KR20000034434A - Digital terrestrial broadcasting and cable broadcasting receiver - Google Patents

Abstract

A digital terrestrial broadcasting and cable broadcasting receiver is disclosed in which a hardware implementation is simplified. In this demodulation circuit, the analog / digital conversion unit converts the IF signal received through the channel into a digital signal, and the variable rate demodulator demodulates the IF signal output from the analog / digital conversion unit to generate baseband I and Q signals Conversion. The first and second SQRC filters / FFEs remove noise and linear interference using baseband I and Q signals output from the variable rate demodulator using a predetermined filter coefficient, and the DFE removes first and second SQRC filters / And outputs a signal obtained by removing the post-cursor. The first and second subtracters calculate the difference between the outputs of the first and second SQRC filters / FFE and the output of the DFE, and the first and second slicers determine the signals output from the first and second subtractors , The FEC decoder performs forward error correction on the signals output from the first and second slicers. The filter coefficient control unit controls the filter coefficients of the first and second SQRC filters / FFE and DFE according to the initial operation mode and the normal operation mode. According to this configuration, since the SQRC filtering function and the FFE function are implemented as a single filter and the filter coefficient update is controlled according to the initial operation mode and the normal operation mode, the noise and interference included in the received signal can be removed at the same time, do.

Description

(Digital Terrestrial Broadcasting and Cable TV Receiver)

The present invention relates to digital terrestrial broadcasting and cable broadcasting receivers, and more particularly to a digital terrestrial broadcasting and cable broadcasting receiver, which integrates a square-root raised cosine (SQRC) filter and an adaptive equalizer during equalization for a received signal, And to improve the signal-to-noise ratio.

Unlike conventional analog TVs, digital TVs convert video and audio signals to digital, so that they can receive original signals without distorting the signal due to transmission noise, as well as compress and expand video and audio data. So that a larger amount of data can be transmitted to the transmission channel of the same band as compared with the analog transmission method, thereby enabling high-definition HDTV broadcasting. There is also the advantage that more than one program can be transmitted simultaneously on one channel. Modulation schemes for fully digital HDTV use 16/32 QAM (Quadrature Amplitude Modulation) for cable broadcasting or 8/16 VSB (Vestigial SideBand) for terrestrial broadcasting.

On the other hand, the signal transmitted from the transmitting terminal has various distortions as it passes through the transmission channel. Factors that cause distortion include gaussian thermal noise, additive or multiplied noise due to fading, frequency variation, nonlinearity, and time dispersion. Such distortion is caused by image quality degradation due to distortion in the conventional analog TV system, but in the system of the digital transmission system, bit detection error occurs at the receiving side and data restoration is impossible or unexpected result is obtained. In particular, the multipath due to the time delay and the phase change of the transmission signal seriously causes intersymbol interference, which is a main cause of bit detection error. Channel equalization is a technique that compensates for distortion caused by non-ideal transmission channels and reduces bit detection errors at the receiving end. However, since the channel is variable depending on various factors such as the location and distance of the transceiver, the terrain, the building, and the weather, an equalization technique that can be adaptively replaced with a variable channel is required. To this end, the tap coefficients are adjusted such that the transfer function of the equalizer is a reciprocal of the transfer function of a given channel, thereby equalizing the linear distortion in the channel so as to eliminate the channel distortion effect of interference between adjacent symbols, The tap coefficients are continuously updated so as to equalize the channel characteristics in time.

1 is a block diagram schematically showing a general cable broadcasting receiver, which includes an analog / digital (A / D) converter 11, a variable rate demodulator 12, a first and a second SQRC filters 131 and 132, A DFE (decision feedback equalizer) 146, and a 12-tap DFE (decision feedback equalizer) 146. The first and second subtractors 142 and 144, the phase recovery unit 13, the phase restoring unit and the 8-tap FFE (Feed Forward Equalizer) 141, the first and second subtractors 142 and 144, An acquisition / tracking loop & clock generator 16, a phase ROM 17, and a deinterleaver 18. The adaptive equalizer 14, 204, 188, and the RS (Reed Solomon) decoder 15, do.

1, an A / D converter 11 converts an input intermediate frequency (IF) signal into a digital signal and outputs the digital signal to a variable rate demodulator 12. The variable rate demodulator 12 demodulates the IF signal output from the A / D converter 11 in synchronism with the clock signal output from the acquisition / tracking loop & clock generator 16 to generate the in-phase (I) and quadrature (Q) baseband bitstream to the first and second SQRC filters 131 and 132, respectively. The first and second SQRC filters 131 and 132 remove the Gaussian noise existing in the I and Q signals output from the variable rate demodulator 12 and output the Gaussian noise to the phase recovery unit 8-tap FFE 141.

