KR100744511B1 - Carrier recovery apparatus and its method in digital broadcasting receiver - Google Patents

Abstract

The present invention relates to a carrier recovery apparatus and method in a digital broadcast receiver for receiving and demodulating a signal transmitted by being modulated in a VSB scheme. In particular, the present invention frequency modulation of the pilot signal included in the baseband complex signal to a specific frequency, so that the normalization of the phase error can be easily applied, and the carrier frequency and phase can be captured and tracked even when the pilot signal is severely attenuated. Since the carrier residual phase error correction process is based on the symbol timing recovery, the phase error can be detected from both ends, so that the carrier frequency and phase can be captured even when the pilot is completely attenuated.

Fine PLL, Carrier Residual Phase

Description

Carrier recovery apparatus and method in digital broadcasting receiver

1 is a block diagram of a general digital broadcast receiver

2 is a block diagram illustrating a digital broadcast receiver according to the present invention.

3 is a block diagram showing an embodiment of a carrier recovery apparatus according to the present invention;

4A and 4B show examples of the multiplier, the prefilter, the gain control unit, and the frequency response of each step in FIG.

5 is a detailed block diagram illustrating an embodiment of a gain normalization unit according to the present invention.

Explanation of symbols for main parts of the drawings

200: VSB demodulation section 201: CFLL section

202: passband symbol timing recovery unit

203: Fine PLL section 301: complex multiplier

302 modulator 303 prefilter

304: gain control unit 305: phase error detection unit

306 loop filter 307 NCO

308: Lookup Table

The present invention relates to a digital broadcast receiver, and more particularly, to a carrier recovery apparatus and method in a digital broadcast receiver for receiving and demodulating a signal transmitted after being modulated in a VSB scheme.

In general, the ATSC A / 53 digital television standard, proposed by the Grand Alliance and adopted as the SDTV / HDTV terrestrial transmission standard in the United States and Korea, delivers payload data at 19.4 MHz over 8VSB (8 MHz) on 6 MHz channels. -level Vestigial SideBand) modulates and transmits. The VSB method modulates only the remaining part when one sideband signal of the two sidebands generated up and down about a carrier is greatly attenuated when the signal is amplitude modulated. In other words, it takes one side waveband spectrum of the baseband and transfers it to the passband to transmit the band.

In this case, when the DC spectrum of the base band is shifted to the pass band during the VSB modulation, it is converted into the tone spectrum, and this signal is often called a pilot signal. In other words, when VSB modulation is performed in a broadcasting station, a small size pilot signal is sent to the air to facilitate carrier recovery in a receiver.

According to the above specification, the data frame is composed of two fields, and each field is composed of 313 segments. The 313 segment again consists of a two-level field sync segment and 312 data segments. The first four symbols of each data segment consist of a two-level Data Segment Sync pattern.

1 is a general block diagram of a digital broadcast receiver for receiving and restoring such a VSB signal.

First, the airwave signal input to the antenna 101 is converted into a passband signal of an intermediate frequency (IF) by the tuner 102. This signal is input to the A / D converter 104 via the analog processor 103. The analog processor 103 is composed of a SAW filter for removing high frequency components generated from adjacent channel interference and a tuner, a gain control unit (AGC) for adjusting the level of an input signal, and the like.

The A / D converter 104 converts the analog passband signal output from the analog processor 103 into a digital passband signal and outputs the signal to the phase separator 105. For example, when the fixed oscillator is used in the A / D converter 104, the analog signal is converted into a digital signal having a fixed frequency.

The phase separator 105 separates the digital passband signal into a passband signal having a real component and an imaginary component whose phases are 90 ° to each other, and outputs the digital passband signal to the carrier recovery unit 106. Here, for convenience of description, the real component signal output from the phase separator 105 is called an I signal, and the imaginary component signal is called a Q signal.

