CN100553175C - Be applicable to the carrier tracking loop of Digital Television Terrestrial Broadcasting - Google Patents
Be applicable to the carrier tracking loop of Digital Television Terrestrial Broadcasting Download PDFInfo
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- CN100553175C CN100553175C CNB2006100259882A CN200610025988A CN100553175C CN 100553175 C CN100553175 C CN 100553175C CN B2006100259882 A CNB2006100259882 A CN B2006100259882A CN 200610025988 A CN200610025988 A CN 200610025988A CN 100553175 C CN100553175 C CN 100553175C
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Abstract
A kind of carrier tracking loop that is applicable to Digital Television Terrestrial Broadcasting belongs to digital signal transmission field.The present invention includes FIR, DFE, multiplier, adder, decision device, subtracter, real device, accumulator and the loop low pass filter taken advantage of of equalizer; The complex signal that its demodulation reprocessing obtains is made up of I and Q two-way, is output as complex signal through multiple balanced FIR, takes advantage of again with always differing φ, takes out real baseband signal wherein; Send into adder with DFE output again, obtain the output of equalizer; Enter a decision device again, it is sent into DFE on the one hand import, enter subtracter again as it; The imaginary part Q ' of the FIR output of this signal and equalizer sends into the real device phase demodulation output of taking advantage of; Send into an accumulator and eliminate the phase demodulation noise; Obtain its output at last and just obtain digital controlled oscillator driving frequency error signal Δ f.The damage that the present invention's energy compensating signal is subjected to is carried out carrier wave and is recovered to handle, and removes the carrier frequency shake, keeps system's operate as normal, has the more characteristic of rapid convergence.
Description
Technical field
The present invention relates to a kind of carrier tracking loop of digital signal transmission technique field, relate in particular to a kind of carrier tracking loop that is applicable to Digital Television Terrestrial Broadcasting.
Background technology
In the high-speed digital signal wireless transmitting system such as digital high-definition television (HDTV), the linearity and the non-linear decline of signal process channel in the wireless transmission process, and in the receiver because the unoptimizables of sampling interval, carrier phase etc. cause the damage of signal, changed the state of original digital signal, these distortion variations all need be handled in receiver, thereby recover the correct data of making a start.
At single-carrier modulated transmission VSB (residual sideband), QAM (quadrature amplitude modulation), in OQAM (offset orthogonal amplitude modulation(PAM)) system, will all will carry out the operation of 4 steps to the received signal usually: promptly carrier wave recovers, and regularly recovers equilibrium, decoding.
In ADTB-T advanced digital television terrestrial broadcasting transmission system, adopted the OQAM modulation, and utilize add double pilot method in sending data on the lower sideband center add that respectively 1 pilot tone comes subcarrier to recover.And in receiver, the redundant information that also makes full use of lower sideband symmetry on the OQAM signal that forms of making a start comes common subcarrier recovery loop to carry out the trivial phase of frequency locking (DPDFLL).Referring to Fig. 1, this figure is a spectrogram, wherein represents with relative amplitude size in the frequency spectrum.This loop is based on classical COSTAS (Coase reaches this) loop generally speaking, to the frequency locking phase-locked loop of frequency sensitive, has the frequency-locking range of frequency locking ability and broad faster, and capturing carrier speed is very fast.But simultaneously because the error variance of output is also big, frequency jitter severity, so system also needs another carrier tracking loop, and these residual frequencies shakes are removed.And consider the most abominable situation, be that pilot tone and side information are all destroyed and can't extract the time, the capturing carrier failure, but simultaneously since equalizer and decoder still in work and dateout, if therefore also have a carrier tracking loop behind the equalizer, output resume with equalizer carries out carrier track, and system still can work to a certain extent so, can start once more up to the capturing carrier loop.
Phase demodulation equation based on the common error information of equilibrium output both can compensate intersymbol interference in actual applications, again can compensating frequency shake and phase jitter.
The equalizer of transverse filter structure mainly is the intersymbol interference that the antagonism channel fading causes, remedy the amplitude of multipath interference and the influence of time delay, but equalizer is little to the sensitiveness of frequency and phase place.Therefore the wobble information that has still comprised frequency jitter and phase place in the balanced data.Equaliser structure commonly used at present comprises a FIR finite impulse response filter and a DFE DFF.Owing to adopt different modulation systems, obtain the phase demodulation equation from the output of equalizer and also have nothing in common with each other.
