KR100697526B1 - Tracking device for digital broadcast receiver - Google Patents

Abstract

A tracking apparatus for a digital broadcast receiver according to the present invention is a tracking apparatus for a digital broadcast receiver, comprising: a frequency corrector for performing compensation on a digital signal component input by a frequency tuning signal; Frequency FFT processing unit interpolates the frequency-converted data in the time direction, interpolates the frequency-converted data in the frequency direction, calculates the channel response in all the frequency indexes, divides the input frequency data, and performs equalization FFT window timing tracking means for calculating the power of each channel response by outputting the time interpolation in the equalizing means and outputting an index value having the largest power; The frequency of the data It characterized in that it comprises an application timing synchronization in the FFT processing in temporal synchronization of the timing component.

According to the present invention, in order to extract FFT window timing information, it is possible to continuously detect FFT window timing by detecting an index having a maximum power based on the output power of the equalizer.

Description

TECHNICAL FIELD [0001] The present invention relates to a tracking device for a digital broadcast receiver,

1 is a block diagram showing a tracking apparatus of a conventional digital broadcast receiver.

2 is a transmission diagram of an OFDM symbol.

3 is a layout diagram of distributed pilots of a digital broadcast receiver;

4 is a configuration diagram for extracting a time response using a conventional IFFT.

5 is a block diagram illustrating a tracking apparatus of a digital broadcast receiver according to the present invention.

FIG. 6 is a detailed configuration diagram of an equalizer and an FFT window timing tracking unit in FIG. 5 of the present invention. FIG.

7 is a diagram showing a guard interval showing the relationship between time response and frequency interpolation for the present invention.

Description of the Related Art

101.201 ... tuner block 102,202 ... A / D converter

103, 203 ... I / Q generating units 104, 204 ... frequency compensator

105, 205, ... FFT processing units 106, 206,

107, 207 ... demapper 108, 208 ... internal interleaver

109, 209 ... FEC 110, 211 ... timing synchronization unit

111,212 ... AGC 112,213 ... frequency tuner

113, 214 ... clock synchronization unit 114, 215 ... VCO

121 ... pilot extracting unit 122 ... IFFT

123 ... FFT window generation unit 210 ... FFT window timing tracking unit

206a ... Time interpolator 206b ... Frequency interpolator

206c ... frequency divider 210a ... phase rotator

210b ... Digital filter 210c ... Power calculation unit

210d,

The present invention relates to a tracking device for a digital broadcast receiver, which is capable of continuously extracting information necessary for simple hardware in FFT window timing recovery in a digital receiver.

Currently, the DVB-T system has recently been decided to be the next generation terrestrial digital broadcasting system in Europe. Currently, it has started trial broadcasting and parts development in European countries, and divides terrestrial digital market together with US terrestrial standard .

Considering that the DVB-T standard is a terrestrial wave in the modulation / demodulation scheme, it adopts the OFDM scheme, which is quite different from DVB-S and DVB-C using QPSK and QAM. Unlike general single carrier modulation and multicarrier modulation, in which information is continuously transmitted on the time axis, the OFDM scheme distributes information to a plurality of frequencies and transmits the information to a plurality of channels, Channels and the like.

The Orthogonal Frequency Division Multiplex (OFDM) is a simple equalizer with a single tap, and can cope with severe frequency selective fading by multipath. By setting a guard interval between adjacent OFDM symbols, interference (ISI: Inter Symbol Interference and Inter Carrier Interference (ICI) can be eliminated. Currently, systems using OFDM include Digital Audio Broadcasting (DAB) and Asymmetric Digital Subscriber Line (ADSL).

The configuration of a conventional digital receiver is shown in Fig.

Referring to FIG. 1, a tuner block 101 receives an OFDM-modulated bitstream of a baseband signal, tunes a desired channel and outputs the modulated bitstream at an intermediate frequency, and a demodulator 102 for converting an analog signal output from the tuner block 101 into a digital signal And an I / Q generator (I / Q) generator 102 for generating the digital signal output from the A / D converter 102 as an inphase (I) and quadrature (Q) A frequency corrector 104 for compensating for the inphase and quadrature components by a frequency tuning signal AFC and a fast Fourier transformer 104 for converting the inphase and quadrature components output through the frequency corrector 104 into a frequency, An equalizer 106 for equalizing the data frequency-converted by the FFT processor 105, and an equalizer 106 for equalizing the data equalized by the equalizer 106 according to the modulation scheme, A demapper (107) for associating the demapper (107) with an original bit, An inner deinterleaver 108 and a forward error correction (FEC) 109 for detecting and correcting an error on a bit stream generated during transmission of a demapped signal in the IFFT processor 105 An AGC (Auto Gain Controller) 111 for adjusting a received signal by applying a signal output from the frequency corrector 104 to the tuner block 101, A frequency tuner 112 for receiving the data output from the FFT processor 105 and performing automatic frequency control for the data, a clock synchronizer 113 for synchronizing the clock synchronous signal, and an A / D converter And a VCO (Voltage Control Oscillator)

 The tracking apparatus of the conventional digital broadcast receiver configured as above will be described with reference to the accompanying drawings.

