KR20080088308A - Apparatus for recovering carrier wave in digital broadcasting receiver and method therefor - Google Patents

Abstract

An apparatus for recovering a carrier wave in a digital broadcasting receiver and a method thereof are provided to compensate a frequency offset of the carrier wave by using a complex signal at a baseband independently of a pilot signal to recover the carrier wave, thereby obtaining improved carrier wave recovery capability even in a selective fading environment to improve the performance of the digital broadcasting receiver. An apparatus for recovering a carrier wave in a digital broadcasting receiver includes a phase divider(170), a downsampler(250), and a carrier wave recovery unit(190). The phase divider receives a digitally converted pass band signal, divides the pass band signal into pass band complex signals of actual and imaginary number components with different phases, and outputs the pass band complex signals. The downsampler samples and outputs the complex signal at a baseband outputted through the phase divider in the same frequency as a symbol frequency. The carrier wave recovery unit receives the complex signal outputted from the downsampler, multiplies the complex signal by a complex sine wave, of which a center frequency is 1/n of the symbol frequency, to create an OQAM(Offset-Quadrature Amplitude Modulation) signal of actual and imaginary number components, calculates a phase error value from the OQAM signal, creates a complex sin wave for compensating the calculated phase error value, multiplies the complex signal outputted from the phase divider by the complex sine wave, and converts the complex signal into a baseband signal in which a frequency offset is compensated.

Description

Apparatus and method for recovering carrier of digital broadcasting receiver {APPARATUS FOR RECOVERING CARRIER WAVE IN DIGITAL BROADCASTING RECEIVER AND METHOD THEREFOR}

1 is a block diagram showing a carrier recovery apparatus of a digital broadcast receiver according to the prior art.

FIG. 2 is a diagram illustrating a detailed configuration of a carrier restoration unit and a symbol timing restoration unit of FIG. 1.

3 is a circuit block diagram showing a carrier recovery apparatus of a digital broadcast receiver according to an embodiment of the present invention.

4 is a diagram illustrating a detailed configuration of a carrier restorer and a symbol timing restorer of FIG. 3 according to an embodiment of the present invention.

5 is a view showing a detailed configuration of a symbol timing restorer applied to the present invention.

6A and 6B are flowcharts illustrating a carrier recovery process according to an embodiment of the present invention.

7A to 7G are diagrams illustrating signal spectra output from respective elements of FIG. 4.

8 is a diagram illustrating the configuration of a carrier recovery unit and a symbol timing restoration unit according to another embodiment of the present invention.

* Explanation of symbols for the main parts of the drawings

150: A / D converter 170: phase separator

190: carrier recovery unit 191: complex multiplier

193: OQAM signal generator 195: phase error detection unit

197: second downsampler 199: upsampler

201: loop filter 203: adder

205: NCO 210: Symbol Timing Restoration Unit

211: resampler 213: passband timing error detection unit

215: loop filter 217: numerically controlled oscillator

230: matching filter 250: downsampler

270: DC eliminator

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for correcting a symbol timing and a frequency offset of a carrier, and in particular, in a digital broadcast receiver receiving a broadcast sideband (VSB) modulated broadcast signal, correcting a frequency offset of a carrier without depending on a pilot signal. The present invention relates to a carrier recovery apparatus and a method for recovering a carrier by a digital broadcast receiver.

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 8-VSB on 6 MHz channels. It is based on the modulation and transmission to (8-level Vestigial SideBand). 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.

At this time, when the baseband DC spectrum is shifted to the passband during the VSB modulation, it is converted into a tone spectrum, and this signal is often referred to as a pilot signal. That is, when VSB modulation is performed in a broadcasting station, a pilot signal of a small size is loaded on the receiver to facilitate carrier recovery.

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

First, the airwave RF signal input to the antenna is converted into a passband signal of intermediate frequency (IF) in the tuner 11, and the passband signal is analog signal processed via the IF processor 13. It is then input to the A / D converter 15. The IF processor 13 includes a SAW filter for removing high frequency components generated from interference and tuners of adjacent channels, a gain controller (AGC) for adjusting the level of an input signal, and the like.

The A / D converter 15 converts the analog passband signal output from the IF processor 13 into a digital passband signal and outputs the signal to the phase separator 17. For example, when the fixed oscillator is used in the A / D converter 15, the analog signal is converted into a digital signal having a fixed sampling frequency (25 MHz).

The phase separator 17 converts a digitally transformed passband signal into a complex signal (I signal, Q signal). The phase separator 17 separates the carrier band by separating the passband signals of real and imaginary components whose phases are 90 서로 to each other. Output to the restoration unit 19.

The carrier recovery unit 19 converts the passband complex signal output from the phase separator 17 into a baseband complex signal and outputs the signal to the symbol timing restoration unit 21 for symbol clock recovery.

The symbol timing restoration unit 21 serves to synchronize the clock of the transmitter and the clock of the receiver, and ultimately, by sampling the baseband or passband signal at an optimum point in time, at the output of the channel equalizer 27. It should be operated to minimize decision error.

The output of the symbol timing restorer 21 passes through the matched filter 23. The matched filter 23 uses a square root cosine filter having a roll-off factor. The output signal of the matched filter 23 is a DC eliminator. After passing through 25, the pilot signal is removed and input to the channel equalizer 27.

The channel equalizer 27 removes the inter-symbol interference (ISI) included in the signal passing through the symbol timing restoring unit 21 and outputs it to the phase tracker 29. That is, in a digital transmission system such as HDTV, a bit detection error is caused at the 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 27 eliminates this inter-symbol interference (ISI).

The phase tracker 29 corrects the residual phase of the carrier that is not completely removed by the carrier restorer 19 and outputs the frequency to the frequency error corrector 31.

The frequency error corrector 31 corrects the error of the phase-corrected signal and outputs it to the A / V processor 33. The A / V processor 33 restores the video and audio signals compressed by the MPEG-2 and Dolby AC-3 schemes to the original state, and transfers the video signals to the monitor 37 so that the screen can be viewed. Is transmitted to the speaker 39 so that the sound can be heard.

2 illustrates an example of the carrier recovery unit 19 and the symbol timing restoration unit 21 of FIG. 1 according to the prior art.

