time domain.

Here, the predetermined number is N approximations, and when N = K × M (N, K, M is a natural number), the parallel data is composed of the K data, and preferably, the synchronization information insertion step Spreading the lengths of the K data by the length of the synchronization information; Multiplying the synchronization information to insert the synchronization information into the K data whose length is spread by the length of the synchronization information; And accumulating the K data multiplied by the synchronization information M times and outputting the N data.

According to the present invention, by inserting a PN sequence into a plurality of symbols in the frequency domain it is possible to improve the reception performance than the conventional multi-carrier transmission system.

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

2 is a block diagram of a BDB-T transmission system using a COFDM scheme according to a preferred embodiment of the present invention.

A typical BDB-T transmission system is capable of transmitting to fixed, portable, and mobile receiving environments and has similar characteristics to the DVB-T for Europe.

1) COFDM modulation method is used,

2) It additionally supports non-hyrarchical signal transmission mode, hierarchical transmission mode, as well as non-hierarchical hybrid transmission mode. Accordingly, each frame structure is applied differently.

3) FFT mode supports 2K, 8K mode as well as 4K mode.

4) It has a synchronization signal for synchronization between a transmitter and a receiver in the frequency domain.

The BDB-T transmission system shown in FIG. 2 is divided into a splitter 100, a channel encoding unit 200, and an OFDM modulation unit 300.

The code streams input by the splitter 100 are input into the channel encoding unit 200 by being separated into high and low.

The channel encoding unit 200 has a scrambler 210 for scrambling, an external encoder 220 for RS encoding, an external interleaver 230 for convolutional interleaving, and an internal encoder 240 for convolutional encoding. In addition, the bit interleaver 251 is executed in a data block capable of bit interleaving, and a predetermined bit word is mapped to 1392 (2K operation mode), 2784 (4K operation mode), and 5568 (8K operation mode) which are valid carriers of an OFDM symbol. It has an internal interleaver 250 having a symbol interleaver 252 to make it.

The OFDM modulator 300 includes a mapping unit 310, a serial / parallel conversion unit 320, a synchronization information insertion unit 330, a frame forming unit 340, an IFFT (Inverse Fast Fourier Transform) unit 350, and parallelism. / Serial conversion unit 360, and the protective section insertion unit 370 and the like.

The mapping unit 310 maps the error coded data to symbol constellations such as QPSK, 16QAM, and 64QAM.

The serial / parallel conversion unit 320 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 synchronization information inserter 330. For example, when the length of the PN sequence is 63 (2 ⁿ -1), the parallel data in the serial / parallel converter 320 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.

The synchronization information insertion unit 330 inserts a PN sequence, which is synchronization information, into 4096 pieces of data input to the IFFT unit 350. Hereinafter, referring to FIG. 3, the PN sequence is inserted in response to the 2K, 4K, and 8K modes.

The synchronization information insertion unit 330 includes a diffusion unit 331, a multiplication unit 333, and a buffer 335.

The spreader 331 spreads the length of each of the 63 pieces of data from the serial / parallel converter 320 by 63, the length of the PN sequence multiplied by the multiplier 333.

The multiplication unit 333 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.

The buffer 335 collects and outputs 63 pieces of data multiplied by the PN sequence by a predetermined number corresponding to the operation mode of the IFFT unit 350. For example, according to the BDB-T standard, the IFFT unit 350 can support 2K, 4K, and 8K modes as shown in [Table 1]. That is, the OFDM symbol corresponds to the 2K, 4K, and 8K modes. As shown in Table 1, it is composed of a plurality of subcarriers.

MODE 2K 4K 8K Occupied 7.62 MHz OFDM carrier 1561 3121 6241 Carrier spacing 4.88KHz 2.44KHz 1.22KHz Data carrer 1392 2784 5568 Scattered Pilots 130 260 520 Continual Pilots 41 81 161 TPS 8 16 32

That is, 1392 data carriers, which are effective carriers of an OFDM symbol, are used in 2K mode, 2784 in 4K mode, and 5568 in 8K mode. Accordingly, in response to the 63 symbols output from the serial / parallel conversion unit 320, the buffer 335 has 63 symbols in the buffer 335 to obtain the number of symbols approximating 1392 data carriers in the 2K mode. It collects 22 each and outputs 1386 (63 × 22) symbols. In this way, the buffer 335 in 4K mode outputs 2772 (63 x 44) symbols approximating 2784 data carriers, and the buffer 335 in 8K mode approximates 5544 (63 x 88) approximating 5568 data carriers. Print) symbols. That is, the number of symbols output from the buffer 335 is preferably the size of the buffer 335 to output the number of symbols approximate to the number of data carriers corresponding to each mode.