First, the OFDM signal received by the tuner block 101 is input to the A / D converter 102 as an RF modulated baseband signal and is converted into a digital signal. The digital signal is input to the I / Q generator 103 (I) and quadrature (Q) components of the inphase (I) component and the quadrature (Q) component are generated by the frequency corrector 104 And is input to the FFT processing unit 105, the timing synchronization unit 110, and the AGC 111 after being corrected by an automatic frequency control component (AFC).

The FFT processor 105 converts the inphase and quadrature components into frequency components and outputs them to the equalizer 106. The timing synchronization unit 110 generates a start pulse of the FFT processor 105 using the in- And the AGC 111 adjusts the received signal by applying the AGC_IF signal to the tuner block 101. [

These frequency components are equalized in the equalizer 106 and then input to the demapper 107 to correspond the symbols to the original bits according to the modulation scheme (DQPSK, QPSK, QAM, etc.). This signal is deinterleaved and decoded by the internal deinterleaver 108 and the forward error correction unit 109 so that the mode in which the OFDM signal is transmitted from the transmitter to the receiver is a bit stream Find or correct errors on

The frequency component converted from the FFT processing unit 105 is input to the AFC 112 and the clock synchronization unit 113 so that the AFC 112 applies the frequency component to the frequency corrector 104 for tuning the frequency components, The clock synchronization unit 113 generates a clock signal at the VC0 114 and applies the clock signal to the A / D converter 102 in order to synchronize the clock signal.

This symbol timing recovery in the OFDM scheme is quite different from the symbol concept in single carrier modulation. That is, in a single carrier method, since each symbol in a time component becomes one information unit, its timing recovery eventually results in recovery of the sampling time, and phase and frequency synchronization are usually performed by a PLL (Phase Lock Loop) As shown in Fig.

On the other hand, the concept of an OFDM symbol in the OFDM scheme is a unit composed of samples of FFT points (usually several thousands or more), and a timing synchronization unit 110 for searching for a starting point of the FFT processing unit 105 Timing synchronization is referred to as FFT window timing recovery and is separate from sampling frequency recovery of the A / D converter 102.

2 is a diagram showing a transmission structure of an OFDM symbol and an FFT window timing. One OFDM symbol includes guard data (guard data, generally 1/2 of a useful section) which is useful for an effective data interval of FFT size and orthogonalization under a multipath channel, 4 to 1/32).

This guard interval interval is one of the key standards of the OFDM scheme. In the multi-path environment, which is the most common characteristic of the terrestrial wave, the OFDM symbol orthogonality is maintained by eliminating the inter-symbol interference (ISI) It plays a role.

If the orthogonality of the OFDM signal is undermined, the signal processing after the FFT processing unit 105 is seriously hindered, thereby significantly degrading system performance. Therefore, it is very important to acquire the FFT window timing at the receiver so that the ISI is minimized.

If there is no multi-path, the entire interval of the guard interval may be a fine window timing as shown in FIG. However, if the channel is complex, it is not obvious to acquire proper window timing in the case of mobile reception, in which the main signal may not exist, and it may have a large effect on the performance of the system.

Such FFT window timing recovery can be divided into an initial acquisition mode (Acquisition Mode) and a tracking mode (Tracking Mode) as well as single carrier modulation. The initial acquisition mode is the first synchronization process in the receiver, followed by synchronization and signal processing at the end of the FFT. On the other hand, the tracking process is a process in which the system keeps track of the timing during normal operation (ready state), and tracks that the multi-pass channel response, which is the main characteristic of the terrestrial channel, changes in time.

For this purpose, as an approach for tracking, an algorithm may be used as well as a trap phase in a time component. An injection pilot signal used in the equalizer unit 106, which receives the frequency component, is IFFT-processed and analyzed in time components There is a way.

The time domain analysis method will be described in more detail as follows. In the DVB-T scheme, a scattered pilot as shown in FIG. 3 must be applied in order to perform channel equalization. The channel response (in the frequency domain) is derived from the scattered pilot through interpolation, and the data applied with this value is complex divided to perform equalization.

