KR20040029824A - TDS-OFDM transmission system having 3600-point IDFT procseeor and a method proessing OFDM signal thereof - Google Patents

Abstract

PURPOSE: A TDS-OFDM(Time Domain Synchronous Orthogonal Frequency Division Multiplexing) transmitter system is provided which has a 3600-point IDFT(Inverse Discrete Fourier Transform) processor to be realized easily in a hardware, and its signal processing method is also provided. CONSTITUTION: A FEC(Forward Error Correction) part(120) codes an OFDM signal in a frequency domain to sense an error in a receiver side and to correct the error. A mapping part(210) maps the coded OFDM signal in a frequency domain by a mapping method. A 3600-point IDFT part(400) modulates the OFDM signal in a frequency domain comprising 3600 parallel data into an OFDM signal in a time domain having 3600 sample data. A guard interval insertion part(240) inserts a guard interval to a front of the OFDM signal in a time domain. A synchronous information insertion part(250) inserts a synchronous signal for synchronization and channel equalization of a transmitter and the receiver to the OFDM signal in a time domain where the guard interval is inserted. And a forming filter part(260) performs a forming filtering of the synchronous signal inserted to the OFDM signal in a time domain.

Description

TDS-OPDM transmission system having a 3600-FMTI IDT processor and a signal processing method therefor {TVS-OPDM transmission system having a 3600-FCF procedure and a method proessing OFDM signal}

The present invention relates to an orthogonal frequency division multiplexing (OFDM) digital broadcasting system, and more particularly, to a TDS-OFDM system having a 3600-point IDFT processor and a signal processing method thereof.

Orthogonal Frequency Division Multiplexing (OFDM) is a type of multicarrier modulation that 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 scheme, 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 using IFFT and FFT, which are the same results as performing the IDFT and DFT, respectively. Can be.

1 is a schematic block diagram of a transmission system of a TDS-OFDM (Time Domain Synchronous-Orthogonal Frequence Division Multiplexing) scheme, which is one of such OFDM schemes.

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 a 3780-point Inveres Discrete Fourier Transform (IDFT) unit 30 that modulates an OFDM signal in a frequency domain into an OFDM signal in a time domain, and modulates OFDM to prevent inter symbol interference in an multipath environment. A guard section inserting section 40 for inserting a signal end 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 method, and inserting And a shaping filter unit 60 for filtering the pulse shaping of the synchronized information, and an RF unit 70 carrying a signal in a frequency band to which the OFDM signal is to be sent.

In the above-described conventional TDS-OFDM transmission system, 3780 subcarriers are arranged at a frequency interval of 2 KHz through the 3780-point IDTF unit 40, and the sampling rate is 7.56 MHz. In addition, the 3780-point DFT module is divided into 60 × 63 or 63 × 60 is configured using a 60-point DFT module and a 63-point DFT module, respectively.

As shown in FIG. 2, the 3780-point IDTF unit 40 multiplies the input data by a 60-point DFT module 41 which performs a 60-point DFT and a complex number by the 60-point DFT. Complex multiplier 42, matrix multiplier 43 for intersecting the matrix multiplied by the complex number, and 63-point DFT module 44 for performing 63-point DFT on the matrix-processed data. have. Here, the complex multiplier 42 and the matrix crossover 43 can be used interchangeably, and the matrix crossover 43 has a transpose memory (not shown) for obtaining a transpose matrix. The 60-point DFT module 41 and the 63-point DFT module 44 may also be used in reverse order.

As such, the 60-point DFT module 41 and the 63-point DFT module 44 are used to generate 3780 subcarriers, and the number of multipliers required for each module is shown in Table 1 below.

Type of n-point DFT module Number of multipliers required 3-point DFT module 2 X 2 (real, imaginary) = 4 4-point DFT module 0 5-point DFT module 5 X 2 (real, imaginary) = 10 7-point DFT module 8 X 2 (real, imaginary) = 16 9-point DFT module 12 X 2 (real, imaginary) = 24

Accordingly, when using the 60-point DFT module 41 and the 63-point DFT module 44, the total number of multipliers required is about 14 + 40 = 54.

Therefore, there is a problem that the hardware implementation of the 3780-point IDTF unit 40 is complicated.

An object of the present invention for solving the above problems is to provide a TDS-OFDM transmission system having a 3600-point IDFT processor that is simple to implement in hardware.

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

2 is a detailed block diagram of a 3780-point IDFT unit of FIG. 1;

3 is a schematic block diagram of a DMB-T transmission system having a 3600-point IDFT unit according to the present invention;

4 is a detailed configuration diagram of a 3600-point IDFT unit according to an embodiment of the present invention;

5 is a detailed configuration diagram of the 60-point DFT module of FIG. 4;

6 is a detailed configuration diagram of a 3600-point IDFT unit according to another embodiment of the present invention;

7 is a distribution diagram of subcarriers in the frequency domain by a 3600-point IDFT unit, and

8 is a flowchart illustrating a signal processing method of the DMB-T transmission system shown in FIG. 3.

