Presentation is loading. Please wait.

Presentation is loading. Please wait.

Doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 1 DTV Signal Sensing Using Pilot Detection IEEE P802.22 Wireless RANs.

Similar presentations


Presentation on theme: "Doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 1 DTV Signal Sensing Using Pilot Detection IEEE P802.22 Wireless RANs."— Presentation transcript:

1 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 1 DTV Signal Sensing Using Pilot Detection IEEE P802.22 Wireless RANs Date: 2007-03-11 Authors: Notice: This document has been prepared to assist IEEE 802.22. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEEs name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEEs sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.22. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures http://standards.ieee.org/guides/bylaws/sb-bylaws.pdf including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chairhttp://standards.ieee.org/guides/bylaws/sb-bylaws.pdf Carl R. StevensonCarl R. Stevenson as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.22 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at patcom@iee.org.patcom@iee.org >

2 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 2 Sensing the DTV pilot The DTV pilot is an unique feature that can be used to sense the presence of the DTV signal. Standard approach: –Narrow-band filter (~ 10 kHz) centered around nominal DTV pilot location. –Calculate energy of filtered signal, compare to a threshold. Problems: –Pilot could be in a deep fade: quite common. –Threshold is susceptible to noise uncertainty. –Uncertainty in pilot location: could require a 100kHz bandwidth filter. The larger the filter bandwidth, the worse the performance. Challenge: Can DTV pilot detection be made to provide robust sensing at SNR = -20 dB?

3 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 3 Alternate approaches Pilot-energy detection: can be made more robust by narrowing the filter-bandwidth. –Can this be done without compromising the detectability of signals with large frequency offsets? Pilot location detection, rather than pilot energy. –More robust to thresholds: insensitive to noise uncertainty. –Performance is determined by pilot energy, however increasing sensing time improves performance. Two methods proposed in this presentation: –FFT-based approach: pilot-energy and location detection. –Loop-based: pilot-location detection.

4 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 4 FFT-based pilot detection Demodulate signal to baseband, using nominal pilot position. Filter, using a low-pass filter. We used a BW of +/- 20 kHz. Subsample the signal. We reduced the sample rate from 21.52 MHz to 53.8 kHz (1/400). Take FFT of the subsampled signal. The FFT size will depend on the dwell-time. With parameters above: –1 ms dwell will allow 32-point FFT. –5 ms dwell will allow 256-point-FFT. Pilot-energy detection: find maximum of FFT output-squared, and compare to a threshold. (NOT average over all FFT bins, but maximum). Pilot-location detection: compare location of maximum of FFT-output between multiple dwells.

5 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 5 Frequency Domain 0 x(t) 0 y(t) 53.8 kHz - 53.8 kHz … … 21.52 MHz - 21.52 MHz … …

6 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 6 Pilot Location Detection Let no. of dwells = N. Let be the location of the maximum of the FFT-output averaged over the first N/2 dwells. Let be the location of the maximum of the FFT-output averaged over the second N/2 dwells. Detection statistic: If D < N T, signal present. Other variations: –Any PSD algorithm can be used instead of FFT. –Other averaging intervals could be used. P FA using this method is extremely low and robust. Threshold value N T will depend on the FFT-size.

7 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 7 Signals From MSTV Signal 1WAS_3_27_06022000_REF.ASC Signal 2WAS_51_35_05242000_REF.ASC Signal 3WAS_311_36_06052000_ref.ASC Signal 4WAS_311_48_06052000_ref.ASC Signal 5WAS_68_36_05232000_ref.ASC Signal 6WAS_49_34_06142000_opt.ASC Signal 7WAS_311_35_06052000_ref.ASC Signal 8WAS_06_34_06092000_ref.ASC Signal 9WAS_49_39_06142000_opt.ASC Signal 10WAS_47_48_06132000_opt.ASC Signal 11WAS_32_48_06012000_OPT.ASC Signal 12WAS_86_48_07122000_ref.ASC

8 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 8 Performance with 1 ms dwell time, 10 dwells 32-point FFT

9 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 9 Performance with 5 ms dwell time, 6 dwells 256-point FFT

10 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 10 Performance with 5 ms dwell time, 10 dwells 256-point FFT

11 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 11 32-point FFT for Signal 7 (WAS_311_35_06052000) Strong pilot, easily detected.

12 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 12 32-point FFT for Signal 9 (WAS_49_39_06142000) Faded pilot, hard to detect

13 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 13 256-point FFT for Signal 9 (WAS_49_39_06142000) Faded pilot, easily detected

14 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 14 Threshold sensitivity for signal energy detection

15 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 15 Threshold sensitivity for pilot energy detection

16 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 16 Threshold sensitivity for pilot location detection

17 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 17 Summary Of FFT-based detection SNR = -20 dB, pilot-energy detection: P D = 100% for all 12 channels, P FA = 2%, with ten 5 ms dwells. SNR = -20 dB, pilot-location detection: P D = 100% for 11 channels, and 90% for 1 channel, P FA = 3%, with ten 5 ms dwells. Thresholds for pilot-energy and pilot-location detection are less sensitive than threshold for signal-energy detection.

18 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 18 Loop-based pilot detection Two carrier recovery modules, each preset to a different frequency. The difference of the loop outputs of the two carrier recovery modules is compared against a threshold: –Signal is assumed to be present if the difference is less than the threshold. Not very sensitive to the threshold: –We used very conservative thresholds. Probability of false alarm is very low (close to 0) for a large range of threshold values. Sensing time can be reduced by adjusting the loop parameters.

19 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 19 Loop output behavior in the absence of DTV Not much variation from the initial frequency setting for the two loops. –Loops do not converge.

20 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 20 Loop output behavior in the presence of DTV Monotonic behavior in loop output in the presence of DTV signal for wide range of gain settings and SNRs. –Large threshold margin for reliable detection.

21 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 21 Performance after 75 ms, P FA <<.01

22 doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 22 Conclusions Pilot detection is a robust means of sensing, down to -20 dB. –Two methods presented: FFT-based and loop- based. Pilot-location detection is extremely robust against noise uncertainty. Pilot-energy detection, using the FFT based method, essentially reduces the bandwidth of the filter and hence performance is improved, even for severely faded pilots. Both pilot energy and pilot location detection can be used with multiple short dwell times to deliver robust sensing, thus avoiding the need for a single long quiet period. –QoS can be maintained for voice traffic.


Download ppt "Doc.: IEEE 802.22-07/0125-00-0000 Submission March 2007 Monisha Ghosh, PhilipsSlide 1 DTV Signal Sensing Using Pilot Detection IEEE P802.22 Wireless RANs."

Similar presentations


Ads by Google