CN100499616C - Carrier recovering apparatus for digital vestigial single sideband modulating system and recovering method thereof - Google Patents
Carrier recovering apparatus for digital vestigial single sideband modulating system and recovering method thereof Download PDFInfo
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- CN100499616C CN100499616C CNB200510028181XA CN200510028181A CN100499616C CN 100499616 C CN100499616 C CN 100499616C CN B200510028181X A CNB200510028181X A CN B200510028181XA CN 200510028181 A CN200510028181 A CN 200510028181A CN 100499616 C CN100499616 C CN 100499616C
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Abstract
The invention discloses a carrier wave recovery device for a digital vestigial sideband-amplitude modulation (VSB-AM) system, comprising high-pass filter, Hilbert filter, first pilot tracking loop, low-pass filter, second pilot tracking loop, pilot amplitude estimation module, and DC eliminating module, where the high-pass filter extracts sideband signal; the Hilbert filter extracts pilot signal on a sideband, which is gained and sent to the first pilot tracking loop for spectrum shift, and sent through the low-pass filter to the second pilot tracking loop; after the frequency of the first pilot tracking loop is locked, it estimates the strength of the pilot signal by processing the input signals of the pilot tracking loops and the signal of digitally controlled oscillator, and regulates the gains of the input signals of the pilot tracking loops, and sends them to the DC eliminating module to eliminate the pilot signal; and it synthesizes the carrier wave signals produced by the two pilot tracking loops to obtain a synthesized carrier wave recovery signal.
Description
Technical field
The present invention relates to the residual monolateral band of a kind of numeral (VSB Vestigial Side Band) modulating system carrier resetting device and restoration methods thereof, particularly a kind of carrier resetting device of residual single sideband modulated signal of digital television receiver and restoration methods thereof.
Background technology
The residual single-side band modulation mode that the ground digital television broadcast standard of present North America is adopted utilizes existing analog television broadcast frequency range to send digital TV broadcast signal.In order to reduce influence to present analog television broadcast, and under the environment of low carrier-to-noise ratio the reliable transmission digital television signal, adopted channel equalizer and multiple channel coding method in the standard, guarantee the normal reception of signal.In addition, different with simulated television, when Digital Television was lower than a thresholding at received signal quality, the receiver cisco unity malfunction be can't see image fully; Otherwise,, then can recover picture signal if when being higher than this thresholding almost error freely.This just requires Digital Television to receive can operate as normal under abominable channel condition.
The demodulator of receiver will demodulate semaphore request and realize three functions: the timing of sign synchronization recovers, and carrier wave recovers and channel equalization.Regularly recovery is to make the symbol clock of receiver be synchronized with the symbol clock of transmitter, guarantees the symbol time sampling that the receiver realization is best; It is that the signal spectrum of radio frequency/intermediate frequency is moved base band that carrier wave recovers, and realizes the process that baseband signal is recovered; Equilibrium is in order to remove the intersymbol interference (ISI Inter-SymbolInterference) owing to the multipath effect in the channel causes.
The pilot signal that has added 0.3dB in the VSB system at the direct current place of baseband signal is used for subcarrier and recovers.When the VSB signal departed from base band, this direct current signal became a simple signal, in vsb receiver, can lock pilot signal with phase-locked loop, and the pilot signal after being restored is used for demodulation VSB signal, makes it return to base band.Pilot signal is in the middle of the VSB signal, and for pilot signal, the data modulated signal of VSB is a kind of zoop.In the pilot signal phase-locked loop of receiver, these modulation signals are taken as noise and handle.
U.S. Pat Patent 6005640 has adopted the method for pilot tone phase-locked loop, realizes that the carrier wave of VSB signal recovers.In order to extract pilot signal, can before phase-locked loop, adopt narrow band filter.Simultaneously, in order to suppress the data-modulated noise, need the very narrow filter of utilized bandwidth as much as possible.But, can cause phase-locked loop can't follow the tracks of all frequencies of input signal and phase drift like this.Yet, because the cost factor of consumption appliance product can not adopt high-grade tuner to guarantee that the radiofrequency signal processing does not bring certain frequency and phase drift.On the other hand, have under the abominable channel of deep fade, when pilot signal was in the frequency place of deep fade just, the pilot signal amplitude was declined, and the performance that influences the carrier wave recovery is recovered cisco unity malfunction until carrier wave.