4, the pilot detection unit 121 includes an IFFT 122 and an FFT window generation unit 123. The pilot detection unit 121 receives the output of the FFT processing unit 121, Frequency domain channel response (FDCR), and when the channel response is converted to time component data through an IFFT (Inverse FFT) 122, a time domain component (TDCR) Response can be obtained.

When the time response is derived through this process, the optimum timing can be calculated and corrected based on various criteria.

However, even though only a scattered file is required, IFFT 122 must be performed again in order to find the time response component (TDCR) of the channel. Therefore, when processing in the IC without being processed offline in the processor or the like, it is necessary to embed the IFFT for timing recovery in addition to the built-in FFT processor 104, which makes hardware implementation difficult.

In addition, if the FFT window timing recovery is not properly performed, if FFT is performed by generating inter-symbol interference (ISI), the orthogonality is degraded, thereby reducing the amplification of the channel response and increasing the noise. If the channel response is out of the guard interval, it becomes an ISI factor, which degrades the performance of the system. As a result, the overall system performance There is a problem of deterioration.

SUMMARY OF THE INVENTION The present invention has been conceived to solve the above-mentioned problems, and it is an object of the present invention to provide a method and an apparatus for estimating optimal timing information by using output power of a channel equalizer as a reference and estimating FFT window timing by complex output of time interpolation of the channel equalizer And it is an object of the present invention to provide a tracking device for a digital broadcast receiver for extracting necessary information.

According to another aspect of the present invention, there is provided a tracking apparatus for a digital receiver,

A tracking apparatus for a digital broadcast receiver,

A frequency corrector for performing compensation on a digital signal component input by the frequency tuning signal,

An FFT processor for converting the data outputted through the frequency corrector into a frequency,

Equalizing means for interpolating the frequency-converted data in the time domain by the FFT processor, interpolating the frequency-domain data again in the frequency domain to calculate a channel response in all the frequency indexes,

FFT window timing tracking means for calculating the power of each channel response by outputting the time interpolation in the equalizing means and outputting an index value having the largest power,

And a timing synchronization unit for applying a timing synchronization of a data component input from the frequency corrector to an FFT processor according to an index value input from the FFT window tracking unit.

Here, the equalization means includes a time interpolator for receiving the output of the FFT processor and interpolating the scattered pilot in a time-domain channel response of about 1/3, and interpolating the scattered pilot interpolated by the time interpolator in the frequency domain A frequency interpolator for calculating a channel response at every frequency index and a frequency divider for dividing the output data of the FFT processor in response to the channel response calculated by the frequency interpolator.

The FFT window timing tracking means includes a phase rotator for sweeping a time-component response of the time-averaged channel response output from the equalizer on a time axis, and an output swept from the time axis by the phase rotator to a bandwidth a power calculator for outputting each of the outputs filtered by the digital filter with a power according to a frequency index value with respect to a time offset; And a comparator for calculating power by varying a time offset with respect to a preset sweeping range of the power calculated by the comparator and outputting the index having the largest power value as an optimal time offset to the timing synchronization unit.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

FIG. 5 is a block diagram showing a tracking apparatus of a digital broadcast receiver according to the present invention, FIG. 6 is a detailed configuration diagram of an equalizer and an FFT window timing tracking unit according to the present invention, FIG. 7 is a time- And the guard interval showing the relationship with the frequency interpolation.

Referring to FIG. 5, a tuner block 201 receives an OFDM-modulated bitstream of a baseband signal and tunes a desired channel to output the modulated bitstream at an intermediate frequency. The tuner block 201 converts an analog signal output from the tuner block 201 into a digital signal And an I / Q generating unit 202 for generating a digital signal output from the A / D converting unit 202 as an in-phase (I) and quadrature (Q) A frequency corrector 204 for compensating for the in-phase component and quadrature component of the digital signal by a frequency tuning signal AFC, an FFT (FFT) 204 for converting the data component output through the frequency corrector 204 to a frequency A Fast Fourier Transform (FFT) processing unit 205, and an FFT processing unit 205. The FFT processing unit 205 interpolates the frequency-converted data in the time direction, interpolates the data in the frequency direction again, calculates channel responses in all frequency indexes, Divide An FFT window timing tracking unit 206 for calculating the power of each channel response by the output of the time interpolation of the equalizer 206 and outputting an index value having the largest power, And a timing generator 210 for generating a timing signal to be applied to the FFT processing unit 205 by timing synchronization of the inphase and quadrature components input from the frequency corrector 204 according to an index value input from the FFT window timing tracking unit 210. [ And a synchronization unit 211.