Explanation of symbols on the main parts of the drawings

400,500: 3600-point IDFT unit 410,440: 60-point DFT module

411: 3-point DFT module

415: 4-point DFT module 412,414: suffix mapping part

510: multiplexer 520: 60-point DFT module

530: demultiplexer 540: complex multiplier

550: matrix crossover

In order to achieve the object of the present invention, a TDS-OFDM transmission system according to the present invention comprises: an FEC unit for coding an OFDM signal in a frequency domain for detecting and correcting an error at a receiving side, and a coded OFDM signal in the frequency domain. A mapping unit for mapping by a predetermined mapping method, a 3600-point IDFT unit for modulating the OFDM signal in the frequency domain of 3600 parallel data into an OFDM signal in the time domain of 3600 sample data, and the time domain A guard interval inserter for inserting a guard interval at the front of the OFDM signal, and a sync information inserter for inserting synchronization information for synchronization and channel equalization between the transmitter and the receiver in the OFDM signal of the time domain where the guard interval is inserted. And a shaping filter section for shaping the inserted synchronization signal of the OFDM signal in the time domain. Here, the interval between the subcarriers carrying the 3600 parallel data in the frequency domain is characterized in that the 2.1KHz.

Preferably, the 3600-point IDFT unit is made of a combination of two 60-point DFT modules, or is characterized by consisting of one 60-point DFT module.

On the other hand, the signal processing method of the TDS-OFDM transmission system according to the present invention comprises the steps of: coding the OFDM signal in the frequency domain to detect and correct the error at the receiving side; Mapping the coded OFDM signal in the frequency domain by a predetermined mapping method; An inverse discrete Fourier transform step of modulating the OFDM signal in the frequency domain consisting of 3600 parallel data into the OFDM signal in the time domain consisting of 3600 sample data; Inserting a guard interval in front of the OFDM signal of the time domain; Inserting synchronization information for synchronization and channel equalization of a transmitting side and a receiving side into the OFDM signal of the time domain into which the guard interval is inserted; And shaping filtering the inserted synchronization signal of the OFDM signal in the time domain. Further, in the inverse Fourier transform step, the interval between the sub-carrier carrying the 3600 parallel data in the frequency domain is characterized in that the 2.1KHz.

Preferably, the inverse Fourier transform step may be inverse Fourier transformed by two 60-point DFT modules or inverse Fourier transformed by one 60-point DFT module.

Therefore, in the conventional 3780-point IDFT processor, the required multiplier is reduced by using the 3600-point IDFT processor to improve the problem of hardware complexity, and also simplify the complex address structure of the pre-memory memory for pre-matrix processing. It becomes possible.

Hereinafter, a TDS-OFDM transmission system having an improved 3780-point IDFT processor according to the present invention will be described with reference to the drawings.

Recently, China has proposed a new terrestrial digital TV transmission standard, DMB-T, which can be applied in China in order to improve the speed of the terrestrial digital TV transmission system. DMB-T transmission system is a DVB transmission plan developed by Tsinghua University according to service requirements, transmission conditions and channel characteristics of terrestrial multimedia TV broadcasting. Is applying. In addition, the OFDM modulator of the DMB-T system uses a 3780-point IDFT / DFT processor.

Figure 3 is a schematic block diagram of a Chinese DMB-T transmission system having a 3780-point IDFT processor, with reference to this it will be described in detail 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 (FEC) unit 120, and the OFDM modulation unit 200 includes a mapping unit 210 and a 3600-point Inveres discrete fourier transform (IDFT) unit ( 400, a protection section insertion section 240, a synchronization information insertion section 250, a shaping filter section 260 and the RF section 270.

The channel encoding unit 100 includes a scrambler 100 that randomizes transmitted data to prevent data loss during synchronous data transmission, and a forward error correction (FEC) unit that performs coding for detecting and correcting an error at a receiving end. Has 100.

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 code, convolutional code, and red-solomon (RS) code is used as forward error correction (FEC) of a TV broadcast program.

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

Subsequently, 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. Multi-level BPS is a system code composed of block codes, and is a code composed of portions of two Dimensional Product Codes (DPS). And, the decoder of the multi-level BPC can adopt a high performance turbo algorithm. Multi-level BPS is divided into three levels. Different levels are mapped onto different bits of the 64QAM symbol constellation according to the set point set to give different anti-interference adaptability.