The carrier recovery unit 106 transitions the I, Q digital passband signal output from the phase separation unit 105 to an I, Q digital baseband signal, and then returns to the symbol timing recovery unit 107 for symbol clock recovery. Output

The symbol timing recovery unit 107 synchronizes a clock of a transmitter and a clock of a receiver, and ultimately, a decision error at an equalizer output by sampling a baseband or passband signal at an optimal point in time. Should be operated to minimize

The output of the symbol timing recovery unit 107 is input to the channel equalizer 108. The channel equalizer 108 removes Inter-Symbol Interference (ISI) included in the signal that has passed through the symbol timing recovery unit 107 and outputs it to the phase tracking unit 109. That is, in a digital transmission system such as HDTV, a bit detection error occurs at a receiving side due to distortion caused by a transmission signal passing through a multi-path channel, interference by an NTSC signal, and distortion by a transmission / reception system. In particular, propagation of signals through multipaths causes intersymbol interference (ISI), which is a major cause of bit detection errors. Thus, the channel equalizer 108 eliminates such inter-symbol interference (ISI).

The phase tracker 109 corrects a residual phase of a carrier that is not completely removed by the carrier recovery unit 106 and outputs the residual phase to a forward error correction 110.

The FEC unit 110 corrects an error of the phase-corrected signal and outputs it to the A / V signal processor 111. That is, a transmitter such as a broadcasting station selects an appropriate technique for the system and encodes and transmits a transmission signal, and a receiver, such as a digital broadcast receiver, decodes the transmitted signal and corrects an error generated while passing through a channel. The block for performing the decoding process is the FEC unit 110.

The A / V signal processing unit 111 restores the video and audio signals compressed by MPEG-2 and Dolby AC-3 methods to their original state, and transmits the video signals to a monitor so that the screen can be viewed and the audio signal is a speaker. To be heard.

However, when using the digital broadcast receiver structure as shown in FIG. 1, there are the following problems.

First, there is a burden that the carrier recovery unit 106 must bear both acquisition and tracking with one loop filter bandwidth. That is, the capture performance and the tracking performance of the carrier recovery unit 106 are always obtained through the trade-off of loop filter parameters. A partial alternative to this problem is to apply different loop filter parameters to the acquisition and tracking modes, which often cause system instability.

Second, the performance of the timing recovery unit 107 depends on the performance of the carrier recovery unit 106. In particular, FPLL (Frequency & Phase Locked Loop), which is a carrier recovery algorithm used in the conventional structure, uses a pilot signal of the VSB spectrum. When long ghost is applied, jitter is severe due to the data pattern. You lose. This degrades the performance of the symbol timing recovery unit 107, resulting in performance degradation of the entire system.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an apparatus and method capable of accurately recovering a carrier when a pilot signal is attenuated.

Another object of the present invention is to provide an apparatus and method capable of accurately recovering a carrier even when a pilot signal is severely attenuated by a long ghost.

In order to achieve the above object, a carrier recovery apparatus of a digital broadcasting receiver according to the present invention comprises: a complex multiplier for receiving a digital passband signal in which carrier frequency components and symbol timing recovery are received and transitioning to a baseband; A pre-filter for frequency-modulating the output of the complex multiplier and filtering at least side bands in which a pilot signal exists; A phase error detector for detecting a carrier residual phase error after adjusting a gain of the signal filtered by the prefilter; And a frequency generator for generating a complex sine wave corresponding to the low band component of the carrier residual phase error and feeding it back to the complex multiplier.

(fs는 심벌 주파수)인 복소 정현파로 주파수 변조한 후 측대역을 필터링하는 것을 특징으로 한다. The pre-filter is a center frequency of the baseband complex signal output from the complex multiplier

(fs is a symbol frequency) and the frequency band modulated with a complex sine wave, characterized in that the sideband filtering.

A gain normalizer for performing complex gain normalization on the input signal may be further included in front of the phase error detector.