Find through literature search prior art, in the disclosed patent No. of 2005.12.28 is in the Chinese patent " carrier tracking loop lock detector " of " CN200380103709.4 ", has proposed a kind of ATSC (Advanced Television Systems Committee) VSB (vestigial sideband) receiver.Obviously, this receiver can be used to adopt the system that is applicable to based on the VSB modulation.But can there be improved device in the system for adopting the OQAM modulation, to make full use of the information on I road and Q road.In the transmission system (such as the ATSC of the U.S.) based on the VSB modulation, equalizer is a real equilibrium, has only one road I road signal to participate in equalizer and decoding, and the Q road signal in the phase demodulation equation is to change through Hilbert from I road signal to get.Therefore actual frequency discrimination phase demodulation information is all from I road information.
Fig. 2 has shown a kind of carrier recovery loop block diagram commonly used in conjunction with equalizer.Yet in the transmission system based on the QAM modulation, equalizer is a multiple equilibrium, and I road and Q road are the two independent data messages, can extract carrier phase information respectively and carry out the frequency discrimination phase demodulation.Therefore, for the system that adopts the OQAM modulation, the information that can make full use of I road and Q road improves its carrier track characteristic.
Summary of the invention
The present invention is directed to the deficiencies in the prior art, a kind of carrier tracking loop that is applicable to Digital Television Terrestrial Broadcasting is provided.The technical issues that need to address of the present invention, be at high-speed digital signal in the wireless transmission process, the damage that signal is subjected to, distortion, need in receiver, carry out the processing that carrier wave recovers, make it return to out the correct data of making a start, the objective of the invention is in the receiver of ADTB-T OQAM system, after equalizer, add a carrier tracking loop, remove the shake of residue carrier frequency.Simultaneously also can be when capturing carrier be failed, system still can keep operate as normal a period of time and wait for capturing carrier once more.
The objective of the invention is to rely on following technical scheme to realize, carrier tracking loop in a kind of Digital Television Terrestrial Broadcasting, in the receiver of signal transmission system, produce and phase place is untwisted and formed jointly by the digital controlled oscillator drive signal, this carrier tracking loop comprises the FIR of an equalizer, DFE with an equalizer, a multiplier, an adder, a decision device, a subtracter, a reality is taken advantage of device, an accumulator, a loop low pass filter, the step of its production process is that the complex signal that OQAM demodulation reprocessing obtains is formed (I+jQ) by I and Q two paths of signals; Through output after the multiple balanced FIR still be complex signal (I '+jQ '), (I '+jQ ') and total differing
Take advantage of the back to remove frequency and phase jitter again, take out real baseband signal wherein; This real baseband signal is sent into an adder with DFE output, and addition obtains the output SUM of equalizer; Entering a decision device again adjudicates and obtains decision signal DATA; It is sent into DFE on the one hand import, enter a subtracter together with SUM on the other hand as it; The output error signal of subtracter is ERR; The imaginary part Q ' of the FIR of this signal and equalizer output sends into a reality together and takes advantage of device to obtain (SUM-DATA) * Q ' to export for phase demodulation; Send into an accumulator subsequently and eliminate the phase demodulation noise; Phase discrimination signal after the denoising send into a loop low pass filter LPF again, obtain its output and just obtain digital controlled oscillator driving frequency error signal Δ f.In NCO of the present invention (digital controlled oscillator) driving signal generating method, decision device promptly can be the hard decision device, also can be a soft-decision device.
In the various transmission modes of ADTB-T, decision device can be finished in conjunction with the channel-decoding after the equilibrium:
32-OQAM, 16-OQAM and 4-OQAM: decision device has adopted the hard decision of constellation point.
4-OQAM-E: decision device adopts Nordstrom-Robinson sign indicating number (NR) decoder of soft inputting and soft output (SISO).Described loop low pass filter can be active proportional-integral filter.
This driving frequency error signal Δ f can directly drive digital controlled oscillator NCO and be differed
Send into multiplier behind the FIR and carry out phase place and untwist, form a carrier tracking loop jointly with digital controlled oscillator, multiplier.
This driving frequency error signal Δ f can directly drive digital controlled oscillator NCO and be differed
With differing in the dependent phase track loop
Addition obtains total differing
Sending into multiplier behind the FIR together carries out phase place and untwists; This frequency error signal, digital controlled oscillator,
With carrier phase tracking loop of the common composition of multiplier.
This driving frequency error signal Δ f can directly feed back in the balanced preceding capturing carrier loop that combines with demodulation, drives a digital controlled oscillator with carrier deviation Δ w, is differed
Multiplier in the incoming carrier Capture Circle carries out phase place and untwists; Also can be used as independently carrier tracking loop and the big loop of the common composition of capturing carrier loop second order carrier wave recovery feedback.