Regarding the channel characteristics of terrestrial radio broadcasting, interleaved encoding is performed on data in time domain and frequency domain. Interleaved encoding in the time domain is performed among a plurality of frames, and has four operation modes according to a symbol constellation based on a convolutional interleaved encoder.

The OFDM modulator 200 applies the TDS-OFDM scheme.

The mapping unit 210 maps the error coded OFDM 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. In addition, the DMB-T transmission system using forward error correction (FEC) of the multimedia integrated data traffic service has a coordinate of projections of I and Q (-9, -7, -4, -2,2,4,7, 9) has irregularly distributed symbol constellations.

The 3600-point IDFT (Inveres discrete fourier transform) unit 400 allocates and modulates an OFDM signal of 3600 parallel data in the frequency domain to 3600 subcarriers and modulates an OFDM symbol composed of 3600 sample data in the time domain. Output Here, the 3600-point IDFT unit 400,

1) a combination of a 60-point DFT module and a 60-point DFT module, and

2) It consists of any one of the 3600-point IDFT unit 400 composed of one 60-point DFT module twice as fast operation time. The structure of the 3600-point IDFT unit 400 will be described later in detail with reference to FIGS. 4 to 6.

The guard interval insertion unit 240 inserts a guard interval GI at the front end of the inverse Fourier transformed and output OFDM symbol. That is, the guard interval GI copies sample data of a portion of an end of an OFDM symbol and inserts it in front of the OFDM symbol in order to prevent inter symbol interference (ISI) in a multipath environment.

The synchronization information insertion unit 250 inserts a PN sequence, which is synchronization information for time synchronization acquisition and channel equalization, in front of the guard period GI at the receiving side.

The shaping filter 260 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 270.

Hereinafter, various embodiments of the 3600-point IDFT unit 400 according to the present invention will be described in detail with reference to FIGS. 4 to 6.

FIG. 4 is a block diagram illustrating a case where two 60-point DFT modules 410 and 440 are configured as one embodiment of the 3600-point IDFT unit 400.

The 3600-point IDFT unit 400 includes a 60-point DFT module 410 that performs 60-point DFT, a complex multiplier 420 that multiplies a complex number by the data on which 60-point DFT is performed, and a matrix multiplied by a complex number. It has a matrix crossover 430 that transposes the data, and a 60-point DFT module 440 that performs 60-point DFT on the processed data when the matrix is crossed. Of course, the matrix crossover 43 has a transpose memory (not shown) for transposing the matrix.

That is, each 60-point DFT module 410, 440 is a three-point DFT module 411, 5-point DFT module configured by a small-N Winograd Fourier Transform Algorithm (WFTA) that can reduce the number of multipliers. 413, a 4-point DFT module 415 is configured in combination. 5 is a block diagram of the configuration of the 60-point DFT module 410, where the 3-point IDFT module 411, the 5-point DFT module 413, and the 4-point DFT module 415 are suffix mapped. (suffix mapping) unit 412,414. Here, the 3-point IDFT module 411, the 5-point DFT module 413, and the 4-point DFT module 415 may be reversed. Here, each of the modules 411, 413, 415 is a suffix mapping unit corresponding to each of the modules 411, 413, 415 by a Prime Factor Algorithm (PFA) that does not need a complex multiplier because they are mutually 'small'. 412,414).

FIG. 6 is a block diagram illustrating a case where the 3600-point IDFT unit 400 includes one 60-point DFT module 520 as an embodiment of the 3600-point IDFT unit 400.

The 3600-point IDFT unit 500 includes a multiplexer 510, a 60-point DFT module 520, a demultiplexer 530, a complex multiplier 540, a matrix crossover 550, and the like.

That is, when data is input to the multiplexer 510, the 60-point DFT is performed by the 60-point DFT module 520, the complex multiplier is multiplied by the complex multiplier 540, and then transposed by the matrix crossover 550. After processing into a matrix, it is input to the multiplexer 510 again. At this time, the multiplexer 510 selects the data pre-matrixed by the predetermined control signal as input data of the 60-point DFT module 520. Therefore, if the pre-matrixed data is input to the demultiplexer 530 after performing a 60-point DFT in the 60-point DFT module 520, the demultiplexer 530 is a 60-point DFT by a predetermined control signal. The performed data is output as output data of the 3600-point IDFT unit 500. At this time, the 60-point DFT module 520 sets the operation time twice as fast as the 60-point DFT module 410 and 440 of FIG. 4. In addition, as shown in FIG. 5, a combination of the 3-point IDFT module 411, the 4-point DFT module 413, and the 5-point DFT module 415 is provided.

As such, the multiplier required for the 3600-point IDFT unit 400 using the 60-point DFT module requires 14 × 2 = 28 units according to the embodiment of FIG. 4 when referring to [Table 1]. According to another embodiment of FIG. 6, about 14 are required.

