KR20040032676A - TDS-OFDM transmission system and a method proessing OFDM signal thereof - Google Patents

Abstract

PURPOSE: A TDS-OFDM(Time Domain Synchronous-Orthogonal Frequency Division Multiplexing) transmission system and a method for processing a signal thereof are provided to simplify a structure and an operation of a hardware by using a 4K-point IFFT processor instead of a 3780-point-IDFT processor. CONSTITUTION: A TDS-OFDM transmission system includes an FEC(Forward Error Correction) unit(120), a serial/parallel conversion unit(220), an interpolation unit, a 4096-point IFFT unit, a decimation unit, a protective block insertion unit(240), and a synchronous information insertion unit(260). The FEC unit(120) codes data of a frequency region to sense and correct an error of a receiving side. The serial/parallel conversion unit(220) outputs the coded data of the frequency region as parallel data. The interpolation unit interpolates the data to outputs 4096 data. The 4096-point IFFT unit transforms 4096 data of the frequency region to 4096 sample data according a sample rate of a time region. The decimation unit decimates 4096 sample data and outputs the sample data as OFDM signals of the time region. The protective block insertion unit(240) inserts protective blocks into the OFDM signals of the time region. The synchronous information insertion unit(260) inserts the synchronous information into the OFDM signals including the protective blocks.

Description

TDS-OPEM transmission system and signal processing method thereof {TSD-OPEM transmission system 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 transmission system capable of being compatible with 3780 mode and 4K mode.

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 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.

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 the end of the signal 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 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.

As shown in FIG. 2, 3780 parallel data in the frequency domain are inputted to the 3780-point IDFT unit 30 and inversely transformed to obtain 3780 sample data and a sampling rate of 3780 × 2.0KHz (carrier spacing) = 7.56 MHz. This is a conceptual diagram of processing in the time domain at a sampling rate. That is, 3780 parallel data are allocated to each subcarrier in the frequency domain, and are then modulated and output to 3780 sample data by performing inverse Fourier transform in the time domain. Accordingly, the sampling rate is 7.56 MHz.

As described above, the 3780-point IDFT unit 30 converts an OFDM symbol from a frequency domain into a time domain and processes the same. However, references in such IDFT processors Zhi-Xing Yang, Yu-Peng Hu, Chang-Yong Pan, and Lin Yang, "Design of a 3780-Point IFFT Processor for TDS-OFDM", IEEE TRANSACTIONS ON BROADCASTING, VOL, Referring to the description of 48, NO, 1, MARCH 2002, the comparison of 3780-point IDFT processor and 4K-point IFFT processor, as shown in Table 1, can be obtained.

3780-point IDFT 4096-point IFFT Real additions 140184 123792 Real Multiplications 50712 48248 Latency Prouduced by buffer 8064 sample clocks 4095 sample clocks Buffer Requirement 141612 bits 106470 bit

That is, as shown in the results of [Table 1], the hardware is more complicated when using the 3780-point IDFT processor than the 4K (4096) -IFFT processor, there is a problem that is inefficient because of the large amount of computation.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and improves the complexity and computational complexity of hardware by using a simple 4K-point IFFT processor in a conventional TDS-OFDM transmission system using a 3780-point IDFT processor. In addition, to provide a TDS-OFDM transmission system that can be compatible for the 3780 mode and 4K mode.

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

2 is a conceptual diagram illustrating that an OFMD signal is processed by a 3780-point IDFT processor of FIG. 1;

3 is a schematic block diagram of a DMB-T transmission system having a 4K-modulator as a preferred embodiment according to the present invention;

4 is a detailed block diagram of the 4K-modulator 230 of FIG.

5A to 5C are conceptual views illustrating the operation of the interpolation unit 231 of FIG.

6 is a conceptual diagram illustrating that an OFDM signal is processed by a 4096-point IFFT processor of FIG. 4, and

7 is a flowchart illustrating a signal processing method of a DMB-T transmission system having a 4K-modulator 230 according to the present invention.

