Method and apparatus for detecting the presence of a DTV pilot tone in a high noise environment

• US 8,949,061 B2
• Filed: 07/13/2011
• Issued: 02/03/2015
• Est. Priority Date: 07/13/2011
• Status: Expired due to Fees

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: Quarterhill Inc. (f/k/a Wi-LAN Inc.)
• Inventors: Samarasooriya, Vajira, Payer, Daniel, Wight, James S.
• Primary Examiner(s): Feliciano, Eliseo Ramos
• Assistant Examiner(s): Stifter, Jr., Terence
• Application Number:
  US13/182,172
• Publication Number:
  US 20130018622A1
• Time in Patent Office: 1,301 Days
• Field of Search: 702/111
• US Class Current: 702/111
• CPC Class Codes: H04B 1/76 Pilot transmitters or receivers for control of transmission or for equalising
• CPC Class Codes: H04N 5/50 Tuning indicators; Automatic tuning control

Abstract

A DTV pilot tone is detected in a noisy environment by computing a power average of Fast Fourier Transform (FFT) output spectra of a received signal, finding a power peak in the averaged outputs, computing an adjustment parameter to center the power peak in a Discrete Fourier Transform bin of the averaged output spectra, applying the adjustment parameter to adjust the received signal, computing a coherent average of FFT output spectra of the adjusted signal, and, testing a power spectrum of the coherent average for the presence of the DTV pilot tone.

Claims

1. A method of detecting the presence of a digital television (DTV) pilot tone in a high noise environment, comprising:

computing a power average of a plurality of Fast Fourier Transform (FFT) output spectra of a digital baseband signal derived from a TV band channel to create a power averaged output spectrum;

estimating a power peak in the power averaged output spectrum;

computing based upon the estimated power peak, an adjustment parameter to adjust the signal to center the power peak in a Discrete Fourier Transform (DFT) bin of the FFT output spectra;

applying the computed parameter to adjust the signal;

computing a coherent average of FFT output spectra of the adjusted signal;

computing a power spectrum of the coherent averaged output spectrum;

testing the power spectrum for the DTV pilot tone by identifying a peak power in the power spectrum of the coherent averaged output spectrum; and

determining whether the test exceeds a threshold.

2. The method as claimed in claim 1 wherein computing the power average comprises computing:

P_k=1/NΣ

_i=1^N|X_k^real(i)+jX_k^imag(i)|²

Where;

P_k is the power average;

|X_k(i)|=|X_k^real(i)+jX_k^imag(i)| is the DFT magnitude for DFT bin k at i-th averaging cycle;

k=1, 2, . . . , N_FFT; and

X_k^real(i) &

X_k^imag(i) are the in-phase and quadrature components of the FFT output of the k-th bin in the i-th averaging cycle.

3. The method as claimed in claim 2 wherein computing the adjustment parameter comprises computing a frequency adjustment parameter.

4. The method as claimed in claim 3 further comprising computing a normalized offset of the power peak from a center of a DFT-bin with a highest power magnitude;

using;

5. The method as claimed in claim in claim 4 wherein computing the frequency adjustment parameter further comprises computing a frequency offset (Δ

f) of the DTV pilot tone with respect to the center of a DFT bin as follows;

6. The method as claimed in claim 5 further comprising estimating a frequency (f_P) of the power peak by computing:

7. The method as claimed in claim 6 further comprising computing the frequency adjustment parameter (f_Corr) by computing:

8. The method as claimed in claim 1 wherein computing the adjustment parameter comprises computing a sampling rate adjustment parameter.

9. The method as claimed in claim 8 wherein computing the sampling rate adjustment parameter comprises computing a normalized offset of the power peak from a center of a DFT-bin (k_max) having a highest power magnitude:

10. The method as claimed in claim 9 wherein computing the sampling rate adjustment parameter further comprises computing:

11. The method as claimed in claim 10 wherein applying the adjustment parameter comprises computing:

f<sub>s—

new</sub>=f_s×

(1+β

)

Where;

f<sub>s—

new</sub> is the adjusted sampling rate.

12. The method as claimed in claim 1 wherein computing the coherent average comprises computing:

13. The method as claimed in claim 12 wherein testing the power spectrum for the DTV pilot tone comprises identifying a DFT bin number (k_peak) with a peak power (P_Max) in the power spectrum.

14. The method as claimed in claim 13 further comprising computing a noise floor around P_Max using a programmable number (k_N) of DFT bins around P_max.

15. The method as claimed in claim 14 wherein (K_N-PSD) defines a set of DFT bins used to compute a noise floor power spectral density around (P_Max) as follows:

K_N-PSD≡

└

k_peak−

1−

k_N,k_peak−

2┘

∪

└

k_peak+2,k_peak+1+k_N┘

.

16. The method as claimed in claim 15 noise power spectral density in then computed using the following DFT bins:

kε

K_N-PSD.