In this case, the number of parallel data output from the serial / parallel converter 320 is set to correspond to the length of the inserted PN sequence, and the length (2 ⁿ -1) of various PN sequences can be applied. The size of the buffer 335 is also determined according to the number.

The frame forming unit 340 inserts a distributed pilot, a continuous pilot, and a TPS into a predetermined subcarrier other than the data carrier, and inserts a guard band corresponding to 2K, 4K, and 8K operating modes of the IFFT unit 350 to insert a frame. Form.

That is, as shown in [Table 1], the plurality of subcarriers corresponding to each mode have a data subcarrier, a distributed pilot and a continuous pilot for channel estimation and synchronization acquisition, and are system information according to a transmission service type. It has a transmission parameter signal (TPS).

The inverse fast fourier transform (IFFT) unit 350 converts the OFDM signals having the corresponding frames of 2K, 4K, and 8K modes output from the frame forming unit 340 into inverse fast Fourier transforms to OFDM symbols in the time domain.

The parallel / serial converter 360 converts the parallel OFDM symbols into a serial form of the OFDM symbol output from the IFFT unit 350.

The guard interval (GI) insertion unit 370 inserts a guard interval (GI) at the front end of the OFDM symbol in units of the OFDM symbols output after the inverse fast Fourier transform (IFFT). That is, the guard interval GI copies a portion of the end of the OFDM symbol and inserts it to the front of the OFDM symbol in order to prevent inter symbol interference (ISI) in a multipath environment.

The OFDM signal processed as described above is transmitted to a wireless channel by being loaded on a frequency band to be transmitted by an RF unit (not shown).

That is, performance of the receiving side can be improved by inserting PN sequences, which are separate synchronization information, into the mapped symbols in addition to the distributed pilot and the continuous pilot carried on the determined subcarriers.

Here, the Chinese BDB-T transmission system using the COFDM scheme has been described as an example, but it is natural that the present invention can be widely applied to all systems using the OFDM modulation scheme.

4 is a flowchart illustrating a process of processing a signal by a BDB-T transmission system applying the COFDM scheme according to the present invention.

The FEC unit 220 for detecting and correcting an error in the receiving apparatus encodes the corresponding apparatus according to each mode, that is, a non-hyrarchical signal transmission mode, a hierarchical transmission mode, and a non-hierarchical hybrid transmission mode (S10).

The mapping unit 310 maps the OFDM signal encoded according to each mode to symbol constellations such as QPSK, 16QAM, and 64QAM (S20).

The serial / parallel converter 320 collects a predetermined number of symbols and outputs them in parallel (S30). That is, the parallel symbol corresponding to the length (bit) of the PN sequence which is the synchronization information inserted by the synchronization information insertion unit 330 is output.

The synchronization information insertion unit 330 inserts a PN sequence as synchronization information into parallel symbols output from the serial / parallel conversion unit 320 (S40). FIG. 5 is a detailed flowchart illustrating a step of inserting a PN sequence as synchronization information (S40). When the operation mode of the IFFT unit 350 is 2K with reference to FIGS. 6A to 6E, the symbols D1, D2, .. The following describes how to insert PN sequences (PN1, PN2, ...) as synchronization information.

The spreader 331 spreads the length of the parallel data output from the serial / parallel converter 320 by the length of the PN sequence (S41). As shown in FIG. 6A, the serial / parallel conversion unit 320 collects 63 symbols D1, D2,..., Which are serial data output from the mapping unit 310, in parallel as shown in FIG. 6A. Output as data (D1, D2, ...). The spreader 331 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 320 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 PN sequences PN1, PN2,... Which are different from each other are multiplied by 63 symbols D1, D2,... Output from the spreading unit 231 in the multiplier 333. Multiply. The 63 symbols (D1, D2, ...) multiplied by the PN sequence are shown in FIG. 6E.