Summary of the invention
The technical problem to be solved in the present invention provides a kind of numeral residual single-side band modulation system carrier recovery device and restoration methods thereof.
For solving the problems of the technologies described above, the residual single-side band modulation system carrier of numeral of the present invention recovery device comprises:
High pass filter is used for the filtering sideband with interior data-modulated noise, obtains upper and lower sideband signals;
Hilbert filter is used for the useless sideband of filtering again, takes out the pilot signal on the useful sideband;
The pilot amplitude estimation module, be used for after the first pilot tone track loop frequency lock, estimate the amplitude of input pilot signal and in view of the above dynamic adjustments be input to the gain of the first pilot tone track loop signal, also the pilot signal amplitude that estimates is sent into direct current and is removed module;
The first pilot tone track loop is used for accepting carrying out the locking first time through the adjusted pilot signal that gains, and the filtering band is outer to be disturbed and broadband noise;
Low pass filter, pilot signal and filtering data-modulated noise and interference after being used to accept to lock for the first time;
The second pilot tone track loop is accepted low-pass filter output signal and frequency and phase error is locked once more the phase drift that the tracking tuner is introduced;
Direct current is removed module, the VSB baseband signal is carried out direct current remove, and described VSB baseband signal is obtained by VSB signal after postponing and the synthetic local recovery carrier frequency mixing of the carrier signal after the first pilot tone tracking loop and twice locking of the second pilot tone track loop;
The described first pilot tone track loop adopts low loop gain, and the second pilot tone track loop adopts high loop gain;
Described low pass filter comprises that piece is average, down-sampling, narrowband low-pass filter and up-sampling; Pilot signal after the locking is for the first time carried out successively the down-sampling of the average and 1/N speed of piece, low-rate signal behind the down-sampling enters narrowband low-pass filter, interference and noise beyond the filtering direct current carry out N times of up-sampling again, and restoring signal speed is to sampling rate; Wherein, N is 8 to 64 integer.
The residual single-side band modulation system carrier of numeral of the present invention restoration methods is: the signal that comes the self-timing recovery is through behind the high pass filter, and having taken out centre frequency is that (fs is the character rate of VSB modulation signal to fs/4, sideband signals 10.76MHz); Further adopt hilbert filter, taking-up is in a pilot signal on the sideband; This pilot signal is sent into first pilot tone track loop (phase-locked loop) through once gaining to adjust; After the phase detectors (complex multiplier) of first pilot tone track loop carry out the fs/4 frequency spectrum shift, the pilot signal (direct current signal) of getting back to base band by the narrow low pass filter of very bandwidth after, send into second pilot tone track loop; After the frequency lock of first pilot tone track loop, by the pilot amplitude estimation module output signal of the digital controllable oscillator of the pilot signal of hilbert filter output and the first pilot tone track loop is handled, estimate the amplitude of input pilot signal, and dynamically regulate the gain of the first pilot tone track loop input signal in view of the above; The pilot signal amplitude that estimates is sent into direct current and is removed module, removes pilot signal; Synthesize from the carrier signal that two pilot tone track loop digital controllable oscillator (NCO Numerically Controlled Oscillator) separately generates, obtain a synthetic carrier wave restoring signal, be used for the VSB signal is carried out demodulation; Signal after the demodulation is sent into channel equalizer through after removing direct current signal, eliminates intersymbol interference;
The described first pilot tone track loop adopts low loop gain, and the second pilot tone track loop adopts high loop gain;
Described low pass filter comprises that piece is average, down-sampling, narrowband low-pass filter and up-sampling; Pilot signal after the locking is for the first time carried out successively the down-sampling of the average and 1/N speed of piece, low-rate signal behind the down-sampling enters narrowband low-pass filter, interference and noise beyond the filtering direct current carry out N times of up-sampling again, and restoring signal speed is to sampling rate; Wherein, N is 8 to 64 integer.
The present invention is owing to adopted said apparatus and method, even adopt at radio frequency under the situation of low-grade tuner, and under the abominable channel circumstance, carrier wave recovers to guarantee operate as normal.
Description of drawings
Fig. 1 is the structured flowchart of existing VSB digital television receiver;
Fig. 2 is the detailed diagram of carrier resetting device of the present invention;
Fig. 3 is the structure chart of low pass filter among Fig. 2;
Fig. 4 is the structure chart that pilot amplitude is estimated among Fig. 2.
Embodiment
The present invention is further detailed explanation below in conjunction with accompanying drawing and embodiment.