The Fourier transformer 141 and the 8-tap FFE 141 restore the phases of the I and Q signals output from the first and second SQRC filters 131 and 132 using the sine and cosine values output from the phase ROM 17 Next, the filtered filter coefficient is filtered and output. The first and second subtractors 142 and 143 calculate the difference between the I and Q signals output from the phase recovery unit and the 8-tap FFE 141 and the signal output from the 12-tap DFE 146, And outputs it to the slicers 144 and 145. The first and second slicers 144 and 145 receive the filter signals output from the first and second subtractors 142 and 143 to discriminate the signals and output the signals to the 12-tap DFE 146 and the RS decoder 15. The 12-tap DFE 146 uses the previously detected signal with the updated filter tap coefficients to eliminate interference between the existing signals, the input signal of the 12-tap DFE 146 being applied to the first and second slicers 144, and 145, respectively.

The RS decoder 15 uses the (204, 188) codes, performs RS decoding on the equalized I and Q signals in the adaptive equalizer 14 to correct errors occurring during channel transmission, and the deinterleaver 18 Deinterleaves the error-corrected signal output from the RS decoder 15 and outputs the deinterleaved signal. The acquisition / tracking loop & clock generator 16 restores the synchronization signal and the timing information through elimination of the DC offset, gain control, and segment and frame synchronization detection on the inputted symbol data.

In FIG. 1, the first and second SQRC filters 131 and 132 are filters used to guarantee a maximum signal-to-noise ratio at a receiver for a signal transmitted through a channel including only Gaussian noise. However, cable channels and terrestrial broadcasting channels have many linear interferences due to the presence of reflected waves due to impedance mismatching in case of cable broadcasting due to multipath transmission in the case of terrestrial broadcasting as well as Gaussian noise.

Therefore, in the conventional terrestrial broadcast / cable broadcasting receiver, as shown in FIG. 1, the first and second SQRC filters 131 and 132 for guaranteeing the maximum signal-to-noise ratio, as well as the 8-tap-FFE 141 and 12 A tap-DFE 146 and first and second slicers 143 and 145. The adaptive equalizer 14 includes a tap- Here, the 8-tap FFE 141 is largely used for a fractional spaced equalization (FSE) algorithm resistant to symbol timing errors, and the 12-tap DFE 146 is composed of 1 symbol interval taps.

As described above, in the conventional digital terrestrial broadcasting and cable broadcasting receiver, there are three filters for eliminating the noise and interference of the received signals, thereby increasing the cost of hardware implementation.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in order to solve the above-mentioned problems, and it is an object of the present invention to provide a digital terrestrial broadcasting and cable broadcasting receiver, which can realize a noise elimination function using an SQRC filter and an interference elimination function using an adaptive equalizer, The purpose of the query is to provide.

According to an aspect of the present invention, there is provided a digital terrestrial broadcasting and cable broadcasting receiver including: an analog / digital converter for converting an IF signal received through a channel to a digital signal; A variable rate demodulator for demodulating the IF signal output from the analog / digital converter and converting the IF signal into baseband I and Q signals; First and second SQRC filters / FFEs for removing noise and linear interference using a predetermined filter coefficient for baseband I and Q signals output from the variable rate demodulator; A DFE for receiving a signal output from the first and second SQRC filters / FFEs and outputting a signal obtained by removing a post cursor; First and second subtractors for calculating a difference between an output of the first and second SQRC filters / FFEs and an output of the DFE; First and second slicers for determining a signal output from the first and second subtractors; An FFE decoder for performing a forward error correction on a signal output from the first and second slicers; And a filter coefficient control unit for controlling the filter coefficients of the first and second SQRC filters / FFE and DFE according to the initial operation mode and the normal operation mode.

The filter coefficient controller may further include: a threshold value generator for generating an error threshold value; An error value generation unit for generating an error value between a determination value of the signal output from the FFE and a signal output from the FFE; A comparator comparing a first selection control signal corresponding to an initial operation mode and a second selection control signal corresponding to a normal operation mode by comparing an error threshold value output from the threshold generator and an error value of the error value generator; A ROM table for storing SQRC filter coefficients; A coefficient updating unit for updating the filter coefficient using the output of the DFE and updating the filter coefficient using the output of the FFE; And a multiplexer for outputting the SQRC filter coefficient stored in the ROM table or the update filter coefficient output from the coefficient updating unit to the FFE and the DFE in accordance with the first or second selection control signal output from the comparator .

1 is a block diagram schematically illustrating a general cable broadcast receiver,

2 is a block diagram showing a demodulating circuit according to the present invention in a digital terrestrial broadcasting and cable broadcasting receiver, and Fig.

3 is a detailed block diagram of the filter coefficient control unit in FIG.