The gain normalization unit squares an input real signal and an imaginary signal, adds them, and takes a root of the addition result and divides the result by a constant 1; A delayer for delaying an input real signal by a processing time of the operation unit; And a multiplier configured to multiply the real signal delayed by the delay unit to the output of the operation unit and output the multiplier to the phase error detector.

In the carrier recovery method of the digital broadcast receiver according to the present invention,

(a) receiving a digital passband signal having a carrier frequency component and symbol timing recovery and transitioning to a baseband;

(b) frequency modulating the baseband complex signal of step (a) and then filtering the sideband where the pilot signal is present;

(c) detecting a carrier residual phase error after adjusting the gain of the signal filtered in step (b); And

(d) generating a complex sine wave corresponding to the low band component of the carrier residual phase error detected in step (c), and then feeding back to step (a) for baseband transitions. .

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention that can specifically realize the above object will be described. At this time, the configuration and operation of the present invention shown in the drawings and described by it will be described as at least one embodiment, by which the technical spirit of the present invention and its core configuration and operation is not limited. .

The same components as in the related art are denoted by the same names and the same reference numerals for convenience of description, and detailed description thereof will be omitted.

2 is a schematic diagram of a digital broadcast receiver according to the present invention, which has been previously filed by the present applicant (Domestic Application No .: P04-77817, filing date: September 30, 2004).

2 is a structure for improving performance of a digital broadcast receiver by preventing a carrier recovery block from affecting a symbol timing recovery block even under a severe fading channel.

That is, the analog IF signal having a center frequency of about 6 MHz or 5.38 MHz is digitized by the A / D converter 104 and then input to the coarse frequency locked loop (CFLL) unit 201 of the VSB demodulator 200. Unlike the FPLL of the prior art, the CFLL unit 201 does not track the phase component in the carrier but only tracks the frequency component of the carrier. The data passing through the CFLL unit 201 is close to the baseband signal, but may be referred to as a passband signal because it includes a residual phase of a carrier wave. When the CFLL unit 201 tracks only the frequency components of the carrier, it is possible to secure fast acquisition time during carrier recovery, thereby making it possible to quickly track the frequency of the carrier in a dynamic channel environment. In addition, by allowing the CFLL unit 201 to capture only the frequency of the carrier, it can bring a much wider pull-in characteristics than the prior art.

The data passing through the CFLL unit 201 is input to the symbol timing recovery unit 202. In this case, since the input signal includes a carrier residual phase component, the symbol timing recovery unit 202 should be designed to operate in a passband, which is referred to as pass-band TR in FIG. 2. The data passing through the symbol timing recovery unit 202 is applied to a fine phase locked loop (PLL) unit 203 to track the residual carrier phase component. Since the Fine PLL unit 203 does not have to cope with the frequency offset of the large carrier, it is possible to apply an algorithm optimized for carrier phase acquisition and tracking performance in the presence of ghosts. Therefore, it is possible to improve the performance of the digital broadcast receiver as a whole.

The present invention relates to a carrier recovery apparatus and method capable of extracting accurate carrier phase information from a signal including a carrier residual phase on the premise that symbol timing recovery is preceded. In particular, the carrier recovery apparatus of the present invention is premised on the use of a passband symbol timing recovery unit, and can be robustly operated even in the presence of carrier frequency offset of about several tens of KHz as well as carrier phase.

3 is a block diagram illustrating an embodiment of a carrier recovery apparatus according to the present invention, which is a detailed block diagram of the fine PLL unit of FIG. 2.

3 illustrates a complex multiplier 301, a modulator 302, a prefilter 303, a gain controller 304, a phase error detection (PED) unit 305, a loop filter 306, NCO (Numerically Controlled Oscillator) 307 and lookup table 308.

That is, the complex signal having the carrier frequency offset and the symbol timing frequency corrected through the coarse frequency locked loop (CFLL) unit 201 and the pass-band timing recovery unit 202 is input to the complex multiplier 301.