Fig. 1 is the structured flowchart of existing VSB digital television receiver.When receiving the radiofrequency signal of VSB modulation system by antenna, tuner carries out frequency spectrum shift to intermediate frequency (IF intermediate frequency with the radiofrequency signal of the selected channel of user; General extensive employing 44MHz), and by the outer signal of Surface Acoustic Wave Filter filtering receiving channels disturb.Intermediate-freuqncy signal drives A/D by after suitably amplifying, and signal converts the digital band pass signal to through behind the A/D.This bandpass signal enters quadrature demodulator, and the VSB modulation signal is further carried out frequency spectrum shift, and making its centre frequency is fs/4, and timing recovery and the carrier wave be convenient to thereafter recover to handle.
Regularly recovery makes the symbol clock of receiver be synchronized with the symbol clock of transmitter, realizes best symbol time sampling.Signal incoming carrier recovery section after regularly recovering, extract the carrier wave in the received signal after, utilize it to finish the frequency spectrum shift of VSB baseband signal demodulation.After carrier wave recovers, also just no longer need in the pilot signal that the direct current place of VSB baseband signal inserts for subcarrier recovers at transmitting terminal, this direct current signal is removed by direct current removal portion.
Channel equalizer will be eliminated owing to residual phase noise in the intersymbol interference of multipath channel effect introducing in the radio wave propagation and the baseband signal.The VSB restituted signal of removing behind the various interference noises outputs to channel decoding portion, carries out multiple decoding in channel decoding portion and handles, and recovers the transmission code stream (TS:Transport Stream) of transmitting terminal like clockwork.
Fig. 2 is the detailed diagram of carrier resetting device of the present invention, is equivalent to carrier wave recovery section among Fig. 1.The centre frequency of VSB signal is fs/4 after the quadrature demodulation, and equivalence is a complex baseband signal.Pilot signal also is in the upper sideband or the lower sideband (specifically which sideband depending on the spectrum position of IF signal and the carrier phase of quadrature demodulation at) of complex baseband signal.High pass filter filtering among Fig. 2 sideband with interior data-modulated noise, obtain/lower sideband signal.Hilbert filter is useless sideband of filtering again, has taken out the pilot signal that drops on another sideband.
The pilot signal that obtains by filtering is admitted to first pilot tone track loop after adjusting through gain.Input pilot signal and local NCO carrier wave complex multiplication detect phase error.Detected phase error outputs to loop filter, by this loop filter control NCO, finishes frequency lock and phase locking again.
Carried out expendable locked pilot signal, residual frequency error and phase error necessarily, and its frequency spectrum is shifted to base band.The pilot signal that is in base band outputs to a low pass filter that very bandwidth is narrow, filtering data-modulated noise and other various interference.The output signal of this low pass filter is sent to second pilot tone track loop, and residual frequency and phase error are locked.Except that concrete loop filter parameters, the structure of second pilot tone track loop and first pilot tone track loop is just the same, no longer repeats here.
The carrier wave synthesis module synthesizes the carrier signal of the NCO output of the carrier signal of the NCO of first pilot tone track loop output and second pilot tone track loop, form last local recovery carrier wave, and carry out mixing with VSB signal after postponing, obtain the VSB baseband signal.Separate the VSB baseband signal that mixes up and output to direct current removal module, remove the direct current (being pilot signal) that wherein no longer needs.
After the frequency lock of first pilot tone track loop, the pilot amplitude estimation module begins to estimate to import the amplitude of pilot signal, and is input to the gain of the first pilot tone track loop signal according to the amplitude dynamic adjustments of estimated pilot signal.The amplitude of the pilot signal that estimates is admitted to direct current and removes module, the weight of pilot frequency in the VSB signal after making it can remove distortion like clockwork.
Fig. 3 is the implementation structure figure of low pass filter among Fig. 2, and described low pass filter comprises that piece is average, down-sampling, narrowband low-pass filter and up-sampling.For the first time the pilot signal after the locking carry out piece average after, carry out the down-sampling of 1/N speed, make signals sampling speed reduce to original 1/N; Low-rate signal after the sampling enters narrowband low-pass filter, thoroughly various interference and the noise beyond the filtering direct current; Carry out N times of up-sampling, make signal rate return to the sampling rate of input signal; Wherein, N is 8 to 64 integer.
