WO2006077559A2 - Procede et dispositif pour la detection de la presence de signal de television numerique - Google Patents

Procede et dispositif pour la detection de la presence de signal de television numerique Download PDF

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Publication number
WO2006077559A2
WO2006077559A2 PCT/IB2006/050229 IB2006050229W WO2006077559A2 WO 2006077559 A2 WO2006077559 A2 WO 2006077559A2 IB 2006050229 W IB2006050229 W IB 2006050229W WO 2006077559 A2 WO2006077559 A2 WO 2006077559A2
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WO
WIPO (PCT)
Prior art keywords
autocorrelation
signal
digital television
received signal
delay
Prior art date
Application number
PCT/IB2006/050229
Other languages
English (en)
Other versions
WO2006077559A3 (fr
Inventor
Dagnachew Birru
Kiran S. Challapali
Original Assignee
Koninklijke Philips Electronics N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Priority to JP2007551801A priority Critical patent/JP2008538166A/ja
Publication of WO2006077559A2 publication Critical patent/WO2006077559A2/fr
Publication of WO2006077559A3 publication Critical patent/WO2006077559A3/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N17/00—Diagnosis, testing or measuring for television systems or their details
    • H04N17/004—Diagnosis, testing or measuring for television systems or their details for digital television systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only

Definitions

  • This invention pertains to the field of signal detection, and more particularly to a method and apparatus for detecting the presence of a digital television (DTV) signal.
  • DTV digital television
  • the Commission proposed to require that these unlicensed transmitters incorporate the capability to identify unused or vacant TV channels and to only transmit on such vacant channels.
  • One idea advanced by the FCC would be to incorporate sensing capabilities in the unlicensed transmitter to detect whether other transmitters (i.e., licensed terrestrial TV broadcast transmitters) are operating on a particular channel in the area before the unlicensed transmitter could be activated.
  • a fixed unlicensed transmitter could be required to incorporate an antenna and a receiver capable of detecting whether a particular terrestrial TV channel is actually in use in the area where the transmitter is to be installed. If the antenna and receiver detect a terrestrial television broadcast signal on a particular channel, then the unlicensed transmitter would be prevented from using that channel.
  • the unlicensed transmitter would only be permitted to operate on a particular channel in a particular location if the antenna and receiver verify that no terrestrial television broadcast signal is present on that channel.
  • sensing would have to be much more sensitive than the receivers normally used to receive the terrestrial TV signal and decode the audio and video signals. That is because the terrestrial TV signal is subject to fading, structural blockage, etc., and therefore it is possible that the measurements might be made at a location where the terrestrial television signal is lower than in surrounding areas.
  • a method and apparatus for detecting the presence of a terrestrial television signal particularly, a terrestrial digital television (DTV) signal. It also would be desirable to provide such a method and apparatus which can detect such signals at low power levels, well below the level necessary for a viewable picture. It would further be desirable to detect a DTV signal without requiring synchronization to the DTV signal. It would still further be desirable to provide such a method and apparatus which can be provided at low cost.
  • DTV terrestrial digital television
  • a method of detecting the presence of a digital television signal comprises sampling a received signal; performing at least one autocorrelation of the sampled received signal over a correlation window comprising N samples to produce autocorrelation results, wherein the autocorrelation is performed with a delay that is an integer multiple of a period between transmissions of a training sequence within a digital television signal; and comparing the autocorrelation results to a threshold and determining that a digital television signal is present when one of the autocorrelation results is greater than the threshold.
  • a receiver for detecting the presence of a digital television signal comprises a sampler adapted to sample a received signal at a set rate; an autocorrelator adapted to autocorrelate the sampled received signal to produce autocorrelation results, wherein the autocorrelation is performed with a delay that is an integer multiple of a period between transmissions of a training sequence within a digital television signal; and a comparator adapted to compare the autocorrelation results to a threshold and to indicate detection of a digital television signal when one of the autocorrelation results is greater than the threshold.