(fs = 10.76MHz, 심벌 주파수)인 복소 정현파로 주파수 변조하여 전치 필터(303)로 출력한다. 상기 전치 필터(303)는 주파수 변조된 신호 중에서 반송파 위상 정보를 포함하고 있는 파일롯 신호만을 추출하여 이득 제어부(304)로 출력함에 의해 패턴 지터(pattern jitter)의 양을 줄인다. The complex multiplier 301 multiplies the passband complex signal by the complex sine wave output from the lookup table 308 to convert the baseband complex signal into a baseband complex signal and outputs the result to the modulator 302. The modulator 302 converts a baseband complex signal into a center frequency.

The frequency is modulated with a complex sine wave (fs = 10.76 MHz, symbol frequency) and output to the prefilter 303. The prefilter 303 reduces the amount of pattern jitter by extracting only a pilot signal including carrier phase information from the frequency-modulated signal and outputting it to the gain control unit 304.

In this case, the strength of the sinusoidal signal passing through the prefilter 303 depends on the strength of the pilot signal. When the pilot is severely attenuated by the ghost, it is directly affected. Therefore, a gain control 304 is used to extract a phase error even when the pilot signal is attenuated by ghost. This helps to maintain consistent capture and tracking even in the presence of ghosts.

에 반송파 잔류 주파수 및 위상 옵셋의 정보를 포함하고 있다. 그러므로 상기 PED부(305)는 이러한 특성을 이용하여 간단한 제로 크로싱 검출기(zero-crossing detector)를 사용하여 구현할 수 있다. The sinusoidal wave whose gain is controlled by the gain control unit 304 is output to the PED unit 305 to detect a phase error. At this time, the sine wave input to the PED unit 305 is the center frequency

Contains information of carrier residual frequency and phase offset. Therefore, the PED unit 305 may be implemented by using a simple zero-crossing detector using this characteristic.

The phase error detected by the PED unit 305 is low-pass filtered by a loop filter 306. The low pass filtered signal output from the loop filter 306 becomes a DC component, and the DC signal is accumulated in the integrator 307 for a predetermined time and then input to the SIN / COS lookup table 308. The SIN / COS lookup table 308 corrects the carrier residual phase by outputting the complex sine wave corresponding to the output of the integrator 307 to the complex multiplier 301.

The signal whose carrier residual frequency and phase are completely restored through the complex multiplier 301 is output to the channel equalizer 108 through DC elimination and matched filtering.

In this way, the carrier residual frequency and phase are completely restored by the center frequency of the sine wave input to the PED unit 305 being 1/2 of the symbol clock frequency fs (= 10.76 MHz).

FIG. 4A illustrates a modulator 302, a prefilter 303, and a gain control unit 304. FIG. 4B illustrates frequency response characteristics of each stage that passed through each block of (a). It is shown in detail.

되는 지점에 위치할 것이다. For example, if the residual carrier frequency and the phase offset are Δ, the output of the complex multiplier 301 of the fine PLL unit 203 has a frequency response as shown in 401 of FIG. 4B. That is, if the symbol clock is already restored in the timing recovery unit 202, the pilot signal is located at a distance Δ from DC as shown in 401 of FIG. 4 (b), and the upper side band of the spectrum is

Will be located at that point.

과 Δ인 곳에 각각 위치하게 된다. When this signal is frequency modulated by the modulator 302 to -fs / 2, the pilot signal and the upper sideband signal have the frequency response of 402 in FIG.

And Δ respectively.

In this case, assuming that the symbol clock is restored, both sideband signals have carrier frequency and phase offset information, but the pilot signal is mainly used in the present invention. However, this is only one implementation and may use the top sideband simultaneously or auxiliary.

Meanwhile, in order to reduce the amount of data pattern jitter included in the pilot signal frequency modulated by the modulator 302, only the vicinity of the pilot signal in the prefilter 303 is prefiltered as shown in the 403 frequency response of FIG. filtering).

