KR20040025294A - Symbol timing recovery with Gardner algorithm for DTV using 8VSB - Google Patents

Abstract

PURPOSE: A digital television symbol timing synchronous algorithm is provided to square an existing Gardner method with a received signal, and to apply the squared value to a Gardner symbol timing detector, then to recover a symbol clock, thereby restoring symbol timing without frequency components. CONSTITUTION: A Gardner symbol timing recoverer using a prefilter is independently operated from a squared Gardner symbol timing recoverer. The Gardner symbol timing recoverer using the prefilter filters a signal passing through a square root cosine filter1(303) to a prefilter1(304), and uses the filtered signal as an input of a timing detector1(308). The timing detector(308) generates a timing error, amplifies an error value in an amplifier1(312), and obtains an average in a loop filter1(311), then controls parameters of an interpolation filter1(302) in an address calculator1(310). Power of a signal passing through the prefilter1(304) is measured in a power calculator1(306). A distributive calculator1(309) measures changes of the power, and controls a gain value of the amplifier1(312). The distributive calculator1(309) measures how fast a channel changes.

Description

Digital television symbol timing synchronization algorithm {Symbol timing recovery with Gardner algorithm for DTV using 8VSB}

The present invention relates to a Gardner symbol timing recoverer in combination with a symbol timing recoverer squared with a received signal, and is an indoor ATSC (Advanced Television Systems Commttee) method that is a digital TV broadcasting standard adopted in North America and Korea. The purpose is to improve the reception performance and the mobile reception performance.

In general, the digital communication system can accurately restore the signal of the transmitter only when the sampling moment at the transmitter and the sampling moment restored at the receiver are the same. In the case of ATSC (Advanced Television Systems Commttee), a digital TV broadcasting standard adopted in North America and Korea, the 8_VSB signal of the transmitter must be correctly restored when the moment when the transmitter samples the 8-VSB signal and the moment when the receiver restores the same. It is possible.

1 is a block diagram of a receiver of a typical VSB terrestrial broadcast transmission system.

Referring to FIG. 1, the tuner 100 selects a channel, passes through an intermediate band filter in the IF filter 200, and finds a frequency with the synchronous frequency detector 300. The synchronization signal and the clock signal are found by the synchronization detector 300 and the timing detector 300, and then passed through the NTSC interference cancellation filter 400 to remove the interference by the multipath in the equalizer 500. The phase tracker 600 compensates for the remaining phase error. The trellis decoder 700 is data modified by the trellis encoder, the data deinterleaver 800 restores the interleaved data in the transmission, and the RS decoder 900 replaces the incoming data with randomly input data. The data is separated into 20-byte parity codes, and the input data randomized through the data inverse number generator 1000 is restored to the information data that we want to obtain.

As a method for symbol timing recovery, the segment sync is inserted repeatedly for every 77.3us introduced in the Advanced Television Systems Commttee (ATSC) specification. There is a Gardner method. In the segment sync method, +5, -5, -5, and +5 are repeatedly inserted in each segment, and the sampling frequency error is calculated using the result of multiplying the signal with 0, +, 0, and-signals. Next, the Gardner method estimates a sampling timing error d (t) as a signal sampled at twice the symbol rate as follows. There are two methods for estimating the error d (t), one of which is the balance maintenance method (GardnerA) and the other is the zero crossing detection method (Gardner B).

Equation 1 is an expression representing the balance maintenance method (Gardner A), and the sampling timing error is estimated by using how much the signals are symmetrical with respect to the position at which the signal is taken. Where y (t) is the received data sampled at 21.52MHz, which is twice the symbol rate of 10.76MHz.

Equation 2 expresses a zero crossing detection method (Gardner B), and estimates a sampling timing error by detecting whether a signal crosses zero. Where y (t) is the received data sampled at 21.52MHz, which is twice the symbol rate of 10.76MHz.

A signal having multiple levels is a signal sampled at twice the symbol rate. If the sampling timing error is estimated using the above equation, there is an error even when accurately sampled. However, in general, since data is randomly transformed through data randomization at a transmitting end, an accurate sampling timing error can be estimated by accumulating and calculating an average of error estimates. The loop filter accumulates the error estimates and calculates an average. This estimated error enters the input of the voltage-controlled oscillator (VCO), and the voltage-controlled oscillator (VCO) changes the clock frequency of the analog-to-digital converter to enable accurate data recovery.

2 is a block diagram of a Gardner timing detector.

Referring to FIG. 2, a double oversampled input signal undergoes two time delays and detects a timing error by using a difference between signals.