  • FIG. 1 shows the frame structure of a digital television (DTV) signal
  • FIG. 2 shows a flowchart of a method of detecting the presence of a DTV signal
  • FIG. 3 shows a block diagram of a receiver capable of detecting the presence of a DTV signal
  • FIG. 4 shows a block diagram of a first embodiment of a correlator that can be used in the receiver of FIG. 3;
  • FIG. 5 shows a block diagram of a second embodiment of a correlator that can be used in the receiver of FIG. 3;
  • FIG. 6 shows a simplified block diagram of one embodiment of a portion of the receiver of FIG. 3.
  • FIG. 7 shows the output of an embodiment of the correlator of FIG. 4 where the input signal to noise ratio is -5dB;
  • FIG. 8 shows the output of an embodiment of the correlator of FIG. 4 in the presence of a strong multipath "ghost" signal where the input signal to noise ratio is -5dB.
  • FIG. 1 shows the frame structure of a digital television (DTV) signal according to the North American DTV standard.
  • a frame consists of 313 segments. Each segment consists of 832 symbols.
  • a training sequence is transmitted. This is also commonly known as a field sync. Accordingly, the training sequence is a periodic signal within the DTV signal, transmitted once every 24.2 ms.
  • T is the sampling rate
  • f 0 is the carrier frequency error
  • n(mT) is the noise component.
  • the sampling rate T is not necessarily identical to the sampling rate of the DTV signal. In fact, such a feature would lead to simpler implementation since the detector does not have to synchronize with the DTV signal.
  • a(mT) is the received signal component described by equation (2):
  • x is the transmitted DTV information and h is the terrestrial channel impulse response.
  • the channel impulse response can be time-variant. Nevertheless, for the purpose of the following analysis, it is assumed that the time- variation within the detection window will be minimal.
  • the DTV signal periodically sends a known training sequence every 24.2ms.
  • this periodic component (the training sequence) is typically accomplished by correlating the received signal with the local replica of the training sequence.
  • this method requires almost perfect timing and carrier frequency synchronization with the transmitted signal.
  • synchronization of the DTV signal has been found to be problematic in the presence of frequency-selective fading. It is also computationally expensive.
  • FIG. 2 shows a flowchart of a robust method of detecting the presence of a DTV signal by use of this periodic signal, without requiring precise timing and carrier frequency synchronization.
  • a receiver tunes to a channel where it is desired to determine whether or not a DTV signal is present.
  • the receiver receives whatever signal (including noise) is present in the channel, and downconverts the received signal such that the channel can be digitally sampled.
  • the receiver may be possible to sample the channel directly at RF frequency.
  • the signal is digitally sampled at a sampling rate, 1/T.
  • the sampling rate may be the same as, or approximately the same as, the data rate of the bits in the training sequence, but this is not necessary.
  • the sampling rate 1/T > 10.6 Msamples/sec (T ⁇ 94.3 nsec).
  • a fourth step 240 the sampled received signal is autocorrelated over a window on N samples to produce an autocorrelation result, according to equation (3):
  • N is 500.
  • the delay used in the autocorrelation is equal, or approximately equal, to the period between transmissions of the training sequence in the DTV signal.
  • the autocorrelation determines the degree of correlation of the sampled, received signal with a delayed version of itself, where the delay is equal to the period between training sequence transmissions.
  • the periodic components of the DTV signal every 24.2ms are almost the same. Accordingly, if a DTV signal is present, the autocorrelation result of equation (4) will show a large peak every 24.2ms.
  • a fifth step 250 the correlation results of equation (4) are compared at each sample interval T with a threshold, X, for determining whether a digital television signal is present. That is, so long as the threshold X is greater than the autocorrelation results f(m), no DTV signal is detected.
  • the threshold value, X is a function of the noise level, the AGC setting and expected signal strength. Usually, the AGC is maximized to catch the weak signals.
  • the main idea is to detect the existence of a correlation peak with respect to the correlation noise floor.
  • the AGC is set to a fixed value so that it does not affect the operation. Usually, it is set to the maximum value to catch weak signals.