The carrier recovery unit 19 is composed of a frequency and phase locked loop (FPLL) system that simultaneously performs frequency acquisition and tracking using a pilot signal. The process of restoring a carrier using the pilot signal will be described below. same.

First, a phase splitter 17 is passed to obtain a complex signal from a passband real signal converted into a digital signal by the A / D converter 15. The complex signal passed through the phase separator 17 is converted into a baseband signal by the carrier recovery unit 19.

The first complex multiplier 19-1 of the carrier recovery unit 19 is a frequency offset of f _{P, est} which is a frequency offset of the pilot signal estimated at f _P , which is a pilot frequency, to the passband complex signal passing through the phase separator 17. When the complex conjugate is multiplied, the pilot signal is present at a position deviated by the amount of f _P -f _{P, est which} is a frequency offset Δf _P from DC. Here, in order to reduce the influence of the data pattern jitter from the pilot signal having the frequency offset of Δf _P , the pilot signal is passed through the low pass filter 19-2 (LPF) and then the frequency / The phase error detection means 19-3 to 19-7 extract the error and phase error of the carrier frequency to correct the baseband frequency offset output from the first complex multiplier 19-1.

Here, the real component signal Re (·) output through the low pass filter 19-2 is input to the multiplier 19-4 directly or through a delay unit 19-3. The signal Imag (·) is input directly to the multiplier 19-4. This configuration is used to widen the frequency recovery range. For example, the multiplexer (MUX) selects and outputs the delayed real component signal through the delay unit 19-3 before the carrier frequency is restored. After the carrier frequency is restored, a signal of a real component that is not delayed is selected and output.

Subsequently, the symbol timing restoring unit 21 restores symbol timing from a signal converted to baseband through a frequency and phase locked loop (FPLL), which is a carrier restoring system of the carrier restoring unit 19.

The symbol timing restoring unit 21 employs a typical Gardner type timing error detector (TED), and in order to reduce the influence of pattern jitter due to transition of 8-level VSB symbols, the upper side band After passing a band pass filter 21-2 (BPF) having a bay as a pass band, an error required for symbol timing recovery is extracted through the Gardner TED (Gardner TED).

The error thus obtained is low pass filtered by the loop filter 21-4, and then passes through the NCO 21-5 to control the control signal of the re-sampler 21-1. Will be created. The resampler 21-1 is converted from a baseband digital signal sampled at a fixed frequency used in A / D conversion to a baseband digital signal sampled at a frequency corresponding to exactly two times the symbol frequency.

The signal in which the symbol timing is restored is passed through the matching filter 23 and then passed through the DC remover 25 to the channel equalizer 27.

In the carrier recovery system of FIG. 2, since carrier recovery depends solely on the pilot signal and its frequency and phase, when the frequency corresponding to the position of the pilot signal is severely attenuated in the selective channel environment of the frequency, the carrier recovery is performed. It becomes impossible.

In addition, when the coherence bandwidth of the channel is very narrow compared to the signal band, only the pilot signal is severely attenuated, and the lower sideband signals located around the pilot signal are often not attenuated. The lower sideband signals, which are not attenuated, act as pattern jitter, resulting in overall performance degradation of the receiver.

An object of the present invention is to provide a carrier recovery apparatus and method for a digital broadcast receiver, which does not depend on a pilot signal and does not degrade carrier recovery performance even in a frequency selective fading channel environment.

Another object of the present invention is to provide a carrier recovery apparatus and method for a digital broadcast receiver capable of correcting a frequency offset of a carrier using a baseband complex signal without using a pilot signal.

Technical means of the present invention for achieving the above object, in the carrier recovery system for receiving a passband signal of a specific channel and converts the passband digital signal and extracts the transmission symbol through carrier recovery, the digitally converted pass A phase separator for receiving a band signal and separating the band signal into I / Q signals of real and imaginary components having different phases; A downsampler sampling the baseband complex signal output through the phase separator at a frequency equal to a symbol frequency; And receiving a complex signal output from the downsampler and multiplying with a complex sine wave whose center frequency is 1/4 of a symbol frequency to generate an OQAM signal of real and imaginary components, and calculating a phase error value from an OQAM signal of real and imaginary components. And a carrier recovery unit for generating a complex sine wave to compensate the calculated phase error value and multiplying the complex signal output from the phase separator by converting the complex signal into a baseband signal whose frequency offset is corrected. It features.

Also, a complex signal installed between the phase separator and the downsampler is sampled at a multiple of the symbol frequency at two times the symbol frequency, the sampled signal is analyzed to detect a timing error, and then the sampling time is adjusted according to the timing error. And a matching filter for synchronizing symbol frequencies and timings, wherein the matching timing filter is arranged between the symbol timing restoring unit and the downsampler to remove aliasing of the complex signal of the baseband from the complex signal output from the symbol timing restoring unit. It further comprises.

Specifically, the symbol timing restorer may include: a resampler configured to sample the baseband signal output through the carrier restorer at a clock frequency corresponding to twice the symbol frequency predetermined by the transmitter; A passband timing error detection unit configured to extract a signal of an upper side band from the signal spectrum generated from the resampler and monitor a state of zero-crossing to detect a synchronization error of timing; A loop filter which receives the timing error signal output from the passband timing error detection unit and performs low pass filtering; And a numerically controlled oscillator for generating a sampling clock compensated for the error timing according to the signal output from the loop filter and supplying it to the resampler.

The carrier restorer is an OQAM signal generator for multiplying and receiving a complex signal output from the downsampler and a complex sine wave having a center frequency of 1/4 of a symbol frequency from the outside, and multiplying the complex signal into real and imaginary components. ; A phase error detector for calculating and outputting a phase error value from an OQAM signal of real and imaginary components output from the OQAM signal generator; A second down sampler extracting a phase error value corresponding to the frequency offset output from the phase error detection unit at a frequency 1/2 of a sampling frequency fs; An upsampler sampling the baseband phase error inputted from the second downsampler at a symbol frequency rate by increasing a clock speed to match an operating frequency with a portion that compensates for the phase of the baseband; A loop filter for lowpass filtering the phase error of the baseband output from the upsampler; An adder for outputting an estimated carrier frequency offset signal by adding a predetermined pilot frequency f _P to the output signal Δf _P of the loop filter; A numerically controlled oscillator for receiving a DC signal with respect to the estimated carrier frequency offset from the adder and generating a complex sine wave having a frequency of the estimated carrier frequency offset; And a complex signal of the complex sine wave output from the numerically controlled oscillator and multiplied by the complex signal output from the phase separator to correct the frequency offset and then base the complex signal output from the phase separator. And a complex multiplier for converting the signal into a band signal.