DESCRIPTION OF THE REFERENCE NUMERALS

211 ... analog / digital converter 213 ... variable rate demodulator

215,217 ... SQRC filter / FFE 219,223,33 ... subtractor

221,225,32 ... slicer 227 ... DFE

229 ... FEC decoder 231 ... filter coefficient control section

31 ... threshold value generator 34 ... comparator

35 ... SQRC filter coefficient ROM table 36 ... coefficient update unit

37 ... multiplexer

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram of a digital terrestrial broadcasting and cable broadcasting receiver according to the present invention. The digital terrestrial broadcasting and cable broadcasting receiver includes an analog / digital (A / D) converter 211, a variable rate demodulator 213, The first and second subtractors 219 and 223, the first and second slicers 221 and 225, the DFE 227, the FEC decoder 229, and the filter coefficient control unit 231. The first and second SQRC filters / FFEs 215 and 217,

3 is a detailed block diagram of the filter coefficient control unit 231 shown in FIG. 2 and includes a threshold value generating unit 31, a slicer 32, a subtracter 33, a comparator 34, an SQRC filter coefficient ROM table 35, A coefficient updating unit 36, and a multiplexer 37. [0053]

Hereinafter, a demodulation circuit according to the present invention will be described with reference to FIGS. 2 and 3. FIG.

First, the FSE algorithm adopted in the SQRC filter of the present invention will be described. The FSE algorithm is an algorithm for obtaining the output of the equalizer at a symbol interval using a delay in a conventional LMS (Least Mean Square) equalizer, i.e., a delay smaller than a symbol interval by a tap interval. In a symbol interval equalizer such as an LMS equalizer, if an accurate sampling phase is not designated, a null will occur in frequency when frequency aliasing occurs. To compensate for the nulls in the frequency band, an infinite number of coefficients are needed, which increases noise. On the other hand, FSE has the following advantages. First, since the receiver can not know the information about the channel in advance, it can not directly implement the matched filter at the receiving end by calculation at the receiving end. The FSE has an ability to adaptively configure the role of the matched filter . That is, the FSE is equal to the sum of the matched filter and the cross-line equalizer. This is possible because the sampling rate of the matched filter is higher than the symbol rate. Second, the FSE is less affected by the sampling phase. Since the symbol interval equalizer uses the one after the null is generated in the frequency, if the sampling phase is wrongly selected, the noise will be amplified as well. Noise amplification leads to performance degradation. FSE does not cause frequency overlap before filtering. As a result, it is possible to automatically compensate for the influence of the sampling phase, thereby reducing the influence on the noise amplification. In addition, since the input signal is sampled so that no frequency overlap occurs, the FSE can regard the input signal as a baseband signal that has not been sampled and can calculate it. In addition, the transfer function of the FSE has the ability to adjust all information of the input signal. Therefore, even if the sampling phase is wrong at the time of sampling, the FSE has the ability to modify the information and make it into the desired spectrum when outputting. When comparing the FSE with the symbol interval equalizer with the same number of taps, the FSE has a better time interval with only half the symbol interval equalizer.

2, an analog / digital (A / D) converter 211 converts an input IF signal into a digital signal and supplies the digital signal to a variable-rate demodulator 213, The demodulator 213 demodulates the IF signal output from the A / D converter 211 while synchronizing with the symbol clock, and converts the demodulated signal into baseband I and Q signals.

The first and second SQRC filters / FFEs 215 and 217 remove noise and linear interference using the filter coefficients output from the filter coefficient control unit 231 with respect to the I and Q signals output from the variable rate demodulator 213, 1 and the second subtracters 219 and 223, respectively. The first and second subtractors 219 and 223 calculate the difference between the outputs of the first and second SQRC filter / FFEs 215 and 217 and the output of the DFE 227, respectively, and output the calculated difference to the first and second slicers 221 and 225 And the first and second slicers 221 and 225 receive the difference between the two filter outputs and discriminate the signal. The DFE 227 receives the output from the first and second slicers 221 and 225 and outputs a signal obtained by removing a post-cursor, that is, a signal received later than the reference highest signal, to the first and second subtractors 219 and 223 And the FEC decoder 229 performs forward error correction on the signals output from the first and second slicers 221 and 225. [

The filter coefficient control unit 231 is for controlling the filter coefficients of the first and second SQRC filters / FFEs 215 and 217 and the DFE 227 in accordance with the initial operation mode and the normal operation mode, The following is an explanation.

The initialization mode can be divided into an initial operation mode and a normal operation mode. The initial operation mode is an operation mode in case of channel conversion or a locking failure of a receiver. In this case, the adaptive equalizer can not converge, The operation mode starts when the errors inputted to the first and second slicers 221 and 225 fall within the allowable range.