  • the threshold X may be determined by calculating a moving average of all of the autocorrelation results f(m) over a moving window, M, larger than the correlation window N.
  • the correlation output is passed through a window averaging unit that can be implemented using a simple low pass filter. This may be achieved by comparing the correlation peak over a certain window to the average correlation output as discussed in further detail with respect to FIG. 6 below.
  • this scheme will normally provide detection within 1 frame symbol period (i.e., 24.2ms). If a DTV signal is detected, then the process returns to step 210, tunes to a new channel, and repeats the process until all permissable DTV channels have been checked. If a DTV signal is not detected, then the steps 240 and 250 are repeated until a set time period for DTV signal detection has expired without detecting a DTV signal. In that case, in a step 260, it is determined that the channel does not have a DTV signal at that location. In that case, in a step 270 it is determined whether all available DTV channels have been checked. If so, then the process ends.
  • FIG. 3 shows a block diagram of a receiver 300 capable of detecting the presence of a DTV signal by performing an autocorrelation to take advance of the periodic transmission of the training sequence in the DTV signal.
  • the receiver 300 includes a tuner 310, a downconverter 320, a signal sampler 330, an autocorrelator 340, and a comparator 350.
  • the operation of the receiver 300 has been explained above with respect to FIG. 2 and for conciseness will not be repeated.
  • FIG. 4 shows a block diagram of a first embodiment of an autocorrelator 400 that can be used in the receiver of FIG. 3.
  • the autocorrelator 400 includes a D-length delay 410, a multiplier 420, an N-length delay 430, a summation circuit 440, and a T delay 450.
  • the autocorrelator 400 implements the equation (4) above, and can be implemented at relatively low cost.
  • FIG. 5 shows a block diagram of a second embodiment of an autocorrelator 500 that can be used in the receiver of FIG. 3 and that employs multiple (e.g., two) autocorrelation branches.
  • the autocorrelator 500 includes: correlation branches 505, each including a D-length delay 510 and a multiplier 520; a correlation branch output summer 525; an N-length delay 530; a summation circuit 540; and a T delay 550.
  • the autocorrelator 500 implements the equation (5) above. Of course, more than two correlation branches 505 can be employed.
  • FIG. 6 shows a simplified block diagram of one embodiment of a portion of the receiver of FIG. 3, including the autocorrelator 340 and comparator 350. In the embodiment of FIG.
  • the comparator 350 includes a window averaging unit 610 adapted to average the autocorrelation results over a moving window, M, and to output the threshold, X, to a decision circuit 620.
  • the size of the moving window M is larger than the size of the autocorrelation window, N.
  • the threshold, X for determining whether or not a DTV signal is present, is set as an average of all of the autocorrelation results over the moving window, M.
  • the window averaging unit 610 may be a low pass filter. In order to evaluate the performance of the method and system described above, simulations were performed using a model for the DTV signal.
  • FIG. 7 shows the simulated output of an embodiment of the autocorrelator of FIG. 4 where the input signal-to-noise ratio is -5dB.
  • the threshold of visibility for DTV signals is about 15dB SNR. This means that the simulated signal SNR is 2OdB worse. This 2OdB SNR difference will provide sufficient margin for practical agile radio systems.
  • the signal power at the receiver making the detection can be lower by 2OdB while the signal power at the nearby DTV can be the minimum that the TV receiver can reliably decode.
  • this 2OdB difference can be margin that can account for, e.g., deep fading.
  • a simulation was performed by adding a strong (OdB) echo at 1 ⁇ s delay. This echo was subjected to 5Hz Doppler frequency to account for channel variation.
  • FIG. 8 shows the simulated output of an embodiment of the correlator of FIG. 4 in the presence of a strong multipath "ghost" signal where the input signal to noise ratio is again -5dB.
  • FIG. 8 clearly demonstrates that the DTV signal can still be detected even if it is subject to such multipath conditions.
  • a conventional DTV receiver would require 22- 3OdB SNR to decode such a signal. This indicates that the receiver of FIG. 3 is working at least 27dB below the requirement for a DTV receiver, hence a 27dB margin.
  • the above-described method and apparatus can detect a terrestrial digital television (DTV) signal at low power levels well below the level necessary for a viewable picture. They do so without requiring synchronization to the DTV signal, and can be implemented at relatively low cost.
  • DTV terrestrial digital television