Another technical means of the present invention for achieving the above object is, in a carrier recovery system for receiving a passband signal of a specific channel and converts it into a passband digital signal and extracts the transmission symbol through carrier recovery, digital conversion A phase separator for receiving a passband signal and separating the same into a passband complex signal (I signal, Q signal) of real and imaginary components having different phases; A down converter converting the digital passband signal output from the phase separator into a baseband signal; The symbol timing restoring unit is configured to sample the complex signal output from the down converter at 2 times the symbol frequency, analyze the sampled signal, detect a timing error, and adjust the sampling time according to the timing error to synchronize the symbol frequency with the timing. ; A downsampler that samples and outputs a complex signal output from the symbol timing restoration unit at a frequency equal to a symbol frequency; And receiving a complex signal output from the downsampler and multiplying with a complex sine wave whose center frequency is 1/4 of a symbol frequency to generate an OQAM signal of real and imaginary components, and calculating a phase error value from an OQAM signal of real and imaginary components. And a carrier restoring unit for calculating a complex sine wave to compensate the calculated phase error value and multiplying the complex signal output from the symbol timing restoring unit to correct the frequency offset of the complex signal.

The apparatus may further include a matched filter installed between the symbol timing restorer and the downsampler to remove and output aliasing of the baseband complex signal output through the symbol timing restorer.

The technical method of the present invention for achieving the above object is, in the carrier recovery method for receiving a passband signal of a specific channel and converts it into a passband digital signal and extracts the transmission symbol through carrier recovery, the digitally converted pass Converting a complex signal of a band to a baseband; A second step of receiving the baseband complex signal and sampling and outputting the same frequency as a symbol frequency; Generating a real and imaginary OQAM signal by multiplying a complex signal sampled at the same frequency as the symbol frequency by a complex sine wave having a quarter frequency of a symbol frequency; And calculating and obtaining a phase error value from the OQAM complex signal, estimating a frequency offset with respect to the phase error value, and generating a complex sine wave corresponding to the estimated frequency offset to correct the frequency offset of the baseband complex signal. It characterized in that it comprises a step.

Specifically, the baseband complex signal is characterized in that the timing error of the symbol frequency is restored.

The correcting of the frequency offset may include calculating and outputting a phase error value from the OQAM complex signal; Extracting the phase error value output from the half frequency of the sampling frequency fs; Sampling the extracted phase error value by increasing a clock speed to match an operating frequency with a portion compensating for a phase of a baseband; Lowpass filtering the upsampled phase error; Receiving a DC signal for the phase error and generating a complex sine wave having a frequency of an estimated carrier frequency offset; And correcting the frequency offset by multiplying the conjugate complex value of the complex sine wave generated by the complex signal of the baseband.

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

3 is a circuit block diagram showing a carrier recovery apparatus for a digital broadcast receiver according to an embodiment of the present invention, and includes a tuner 110, an IF processor 130, an A / D converter 150, a phase separator 170, and a carrier wave. The restoration unit 190, the symbol timing restoration unit 210, the matching filter 230, the downsampler 250, the DC eliminator 270, and the like are formed.

The tuner 110 is configured to receive an airwave RF signal input to the antenna and convert it into a passband signal of an intermediate frequency (IF).

The IF processor 130 is configured to receive the passband signal output from the tuner 110, process the analog signal, and output the analog signal to the A / D converter 150. The IF processor 130 is composed of a SAW filter for removing high frequency components generated from adjacent channel interference and the tuner 110, and a gain controller (AGC) for adjusting the level of an input signal.

The A / D converter 150 receives an analog passband signal output from the IF processor 130, samples the signal using a fixed sampling frequency, and converts the signal into a digital passband signal through quantization to the phase separator 170. It is configured to output.

The phase separator 170 receives a digitally-transformed passband signal from the A / D converter 150 and converts it into a complex signal (I signal, Q signal). It is separated into a passband signal of an imaginary component and output to the carrier recovery unit 190. Here, for convenience of description, the real component signal output from the phase separator 170 is called an I signal, and the imaginary component signal is called a Q signal.

The carrier recovery unit 190 estimates the passband complex signal output from the phase separator 170 by the form of a complex signal, not a pilot signal, by a frequency and phase locked loop (FPLL) system in which a predetermined OQAM scheme is applied. After correcting the frequency offset by multiplying the complex conjugate of the complex sine wave with the pilot frequency (f _{p, est} ), the signal is a baseband signal where the pilot signal is located near 0 (f = 0). It is configured to convert.

The symbol timing restoring unit 210 receives the signal converted by the carrier restoring unit 190 and receives a resampler 211, a passband timing error detection unit 213, a loop filter 215, and a numerically controlled oscillator. Through a predetermined FPLL system consisting of (217; NCO, Numerically Controlled Oscillator), the baseband signal is sampled at exactly twice the frequency (2f _{S, VSB} ) of the symbol frequency, the sampled signal is analyzed, and the timing error is detected. It is configured to synchronize the symbol timing by adjusting the sampling time according to the error.

The matched filter 230 is a fixed coefficient I, Q digital having a roll-off value defined around 6 MHz, which is the same as the complex square root raised cosine filter used in the transmission stage. The matching filter is configured to remove and output aliasing from the baseband complex signal output through the symbol timing restoration unit 210.

The downsampler 250 receives a signal in which the symbol frequency and the clock output from the symbol timing restoration unit 210 are synchronized, and downsamples the frequency to the same frequency (1f _{S, VSB} ) as the symbol frequency and outputs the downsampler. It is configured to output to the carrier recovery unit 190 and the DC remover 270 for correcting the frequency offset of the signal, respectively.

