KR20050000261A - TDS-OFDM receiver for oversampling OFDM signals to equalize channel - Google Patents

Abstract

PURPOSE: A TDS-OFDM(Time Domain Synchronous Orthogonal Frequency Division Multiplexing) receiver is provided to compensate for influences caused due to sampling time error and symbol timing error, and improve performance of compensating for distortions of multi-path by performing a channel equalization through the use of oversampled OFDM signals. CONSTITUTION: A TDS-OFDM receiver comprises a synchronization unit(140) for performing a synchronization on an OFDM broadcast signal which is received through an antenna, down converted to a baseband, and sampled at a predetermined sampling rate; a first sampler(210) for sampling the signal output from the synchronization unit at a first sampling rate; a time domain equalization unit(200) for performing a channel equalization in a time domain by the synchronization signal included in the signal output from the first sampler; a second sampler(250) for sampling the signal output from the time domain equalization unit at a second sampling rate; an FFT(Fast Fourier Transform) unit(220) for performing FFT on the signal output from the second sampler, and outputting a signal; and a forward error correction unit(400) for detecting and correcting error of the signal output from the FFT unit.

Description

TDS-OFDM receiver for oversampling OMD signal to equalize channel

The present invention relates to a TDS-OFDM receiver for oversampling an OFDM signal and performing channel equalization. It is about.

The OMD method converts a symbol string input in a serial form into parallel data of a predetermined block unit and then multiplexes the parallelized symbols with different subcarrier frequencies. The OMD system uses a multi-carrier, and has a considerable difference from the conventional single carrier. Multiple carriers have orthogonality with each other. Orthogonality means a property in which the product of two carriers becomes '0', which is a requirement for using multiple carriers. The implementation of the UFDM method is performed by the Fast Fourier Transform (FFT) and the Inverse Fast Fourier Transform (IFFT), which are simply obtained by the definition of orthogonality and fast Fourier transform between carriers. .

The OMD signal is composed of multiple carriers and each carrier has a very small band. Thus, the overall spectral shape is almost square, resulting in a relatively higher frequency efficiency than a single carrier. In addition, the advantages of the UF DM method is that the waveform of the UF DM signal is the same as White Gaussian Noise, so the PAL (Phase Alternation by Line) and SECAM (Sequential Couleur a Memoire) methods are used. Has less interference than other broadcasting services. Accordingly, in the OMD system, the modulation scheme may be different for each carrier, so that hierarchical transmission is possible.

Recently, a new terrestrial digital TV transmission standard, DMB-T, has been proposed to improve the speed with respect to the specifications of the terrestrial digital TV transmission system. The transmission system using the DMB-T scheme employs a TDS-OFDM (Time Domain Syncronous Orthogonal Frequency Division Multiplexing) scheme, and an OFDM modulator uses a 3780-point IDFT / DFT processor.

It should be considered at this point that the signal is transmitted on the transmission channel according to the channel condition, and the multipath distortion among the distortions affects the signal and is particularly fatal for digital broadcasting. . Therefore, in order to compensate for such distortion, an equalizer is provided for compensating for errors on the transmission channel when the signal is restored on the receiving side.

1 is a block diagram of a conventional TDS-OFDM receiver. The TDS-OFDM receiver includes RF RX 10, ADC 12, synchronizer 14, demultiplexer 16, PN correlator 20, first FFT unit 30, second FFT unit 40, frequency It consists of an area equalizing unit 50 and an FEC unit 60.

The RF RX 10 down-converts the OFDM broadcast signal received through the antenna to baseband, and the analog-to-digital converter (ADC) 12 receives the RF RX ( 10) Convert the analog signal received from the digital signal.

The synchronizer 14 performs symbol timing and frequency synchronization using PN sequence (pseudo noise sequence) information which is transmitted synchronization information. The PN sequence information is synchronization information for predicting synchronization and channel of the OFDM broadcast signal received by the TDS-OFDM receiver receiving the transmitted OFDM broadcast signal, and is inserted in front of a guard interval (GI) to be described later.

The demultiplexer 16 divides the OFDM broadcast signal received from the synchronizer 14 into a PN sequence, a guard period (GI), and an OFDM symbol.

The PN correlator 20 outputs a PN correlation between the reference signal sequence and the PN sequence to the first FFT unit 30 to provide information about channel conditions, and the first FFT unit 30 provides a correlation. Fast Fourier Transform (FFT) and output to the frequency domain equalizer 50.

The OFDM symbol output from the demultiplexer 16 is output to the second FFT unit 40, and the second FFT unit 40 FFTs the OFDM symbol to output to the frequency domain equalizer 50.

The frequency domain equalizer 50 performs channel equalization on the FFT OFDM symbols received from the second FFT unit 40 based on the FFT correlation received from the first FFT unit 30. do.

The forward error corrector (FEC) 60 detects an error by the error detection method set for the equalized OFDM symbol and corrects the detected error.