로 변조하여 사용한다. 상기 전치 필터(303)는 데이터 패턴 지터의 양을 줄이기 위해 유한 임펄스 응답(FIR) SRC 필터를 사용하는 것을 실시예로 한다. In this case, the prefilter 303 has a square root rising cosine having the same roll-off factor as that used by the transmitter, as indicated by the dotted line in the frequency response 402 of FIG. root Raised Cosine (SRC) filter

Modulate with The prefilter 303 uses a finite impulse response (FIR) SRC filter to reduce the amount of data pattern jitter.

In the present invention, the symmetrical filtering of the sidebands using the FIR SRC filter as the prefilter 303 is just an example of implementation, and similar performance may be obtained by using an IIR type passband filter. However, in the case of the IIR type, a small amount of DC is applied to the carrier phase error. When the pilot signal is severely attenuated and the information of the error is very small, the loop is affected by this DC value which is not related to the actual phase error. Receiving may occur.

The sine wave in the vicinity of the pilot extracted by the prefilter 303 is input to the gain control unit 304, and the gain is controlled and then output to the PED unit 305.

In this case, since the carrier recovery apparatus of the present invention uses the pilot signal and the sideband of the spectrum, it is affected by the degree of attenuation at both ends of the spectrum. In other words, when a pilot signal or spectrum sideband is attenuated by a channel, the magnitude of the PED input sinusoid is attenuated, and thus the magnitude of the phase error is also reduced at the same time. In this case, the carrier frequency and phase recovery time become too long or, in the severe case, recovery is impossible.

Accordingly, in order to prevent this, the present invention proposes a carrier error gain normalization unit as shown in FIG. 5, and is disposed at an output terminal of the prefilter 303 or the gain control unit 304 in one embodiment.

The carrier error gain normalization unit of FIG. 5 includes a complex squarer 501, a divider 502, first and second delayers 503 and 504, and first and second multipliers 505 and 506.

For example, if the complex input signal of the carrier error gain normalization unit is C, the carrier error gain normalization unit generates gain normalization by performing gain normalization as shown in Equation 1 below. 305).

If the complex output signal of the prefilter 303 is C (= I + jQ), 1 / | C | is obtained through the complex squarer 501 and the divider 502.

That is, the real signal I output from the prefilter 303 is input to the complex squarer 501 and the first delayer 503, and the imaginary signal Q is the complex squarer 501 and the second. Input to delayer 504.

The complex squarer 501 squares each of the real signal I and the imaginary signal Q, adds them (I ² + Q ² ), and outputs them to the divider 502. The divider 502 loops the output of the complex squarer 501 and outputs the result to the first and second multipliers 505 and 506 using this value as a denominator. That is, the complex squarer 501 and the divider 502 output 1 / | C | of Equation 1, and the blocks 501 and 502 may be implemented using a pre-calculated ROM table. The first and second delayers 503 and 504 delay the real signal I and the imaginary signal Q by the processing time (= clock) of the complex squarer 501 and the divider 502, respectively. Outputs to the first and second multipliers 505 and 506.

The first multiplier 505 multiplies the output 1 / | C | of the divider 502 by the delayed real signal I to output a gain normalized real signal Cnorm, I, and the second multiplier 506 The output 1 / | C | of the divider 502 is multiplied by the delayed imaginary signal Q to output a gain normalized imaginary signal Cnorm, Q.

The normalized sinusoids obtained through the first and second multipliers 505 and 506 are superior to the method of increasing the gain when the average power is small by obtaining the average power of the existing input sinusoid. In other words, in order to accurately calculate the average power, it is necessary to take an average with more samples. In this case, since the delay time is increased, the performance may be degraded when the channel change is fast. In contrast, the complex gain normalization method of the present invention normalizes the complex envelope of the input sinusoid to 1 without delay, and thus is more suitable in a situation in which fast adaptation such as carrier phase tracking is required.