Fig. 4 is the structure chart of pilot amplitude estimation module among Fig. 2, and described pilot amplitude estimation module comprises the average and hysteresis comparator of piece.The quadrature of hilbert filter institute output signal carries out piece on average with filtering noise after multiplying each other with the output in-phase signal of the NCO of the first pilot tone track loop.Signal behind the filtering noise is the pilot amplitude that estimates, and outputs to direct current and removes module.In addition, a series of thresholdings according to the pilot amplitude of estimating and system provide produce a gain control signal, the size that decision pilot tone input signal gains.Described hysteresis comparator is used to prevent near the frequent switching thresholding.
Double pilot track loop of the present invention can be followed the tracks of all frequency/phase drifts of being introduced by tuner or other transmission/reception links.The first pilot tone track loop has adopted low loop gain, has guaranteed the data-modulated noise suppressed performance of own loop, the frequency plot follow-up control requirement that can share small part simultaneously.Low pass filter filters out between two pilot tone track loop band is outer disturbs, guarantee that the second pilot tone track loop can not introduce too much band and disturb outward.Certainly low pass filter itself also can have certain influence to the Phase Tracking ability of the second pilot tone track loop.The second pilot tone track loop adopts high loop gain, thereby has strong Phase Tracking performance.The structure of double pilot track loop and suitable parameter configuration had both kept good loop noise performance, the frequency/phase drift in again can fine tracking input signal.
Band is outer to be disturbed low pass filter between two pilot tone track loop in order to remove better, need carry out the very narrow filtering of bandwidth to signal.In answering (FIRFinite Impulse Response) Filter Design, need the very many FIR of exponent number just can reach filtering requirements at the finite impulse that adopts usually usually, it is unfavorable that circuit is realized.The present invention reduces the sampling rate that enters the FIR filter signal by signal being carried out the processing of the average back of piece down-sampling, greatly reduces the needed exponent number of FIR filter, helps circuit and realizes.
The dynamic adjustment that pilot amplitude detects and imports pilot signal gain: in the actual channel transmission environment, because multipath effect has caused frequency selective fading.Under some specific environment, pilot tone is in the place of the deep fade of frequency just, causes that pilot amplitude reduces greatly in the received signal, finally causes pilot tone track loop cisco unity malfunction.The present invention imports the amplitude of pilot signal by estimation, and according to the situation that pilot tone is declined, dynamically regulates the gain of input pilot signal, guarantees the operate as normal of pilot tone track loop.
Claims (5)
1, the residual single-side band modulation system carrier of a kind of numeral recovery device is characterized in that, comprising:
High pass filter is used for the filtering sideband with interior data-modulated noise, obtains upper and lower sideband signals;
Hilbert filter is used for the useless sideband of filtering again, takes out the pilot signal on the useful sideband;
The pilot amplitude estimation module, be used for after the first pilot tone track loop frequency lock, estimate the amplitude of input pilot signal and in view of the above dynamic adjustments be input to the gain of the first pilot tone track loop signal, also the pilot signal amplitude that estimates is sent into direct current and is removed module;
The first pilot tone track loop is used for accepting carrying out the locking first time through the adjusted pilot signal that gains, and the filtering band is outer to be disturbed and broadband noise;
Low pass filter, pilot signal and filtering data-modulated noise and interference after being used to accept to lock for the first time;
The second pilot tone track loop is accepted low-pass filter output signal and frequency and phase error is locked once more the phase drift that the tracking tuner is introduced;
Direct current is removed module, the residual monolateral tape base band signal of numeral is carried out direct current remove, the residual monolateral tape base band signal of described numeral is obtained by digital residual single sideband singal after postponing and the synthetic local recovery carrier frequency mixing of the carrier signal after the first pilot tone track loop and twice locking of the second pilot tone track loop;
The described first pilot tone track loop adopts low loop gain, and the second pilot tone track loop adopts high loop gain;
Described low pass filter comprises that piece is average, down-sampling, narrowband low-pass filter and up-sampling; Pilot signal after the locking is for the first time carried out the down-sampling of the average and 1/N speed of piece successively, and the low-rate signal behind the down-sampling enters narrowband low-pass filter, and interference and noise carry out N times of up-sampling again beyond the filtering direct current, and restoring signal speed is to sampling rate; Wherein, N is 8 to 64 integer.