The DC canceller 270 is configured to remove an inserted pilot signal in order to facilitate carrier recovery and output the same to a channel equalizer 290 for removing intersymbol interference (ISI).

The phase tracker 310 is configured to correct a residual phase of a carrier that is not completely removed by the carrier restorer 190 and output the correction to a frequency error corrector 330.

The frequency error corrector 330 is configured to correct the error of the phase-corrected signal and output it to the A / V processor. That is, a transmitter such as a broadcasting station selects an appropriate technique for a 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 which performs the decoding process is a frequency error corrector.

The A / V processor 350 restores the video and audio signals compressed in the MPEG-2 and Dolby AC-3 schemes to the original state, and transfers the video signals to the monitor 370 to view a screen. Is delivered to the speaker 390 to allow sound to be heard.

4 is a diagram illustrating a detailed configuration of the carrier restorer 190 and the symbol timing restorer 210 of FIG. 3 according to an embodiment of the present invention, and recovers the timing and phase error of a carrier using an FPLL system. .

The carrier recovery unit 190 may include a first complex multiplier 191, an OQAM signal generator 193, a phase error detector 195, a second down sampler 197, an upsampler 199, and a loop filter 201. , An adder 203 and a numerically controlled oscillator 205.

The symbol timing restoration unit 210 is composed of an FPLL system including a resampler 211, a passband timing error detection unit 213, a loop filter 215, and a numerically controlled oscillator 217.

First, the first complex multiplier 191 of the carrier recovery unit 190 has a passband complex signal output from the phase separator 170 and an estimated pilot frequency f _{p, est} output from the numerically controlled oscillator 205. Multiply the complex conjugate of the complex sine wave to correct the offset of the frequency (locating the pilot signal near 0 (f = 0)) so that the complex signal in the passband is correctly converted to the baseband. .

The complex signal converted to the baseband as described above is sampled at 2f _{S, VSB} , which is exactly twice the symbol frequency while passing through the symbol timing restoring unit 210, and the symbol timing restoring unit 210 is sampled at 2f _{S, VSB} . After determining the error of the sampling timing of the symbol frequency by using and to correct the sampling timing according to the timing error to synchronize the symbol timing (clock).

5 shows an example of the symbol timing restoring unit 210 applied to the present invention, the symbol timing restoring unit 210 includes a re-sampler 211 and a pre-processor 213-1. ), Conjugate multiplicator (213-2), post-processor (213-3; post-processor), timing error detector (213-4; Timing Error Detector), loop filter 215, and numerically controlled oscillator ( 217; NCO).

The reason why the resampler 211 is needed in FIG. 5 is because the A / D converter 150 samples the analog signal using a fixed frequency, and if the A / D converter 150 uses the variable frequency to convert the analog signal. Assuming sampling, no resampler 211 is needed, and instead the output of the NCO is input to the A / D converter 150.

That is, the resampler 211 receives a passband complex signal of which only a carrier frequency offset is corrected from the first complex multiplier 191 and is twice the frequency of a symbol frequency (for example, the symbol frequency fs is 10.76 MHz). Sample the complex signal to generate a sample.

The output of the resampler 211 is output to the matching filter 230 while being output to the preprocessor 213-1.

The preprocessor 213-1 filters the output of the resampler 211 and outputs it to the conjugate multiplier 213-2 to reduce jitter. The conjugate multiplier 213-2 performs a conjugate product on the output of the preprocessor 213-1 and outputs the result to the post processor 213-3 to remove the influence of the carrier wave. That is, the upper sideband of the spectrum of the signal generated by the conjugate multiplier 213-2 is determined by the bandwidth of the input spectrum regardless of the carrier frequency of the input signal. Therefore, the present invention can implement the passband timing error detection unit 213 by using a simple zero-crossing detection method using this characteristic.

In the post processor 213-3, even in the presence of post filtering and severe channel fading to remove jitter due to DC and data generated by the conjugate multiplier 213-2, a constant frequency acquisition performance is obtained. Gain control function to maintain. The output signal of the post processor 213-3 is a sinusoidal wave with a symbol timing offset added to the center frequency fs / 2, which is input to the timing error detector 213-4 (TED). The timing error detector 213-4 may use any type of zero crossing error detector that detects zero-crossing of the input sinusoidal wave.

The timing error signal detected by the timing error detector 213-4 is passed through a loop filter 215 operating at a symbol frequency fs (10.76 MHz) and low-pass filtered. The low pass filtered signal output from the loop filter 215 becomes a DC component, and the DC signal is input to the numerically controlled oscillator 217. The numerically controlled oscillator 217 provides a sampling clock according to the input DC to the resampler 211.

As such, the symbol timing restoration unit 210 may restore the symbol timing of the baseband signal whose frequency offset is not corrected.

The matched filter 230 receives a signal sampled at twice the symbol frequency from the resampler 211, removes aliasing, and outputs the result to the downsampler 250, and the downsampler 250 matches the matched filter 230. The baseband complex signal outputted from the baseband is sampled at 1 fs, the same frequency as the symbol frequency, and then output to the OQAM signal generator 193 and the DC remover 270 of the carrier recovery unit 190, respectively.

The OQAM signal generator 193 of the carrier restoration unit 190 has a complex signal output from the downsampler 250 and a complex sine wave whose center frequency is 1/4 of the symbol frequency from the outside (e ^{-j (n / 2) π).} ), And multiply the complex signals into real and imaginary components and output the multiplication signals.

The complex signal of the real and imaginary components output through the complex multiplier 193-1 is input to the phase error detection unit 195.

The phase error detection unit 195 includes a first tanh calculator 195-1, a first delay unit 195-2, a second delay unit 195-3, a second tanh calculator 195-4, and a first multiplier ( 195-5), a second multiplier 195-6, and an adder 195-7. On the other hand, the carrier recovery of the phase error detection unit 195 is a method of estimating the phase of the baseband from the noise-received received signal, and does not presuppose the pilot signal. It is not affected at all.

As described above, in the present invention, the correlation between the VSB signal and the Offset-Quadrature Amplitude Modulation (hereinafter referred to as 'OQAM') signal is used to apply the carrier recovery without using the pilot signal to the VSB scheme. The equivalence of the VSB signal and the OQAM signal is well known from the known literature, and further description thereof will be omitted.