On the other hand, the address structure of the transpose memory for 60x60 can be implemented much simpler than the address structure of the transpose memory for the pre-matrix processing for 60x63.

Therefore, the hardware is relatively simple compared to the conventional 3780-point IDFT unit.

In addition, using 3600 subcarriers slightly reduces the conventional 3780 sampling rates, but as shown in FIG. 7, the frequency interval between subcarriers is widened from 2KHz to 2.1KHz. This has the advantage of showing strong reception performance in multipath.

Hereinafter, a description of the signal processing method of the DMB-T transmission system of the TDS-OFDM scheme of FIG. 3 will be described in detail with reference to the flowchart of FIG. 8.

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, 16QAM, and 64QAM (S20).

The 3600-point IDFT (Inveres discrete fourier transform) unit 400 converts the OFDM signal in the frequency domain into an OFDM signal in the time domain (S30). That is, an OFDM signal in a frequency domain consisting of 3600 parallel data is allocated to 3600 subcarriers and modulated. This outputs an OFDM symbol consisting of 3600 sample data in the time domain. Here, although the sampling rate is smaller than that of the conventional 3780 subcarriers, the sampling rate has a strong reception performance in multipath as the interval between the subcarriers widens from 2KHz to 2.1KHz.

Thereafter, the guard interval (GI) unit 240 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) (S40). In other words, the sample data of the terminal corresponding to 1/6, 1/9, 1/12, 1/20, 1/30 of all OFDM symbols is a guard period.

Next, the synchronization information inserting unit 250 inserts a time synchronization signal and a PN sequence for channel prediction in front of the guard period GI in the OFDM symbol in which the guard period GI is inserted (S50).

The shaping filter 260 filters the OFDM symbol covered with the PN sequence into a predetermined waveform (S60), and transmits the radio frequency through the RF unit 270 (S70).

By using the 3600-point IDFT processor as described above, the hardware structure is simplified, and as the spacing between subcarriers is widened, it has a strong reception performance in multipath.

According to the present invention, the multiplier required by using the 3600-point IDFT processor is reduced in order to improve the hardware complexity of the conventional 3780-point IDFT processor. Furthermore, the complex address structure of the pre-memory memory for pre-matrix processing is reduced. You can do it simply.

In addition, as the spacing between 3600 subcarriers increases, multipath has a strong reception performance.

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 (8)

An FEC unit for coding an OFDM signal in a frequency domain to detect and correct an error at a receiving side; A mapping unit for mapping the coded OFDM signal in the frequency domain by a predetermined mapping method; A 3600-point IDFT unit for modulating the OFDM signal in the frequency domain consisting of 3600 parallel data into the OFDM signal in the time domain consisting of 3600 sample data; A guard interval inserting unit inserting a guard interval at the front end of the OFDM signal in the time domain; A synchronization information insertion unit for inserting synchronization information for synchronization and channel equalization of a transmitting side and a receiving side into the OFDM signal of the time domain in which the guard interval is inserted; And And a shaping filter for shaping the synchronous signal inserted into the OFDM signal in the time domain. The method of claim 1, And the interval between the subcarriers carrying the 3600 parallel data in the frequency domain is 2.1 KHz. The method of claim 1, The 3600-point IDFT unit, TDS-OFDM transmission system characterized by the combination of two 60-point DFT modules. The method of claim 1, The 3600-point IDFT unit, TDS-OFDM transmission system characterized by one 60-point DFT module. Coding an OFDM signal in a frequency domain to detect and correct an error at a receiving side; Mapping the coded OFDM signal in the frequency domain by a predetermined mapping method; An inverse discrete Fourier transform step of modulating the OFDM signal in the frequency domain consisting of 3600 parallel data into the OFDM signal in the time domain consisting of 3600 sample data; Inserting a guard interval in front of the OFDM signal of the time domain; Inserting synchronization information for synchronization and channel equalization of a transmitting side and a receiving side into the OFDM signal of the time domain into which the guard interval is inserted; And Shaping and filtering the inserted synchronization signal of the OFDM signal in the time domain. The method of claim 5, In the inverse Fourier transform step, The signal processing method of the TDS-OFDM transmission system, characterized in that the interval between the sub-carrier carrying the 3600 parallel data in the frequency domain is 2.1KHz. The method of claim 5, The inverse Fourier transform step, A signal processing method of a TDS-OFDM transmission system, characterized by inverse Fourier transform by two 60-point DFT modules. The method of claim 5, The inverse Fourier transform step, A signal processing method of a TDS-OFDM transmission system, characterized by an inverse Fourier transform by one 60-point DFT module.