Digital TV broadcasting must be able to receive indoors and be portable and mobile. To meet all of these conditions, a symbol timing recoverer that works well in both changing channel and Doppler environments is required.

However, the segment sync method has a segment sync every 77.3us, so if the channel environment changes between them, the segment sync error estimator may not catch the accurate sampling clock. In addition, the Gardner method extracts symbol timing components from normal data and estimates sampling clock errors, so it works relatively well in fast convergence performance and changing channel environment.

However, the Gardner method uses a frequency component of 5.38 MHz, and there is a problem in that the sampling clock error component cannot be extracted when the frequency component disappears due to the multipath environment. As a result, sampling timing may be wrong and correct restoration may not be possible.

Accordingly, the technical problem of the present invention is to solve such a conventional problem, and an object of the present invention is to compensate for the fact that the sampling timing cannot be restored when the frequency component of 5.38 MHz disappears in the Gardner method. By applying the squared signal to the Gardner symbol timing detector to restore the symbol clock, it provides a method to recover the symbol timing even if there is no frequency component at 5.38 MHz.

1 is a block diagram of a typical VSB digital terrestrial broadcast receiver.

2 is a block diagram of a symbol timing detector using a Gardner method.

3 is a structural diagram of a Gardner symbol timing recoverer using a forward filter and a Gardner symbol timing recoverer squared with a received signal. to be.

<Description of the symbols for the main parts of the drawings>

100: tuner

200: IF filter & sync detector

300: synchronization and timing recovery unit

400: NTSC Rejection Filter

500: equalizer

600: Phase Collector

700: Trellis Decoder

800: data deinterleaver

900: RS decoder

1000: Reverse Water Heater

301: analog to digital converter

302: interpolation filter 1

303: Squared square cosine filter 1

304: front filter 1

305: Multiplexer

306: power calculator 1

307: comparator

308: timing detector 1

309: dispersion calculator 1

310: address calculator 1

311: loop filter 1

312 amplifier 1

313: gain controller 1

314: Interpolation filter 2

315 squared cosine filter 2

316: interpolator for timing offset difference compensation

317 squared power

318: front filter 2

319: power calculator 2

320: timing detector 2

321: dispersion calculator 2

322: Address Calculator 2

323 loop filter 2

324: Amplifier 2

325: gain controller 2

The structure of a symbol timing recoverer for realizing the object of the present invention is a symbol clock frequency by squaring a received signal with a Gardner symbol timing recoverer using a prefilter. It is linked with a parallel patterned symbol timing recoverer (Squared Gardner symbol timing recoverer).

First, the received signal is modulated into a baseband signal and then passed through an analog-to-digital converter (ADC) to convert the analog signal into a digital signal. The clock of this analog-to-digital converter (ADC) uses a fixed clock and an interpolation filter to obtain a data rate of 21.52MHz, which is twice the 10.76MHz symbol rate of the Advanced Television System Commitee (ATSC) system. Signals sampled at 21.52 MHz, twice the symbol rate, are Gardner symbol timing recoverer using prefilter and Squared Gardner symbol timing recoverer. Are input in parallel.

The Gardner symbol timing recoverer using prefilter uses a forward filter with 320KHz bandwidth to recover symbol timing after using a frequency component of 5.38MHz.

The squared symbol timing recoverer, which squares the received signal, squares the input signal and uses a forward filter with a bandwidth of 5.38MHz to 320KHz to recover the symbol timing. When the signal is squared, a signal having a 6 MHz bandwidth in the frequency domain is convolved in the frequency domain.

Where * is the convolution operator.

The signal is passed through a bandpass filter to extract 5.38MHz components. Then, the component that was 2.69MHz before squared is shifted to 5.38MHz component by the square of the signal, and the symbol timing is restored using this signal. The extracted signal is used as an input to the Gardner timing detector using the Gardner algorithm. The signal passed through the Gardner timing detector is filtered using a loop filter, and then the address calculator Used as input The sample calculator restores the sample timing by changing the parameters of the interpolation filter.

The present invention is to perform symbol timing recovery (symbol timing recovery) using a 2.69MHz component when the 5.38MHz symbol timing frequency component that has been a problem in the conventional segment sync method or the Gardner method is lost due to multipath or Doppler. 5.38MHz has the disadvantage that the frequency component can be easily lost due to multipath or Doppler due to the low power of the signal.However, if you use the Gardner method after applying the Gardner method after squaring the conventional Gardner method and the received signal, the 5.38MHz frequency component If missing, the 2.69MHz frequency component is used, so that timing recovery (symbol timing recovery) is possible even if the 5.38MHz frequency component, which was a problem with the conventional Gardner method, is lost.