Accordingly, the carrier recovery algorithm based on the assumption of the OQAM signal can be applied to the VSB method by equivalence. In the present invention, the carrier recovery can be performed without the pilot signal by applying the OQAM method to the carrier recovery.

Referring to the operation of the detailed configuration of the phase error detection unit 195, the first tanh calculator 195-1 first calculates a tanh (I (k)) value by inputting the real signal I (k). The first delay unit 195-2 receives the I (k) signal and delays it to generate an I (k-1 / 2) signal.

The second delay unit 195-3 receives the imaginary signal Q (k) and delays it to generate a Q (k-1 / 2) signal, and the second tanh calculator 195-4 receives Q (k-1). / 2) The tanh (Q (k-1 / 2)) value is calculated and output as a signal.

The first multiplier 195-5 calculates and outputs a tanh (I (k) * Q (k)) value from the output of the first tanh calculator 195-1 and the imaginary signal, and the second multiplier 195-6. Calculates and outputs a tanh (Q (k-1 / 2) * I (k-1 / 2)) value from the outputs of the second tanh calculator 195-4 and the first delay unit 195-2.

Finally, when the output signal of the second multiplier 195-6 passes through the adder 195-7, tanh (I (k) * Q (k))-tanh (Q (k-1 / 2) * I (k-1 / 2)) value, which is a phase error value obtained by the OQAM method. The FPLL system including the loop filter 201, the adder 203, and the numerically controlled oscillator 205 of the carrier recovery unit 190 corrects the frequency offset by allowing the obtained phase error value to converge to zero.

In addition, since the carrier recovery of the OQAM method presupposes the restoration of symbol timing due to the characteristics of the algorithm, the phase error detection unit 195 of the carrier restoration unit 190 is located at the rear end of the symbol timing restoration unit 210 as shown in FIG. It is located. In other words, for smooth operation of the synchronization unit, a passband symbol timing recovery algorithm capable of symbol timing recovery even in the presence of a frequency offset of a carrier should be applied, and baseband phase error may be extracted based on the recovered symbol clock. Should be

Then, the carrier recovery process according to the present invention will be described in more detail using the flowcharts of FIGS. 6A and 6B.

First, the A / D converter 150 samples the received passband analog signal at a fixed frequency (for example, 25 MHz) and converts the passband digital signal into a passband digital signal. The converted passband digital signal is a phase separator 170. splitter) (S1). At this time, the signal spectrum input to the phase separator 170 is as shown in Figure 7a, the signal spectrum is formed of the spectrum of the 6MHz band centering around the passband frequency ㅁ 6MHz, this signal spectrum is the phase separator 170 Is entered.

The phase separator 170 converts the passband real signal into a passband complex signal using a Hilbert transform and outputs it to the first complex multiplier 191 of the carrier restorer 190 (S2). In this case, the signal spectrum output from the phase separator 170 is shown in FIG. 7B, and the signal spectrum centered at -6 MHz is removed from the phase separator 170 and only the signal spectrum centered at +6 MHz is first of the carrier restorer 190. The complex multiplier 191 is input.

Subsequently, the first complex multiplier 191 multiplies the passband complex signal output from the phase separator 170 and the conjugate complex value of the complex sine wave output from the numerically controlled oscillator 205 to output the baseband signal (S3). However, since the carrier recovery FPLL system is not operated initially, the baseband signal output from the first complex multiplier 191 is outputted with the frequency offset as shown in FIG. 7C. That is, when the frequency offset is corrected, the pilot signal is located at the zero frequency point f = 0.

As such, the baseband signal including the frequency offset is supplied to the resampler 211 of the symbol timing restoring unit 210, and the resampler 211 transmits the baseband signal to a symbol frequency (predetermined at the transmitting end). fs; for example, a clock frequency (2fs; 21.52 MHz) corresponding to twice the frequency of 10.76 MHz and the sampled signal are output to the matching filter 230 and the passband timing error detection unit 213, respectively.

The passband timing error detection unit 213 extracts a signal of the upper band from the signal spectrum generated from the resampler 211 and monitors a zero-crossing state to determine a synchronization error of timing. The error signal is lowpass filtered through a loop filter 215 operating at a symbol frequency fs (10.76MHz). The low pass filtered signal output from the loop filter 215 becomes a DC component, and the DC signal is input to the numerically controlled oscillator 217. The numerically controlled oscillator 217 provides a sampling clock with the error timing compensated according to the input DC to the resampler 211 (S4). As described above, the symbol timing restoring unit 210 may restore symbol timing even if a frequency offset exists in the baseband signal.

The symbol timing restoring unit 210 restores the symbol timing by checking the timing error of the baseband signal output from the first complex multiplier 191 through the above process. Of course, the symbol timing is restored by the symbol timing restorer 210, but as shown in the signal spectrum of FIG. 7D, the output signal of the resampler 211 still has a frequency offset. In addition, since the baseband signal without frequency offset correction corresponds to the passband signal, the timing error detection unit 213 should be used to accurately set the frequency band of the signal passing through the resampler 211 to a predetermined 5.38 MHz. Can be adjusted.

The baseband signal output through the resampler 211 is supplied to the matching filter 230 to be input to the downsampler 250 after aliasing included in the signal spectrum is removed (S5).

The downsampler 250 downsamples the baseband complex signal output from the matched filter 230 to the same frequency as the symbol frequency, and then restores the baseband complex signal having the spectrum as shown in FIG. 7E to the DC remover 270 and the carrier recovery. Each of the outputs is output to the OQAM signal generator 193 of the unit 190 (S6).

Subsequently, the OQAM signal generator 193 receives and receives a complex signal having a spectrum as shown in FIG. 7E and a complex sine wave whose center frequency is 1/4 of a symbol frequency through the complex multiplier 193-1. S7). At this time, if there is a frequency offset, the output signal of the complex multiplier 193-1 is slightly skewed to one side by the frequency offset as the center frequency of the signal spectrum does not exactly match the zero frequency point f = 0 as shown in FIG. 7F.