Explanation of symbols on the main parts of the drawings

100 channel encoding unit 110 scrambler

120: FEC unit 200: OFDM modulator

210: mapping unit 220: serial / parallel conversion unit

230: 4K-modulation unit 231: interpolation unit

233: 4096-point IFFT processor 235: decimation unit

240: parallel / serial conversion unit 250: protection section insertion unit

260: synchronization information insertion unit 270: molding filter unit

280: RF unit

The TDS-OFDM transmission system according to the present invention for achieving the above object, the FEC unit for coding the data in the frequency domain for detecting and correcting the error at the receiving side, and collects the predetermined data of the coded frequency domain A serial / parallel conversion unit for outputting parallel data, an interpolation unit for interpolating the predetermined data to output 4096 data, and modulating and outputting the 4096 data in the frequency domain at 4096 sample rates in the time domain A 4096-point IFFT unit, a decimation unit for decimating the 4096 sample data and outputting the same number of sample data as the OFDM signal in the time domain, and inserting a guard interval into the OFDM signal in the time domain. A guard interval insertion section and a synchronization between a transmitter and a receiver on an OFDM signal of the time domain into which the guard interval is inserted; And a synchronization information insertion unit for inserting synchronization information for channel equalization.

Preferably, the predetermined data is 3780 data, and the interpolation unit performs interpolation by linear interpolation and zero-order interpolation.

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 data in the frequency domain to detect and correct the error at the receiving side; Collecting predetermined data of the coded frequency domain and outputting the parallel data; An interpolation step of interpolating the predetermined data and outputting 4096 data; An inverse fast Fourier transform step of modulating and outputting the 4096 data in the frequency domain at 4096 sample rates in the time domain; Decimating the 4096 sample data and outputting the same number of sample data as the OFDM signal in the time domain; Inserting a guard interval into the OFDM signal in the time domain; And inserting synchronization information for synchronization and channel equalization of a transmitting side and a receiving side into the OFDM signal in the time domain into which the guard interval is inserted.

According to the present invention, in a TDS-OFDM transmission system that processes 3780 parallel data in one frequency in a frequency domain by one ODP symbol, by using an inverse Fourier transform using a 4K-point IFFT processor instead of a 3780-point-IDFT processor, The hardware implementation and operation of the system can be simplified.

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.

In order to improve the Chinese DMB-T transmission system, FIG. 3 is a schematic block diagram of a TDS-OFDM DMB-T transmission system using a 4K-point IFFT processor instead of a 3780-point IDFT processor. The present invention will be described in detail by way of example.

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 has a scrambler 110 and a forward error correction (FEC) unit 120, and the OFDM modulation unit 200 includes a mapping unit 210, a serial / parallel conversion unit 220, and 4K-modulation. And a protection section insertion section 240, a parallel / serial conversion section 250, a synchronization information insertion section 260, a shaping filter section 270 and an RF section 280.

The channel encoding unit 100 includes a scrambler 110 that randomizes the 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. 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 code, convolutional interleaved code, and reed-solomon (RS) code is used as forward error correction (FEC) of a TV broadcast program.

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. .

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. Interleaved encoding in the frequency domain is performed in one frame according to the map table. For example, an input symbol vector consisting of 3780 symbols is mapped to a new output vector by an interleaving encoder in the frequency domain.

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 serial / parallel converter 220 converts the mapped serial data into 3780 parallel data according to the DMB-T standard and outputs the converted parallel data.

As shown in FIG. 4, the 4K-modulator 230 includes an interpolation unit 231, a 4K-point IFFT processor 233, and a decimation unit 235.

The interpolation unit 231 interpolates the 3780 parallel data output from the serial / parallel conversion unit 220 and inserts predetermined data so that the parallel data corresponds to 4096, that is, 4096-point. . Here, the interpolation used may be performed by various methods such as zero-order interpolation, or zero-order interpolation after linear interpolation, or interpolation using a fractional delay filter.

5A through 5C are conceptual views illustrating a case of performing zero-order interpolation after linear interpolation in the latter case.

As shown in FIG. 5A, 3780 parallel data are arranged, and interpolation is performed by 2 ^m (m is 1,2,3 ...) times by linear interpolation. Thereafter, as shown in FIG. 5C, zero-order interpolation is performed to interpolate 4096 parallel data with adjacent neighbor data values.

The 4096-point IFFT processor 233 modulates 4096 parallel data in the frequency domain interpolated by the interpolation unit 231 into 4096 sample data in the time domain. As shown in Fig. 6, the interpolated 4096 parallel data is modulated into 4096 sample data and a time domain OFDM signal having a sampling rate of 8.192 MHz (4096 x 2 KHz).