First, the threshold value generator 31 generates a different error threshold value according to the constellation size of the modulation signal, for example, 64 QAM or 256 QAM, and supplies the error threshold value to the comparator 34 as an input signal. The slicer 32 receives the output of the FFE (215 in FIG. 2) as input and supplies the signal to the subtracter 33. The subtracter 33 calculates the difference between the discrimination value of the signal output from the slicer 32 and the discrimination value of the FFE 2 of 215) and supplies it as another input signal of the comparator 34. [

The comparator 34 compares the output of the subtracter 33 with the error threshold value output from the threshold value generator 31 and outputs a selection control signal according to the comparison result. That is, when the output of the subtracter 33 is larger than the error threshold value, since the FFE (215 in FIG. 2) is not equalized and converged, the first selection control signal corresponding to the initial operation mode is output. Is smaller than the error threshold value, that is, when the output of the subtracter 33 is within the permissible range, the second selection control signal corresponding to the normal operation mode is outputted.

The SQRC filter coefficient ROM table 35 stores coefficients for SQRC filtering and supplies it to the '0' input terminal of the multiplexer 37. The coefficient update unit 36 receives the output of the DFE (227 in FIG. 2) as input, updates the filter coefficient using the LMS algorithm, and supplies the filter coefficient to the '1' input terminal of the multiplexer 37, 215) and supplies the updated filter coefficient to the '1' input terminal of the multiplexer 37 by updating the filter coefficient by the {symbol interval (T _sym ) / 2} interval tap adaptive equalization algorithm which is the FSE algorithm.

In the initial operation mode, the multiplexer 37 selects the SQRC filter coefficient of the SQRC filter coefficient ROM table 35 supplied to the '0' input terminal and inputs it as coefficients of the first and second SQRC filters / FFEs 215 and 217 do.

In the normal operation mode, the multiplexer 37 selects the SQRC filter coefficient of the SQRC filter coefficient ROM table 35 supplied to the '0' input terminal and outputs the first and second SQRC filters / FFEs (215 and 217 in FIG. 2 ), And the DFE 227 is reset to '0' at this time. On the other hand, the multiplexer 37 selects the FFE filter coefficient and the DFE filter coefficient updated by the coefficient updating unit 36 after the first coefficient, and outputs the selected FFE filter coefficient and DFE filter coefficient to the first and second SQRC filters / FFE (215 and 217 in FIG. 2).

According to the above-described configuration, the SQRC filtering function and the FFE function are implemented as a single filter in the digital terrestrial broadcasting and cable broadcasting receiver, and the filter coefficient update is controlled according to the initial operation mode and the normal operation mode, It is advantageous that the hardware implementation can be simplified.

Claims (2)

An analog / digital converter 211 for converting an IF signal received through a channel to a digital signal; A variable rate demodulator 212 for demodulating the IF signal output from the analog / digital converter and converting the IF signal into baseband I and Q signals; First and second SQRC filters / FFEs 215 and 217 for removing noise and linear interference using baseband I and Q signals output from the variable rate demodulator using a predetermined filter coefficient; A DFE 227 for receiving a signal output from the first and second SQRC filters / FFEs and outputting a signal obtained by removing a post cursor; First and second subtractors (219, 223) for calculating a difference between an output of the first and second SQRC filters / FFEs and an output of the DFE; First and second slicers (221, 225) for determining a signal output from the first and second subtractors; An FFE decoder (229) for performing a forward error correction on a signal output from the first and second slicers; And And a filter coefficient control unit (231) for controlling the filter coefficients of the first and second SQRC filter / FFE (215,217) and the DFE (227) according to the initial operation mode and the normal operation mode. By the playback of the broadcast receiver. The apparatus of claim 1, wherein the filter coefficient control unit (231) A threshold value generator 31 for generating an error threshold value according to the constellation size of the modulation signal; An error value generation unit (32, 33) for generating an error value between a determination value of the signal output from the FFE (215) and a signal output from the FFE (215); A comparator 34 for comparing the error threshold value outputted from the threshold value generator with the error value of the error value generator and outputting a first selection control signal corresponding to the initial operation mode and a second selection control signal corresponding to the normal operation mode, ); A ROM table 35 for storing SQRC filter coefficients; A coefficient updating unit (36) for updating the filter coefficient using the output of the DFE (227) and updating the filter coefficient using the output of the FFE (215); And And a multiplexer (37) for outputting the SQRC filter coefficient stored in the ROM table or the update filter coefficient output from the coefficient updating unit to the FFE and the DFE in accordance with the first or second selection control signal output from the comparator Wherein the digital terrestrial broadcasting and the cable broadcasting receiver are provided with a digital terrestrial broadcasting and cable broadcasting receiver.