In this way, the 63 symbols multiplied by the 63-length PN sequence are collected 22 times in the buffer 335 and output as 1386 parallel data (63 x 22 = 1386) (S45). That is, 1386 symbols approximating 1392 data carriers corresponding to the 2K mode are output.

The frame forming unit 340 forms a frame corresponding to each of the 2K, 4K, and 8K modes. That is, a frame including a symbol, a pilot, a TPS, a guard band, and the like output from the synchronization information insertion unit 330 is formed (S50).

The inverse fast fourier transform (IFFT) unit 350 performs an inverse fast Fourier transform on the OFDM frame formed by the frame forming unit 340 and transforms the OFDM symbol to the time domain (S60).

Next, after converting the parallel OFDM signal into a serial OFDM signal, the guard interval (GI) insertion unit 360 inserts the guard interval (S70). Subsequent intervals are inserted at the front end of the OFDM symbol using the sample data of the terminal corresponding to 1/4, 1/8, 1/16, 1/32 of the entire OFDM symbol as a guard interval.

A guard interval is inserted in the frequency band to which the OFDM signal to be inserted is transmitted over a wireless channel (S80).

Therefore, by adding a separate PN sequence to the data in the frequency domain, it is possible to further improve reception performance such as synchronization acquisition and channel equalization performed on the receiving side.

According to the present invention, by inserting a PN sequence into a mapped symbol in the frequency domain, it is possible to improve reception performance than a conventional COFDM transmission system.

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 serial / parallel converter configured to collect predetermined data of the frequency domain and output the parallel data; A synchronization information insertion unit for inserting different synchronization information of the same length into each of the predetermined data; A frame forming unit configured to form a predetermined frame including the predetermined data and pilot data to which the different synchronization information is added; An inverse fast Fourier transform unit which modulates the formed frame by inverse fast Fourier transform and modulates the OFDM signal in a time domain; And And a guard interval inserter for inserting a guard interval into the OFDM signal of the time domain. The method of claim 1, In the inverse fast Fourier transform unit, At least one of 2K, 4K, and 8K modes is supported, And the predetermined number is the number of effective carriers carrying data in the frequency domain corresponding to each of the modes. The method of claim 1, The predetermined number is N approximations, and when N = K × M (N, K, M is a natural number), the parallel data output from the serial / parallel converter is composed of the K data. The synchronization information insertion unit, A spreader which spreads the length of the K data by the length of the synchronization information; A multiplier for multiplying the synchronization information to insert the synchronization information into the K data whose length is spread by the length of the synchronization information; And And a buffer for accumulating the K data multiplied by the synchronization information M times and outputting the N data as the N data. The method of claim 3, The 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 3, 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. Coding data in the frequency domain to detect and correct errors at the receiving end; Collecting predetermined data of the frequency domain and outputting the parallel data; Inserting different synchronization information of the same length into each of the predetermined data; Forming a predetermined frame including the predetermined data and pilot data to which the different synchronization information is added; An inverse fast Fourier transform step of performing inverse fast Fourier transform on the formed frame to modulate an OFDM signal in a time domain; And And inserting a guard interval into the OFDM signal in the time domain. The method of claim 6, In the inverse fast Fourier transform step, At least one of 2K, 4K, and 8K modes is supported, And wherein the predetermined number is the number of effective carriers carrying data in the frequency domain corresponding to each of the modes. The method of claim 6, The predetermined number is N approximations, and when N = K × M (N, K, M is a natural number), the parallel data consists of the K data, The synchronization information insertion step, Spreading the lengths of the K data by the length of the synchronization information; Multiplying the synchronization information to insert the synchronization information into the K data whose length is spread by the length of the synchronization information; And And accumulating the K data multiplied by the synchronization information M times and outputting the N data. 2. The signal processing method of claim 1, further comprising outputting the N data. The method of claim 8, The synchronization information is characterized in that the PN sequence, The number K of parallel data corresponds to the length of the PN sequence. The method of claim 8, 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.