KR20040090645A - Timing-offset compensation algorithm for DTV - Google Patents

Abstract

The present invention relates to timing offset compensation for improving the performance of an equalizer in a digital TV receiver using an ATSC (Advanced Television System Commitee) type 8-VSB. ATSC (Advanced Television System Commitee) 8-VSB is currently the standard for terrestrial digital broadcasting in North America and Korea. The digital TV receiver using this standard synchronizes symbol timing using a method using segment sync or a method using Gardner algorithm. . Digital TV receivers that receive terrestrial waves receive both multipath signals as well as the main signals. In the timing of symbol timing synchronization using the Gardner algorithm, timing offsets occur due to multipath signals. This results in performance degradation of the equalizer that eliminates multipath signals.

The present invention improves the performance of the equalizer by compensating for timing offsets that occur when using the Gardner algorithm.

As a result of the present invention, digital TV reception performance using 8-VSB of ATSC (Advanced Television System Commitee) method is improved.

Description

Digital TV Timing Offset Compensation Algorithm {Timing-offset compensation algorithm for DTV}

The present invention relates to a timing offset compensation apparatus and method for improving performance at a receiver in a multipath environment of a terrestrial DTV.

North America and Korea use ATSC (Advanced Television System Commitee) as a digital TV broadcasting system. This method mainly uses segment sync and Gardner algorithm as symbol timing synchronization algorithm. Among these methods, the Gardner algorithm generates a timing offset due to the multipath environment, which degrades the performance of the equalizer and thus the reception performance.

1 is a block diagram of a receiver of a general all-digital VSB terrestrial broadcast transmission system.

Referring to FIG. 1, the tuner 100 selects a channel, passes an intermediate band filter in the IF filter 200, and samples the ADC 300 with a fixed clock (f _ADC ) 301 in the IF band. After correct symbol timing is restored by the symbol timing recoverer 500, the interpolation filter 400 generates a signal suitable for the symbol timing under the control of the symbol timing recoverer 500. The frequency and phase are found by the frequency and phase recoverer 700 to produce a signal whose frequency and phase are compensated by the frequency demodulator 600. The output of the frequency demodulator 600 is input to the matching filter 800 so that the received signal is matched. The signal passing through the matched filter 800 passes through the equalizer 900 and the multipath signal is removed. The error correction unit 1000 then detects and corrects an error that may occur while passing through the channel.

As a method for symbol timing recovery, the method using a segment sync repeatedly inserted for every 77.3us introduced in the AdvancedTelevision Systems Commttee (ATSC) specification and the Gardner used for symbol timing recovery of signals having multiple levels. There is a way. In the segment sync method, +5, -5, -5, and +5 are repeatedly inserted in each segment, and sampling frequency error is obtained by multiplying the signal by +1, +1, -1, and -1 signals. Obtain 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 (Gardner A) and the other is the zero crossing detection method (Gardner B).

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

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 21.52 MHz, twice the symbol rate of 10.76 MHz.

A signal having a multi-level is a signal sampled at twice the symbol rate. When the sampling timing error is estimated using Equation 1, there is a timing error related to the magnitude of the multi-level signal 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. The estimated error becomes an input control value of the interpolation filter 400 and its output produces a signal with symbol timing recovery.

2 is a block diagram of a Gardner symbol timing recoverer using a forward filter.

Referring to FIG. 2, a signal demodulated in an IF band is converted into a digital signal through an ADC 300 operating as a fixed clock f _ADC 301. This signal is not a symbol interval signal, and since the Gardner symbol timing detector requires 1/2 times the symbol interval signal, an interpolation filter 400 is used to convert the sampling instants. When the signal passes through the frequency demodulator 600 operated by the control signal generated by the frequency and phase recoverer 700, a signal matching the frequency and phase is generated. The matched filter 800 matches the signal filtered by the square root rising cosine filter used in the transmitter and converts the signal into a rising cosine signal. It is then input to the equalizer 900. The signal passed through the matched filter 800 to recover symbol timing uses a forward filter 501 to remove its own noise and the timing detector 502 detects timing errors through a Gardner algorithm. The loop filter 503 takes an average to remove the timing error because it is random in an instant, and this signal becomes an input signal of the controller 504 generating the control signal of the interpolation filter 400. The controller 504 adjusts the interpolation filter 400 to produce a signal that matches the symbol timing.