The OQAM signal generator 193 is represented by a complex multiplier 193-1 having an output complex signal and a complex sine wave of the downsampler 250 as inputs, but the center frequency of the input complex sine wave is 1/4 of the symbol frequency. In practice, it can be simply implemented without the need of the complex multiplier 193-1.

In other words, in the input complex sine wave (e ^{-j (n / 2) π} ), n is 0, 1, 2, 3,... When, the complex sine wave is 1 (e ^{-j · 0} = 1) , -j (e ^{-j (π / 2)} = cos (π / 2) -jsin (π / 2) =-j) , -1 ( e- ^{j π} = cos ^π -jsin ^π = -1) , j (e- ^{j · (3/2) π} = j) ,... Since it repeats the value of, it can be implemented simply by selecting the input signal with sign conversion.

When the real and imaginary components are separated from the output complex signal of the OQAM signal generator 193 and input to the phase error detection unit 195, the phase error that is frequency offset using the phase error detection unit 195 using the OQAM method without a pilot signal. The value can be obtained (S8).

The first tanh calculator 195-1 of the phase error detection unit 195 calculates and outputs a tanh (I (k)) value by inputting the real signal I (k) and outputs the first delay unit 195-195. 2) generates a delayed I (k-1 / 2) signal by inputting the real signal I (k).

The second delay unit 195-3 generates a delayed Q (k-1 / 2) signal by inputting the imaginary signal Q (k), and the second tanh calculator 195-4 receives Q (k-1). / 2) The tanh (Q (k-1 / 2)) value is calculated and output as a signal.

The first multiplier 195-5 outputs tanh (I (k) * Q (k)) values from the first tanh calculator 195-1 and the output of the imaginary signal, and the second multiplier 195-6 outputs a first value. The tanh (Q (k-1 / 2) * I (k-1 / 2)) values are output from the outputs of the 2tanh calculator 195-4 and the first delay unit 195-2.

Finally, when the output signal of the second multiplier 195-6 passes through the adder 195-7, tanh (I (k) * Q (k))-tanh (Q (k-1 / 2) * The value of I (k-1 / 2)) is obtained, which is a phase error value obtained by the OQAM method. The FPLL system of the carrier recovery unit 190 corrects the frequency offset by causing the phase error value thus obtained to converge to zero.

Meanwhile, the complex signal input to the OQAM signal generator 193 is input at the same frequency as the symbol frequency (10.76 MHz), and when the complex signal input to the phase error detection unit 195 is converted into an OQAM signal, The sampling frequency is the same by the first and second delayers 195-2 and 195-3, but the symbol interval of the converted OQAM signal is doubled as the symbol period is increased. This is a state oversampled twice in terms of the OQAM signal output from the OQAM signal generator 193. In other words, a relationship of 1f _{S, VSB} = 10.76 MHz = 2f _{S, OQAM} is established.

Therefore, since the first and second delay units 195-2 and 195-3 are delayed by one clock on the basis of 1f _{S and VSB, the} delay is 1/2 symbol on the basis of the OQAM signal. Since the phase error detection unit 195 operates in the double-sampled time domain, the second downsampler 197 at the rear stage has a sampling frequency of 1/2 fs (for example, 5.38 MHz) at a base frequency in symbol units among phase error values. Only the phase error value is extracted.

As described above, the second downsampler 197 extracts the phase error value corresponding to the frequency offset output from the phase error detection unit 195 as a 1 / 2fs sampling frequency and outputs the up-sampler 199 (Up-Sampler) ( S9), the upsampler 199 is a first complex multiplier 191 to match the baseband phase error input at a rate of 1f _{S, OQAM} ( _5.38MHz ) with an operating frequency of the baseband phase compensating portion. Sampling is performed at a clock speed (25MHz) on the (S10) side.

The baseband phase error signal of which the operating speed is adjusted through the upsampler 199 is lowpass filtered through a loop filter, and a predetermined pilot frequency f _P (for example, the output signal Δf _P ) of the loop filter is , f _P is fc-2.69 MHz, and f _{P, est} (f _{P, est} = f _P + Δf _P ), which is an estimated carrier frequency offset, is obtained (S11). A numerically controlled oscillator (205; Numerically Controlled Oscillator) are f _P, it receives the DC signal of the _est f _P, by generating a complex sinusoid having a frequency of _est and output to the first complex multiplier (191) (S12), first The complex multiplier 191 multiplies the complex conjugate of the generated complex sine wave with the complex signal output from the phase separator 170 to correct the frequency offset of the complex signal output from the phase separator 170. Assuming that the carrier restoration unit 190 corrects a phase error that is exactly a frequency offset, the output signal of the first complex multiplier 191 has a pilot signal located at a zero frequency point f = 0 as shown in the signal spectrum of FIG. The baseband is exactly converted to baseband (Rear Baseband-> Baseband) (S13).

Thereafter, after passing through the DC canceller 270 that removes the inserted pilot signal to facilitate carrier recovery, it is input to a channel equalizer 290 for removing ISI.

4 is just an example of applying the OQAM scheme to VSB, and may be actually changed in various forms. For example, although the output of the downsampler 250 located at the rear end of the matching filter 230 is used as an input of the OQAM signal generator 193, the position is the output terminal of the matching filter 230, the resampler. The output terminal 211 or the output terminal of the DC eliminator 270 may be varied.

When the output of the matching filter 230 or the resampler 211 is used as the input of the OQAM signal generator 193, the center frequency of the input complex sine wave of the OQAM signal generator 193 should be 1/8 of the operating frequency. The complexity of the OQAM signal generator 193 increases somewhat.

The phase error detection unit 195 of FIG. 4 is just an example of an approximation of the phase error detection unit 195 that can be applied to the VSB method, and various modifications are possible. For example, tanh (I) calculated by the tanh () function can be approximated with sign (I), I, or a multi-level slicer. tanh (Q) can also be approximated in the same way as sign (Q), Q, or a multi-level slicer.

In addition, the position for compensating the carrier frequency or phase offset may also be variable. For example, the position for correcting the carrier offset may be an input terminal or an output terminal of the resampler 211. 8 illustrates a case where the carrier offset is compensated at the output terminal of the resampler 211.