As described above, the decimation unit 235 performs decimation so that the OFDM signal modulated in the 4K mode has the sample data and the sampling rate corresponding to the 3780 mode.

That is, the decimation unit 235 reduces the 4096 sample data processed by the 4096-point IFFT processor to 3780, and also reduces the sampling rate of 8.192 MHz to 7.56 MHz to process the sample processed by the existing 3780-point IDFT processor. Adjust the data and sampling rate equally.

In order to prevent inter symbol interference (ISI) in the multipath environment, the guard interval insertion unit 240 inserts sample data of a part of the end of the OFDM symbol into the guard interval GI in front of the OFDM symbol. The guard intervals GI are 1/6, 1/9, 1/12, 1/20, 1/30 of 3780.

The parallel / serial converter 250 converts the parallel data into serial data and outputs the serial data.

The synchronization information insertion unit 260 inserts a PN sequence, which is synchronization information for time synchronization acquisition and channel equalization, in front of the guard interval GI.

The shaping filter 270 performs shaping filtering on 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 280.

Hereinafter, a signal processing method of a TDS-OFDM transmission system according to the present invention will be described in detail with reference to FIG. 7.

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 interpolation unit 231 performs interpolation on 3780 parallel data output from the serial / parallel conversion unit 220 by a predetermined method and outputs 4096 parallel data (S30).

The 4096-point IFFT processor 232 performs inverse Fourier transform on the interpolated 4096 parallel data (S40). Therefore, the OFDM symbol in the time domain has 4096 sample data and a sampling rate of 8.192 MHz.

Thereafter, the decimation unit 233 decimates the 4096 sample data and the sampling rate of 8.192 MHz to adjust the 3780 sample data and the 7.56 MHz sampling rate (S50).

The guard interval inserter 240 inserts a guard interval GI for 3780 sample data (S60), and the sync information inserter 250 inserts a PN sequence as sync information before the guard interval GI (S70). ).

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 (S80).

As such, by providing a 4K-point IFFT processor having a simple hardware structure in an OFDM transmission system supporting a 3780-point IDFT processor, hardware implementation and operation of the system can be simplified. In addition, compatibility with OFDM systems supporting 4K-point IFFT processors can be achieved.

According to the present invention, in a TDS-OFDM transmission system that processes 3780 parallel data in one frequency in a frequency domain by one ODP symbol, by using an inverse Fourier transform using a 4K-point IFFT processor instead of a 3780-point-IDFT processor, The hardware implementation and operation of the system can be simplified.

In addition, it can be designed to be compatible with OFDM systems that typically support 4K-point IFFT processors.

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 (6)

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 coded frequency domain and output the parallel data; An interpolation unit which interpolates the predetermined data and outputs 4096 data; A 4096-point IFFT unit for modulating and outputting the 4096 data in the frequency domain at 4096 sample rates in the time domain; A decimation unit for decimating the 4096 sample data and outputting the same number of sample data as the OFDM signal in the time domain; A guard interval insertion unit inserting a guard interval into the OFDM signal in the time domain; And And a synchronization information insertion unit for inserting synchronization information for synchronization and channel equalization between a transmitting side and a receiving side into the OFDM signal of the time domain in which the guard interval is inserted. The method of claim 1, And said predetermined data is 3780 pieces of data. The method of claim 1, The interpolation unit, TDS-OFDM transmission system characterized by performing interpolation by linear interpolation and zero-order interpolation. Coding data in the frequency domain to detect and correct errors at the receiving end; Collecting predetermined data of the coded frequency domain and outputting the parallel data; An interpolation step of interpolating the predetermined data and outputting 4096 data; An inverse fast Fourier transform step of modulating and outputting the 4096 data in the frequency domain at 4096 sample rates in the time domain; Decimating the 4096 sample data and outputting the same number of sample data as the OFDM signal in the time domain; Inserting a guard interval into the OFDM signal in the time domain; And And inserting synchronization information for synchronization and channel equalization between a transmitting side and a receiving side into the OFDM signal in the time domain into which the guard interval is inserted. The method of claim 4, wherein And said predetermined data is 3780 pieces of data. The method of claim 4, wherein In the interpolation step, A signal processing method of a TDS-OFDM transmission system, characterized in that interpolation is performed by linear interpolation and zero-order interpolation.