FIG. 3 is a block diagram illustrating a symbol timing recoverer in which a Gardner symbol timing recoverer using a prefilter and a Squared Gardner symbol timing recoverer are formed by squaring a received signal.

Referring to FIG. 5, the baseband signal is converted into a digital signal through the analog-to-digital converter 301. The analog-to-digital converter then samples using a fixed clock and then uses interpolation filter 1 302 and interpolation filter 2 314 to obtain a data rate that is twice the symbol rate. After that, only the signal of the data area is extracted using the square root cosine filter 1 303 and the square root cosine filter 2 315.

The symbol timing recoverer using a prefilter and the squared Gardner symbol timing recoverer square the received signal operate independently of each other. First, the Garner symbol timing recoverer using prefilter filters the signal passing through the square root cosine filter 1 (303) to the front filter 1 (304) and uses it as an input of the timing detector 1 (308). do. The timing detector 1 308 then generates a timing error, raises the error value appropriately in the amplifier 1 312, averages it in the loop filter 1 311, and calculates the average of the interpolation filter 1 302 in the address calculator 1 310. Adjust the variable. Then, the power of the signal passing through the front filter 1 304 is measured by the power calculator 1 306 and the change of power is measured by the dispersion calculator 1 309 to adjust the gain value of the amplifier 1 312. The variance calculator 1 (309) measures how fast the channel changes and increases the gain in the fast changing channel environment and reduces the gain in the slow changing environment so that it adapts well to the channel environment.

The squared symbol timing recoverer squaring the received signal squares the signal passing through the square root cosine filter 2 (315) in the signal squarer (317) and filters the signal through the forward filter 2 (318). It is used as an input of detector 2 (320). The timing detector 2 320 generates a timing error and adjusts the gain in the amplifier 2 324 to take an average in the loop filter 2 323 and adjust the parameters of the interpolation filter 2 314 in the address calculator 2 322. do. The power of the signal passing through the front filter 2 318 is measured by the power calculator 2 319, and the variation of the power is measured by the dispersion calculator 2 321 to adjust the gain value of the amplifier 2 324. The variance calculator 2 321 measures how fast the channel changes, thereby increasing the gain in the fast changing channel environment and reducing the gain in the slowly changing environment so that it adapts well to the channel environment.

4 is a gain compensation curve according to the power of a signal.

4, since the gain compensation is K1 > K2, the gain compensation amount is large when K1. In this case, the channel changes abruptly and is determined by the output of the variance calculator. In contrast, K2 is used when the gain compensation is small and the channel changes slowly. And if the power of the signal is too small, it cannot be grown above the gain limit.

The interpolator 316 for timing offset difference compensation compensates for the difference between the convergence points of the Gardner symbol timing recoverer using prefilter and the Squared Gardner symbol timing recoverer. To compensate.

The comparator 307 generates a control signal of the multiplexer for the selection of each timing recovery block operating independently. Compared with the signal of power calculator 1 (306) and power calculator 2 (319), under the same conditions, the performance of the Gardner symbol timing recoverer using prefilter is better. If it doesn't disappear, use a Gardner symbol timing recoverer using prefilter. Therefore, power is compared with a large weight on the power calculator 1 306 to generate the multiplexer 305 control signal. The signal passed through the multiplexer is oversampled at twice the symbol rate of 10.76MHz, so it is downsampled to 1/2 and output.

Those skilled in the art will appreciate that various modifications and changes can be made in the present invention without departing from the spirit and scope of the invention as set forth in the claims below.

As described above, by extracting and compensating for the timing error by squaring the input signal according to the present invention, it is possible to improve the indoor reception performance of a digital TV and the reception performance in a mobile environment having multiple paths.

Claims (9)

In the symbol timing recoverer for recovering the timing of the signal demodulated to the baseband, A symbol timing decompressor using a Gardner symbol timing decompressor using a forward filter and a symbol timing decompressor squared of a received signal in parallel. Multiplexer to select the output of parallel symbol timing recoverers. Signal power meter that generates a signal to control symbol timing selection in a multiplexer. The method of claim 1, Symbol Timing Restorer Squared Received Signal The method of claim 2, Input squarer to square the received signal. The method of claim 2, Forward filter to extract specific frequency components of the squared signal The method of claim 2, Gardner timing detector used to extract timing error. The method of claim 1, A signal power calculator that measures the power of a signal that comes down to baseband after demodulating a received signal. In the timing restorer using the front filter and the timing restorer squared the received signal, Part of controlling the gain of the timing detector using a variance calculator and a power calculator The method of claim 7, wherein Variance Calculator to calculate the distribution of power The method of claim 7, wherein Part of controlling gain using output of variance calculator