When the carrier offset is compensated for at the output of the resampler 211, in order not to deteriorate the performance of the resampler 211, as shown in FIG. 8, the fixed frequency down converts to the baseband at a fixed frequency f _p as shown in FIG. 8. Converter 180 must be preceded. Even though the baseband is down-converted to a fixed frequency, the carrier offset still remains, and thus the passband timing error restoration unit 213 shown in FIG. 5 is used for the stable symbol timing restoration unit 210.

That is, the carrier recovery system includes a phase separator 170, a down converter 180, a symbol timing restoring unit 210 (211 to 217), a matching filter 230, a down sampler 250, and a carrier restoring unit 190; 191 to 205).

The phase separator 170 is configured to receive a digitally converted passband signal and convert the converted signal into a complex signal (I signal, Q signal), and the down converter 180 is output from the phase separator 170. It is configured to convert a digital passband signal into a baseband signal by receiving a conjugate complex value of a fixed frequency complex sine wave output from the digital passband signal and the numerically controlled oscillator 185 and multiplying it through a complex multiplier 181. have.

The symbol timing restoring unit (210; 211 to 217) samples the complex signal output from the down converter (180) at 2 times the symbol frequency, analyzes the sampled signal, detects the timing error, and then sampling time according to the timing error. It is configured to adjust the symbol frequency and timing.

The matching filter 230 is configured to remove and output an aliasing of the baseband complex signal output through the symbol timing restoration unit 210, and the downsampler 230 outputs the complex signal output from the matching filter 230. Is sampled at the same frequency as the symbol frequency and output.

The carrier restoration unit 190 (191 to 205) receives a complex signal output from the downsampler 250 and multiplies by a complex sine wave whose center frequency is 1/4 of a symbol frequency to generate a real and imaginary OQAM signal. After calculating the phase error value from the real and imaginary OQAM signals, and generating a complex sine wave to compensate the calculated phase error value and multiplying with the complex signal output from the symbol timing restoring unit 210, the frequency offset of the complex signal It is configured to correct.

In addition, the carrier restorer 190 receives a complex signal output from the downsampler 250 and a complex sine wave whose center frequency is 1/4 of a symbol frequency from the outside, and multiplies the complex signal by real and imaginary numbers. An OQAM signal generator 193 for separating and outputting the component, a phase error detection unit 195 for calculating and outputting a phase error value from the OQAM signals of real and imaginary components output from the OQAM signal generator 193, and the phase A second down sampler 197 for extracting a phase error value corresponding to the frequency offset output from the error detector 195 at a 1 / 2fs sampling frequency (for example, 5.38 MHz), and the second down sampler 197. The phase error of the baseband inputted at the symbol frequency rate from the clock frequency (for example, 21.52 MHz) of the symbol timing recovery unit 210 in order to match the operating frequency with the portion compensating the phase of the baseband. sampling Up-sampler 199 for outputting the signal, a loop filter 201 for low-pass filtering the phase error of the baseband output from the up-sampler 199, and a DC signal for the phase error is estimated from the loop filter. A numerically controlled oscillator 205 for generating a complex sine wave having a frequency of carrier frequency offset, and a complex sine wave output between the symbol timing restoring unit 210 and the matching filter 230 and outputted from the numerically controlled oscillator 205. And a complex multiplier 191 for correcting the frequency offset of the complex signal output from the symbol timing restoring unit 210 after correcting the frequency offset by multiplying the complex value of the complex signal with the complex signal output from the phase separator 170. have.

The output signal of the resampler 211 is input to the complex multiplier 191 for correcting the carrier frequency offset to correct the carrier offset. The symbol timing restoring unit 210 operates by extracting a symbol timing error from the signal whose carrier offset is corrected through the complex multiplier 191.

This structure is identical to the operation of the carrier recovery apparatus of FIG. 4, and since the circuit part having the same function as that of FIG. 4 is denoted by the same reference numeral, a detailed description of the operation will be omitted.

On the other hand, while the present invention has been shown and described with respect to specific preferred embodiments, various modifications and changes of the present invention without departing from the spirit or field of the invention provided by the claims below It can be easily understood by those skilled in the art.

As described above, in the present invention, the carrier is recovered by correcting the frequency offset of the carrier by using the baseband complex signal without relying on the pilot signal, so that the carrier recovery performance is excellent even in a selective fading channel environment. There is an advantage to improve.

Claims (16)