As described above, the conventional TDS-OFDM receiver estimates the channel state using the correlation between the reference signal sequence and the PN sequence, and performs equalization of the frequency domain using the estimated channel state. . However, when the equalization is performed in the above-described manner, if the information on the channel state estimated using the correlation is not accurate due to the distortion and noise component of the channel, the equalization performance may be degraded.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a TDS-OFDM receiver that oversamples an OFDM signal and inputs it to a time domain equalizer to compensate for channel distortion.

1 is a block diagram of a conventional TDS-OFDM receiver;

2 is a block diagram of a TDS-OFDM receiver according to the present invention;

3 is a detailed block diagram of a time domain equalizer of FIG. 2, and

4 is a diagram provided to explain the structure and training technique of the OFDM broadcast signal.

Explanation of symbols on the main parts of the drawings

100: RF RX 120: ADC

140: synchronization unit 200: time domain equalizer

210: first sampler 220: FFF

230: FBF 240: adder

250: second sampler 300: FFT unit

400: FEC part

A TDS-OFDM receiver according to the present invention for achieving the above object is an OFDM broadcast signal including synchronization information, received through an antenna, downconverted to baseband, and sampled at a predetermined sampling rate (T ₀ ). A synchronization unit performing synchronization, a first sampler sampling the output signal of the synchronization unit at a predetermined first sampling rate T ₁ , and channel equalization in the time domain by synchronization information included in the output signal of the first sampler. A time-domain equalizer, a second sampler for sampling the output signal of the time-domain equalizer at a predetermined second sampling rate T ₂ , and a fast Fourier transform (FFT) of the output signal of the second sampler And an error correction unit for detecting and correcting an error with respect to an output signal of the FFT unit.

Preferably, the synchronization unit performs synchronization using the synchronization information. The synchronization information is preferably a PN sequence (pseudo noise sequence).

And the predetermined T ₁ is It is preferable that (N is a natural number). In addition, the predetermined T ₂ is preferably the same value as the predetermined T ₀ . In addition, the predetermined T ₀ is It is possible to be seconds.

The time domain equalizer may be a decision feedback equalizer. The time domain equalizer may include: a feed-forward filter for removing pre-ghosts of each symbol from the output signal of the first sampler, a feedback filter for removing post-ghosts of each symbol from the output signal of the first sampler; And an adder configured to add the pre-ghost and the post-ghost removed symbols to the feedback filter and the second sampler.

The time domain equalizer may be any one of a Kalman equalizer and a data recycling equalizer.

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

2 is a block diagram of a TDS-OFDM receiver according to the present invention. Referring to FIG. 2, the TDS-OFDM receiver includes an RF RX 100, an ADC 120, a synchronizer 140, a time domain equalizer 200, an FFT unit 300, and an FEC unit 600. do.

The RF RX 100 down-converts the OFDM broadcast signal received through the antenna to baseband, and the ADC (Analog-to-Digital Converter) 120 converts the RF RX ( The analog signal received from 100 is converted into a digital signal by sampling according to the preset sampling rate T ₀ . For TDS-OFDM, the T ₀ is It is in seconds.

The synchronizer 140 performs symbol timing and frequency synchronization using the transmitted PN sequence.

The time domain equalizer 200 equalizes the OFDM broadcast signal in the time domain by a PN sequence. The time domain equalizer 200 may include a first sampler 210, a feed forward filter 220, a feed back filter 230, an adder 240, and the like. The second sampler 250 is configured. As described above, the time domain equalizer including the FFF 220 and the FBF 230 is called a decision feedback equalizer (DFE).

Since the time domain equalizer 200 receives an OFDM broadcast signal having a structure as shown in FIG. 4 from the synchronizer 140, the time domain equalizer 200 includes a PN sequence and a guard interval (GI). ) And OFDM symbols are sequentially input. Here, the GI is a section inserted between the PN sequence and the OFDM symbol in order to suppress inter-symbol interference (ISI) in a multipath environment.

While the PN sequence is input to the time domain equalizer 200, the time domain equalizer 200 operates in a training mode. Accordingly, the PN sequence input to the time domain equalizer 200 is sampled according to a sampling rate T ₁ preset by the first sampler 210, where T ₁ satisfies the following equation.

In the above equation, N is a natural number, and in this embodiment, N = 2.

As such, the reason for resampling the OFDM broadcast signal input to the time domain equalizer 200 according to T ₁ is to cancel the influence due to the sample timing error and the symbol timing error. This is because the ability to compensate for multipath distortion is improved because equalization is performed by using the equalization method. The time domain equalizer 200 updates the FFF tap coefficient and the FBF tap coefficient by using the PN sequence sampled according to T ₁ .