Put it briefly in the receiver of ADTB-T OQAM system, after equalizer, add a carrier tracking loop, remove the carrier frequency shake.This carrier tracking loop utilizes the FIR plural number output of equalizer, and the judgement data after the equalizer output, obtains the phase demodulation equation, extracts frequency discrimination information from the phase demodulation equation, obtain the activation bit of NCO, and then driving N CO carries out carrier track.This carrier tracking loop promptly can independently carry out carrier track, can also combine with phase tracking loop, eliminates frequency jitter and phase jitter behind the equalizer jointly.Even above-mentioned NCO activation bit can also be fed back to equalizer demodulation module before, drive the NCO in the capturing carrier loop jointly, thereby participate in the capturing carrier process.
The invention has the beneficial effects as follows, this carrier tracking loop can compensate the damage that signal is subjected in the radio transmission process, can carry out carrier wave recovers to handle, remove frequency jitter, simultaneously also can be when capturing carrier be failed, the assurance system still can keep operate as normal a period of time, waits for capturing carrier once more.Be applied to the carrier tracking loop of VSB modulation signal with respect to tradition, the present invention has utilized the information on I road and Q road more fully, thereby has the more characteristic of rapid convergence.
Description of drawings
Fig. 1 adds the double pilot frequency spectrum for ADTB-T OQAM system data
Fig. 2 is the block diagram in conjunction with the carrier recovery loop commonly used of equalizer
Fig. 3 is that the NCO activation bit of carrier tracking loop of the present invention produces block diagram
Fig. 4 is the block diagram (NCO output only provides the data behind the FIR to carry out carrier track) of first embodiment of carrier tracking loop of the present invention
Fig. 5 is the block diagram (output of NCO promptly provides the carrier wave of demodulation module to recover, and also carries out carrier track to the data behind the FIR) of second embodiment of carrier tracking loop of the present invention
Fig. 6 is the block diagram (NCO output only provides the carrier wave in the demodulation module to recover) of the 3rd embodiment of carrier tracking loop of the present invention
Embodiment
Further specify embodiment below in conjunction with accompanying drawing.
Fig. 3 has shown the basic structure of carrier tracking loop of the present invention and the block diagram that the NCO activation bit produces.This carrier tracking loop comprises the FIR of an equalizer and the DFE of an equalizer, a multiplier, and an adder, a decision device, a subtracter, a reality is taken advantage of device, an accumulator and a loop low pass filter.
Wherein, loop low pass filter generally can also adopt active proportional-integral filter to replace.
Its main workflow is: the complex signal that OQAM demodulation reprocessing obtains is formed (I+jQ) by I and Q two paths of signals; Through output after the multiple balanced FIR still be complex signal (I '+jQ '), (I '+jQ ') and total differing
Take advantage of (suitable and phase place is untwisted) back to remove frequency and phase jitter again, take out real baseband signal wherein; Above-mentioned real baseband signal is sent into an adder with DFE output, and addition obtains the output SUM of equalizer; Balanced output SUM enters a decision device (can be hard decision, also can be soft-decision) and adjudicates and obtain decision signal DATA; Above-mentioned judgement output DATA sends into DFE on the one hand and imports as it, enters a subtracter (SUM-DATA) together with SUM on the other hand; The output error signal ERR of subtracter; The imaginary part Q ' of the FIR of error signal ERR and equalizer output sends into a reality together and takes advantage of device to obtain (SUM-DATA) * Q ' to export for phase demodulation; Because the noise of this phase demodulation equation is bigger, above-mentioned phase demodulation output is sent into an accumulator subsequently and is eliminated the phase demodulation noise; Phase discrimination signal after the above-mentioned denoising send into a loop low pass filter LPF (also can be active proportional-integral filter) again, obtain the frequency error signal Δ f that LPF output just obtains driving N CO.
Fig. 4 has shown the block diagram of first embodiment of carrier tracking loop of the present invention.Wherein, be different from embodiment shown in Figure 3 and be, NCO output only provides the data behind the FIR to carry out carrier track.Referring to Fig. 4, above-mentioned NCO drive signal can directly drive a NCO, the phase compensation that obtains
As total differing
Enter above-mentioned multiplier, phase place is carried out in the output of FIR untwist.Because this differs by frequency jitter and causes, so Fig. 4 is exactly an embodiment in conjunction with the carrier track of balanced output.