In addition, the carrier recovery apparatus according to the present invention has less performance deterioration for attenuation of a pilot signal due to a long ghost than a conventional FPLL. In addition, even when the pilot is attenuated by ghost, carrier phase acquisition and tracking performance are excellent by applying the carrier error gain normalization unit. The FIR SRC filter used as a prefilter to reduce jitter caused by data can be replaced by an IIR passband filter to reduce implementation complexity and loop delay. The carrier error gain normalization unit may be replaced by another method such as a method using average power. The PED can be applied without any significant difference in performance if it is a general zero-crossing detector. For example, a modified Gardner type PED which is mainly used as a TED (Timing Error Detector) may be used.

And a data communication system typically consists of a transmission path between a transmitter, a receiver and a transmitter / receiver. Although the present invention can be applied to various communication systems, the present invention has been described in accordance with the HDTV terrestrial transmission method. This is only one example of a communication system and can be applied to many other communication fields.

On the other hand, the terms used in the present invention (terminology) are terms defined in consideration of the functions in the present invention may vary according to the intention or practice of those skilled in the art, the definitions are the overall contents of the present invention It should be based on.

The present invention is not limited to the above-described embodiments, and as can be seen in the appended claims, modifications can be made by those skilled in the art to which the invention pertains, and such modifications are within the scope of the present invention.

The effects of the carrier recovery apparatus and method of the digital broadcast receiver according to the present invention described above are as follows.

First, by modulating the pilot signal, normalization of phase error can be easily applied, and even when the pilot signal is severely attenuated, the carrier frequency and phase can be captured and tracked.

Second, the performance of long ghost is better than the existing FPLL using pilot.

Third, by reconstructing symbol timing, phase error can be detected from both ends, so that carrier frequency and phase can be captured even when the pilot is completely attenuated.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (8)

A complex multiplier for receiving a digital passband signal in which frequency component recovery and symbol timing recovery of the carrier are input and shifted to the baseband; The center frequency of the output of the complex multiplier

a pre-filter for frequency-modulating a complex sine wave (fs is a symbol frequency) and filtering sidebands in which a pilot exists; A phase error detector for detecting a carrier residual phase error after adjusting a gain of the signal filtered by the prefilter; And And a frequency generator for generating a complex sine wave corresponding to the low band component of the carrier residual phase error detected by the phase error detector and feeding it back to the complex multiplier. delete The method of claim 1, wherein the pre-filter is A square root rising cosine (SRC) filter with the same roll-off factor as used at the transmitter

The carrier recovery apparatus characterized in that for filtering the sideband after frequency modulation. The method of claim 1, A gain normalizer for performing complex gain normalization on an input signal is further included in the front end of the phase error detector; The gain normalization unit An arithmetic unit for multiplying the input real signal and the imaginary signal by adding squares and taking the root of the addition result and dividing by a constant 1; A delayer for delaying an input real signal by a processing time of the operation unit; And And a multiplier configured to multiply the real signal delayed by the delay unit to the output of the operation unit and output the multiplier to the phase error detector. The method of claim 1, wherein the phase error detection unit And a carrier residual phase error is detected through zero crossing of the input signal. (a) receiving a digital passband signal having frequency component recovery and symbol timing recovery of a carrier and transitioning to a baseband; (b) frequency modulating the baseband complex signal of step (a) and then filtering at least sidebands in which the pilot signal is present; (c) detecting a carrier residual phase error after adjusting the gain of the signal filtered in step (b); And (d) generating a complex sine wave corresponding to the low band component of the carrier residual phase error detected in step (c) and feeding back to the step (a) for baseband transitions. Carrier Restoration Method. The method of claim 6, wherein step (b) The baseband complex signal output in step (a) has a center frequency

and frequency-modulating the complex sine wave (fs is a symbol frequency) and filtering the sideband including the pilot signal. The method of claim 6, wherein step (c) (c-1) multiplying the input real and imaginary signals by square and adding a root of the addition result and dividing by a constant 1; And (c-2) delaying the input real signal by a predetermined time, multiplying the result of the operation of step (c-1), and outputting the carrier residual phase error to be detected. Way.

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