On the other hand, while the GI and OFDM symbols are input to the time domain equalizer 200, the FFF tap coefficient and the FBF tap coefficient are not updated. In addition, channel equalization is performed while the OFDM symbol is input to the time domain equalizer 200. In this process, the time domain equalizer 200 calculates the FFF tap coefficient and the FBF calculated through an oversampled PN sequence in the training mode. Tap coefficients are used. A process of performing channel equalization by the time domain equalizer 200 in the above-described manner will be described in detail below.

3 is a detailed block diagram of the time domain equalizer 200 of FIG. 2. Referring to FIG. 3, the FFF 220 includes a buffering unit 222, a multiplier 224, and an adder 226. The FBF 230 includes a buffering unit 232, a multiplication unit 234, And an adder 236.

First, the OFDM symbol output from the synchronizer 140 is sampled according to the sampling rate T ₁ preset by the first sampler 210 and output to the FFF 220.

The FFF 220 removes the influence of pre-ghost on each symbol of the OFDM broadcast signal. Referring to FIG. 3, the FFF 220 includes a buffering unit 222, a multiplier 224, and an adder 226. The buffering unit 222 sequentially stores and buffers the OFDM broadcast signal at each stage in symbol units according to an input order. The multiplier 244 removes the pre-ghost by multiplying the FFF tap coefficient by each symbol stored and buffered at each stage of the buffering unit 222. The adder 226 sums the values of the pre-ghosts respectively removed by the multiplier 224.

The FBF 230 removes the influence of post-ghost on each symbol of the OFDM broadcast signal. The FBF 230 has a buffering unit 232, a multiplier 234, and an adder 236. The buffering unit 232 sequentially stores and buffers the output values of the adder 240 at each stage in symbol units according to the input order. The multiplier 234 removes post-ghosting by multiplying the FBF tap coefficient by each symbol stored and buffered at each stage of the buffering unit 232. The adder 236 adds up the post-ghosted values.

The adder 240 adds the value of the pre-ghost removed from the FFF 220 and the value of the post-ghost removed from the FBF 230 to feed back to the FBF 230, and outputs the result to the second sampler 250. . The second sampler 250 samples the equalized OFDM symbol according to a preset sampling rate T ₂ , where T ₂ is equal to T ₀ .

Although the decision feedback equalizer (DFE) is used as the time domain equalizer 200 in the present embodiment, the time domain equalizer 200 is a Kalman equalizer. , And may be implemented as a data recycling equalizer.

Referring to FIG. 2, the equalized OFDM symbol output from the second sampler 250 is FFT (Fast Fourier Transform) in the FFT unit 300 and is output to the FEC unit 400.

The forward error corrector 600 detects an error by using an error detection method set for the FFT OFDM symbol, and corrects the detected error.

As described above, according to the present invention, channel equalization may be performed by oversampling an OFDM broadcast signal. Thus, the effects of the sample timing error and the symbol timing error can be canceled, and the ability to compensate for multipath distortion is improved because equalization is performed using the oversampled signal.

In addition, although the preferred embodiment of the present invention has been shown and described above, the present invention is not limited to the specific embodiments described above, but the technical field to which the invention belongs without departing from the spirit of the invention claimed in the claims. Of course, various modifications can be made by those skilled in the art, and these modifications should not be individually understood from the technical spirit or the prospect of the present invention.

Claims (9)

A synchronization unit configured to perform synchronization of an OFDM broadcast signal including synchronization information received through an antenna, downconverted to baseband, and sampled at a predetermined sampling rate (T ₀ ); A first sampler sampling the output signal of the synchronizer at a predetermined first sampling rate T ₁ ; A time domain equalizer for performing channel equalization in the time domain based on synchronization information included in the output signal of the first sampler; A second sampler sampling the output signal of the time domain equalizer at a second predetermined sampling rate T ₂ ; An FFT unit configured to output a Fourier Transform (FFT) output signal of the second sampler; And And a forward error corrector (FEC) unit for detecting and correcting errors with respect to the output signal of the FFT unit. The method of claim 1, The synchronization unit, TDS-OFDM receiver, characterized in that for performing synchronization using the synchronization information. The method of claim 2, And the synchronization information is a PN sequence (pseudo noise sequence). The method of claim 1, The predetermined T ₁ is (N is a natural number). The method of claim 1, And the predetermined T ₂ is _equal to the predetermined T ₀ . The method of claim 1, The predetermined T ₀ is TDS-OFDM receiver, characterized in that (sec). The method of claim 1, And the time domain equalizer is a decision feedback equalizer. The method of claim 7, wherein The time domain equalizer, A feed-forward filter which removes a pre-ghost of each symbol from an output signal of the first sampler; A feedback filter for removing post-ghosts of each symbol from the output signal of the first sampler; And And an adder configured to add the pre-ghost and the post-ghost removed symbols to the feedback filter and the second sampler. The method of claim 1, The time domain equalizer, A TDS-OFDM receiver, which is one of a Kalman equalizer and a data recycling equalizer.