Here, the equalizer 206 includes a time interpolator 206a that receives the output of the FFT processor 205 and interpolates the scattered pilot in the time direction, and a frequency interpolator 206b that interpolates the time- And a frequency divider 206c for dividing the output data of the FFT processing unit 205 in response to the channel response calculated by the frequency interpolating unit 206b.

The FFT window timing tracking unit 210 includes a phase rotator 210a for sweeping a time component response of the output channel of the time interpolator 206a on the time axis, A digital filter unit 210b for filtering the swept output on the time axis by a low-order filter equal to the bandwidth of the frequency interpolation, and a digital filter unit 210b for filtering the output filtered by the digital filter unit 210b, Calculating a power by changing a time offset with respect to a sweeping range preset in the power calculated by the power calculating unit 210c, and calculating a power of the largest power And a comparison unit 210d for outputting an index having a value as an optimal time offset to the timing synchronization unit 211. [

Reference numeral 207 denotes a demapper, 208 denotes an internal deinterleaver, 209 denotes a forward error correction unit (FEC), 212 denotes an AGC, 213 denotes an AFC, 214 denotes a clock synchronization unit, and 215 denotes a VCO.

Hereinafter, a tracking apparatus for a digital broadcast receiver according to the present invention will be described with reference to the accompanying drawings, and redundant description of the same parts as those of the conventional art will be omitted.

The OFDM signal received by the tuner block 201 is input to the A / D converter 202 as an RF modulated baseband signal and is converted into a digital signal. The digital signal is input to the I / Q generator 203 The in-phase (I) component and the quadrature (Q) component are divided into an inphase (I) component and an orthogonal (Q) component by the frequency corrector 204, And then input to the FFT processing unit 205, the timing synchronization unit 211, and the AGC 212.

The FFT processing unit 205 converts frequency-corrected data of the inphase and quadrature components into frequency components, and outputs the frequency components to the equalizer 206, the AFC 213, and the clock synchronizer 214. At this time, the equalizer 206 interpolates the frequency-converted data in the time domain by the FFT processor 205, interpolates the frequency-domain data again in the frequency domain, calculates the channel response in all the frequency indexes, divides the input frequency data, .

For this, the equalizer 206 includes a time interpolator 206a, a frequency interpolator 206b, and a frequency divider 206c. The time interpolator 206a receives the output of the FFT processor 205 Interpolates the scattered pilot in the time direction and interpolates the scattered pilot signal in the frequency direction in the frequency interpolator 206b to calculate the channel response in all the frequency indexes and the frequency divider 206c calculates the channel response in the frequency interpolator 206b The output data of the FFT processing unit 205 is divided into equal parts by the channel response calculated by the channel response.

Here, the time interpolator 206a interpolates the dispersion pilot of FIG. 3 in the time direction to extract a channel response of about 1/3 of all points. The frequency interpolating unit 206b filters out the extraction response with a multi-tap digital filter to perform frequency component interpolation and obtains a final response to compensate for all linear distortions. Also, no distortion occurs during equalization if all the channel responses are accommodated within the bandwidth of the digital filter.

This equalization distortion is generally such that the orthogonality of the FFT is not impaired in the channel response. Therefore, in the case of the timing response, the distortion due to erroneous estimation of the channel response in the channel estimator is much more serious than the problem caused by the ISI The possible channel responses are matched within the bandwidth of the frequency interpolation.

5 is a guard interval in which the time response of the channel is compared with the bandwidth of the frequency interpolation. As shown in the figure, the channel response moves in the time axis according to the FFT start timing of the FFT processing unit 205, and is valid only from 0 to the guard interval. The reason for this is that if the validity interval deviates from the validity period, it becomes an ISI factor and deteriorates the system performance. Therefore, a time response must come in the validity interval.

In addition, the bandwidth of the frequency response is designed to be narrower than the guard interval at a line that does not exceed the guard interval because if the bandwidth is widened, the response to a relatively long ghost (time-wise multi-path) Instead, it contains a lot of noise, which degrades the SNR (Signal to Noise Ratio) in the equalized block. Therefore, the bandwidth is fixed or variable within the guard interval.

On the other hand, the FFT window timing tracking unit 210 uses a point for maximizing the output power of the time interpolating unit 206a of the equalizer 206 as a criterion for determining an optimum timing to track an optimal FFT start point .