Therefore, 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 timing offset generated by the Gardner symbol timing recoverer so that the value of the input sample of the equalizer is the maximum point of the main signal. To improve the performance.

1 is a block diagram of a typical all-digital VSB terrestrial broadcasting receiver

2 is a block diagram of a Gardner symbol timing recoverer using a forward filter.

3 is an 8VSB data frame structure

4 shows PN511 data in a data field sink.

5 is a block diagram of an all-digital terrestrial broadcast receiver with a timing offset compensator inserted.

Explanation of symbols for the main parts of the drawings

1100: Timing Offset Compensator

1101: channel estimator

1102: maximum point searcher

1103: interpolation filter for timing compensation

A structure for realizing the above object of the present invention is to insert a timing offset compensator between the existing Gardner symbol timing recoverer and the equalizer.

The timing offset compensator includes a channel estimator 1101 using the PN511 signal present in the field sink, a maximum point searcher 1102 for finding the maximum point of the main signal, and an interpolation filter 1103 for timing compensation that compensates for the timing offset. .

3 is an 8-VSB data frame structure.

Referring to FIG. 3, one field includes two frames, and each frame includes 313 segments. Each segment is preceded by segment sync signals of +5, -5, -5, and +5. The first segment of the field is a field sink, which consists of four data segment sinks, 511 symbols of the PN511, 63 symbols of the PN63, 63 symbols of the PN63, 63 symbols of the PN63, 24 symbols of the VSB mode, and 104 symbols of reserved data. have.

4 shows PN511 data in a data field sink.

Referring to FIG. 4, since the PN511 data is fixed at a predetermined position in a field sink existing in every field, it is possible to implement a channel estimator using this data.

5 is a block diagram of an all-digital terrestrial broadcasting receiver with a timing offset compensator inserted.

Referring to FIG. 5, the control signal generated by the Gardner symbol timing recoverer 500 using the front filter adjusts the interpolation filter 400 to generate a signal suitable for the symbol timing, and the control generated by the frequency and phase recoverer 700. The signal produces a signal in phase with the frequency in the frequency demodulator (600). The signal is matched through the matched filter 800 and then input to the equalizer 900. A timing offset compensator 1100 is inserted between the matched filter 800 and the equalizer 900. The timing offset compensator 1100 compensates for the timing offset generated by the Gardner symbol timing recoverer 500 using the front filter. Gardner using a forward filter The symbol timing recoverer 500 generates a timing offset due to various multipath channel environments, which prevents sampling from being at the maximum point of the signal, which is the performance of the equalizer 900. Results in deterioration.

The timing offset compensator 1100 includes a channel estimator 1101, a maximum point searcher 1102, and an interpolation filter 1103 for timing compensation. First, the channel estimator 1101 estimates the PN511 data described with reference to FIG. 4 using double oversampled data as an estimator for estimating a channel through autocorrelation. The estimation of the double oversampled channel is to prevent the timing spectrum of 5.38 MHz from being damaged due to interference between adjacent symbols generated when the symbol unit channel estimation is performed. The maximum point finder 1102 finds a point that becomes the maximum point of the main path signal by using interpolation on the data estimated by the channel estimator 1101. When the maximum point of the main path signal is found by the maximum point finder 1102, a timing offset between the current sampling time point and the maximum point can be obtained. The timing compensation interpolation filter 1103 compensates for the timing offset so as to be input to the equalizer 900.

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, according to the present invention, a timing offset compensator for inputting a signal compensated for the timing offset generated by the Gardner symbol timing recoverer to the equalizer is inserted to receive in a pedestrian reception environment with digital reception indoors and multipath. It can improve performance.

Claims (3)

Timing offset compensation between the matched filter and the equalizer in a receiver consisting of an ADC using a fixed clock, an interpolation filter, a symbol timing recoverer using a Gardner algorithm, a frequency demodulator, a frequency and phase recoverer, a matched filter, and an equalizer A DTV receiver with a built-in timing offset compensator; The method of claim 1, The timing offset compensator uses a channel estimator that estimates twice the oversampled channel using a matched filter output signal, a maximum point finder for finding the maximum point of the main signal using interpolation, and uses a maximum point of the main signal obtained from the maximum point searcher. A DTV receiver comprising: an interpolation filter for timing compensation that compensates for the timing offset using the timing offset obtained by the method; The method of claim 2, Wherein the channel estimator obtains an autocorrelation function with PN511 data of a field sink to estimate a double oversampled channel;