SYSTEMS, METHODS, AND APPARATUSES FOR DETECTING DIGITAL TELEVISION (DTV) COMMUNICATIONS SIGNALS

• US 20110169965A1
• Filed: 11/12/2010
• Published: 07/14/2011
• Est. Priority Date: 01/08/2010
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Kuhn, Matthew, Oh, Seungmok, Nayar, Bob, Kim, Andrew Joo, Hur, Youngsik
• Granted Patent: US 8,599,970 B2
• Time in Patent Office: Days
• US Class Current: 348/181
• CPC Class Codes: H04N 17/004 for digital television systems

Abstract

Embodiments of the invention may provide systems and methods for detecting the presence a DTV signal such as an ATSC DTV signal. The system and methods may be applied to a received RF signal that has been down-converted to a baseband or low-IF digitized signal. The systems and methods may detect a presence of a DTV signal by searching for its characteristic pilot signal, known to reside in a fixed frequency range for all valid DTV signals. This pilot signal may be extracted by processing the baseband or low-IF signal in multiple stages. The first stage may reduce the signal information to that pertaining to the frequency band covering all valid pilot frequencies and commensurately reduces the sampling rate, and hence computational complexity of subsequent operations. A second stage may then efficiently operate on this reduced rate signal to focus on a series of particular pilot frequencies for interrogation. For each such candidate frequency, the cyclostationarity of the signal may be measured and tested for statistical significance relative to the background energy to yield an effective test that is invariant with respect to the background noise level. In a simplified case, this can correspond to measuring the energy in a very tight candidate subband normalized against the energy from a larger subband. Furthermore, the energy in the candidate subband can be taken as the energy in a Fourier series coefficient.

Claims

1. A method for detecting a digital television (DTV) signal, comprising:

modulating a received radio frequency (RF) signal downwards to generate a down-converted modulated signal at a lower intermediate frequency (IF) or baseband frequency;

digitizing the modulated signal to generate a digitized baseband signal;

retaining a real portion of the digitized baseband signal to generate a test signal;

performing an initial focusing of the test signal to generate a focused signal by at least modulating the test signal downwards by a modulation frequency to generate a modulated test signal, wherein the modulation frequency is based upon a specified middle cyclic frequency associated with a band of candidate pilot frequencies, wherein the focused signal is derived from one or both of filtering or decimating the modulated test signal;

performing a fine focusing on the focus signal to generate an output signal by;

collecting, from the focus signal, a sequence of samples spanning a time period less than or equal to a system sensing time requirement;

obtaining Discrete Fourier Transform (DFT) coefficients of the collected sequence of samples, where the sequence of DFT coefficients corresponds to the cyclostationarity present in the received RF signal at various cyclic frequencies;

determining a set of correlation energy estimates based upon the DFT coefficients;

determining a representative correlation energy estimate as a maximum or largest correlation energy estimate from the determined set of correlation energy estimates,

normalizing the representative correlation energy estimate by a normalization factor, wherein the normalization factor is based upon the focused signal,

wherein the normalized correlation energy estimate is used to determine whether a digital television (DTV) signal is present in the received RF signal.

2. The method of claim 1, wherein the RF signal is received from an antenna.

3. The method of claim 1, wherein the modulation frequency is substantially half of the specified middle cyclic frequency approximately centering the band of candidate frequencies around DC.

4. The method of claim 1, wherein the focused signal is derived from one or both of filtering or decimating the modulated test signal by:

(i) applying a low-pass filter to the modulated test signal to generate a filtered output, wherein a bandwidth of the low-pass filter is larger than the band of the candidate pilot frequencies, and (ii) decimating the filtered output of the low-pass filter at a rate to generate the focused signal, wherein the rate is configured to reduce a sampling rate while not aliasing the filtered output.

5. The method of claim 1, wherein the set of correlation energy estimates is determined by taking a magnitude square of the DFT coefficients.

6. The method of claim 1, wherein the normalization factor is determined by measuring signal energy associated with the focused signal.

7. The method of claim 1, wherein normalizing the representative correlation energy estimate includes dividing the representative correlation energy estimate by the normalization factor.

8. The method of claim 1, wherein the normalized correlation energy estimate is compared to a threshold to determine whether the DTV signal is present in the received RF signal.

9. The method of claim 1, wherein the DFT coefficients are obtained by applying an inverse Discrete Fourier Transform to the collected sequence of samples.

11. A system for detecting a digital television (DTV) signal, comprising:

a first modulator that modulates a received radio frequency (RF) signal downwards to generate a down-converted modulated signal at a lower intermediate frequency (IF) or baseband frequency;

an analog-to-digital converter that digitizes the modulated signal to generate a digitized baseband signal;

a real-operator block that retains a real portion of the digitized baseband signal to generate a test signal;

an initial focusing stage, wherein the initial focusing stage generates a focused signal from the test signal by at least modulating, by a second modulator, the test signal downwards by a modulation frequency to generate a modulated test signal, wherein the modulation frequency is based upon a specified middle cyclic frequency associated with a band of candidate pilot frequencies, wherein the focused signal is derived from one or both of filtering or decimating the modulated test signal by a respective filter or decimator;

a fine focusing stage, wherein the fine focusing stage generates an output signal from the focus signal by collecting, from the focus signal, a sequence of samples spanning a time period less than or equal to a system sensing time requirement, and obtaining Discrete Fourier Transform (DFT) coefficients of the collected sequence of samples via a DFT block, where the sequence of DFT coefficients corresponds to the cyclostationarity present in the received RF signal at various cyclic frequencies;

one or more magnitude blocks that determine a set of correlation energy estimates based upon the DFT coefficients;

a max operator block that determines a representative correlation energy estimate as a maximum or largest correlation energy estimate from the determined set of correlation energy estimates,

wherein the representative correlation energy estimate normalized by a normalization factor, wherein the normalization factor is based upon the focused signal,

wherein the normalized correlation energy estimate is used to determine whether a digital television (DTV) signal is present in the received RF signal.

10. The method of claim 11, wherein the correlation energy estimate is determining by taking a magnitude of the DFT coefficients.

12. The system of claim 11, further comprising an antenna that receives the RF signal and delivers the received RF signal to the first modulator.

13. The system of claim 11, wherein the modulation frequency is substantially half of the specified middle cyclic frequency approximately centering the band of candidate frequencies around DC.

14. The system of claim 11, wherein the focused signal is derived from one or both of filtering or decimating the modulated test signal by:

(i) filter low-pass filtering to the modulated test signal to generate a filtered output, wherein a bandwidth of the low-pass filter is larger than the band of the candidate pilot frequencies, and (ii) the decimator decimating the filtered output of the low-pass filter at a rate to generate the focused signal, wherein the rate is configured to reduce a sampling rate while not aliasing the filtered output.

15. The system of claim 11, wherein the set of correlation energy estimates is determined by the one or more magnitude blocks taking a magnitude square of the DFT coefficients.

16. The system of claim 11, further comprising:

an energy detector that measures signal energy associated with the focused signal, wherein the normalization factor is determined from the measured measuring signal energy associated with the focused signal.

17. The system of claim 11, wherein the representative correlation energy estimate is normalized by dividing the representative correlation energy estimate by the normalization factor.

18. The system of claim 11, further comprising:

a threshold block that compares the normalized correlation energy estimate to a threshold to determine whether the DTV signal is present in the received RF signal.

19. The system of claim 11, wherein the DFT coefficients are obtained by applying an inverse Discrete Fourier Transform to the collected sequence of samples.

20. The system of claim 11, wherein the correlation energy estimate is determined by the one or more magnitude blocks taking a magnitude of the DFT coefficients.