That is, the FFT window timing estimator 210 calculates the power of each channel response by the output of the time interpolator 206a of the equalizer 206, and outputs the index value having the largest power to the timing synchronization unit 211 ).

와 같이 주파수 인덱스 값(k)에 따라 로테이션 양이 선형적으로 증가하는 위상 로테이션(phase rotation) 형태로 나타난다.The phase rotator 210a includes a phase rotator 210a, a digital filter 210b, a power calculator 210c and a comparator 210d. The phase rotator 210a includes a time- The influence of the sweep time offset for optimal time tracking is obtained as frequency data to calculate the channel response power of the branch 206a. That is, in order to obtain the power within the filter bandwidth with respect to the temporal offset in FIG. 7, the time component response of the channel must be swept in the time domain. This is because the variation (n) and the FFT size (N) in the frequency axis (F)

The phase rotation is linearly increased according to the frequency index value k.

이므로 인덱스 값(k)에 대해 파워를 계산한다.The output of the phase rotation 210a is input to a digital filter 210b and the digital filter 210b is composed of a low-pass filter substantially equal to the bandwidth of the frequency interpolator 206b. The output of the digital filter 210b is input to the power calculator 210c and values corresponding to the frequency index value k are output for one time offset value n. In other words,

, The power is calculated for the index value (k).

When the output of the power calculation unit 210c is input to the comparison unit 210d, the comparison unit 210d calculates the power by changing the time offset value for the previously set sweeping range, Estimates the index value (n) as an optimal time offset, and outputs it to the timing synchronization unit 211.

The timing synchronization unit 211 synchronizes timing of the inphase and quadrature components input from the frequency corrector 204 according to the index value input from the FFT window timing tracking unit 210, ). This uses the index with the maximum power to estimate the power with an appropriate criterion without having to find the time response with the most time response within the effective bandwidth.

Another embodiment of the present invention uses a point that maximizes the power of the frequency interpolator 206b output as a criterion for determining an optimal timing to track the optimal FFT start point in the FFT window timing tracking unit 210. [ This is because not only the most accurate value can be derived by feeding back the output of the frequency interpolator 206b in which the channel response is actually used, but also because it can be said that the most time response is maximized by setting the power within the effective bandwidth Standard. In addition, since the power is estimated rather than directly obtaining the time interpolation through the IFFT, the hardware for extracting the necessary information from the frequency component can be implemented, which simplifies the hardware.

Therefore, since the power calculation value in the time component and the power calculation value in the frequency component are theoretically the same, it is possible to utilize the power of the output of the time interpolator 206a or the output of the frequency interpolator 206b as much as possible.

As described above, when performing the FFT window time tracking of the DVB-T receiver according to the present invention, by using the reference for maximizing the output power of the equalizer, There is an effect that information necessary for time tracking can be extracted to enable continuous tracking.

In addition, the present invention can be applied to all OFDM transmission systems, resulting in efficient tracking with a simpler system.

Claims (3)

A tracking apparatus for a digital broadcast receiver, A frequency corrector for performing compensation on the inphase and quadrature components of the digital signal component input by the frequency tuning signal, An FFT processor for converting the data outputted through the frequency corrector into a frequency, Equalizing means for interpolating the frequency-converted data in the time domain by the FFT processor, interpolating the frequency-domain data again in the frequency domain to calculate a channel response in all the frequency indexes, FFT window timing tracking means for calculating the power of each channel response by outputting the time interpolation in the equalizing means and outputting a frequency index value having the largest power, A tracking device of the digital broadcast receiver characterized in that it comprises a timing synchronization unit for applying FFT processing to a time of the timing synchronization of the data element received from the frequency compensator according to an index value that is input from the FFT window tracking unit. The method according to claim 1, Wherein the equalization means comprises: a time interpolator for receiving the output of the FFT processor and interpolating the scattered pilot in a time domain with a channel response of about 1/3; and an interpolator for interpolating the scattered pilot interpolated by the time interpolator in the frequency direction A frequency interpolator for calculating a channel response in the frequency index; and a frequency divider for dividing output data of the FFT processor in response to the channel response calculated by the frequency interpolator. The method according to claim 1, Wherein the FFT window timing tracking means comprises: a phase rotator for sweeping a time-component response of the time-averaged channel response output from the equalization means on a time axis; and a frequency- A power calculator for outputting each of the outputs filtered by the digital filter with a power according to a frequency index value with respect to a time offset; And a comparator for calculating power by varying a time offset with respect to a preset sweeping range of the calculated power and outputting the index having the largest power value to the timing synchronization unit as an optimal time offset. .

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