A carrier recovery apparatus for receiving a passband signal of a specific channel, converting the passband digital signal, and extracting a transmission symbol through carrier recovery, A phase separator which receives the digitally converted passband signal and separates and outputs a passband complex signal of real and imaginary components having different phases; A downsampler sampling the baseband complex signal output through the phase separator at a frequency equal to a symbol frequency; And A complex signal output from the downsampler is received and multiplied by a complex sine wave whose center frequency is 1 / n of a symbol frequency to generate an OQAM signal of real and imaginary components, and then from an OQAM signal of real and imaginary components. A carrier recovery unit for calculating a phase error value, generating a complex sine wave to compensate the calculated phase error value, and multiplying the complex signal with the complex signal output from the phase separator to convert the complex signal into a baseband signal whose frequency offset is corrected; Carrier recovery apparatus of the digital broadcast receiver comprising a. The method according to claim 1, It is installed between the phase separator and the downsampler and samples the complex signal output from the phase separator at 2 times the symbol frequency, analyzes the sampled signal, detects the timing error, and adjusts the sampling time according to the timing error. And a symbol timing restorer for synchronizing and outputting the timing. The method according to claim 2, And a matching filter disposed between the symbol timing restorer and the downsampler to remove aliasing of the complex signal of the baseband from the complex signal output from the symbol timing restorer. The method according to claim 2 or 3, The symbol timing restoring unit may include: a resampler for sampling and outputting a baseband signal output through the carrier restoring unit at a clock frequency corresponding to two times a predetermined symbol frequency at a transmitting end; A passband timing error detection unit configured to extract a signal of an upper band from the signal spectrum generated from the resampler and monitor a state of zero crossing to detect synchronization error of timing; A loop filter which receives the timing error signal output from the passband timing error detection unit and performs low pass filtering; And a numerically controlled oscillator for generating a sampling clock compensated for the error timing according to the signal output from the loop filter and supplying the sample clock to the resampler. The method according to claim 1 or 2, And 1 / n complex sine wave of the carrier recovery unit is a fixed oscillation signal whose center frequency is 1/4 of a symbol frequency. The method according to claim 1 or 2, The carrier recovery unit receives and outputs a complex signal output from the downsampler and a complex sine wave whose center frequency is 1 / n of a symbol frequency from the outside, and multiplies the complex signal into real and imaginary OQAM signals. OQAM signal generator; A phase error detection unit extracting a phase error value by calculating a phase error value from the OQAM signals of real and imaginary components respectively output from the OQAM signal generator; And a phase separator provided between the phase separator and the symbol timing restorer to correct a frequency offset by multiplying a complex signal of a complex sine wave corresponding to a phase error value detected by the phase error detector and a complex signal output from the phase separator. And a complex multiplier for converting a complex signal output from the baseband signal into a baseband signal. The method according to claim 6, The phase error detection unit receives the OQAM signals of the real component (I (k)) and the imaginary component (Q (k)) output from the OQAM signal generator, respectively, and calculates a phase error value tanh (I (k) * Q). (k))-tanh (Q (k-1 / 2) * I (k-1 / 2)) values for outputting a carrier recovery apparatus for a digital broadcast receiver. The method according to claim 6, The carrier recovery unit may include: a second down sampler extracting a phase error value corresponding to a frequency offset output from the phase error detection unit as half frequency of a sampling frequency; An upsampler sampling the baseband phase error inputted from the second downsampler at a symbol frequency rate by increasing a clock speed to match an operating frequency with a portion that compensates for the phase of the baseband; A loop filter for lowpass filtering the phase error of the baseband output from the upsampler; An adder configured to add a predetermined pilot frequency to an output signal of the loop filter and output an estimated carrier frequency offset signal; And a numerically controlled oscillator receiving a DC signal with respect to the estimated carrier frequency offset from the adder, generating a complex sine wave having a frequency of the estimated carrier frequency offset and outputting the complex sine wave to a complex multiplier. Carrier recovery device. A carrier recovery apparatus for receiving a passband signal of a specific channel, converting the passband digital signal, and extracting a transmission symbol through carrier recovery, A phase separator which receives the digitally converted passband signal and separates and outputs a passband complex signal of real and imaginary components having different phases; A down converter converting the digital passband signal output from the phase separator into a baseband signal; The symbol timing restoring unit is configured to sample the complex signal output from the down converter at 2 times the symbol frequency, analyze the sampled signal, detect a timing error, and adjust the sampling time according to the timing error to synchronize the symbol frequency with the timing. ; A downsampler that samples and outputs a complex signal output from the symbol timing restoration unit at a frequency equal to a symbol frequency; And Receive the complex signal output from the downsampler and multiply the complex sine wave whose center frequency is 1/4 of the symbol frequency to generate the real and imaginary OQAM signals, and calculate the phase error value from the real and imaginary OQAM signals. And a carrier recovery unit for generating a complex sine wave to compensate the calculated phase error value and multiplying the complex signal output from the symbol timing restoring unit to correct a frequency offset of the complex signal. Carrier recovery device. The method according to claim 9, And a matching filter disposed between the symbol timing restorer and the downsampler to remove and output an aliasing of the baseband complex signal outputted through the symbol timing restorer. The method according to claim 9 or 10, The carrier restorer is an OQAM signal generator for multiplying and receiving a complex signal output from the downsampler and a complex sine wave having a center frequency of 1/4 of a symbol frequency from the outside, and multiplying the complex signal into real and imaginary components. ; A phase error detector for extracting a phase error value by calculating a phase error value from the OQAM signals of real and imaginary components output from the OQAM signal generator; And a complex multiplier installed between the symbol timing restorer and the matching filter to multiply the complex complex value of the complex sine wave corresponding to the phase error value detected by the phase error detector by the complex signal output from the phase separator. Carrier recovery apparatus of the digital broadcast receiver comprising a. The method according to claim 11, The carrier recovery unit may include: a second down sampler extracting a phase error value corresponding to a frequency offset output from the phase error detection unit as half frequency of a sampling frequency; An upsampler sampling the baseband phase error inputted from the second downsampler at a symbol frequency rate by increasing a clock speed to match an operating frequency with a portion that compensates for the phase of the baseband; A loop filter for lowpass filtering the phase error of the baseband output from the upsampler; And a numerically controlled oscillator receiving a DC signal for a phase error from the loop filter, generating a complex sine wave having a frequency of an estimated carrier frequency offset, and outputting the complex sine wave to a complex multiplier. Device. In the carrier recovery method of receiving a passband signal of a specific channel and converting it into a passband digital signal and extracting the transmission symbol through carrier recovery, Converting the complex signal of the digitally converted passband to the baseband; Receiving the baseband complex signal and sampling and outputting a frequency equal to a symbol frequency; Generating a real and imaginary OQAM signal by multiplying a complex signal sampled at the same frequency as the symbol frequency by a complex sine wave having a frequency of 1 / n of a symbol frequency; And Calculating a phase error value from the OQAM complex signal, estimating a frequency offset with respect to the phase error value, and generating a complex sine wave corresponding to the estimated frequency offset to correct the frequency offset of the baseband complex signal; Carrier recovery method of the digital broadcast receiver comprising a. The method according to claim 13, The baseband complex signal is a carrier recovery method of a digital broadcast receiver, characterized in that the timing error of the symbol frequency is restored. The method according to claim 13 or 14, In the step of generating the OQAM signal, 1 / n complex sine wave carrier recovery device of the digital broadcast receiver, characterized in that the center frequency is a fixed oscillation signal of 1/4 of the symbol frequency. The method according to claim 13 or 14, The correcting of the frequency offset may include calculating and outputting a phase error value from the OQAM complex signal; Extracting the phase error value output from the half frequency of a sampling frequency; Sampling the extracted phase error value by increasing a clock speed to match an operating frequency with a portion compensating for a phase of a baseband; Lowpass filtering the upsampled phase error; Receiving a DC signal for the phase error and generating a complex sine wave having a frequency of an estimated carrier frequency offset; And correcting the frequency offset by multiplying the conjugate complex value of the complex sine wave and the complex signal of the baseband.

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