17. The method as claimed in claim 16 wherein the noise power spectral density (N_PSD) is computed as follows:

18. The method as claimed in claim 17 wherein determining whether the test exceeds a threshold comprises computing:

19. Apparatus that detects the presence of a digital television (DTV) pilot tone in a high noise environment, comprising:

a spectrum power averager that averages a plurality of output spectra of a Fast Fourier Transform (FFT) of a baseband signal derived from a television band channel to create an averaged output spectrum;

a peak frequency estimator that estimates a peak power of the averaged output spectrum, determines a frequency of the peak power and computes a frequency adjustment parameter to center the peak power in a Discrete Fourier Transform bin of the output spectra;

a complex frequency shifter that uses the frequency adjustment parameter to adjust a frequency of the signal to center the peak power in the Discrete Fourier Transform bin;

a spectrum coherent averager that averages output spectra of a FFT of the baseband signal at the adjusted frequency and computes a power spectrum from the coherent average;

a peak search algorithm that computes a peak power in the computed power spectrum;

a noise floor estimator that computes a noise floor around the peak power of the computed power spectrum; and

a pilot tone tester that compares the peak power of the computed power spectrum with the noise floor to determine if the DTV pilot tone has been detected when a threshold has been exceeded.

20. Apparatus that detects the presence of a digital television (DTV) pilot tone in a high noise environment, comprising:

a spectrum power averager that averages output spectra of a Fast Fourier Transform (FFT) of a baseband signal derived from a television band channel;

a peak frequency estimator that estimates a peak power of the averaged output spectra, determines a frequency of the peak power and computes a frequency adjustment parameter to center the peak power in a Discrete Fourier Transform bin of the FFT output spectrum;

an analog radio frequency front end which uses the sampling rate adjustment parameter to re-program a high-resolution programmable phase locked loop (PLL) that permits a tuning frequency to be programmed to effect the frequency adjustment;

a spectrum coherent averager that averages output spectra of a FFT of the baseband signal at the adjusted frequency and computes a power spectrum from the coherent average;

a peak search algorithm that computes a peak power in the computed power spectrum;

a noise floor estimator that computes a noise floor around the peak power of the computed power spectrum; and

a pilot tone tester that compares the peak power of the computed power spectrum with the noise floor to determine if the DTV pilot tone has been detected.

21. Apparatus that detects the presence of a digital television (DTV) pilot tone in a high noise environment, comprising:

a spectrum power averager that averages output spectra of a Fast Fourier Transform (FFT) of a baseband signal derived from a television band channel;

a peak frequency estimator that estimates a peak power of the averaged output spectra, determines a frequency of the peak power and computes a frequency adjustment parameter to center the peak power in a Discrete Fourier Transform bin of the output spectrum;

a digital mixer that uses the frequency adjustment parameter to re-program a digital phase locked loop or a direct digital synthesizer that permits a mixing frequency to be tuned to effect the frequency adjustment;

a spectrum coherent averager that averages output spectra of a FFT of the baseband signal at the adjusted frequency and computes a power spectrum from the coherent average;

a peak search algorithm that computes a peak power in the computed power spectrum;

a noise floor estimator that computes a noise floor around the peak power of the computed power spectrum; and

a pilot tone tester that compares the peak power of the computed power spectrum with the noise floor to determine if the DTV pilot tone has been detected.

22. Apparatus that detects the presence of a digital television (DTV) pilot tone in a high noise environment, comprising:

a spectrum power averager that averages output spectra of a Fast Fourier Transform (FFT) of a baseband signal derived from a television band channel;

a peak frequency estimator that estimates a peak power of the averaged output spectra, determines a frequency of the peak power and computes a sampling rate adjustment parameter to center the peak power in a Discrete Fourier Transform bin of the output spectrum;

a phase locked loop that generates an analog-to-digital sampling clock and uses the sampling rate adjustment parameter to adjust the analog-to-digital sampling clock to effect the sampling rate adjustment;

a spectrum coherent averager that averages output spectra of a FFT of the baseband signal at the adjusted sampling rate and computes a power spectrum from the coherent average;

a peak search algorithm that computes a peak power in the computed power spectrum;

a noise floor estimator that computes a noise floor around the peak power of the computed power spectrum; and

a pilot tone tester that compares the peak power of the computed power spectrum with the noise floor to determine if the DTV pilot tone has been detected.

23. Apparatus that detects the presence of a digital television (DTV) pilot tone in a high noise environment, comprising:

a spectrum power averager that averages output spectra of a Fast Fourier Transform (FFT) of a baseband signal derived from a television band channel;

a peak frequency estimator that estimates a peak power of the averaged output spectra, determines a frequency of the peak power and computes a fractional rate adjustment parameter to center the peak power in a Discrete Fourier Transform (DFT) bin of the output spectrum;

a fractional sampling rate converter that uses the fractional rate adjustment parameter to adjust the sampling rate to center the peak power in the DFT bin;

a spectrum coherent averager that averages output spectra of a FFT of the baseband signal at the adjusted sampling rate and computes a power spectrum from the coherent average;

a peak search algorithm that computes a peak power in the computed power spectrum;

a noise floor estimator that computes a noise floor around the peak power of the computed power spectrum; and

a pilot tone tester that compares the peak power of the computed power spectrum with the noise floor to determine if the DTV pilot tone has been detected.