2, the residual single-side band modulation system carrier of numeral according to claim 1 recovery device is characterized in that, the described first pilot tone track loop and the second pilot tone track loop comprise complex multiplier, digital controllable oscillator and loop filter; Wherein, the pilot signal of input pilot tone track loop and the carrier wave of described digital controllable oscillator are in described complex multiplier complex multiplication, detect phase error, this phase error outputs to described loop filter again, by this loop filter control figure controlled oscillator, finish the locking of frequency and phase place.
3, the residual single-side band modulation system carrier of numeral according to claim 1 and 2 recovery device is characterized in that, described pilot amplitude estimation module comprises the average and hysteresis comparator of piece; Described pilot amplitude estimation module is carried out piece on average with filtering noise and estimating pilot frequency amplitude after at first the output in-phase signal of the quadrature of hilbert filter institute output signal and the digital controllable oscillator of the first pilot tone track loop being multiplied each other, and the pilot amplitude that estimates is outputed to described direct current removes module; Thresholding according to the pilot amplitude of estimating and system provide produces a gain control signal, and the gain of decision pilot tone input signal is big or small; Described hysteresis comparator is used to prevent near the frequent switching thresholding.
4, the residual single-side band modulation system carrier of a kind of numeral restoration methods is characterized in that, comprising: adopt high pass filter to taking out sideband signals through signal; Further adopt hilbert filter to take out and be in a pilot signal on the sideband; Described pilot signal is through once sending into the first pilot tone track loop after the gain adjustment; After the complex multiplier of the first pilot tone track loop carries out frequency spectrum shift, get back to the pilot signal of base band and send into the second pilot tone track loop by a low pass filter; The frequency of the first pilot tone track loop reach thick synchronously after, by the pilot amplitude estimation module output signal of the digital controllable oscillator of the pilot signal of hilbert filter output and the first pilot tone track loop is handled, estimate the amplitude of input pilot signal, and regulate the gain of the first pilot tone track loop input signal in view of the above; The pilot signal amplitude that estimates is sent into direct current and is removed module, removes pilot signal; Synthesize from the carrier signal that two pilot tone track loop digital controllable oscillator separately generates, obtain a synthetic carrier wave restoring signal, be used for the residual single sideband singal of numeral is carried out demodulation; Signal after the demodulation is sent into channel equalizer through after removing direct current signal, eliminates intersymbol interference;
The described first pilot tone track loop adopts low loop gain, and the second pilot tone track loop adopts high loop gain;
Described low pass filter comprises that piece is average, down-sampling, narrowband low-pass filter and up-sampling; Pilot signal after the locking is for the first time carried out the down-sampling of the average and 1/N speed of piece successively, and the low-rate signal behind the down-sampling enters narrowband low-pass filter, and outer interference of filtering direct current and noise carry out N times of up-sampling again, and restoring signal speed is to sampling rate; Wherein, N is 8 to 64 integer.
5, the residual single-side band modulation system carrier of numeral according to claim 4 restoration methods is characterized in that, it is fs/4 that described high pass filter takes out the sideband signals centre frequency, and wherein fs is the character rate 10.76MHz of digital residual single sideband modulated signal; The frequency spectrum shift that the complex multiplier of the described first pilot tone track loop is done is the fs/4 frequency spectrum shift.
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| CNB200510028181XA CN100499616C (en) | 2005-07-27 | 2005-07-27 | Carrier recovering apparatus for digital vestigial single sideband modulating system and recovering method thereof |
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| CNB200510028181XA CN100499616C (en) | 2005-07-27 | 2005-07-27 | Carrier recovering apparatus for digital vestigial single sideband modulating system and recovering method thereof |
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| CN100499616C true CN100499616C (en) | 2009-06-10 |
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Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101340526B (en) * | 2007-07-05 | 2011-04-27 | 上海明波通信技术有限公司 | Digital television signal receiving apparatus and method |
| CN102082938B (en) * | 2009-11-30 | 2013-03-27 | 展讯通信（上海）有限公司 | Analog television detection apparatus and method for the same |
| CN102355437B (en) * | 2011-08-05 | 2016-08-31 | 电子科技大学 | A kind of frequency spectrum detection preprocess method, pretreatment system and frequency spectrum detection system |
| CN104618276B (en) * | 2014-12-23 | 2018-07-03 | 大唐半导体设计有限公司 | Carrier frequency bias estimation and system in a kind of FM receiver |
| CN104901912B (en) * | 2015-05-18 | 2018-01-16 | 中国航空无线电电子研究所 | A kind of aviation radio communication double pilot carrier resetting device |
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