Abstract

L'invention concerne un procédé (200) et un système (300) pour la détection de la présence de signal de télévision numérique tirant parti de la séquence d'apprentissage périodique intrinsèque de ce signal, par autocorrélation du signal reçu à échantillonnage numérique sur la base d'un retard (410, 510) environ égal à la période inter-séquence d'apprentissage. Si on détecte une crête de corrélation dépassant un seuil fixé, il est établi qu'un signal de télévision numérique est présent, sinon il est établi qu'aucun signal de ce type n'est présent.
PCT/IB2006/050229 2005-01-21 2006-01-20 Procede et dispositif pour la detection de la presence de signal de television numerique WO2006077559A2 (fr)

Priority Applications (1)

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JP2007551801A JP2008538166A (ja) 2005-01-21 2006-01-20 デジタルテレビ信号の存在を検出する方法及び機器

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US64608805P 2005-01-21 2005-01-21
US60/646,088 2005-01-21

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WO2006077559A3 WO2006077559A3 (fr) 2006-10-12

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008108795A1 (fr) * 2007-03-08 2008-09-12 Thomson Licensing Appareil et procédé pour détecter un signal multiporteur en utilisant une cyclostationnarité
WO2010131139A1 (fr) * 2009-05-14 2010-11-18 Koninklijke Philips Electronics, N.V. Détection robuste de transmissions dvb-t/h en présence de décalages de fréquence
WO2010138006A1 (fr) * 2009-05-29 2010-12-02 Motorola, Inc Procédé et système destinés à une synchronisation de séquence de formation dans un réseau de communication numérique
WO2012136260A1 (fr) * 2011-04-07 2012-10-11 Level 3 Communications, Llc Systèmes de test multimédia
US8839282B2 (en) 2011-04-07 2014-09-16 Level 3 Communications, Llc Multimedia test systems

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EP0266965A2 (fr) * 1986-11-06 1988-05-11 AT&T Corp. Classification de signal à fréquence vocale
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EP0268519A1 (fr) * 1986-10-31 1988-05-25 Office National D'etudes Et De Recherches Aerospatiales(O.N.E.R.A.) Système de traitement de signaux noyés dans un bruit et son application en vélocimétrie laser à franges
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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008108795A1 (fr) * 2007-03-08 2008-09-12 Thomson Licensing Appareil et procédé pour détecter un signal multiporteur en utilisant une cyclostationnarité
WO2010131139A1 (fr) * 2009-05-14 2010-11-18 Koninklijke Philips Electronics, N.V. Détection robuste de transmissions dvb-t/h en présence de décalages de fréquence
CN102422635A (zh) * 2009-05-14 2012-04-18 皇家飞利浦电子股份有限公司 存在频率偏移情况下dvb-t/h传输的鲁棒感测
US9100226B2 (en) 2009-05-14 2015-08-04 Koninklijke Philips N.V. Robust sensing of DVB-T/H transmissions in the presence of frequency offsets
WO2010138006A1 (fr) * 2009-05-29 2010-12-02 Motorola, Inc Procédé et système destinés à une synchronisation de séquence de formation dans un réseau de communication numérique
WO2012136260A1 (fr) * 2011-04-07 2012-10-11 Level 3 Communications, Llc Systèmes de test multimédia
US8839282B2 (en) 2011-04-07 2014-09-16 Level 3 Communications, Llc Multimedia test systems

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WO2006077559A3 (fr) 2006-10-12
JP2008538166A (ja) 2008-10-09

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