Fig. 5 has shown the block diagram of second embodiment of carrier tracking loop of the present invention.Wherein, be different from embodiment shown in Figure 3 and be, the output of NCO promptly provides the carrier wave of demodulation module to recover, and also carries out carrier track to the data behind the FIR.Referring to second embodiment of Fig. 5 in conjunction with the carrier track of equilibrium output, the frequency difference signal of the driving N CO that causes by frequency jitter that obtains among the embodiment of the carrier track that Fig. 4 provides, separate in the capturing carrier loop of mediating before can also directly feeding back to equilibrium, carrier deviation signal driving N CO in the capturing carrier loop forms two rank of carrier wave recovery and feeds back big loop.
Fig. 6 has shown the block diagram of the 3rd embodiment of carrier tracking loop of the present invention.Wherein, be different from embodiment shown in Figure 3 and be, NCO output only provides the carrier wave in the demodulation module to recover.Referring to three embodiment of Fig. 6 in conjunction with the carrier track of equilibrium output, the phase difference signal that causes by frequency jitter among Fig. 4
Also can with the phase difference signal of relevant phase tracking loop
Addition obtains total phase difference signal
Enter above-mentioned multiplier, phase place is carried out in the output of FIR untwist.
Claims (6)
1. method for capturing carrier that is applicable to the carrier tracking loop of Digital Television Terrestrial Broadcasting, comprise: the DFE of the FIR of an equalizer and an equalizer, a multiplier, an adder, a decision device, a subtracter, a reality are taken advantage of device, an accumulator and a loop low pass filter, it is characterized in that the complex signal that OQAM demodulation reprocessing obtains is formed (I+jQ) by I and Q two paths of signals; Through output after the multiple balanced FIR still be complex signal (I '+jQ '), (I '+jQ ') and total differing
Take advantage of the back to remove frequency and phase jitter again, take out real baseband signal wherein; Above-mentioned real baseband signal is sent into an adder with DFE output, and addition obtains the output SUM of equalizer; Balanced output SUM enters a decision device and adjudicates and obtain decision signal DATA; Above-mentioned judgement output DATA sends into DFE on the one hand and imports as it, enters a subtracter together with SUM on the other hand; Subtracter output error signal ERR; The imaginary part Q ' of the FIR of error signal ERR and equalizer output sends into a reality together and takes advantage of device to obtain (SUM-DATA) * Q ' to export for phase demodulation; Above-mentioned phase demodulation output is sent into an accumulator subsequently and is eliminated the phase demodulation noise; Phase discrimination signal after the above-mentioned denoising is sent into a loop low pass filter LPF again, obtains the frequency error signal Δ f that LPF output just obtains driving digital controlled oscillator.
2. the method for capturing carrier that is applicable to the carrier tracking loop of Digital Television Terrestrial Broadcasting according to claim 1 is characterized in that, described decision device is the hard decision device, or the soft-decision device.
3. according to claim 1 or the 2 described method for capturing carrier that are applicable to the carrier tracking loop of Digital Television Terrestrial Broadcasting, it is characterized in that described decision device comprises the hard decision of constellation point, it is applicable to the various transmission modes of ADTB-T, comprise 32-OQAM, 16-OQAM and 4-OQAM; Decision device or the NR sign indicating number decoder that adopts soft inputting and soft to export are applicable to 4-OQAM-E.
4. the method for capturing carrier that is applicable to the carrier tracking loop of Digital Television Terrestrial Broadcasting according to claim 1 is characterized in that, described loop low pass filter is active proportional-integral filter.
5. the method for capturing carrier that is applicable to the carrier tracking loop of Digital Television Terrestrial Broadcasting according to claim 1 is characterized in that, described driving frequency error signal Δ f directly drives digital controlled oscillator and differed
Send into multiplier behind the FIR and carry out phase place and untwist, this Δ f and digital controlled oscillator, multiplier are formed a carrier tracking loop jointly.
6. the method for capturing carrier that is applicable to the carrier tracking loop of Digital Television Terrestrial Broadcasting according to claim 1, it is characterized in that, described driving frequency error signal Δ f directly feeds back in the balanced preceding capturing carrier loop that combines with demodulation, drive a digital controlled oscillator with carrier deviation Δ w, differed
Multiplier in the incoming carrier Capture Circle carries out phase place and untwists; Second order carrier wave of the common composition of this Δ f and capturing carrier loop recovers the big loop of feedback.
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| CNB2006100259882A CN100553175C (en) | 2006-04-24 | 2006-04-24 | Be applicable to the carrier tracking loop of Digital Television Terrestrial Broadcasting |
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| CNB2006100259882A CN100553175C (en) | 2006-04-24 | 2006-04-24 | Be applicable to the carrier tracking loop of Digital Television Terrestrial Broadcasting |
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Granted publication date: 20091021 Termination date: 20130424 |