1. doc.: IEEE 802.22-06/xxxxr0 Submission September 2006 Suhas Mathur, Qualcomm Inc.Slide 1 An Evaluate of the PN sequence based detection of DTV signals in the Draft IEEE P802.22 Wireless RANs Date: 2006-09-18 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 IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s 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 802.22-06/xxxxr0 Submission September 2006 Suhas Mathur, Qualcomm Inc.Slide 2 Abstract In this presentation we evaluate the performance of the the PN sequence detector proposed in the Draft [1] We identify a fundamental issue with the proposed method and we propose a simple fix to this issue We give performance results for the modified approach We show the results of a simpler approach

3. doc.: IEEE 802.22-06/xxxxr0 Submission September 2006 Suhas Mathur, Qualcomm Inc.Slide 3 ATSC Frame Structure A single VSB Data Segment The Data Field SYNC

4. doc.: IEEE 802.22-06/xxxxr0 Submission September 2006 Suhas Mathur, Qualcomm Inc.Slide 4 PN sequence detector proposed in the Draft Correlate the received signal, r(n), with the known PN sequence Use a simple low pass filter to estimate the mean and the variance of the correlator output An ATSC DTV is declared detected when (δ and c are constants set by the BS)

5. doc.: IEEE 802.22-06/xxxxr0 Submission September 2006 Suhas Mathur, Qualcomm Inc.Slide 5 The Problem with this Detector The estimate of the mean approach zero even for noise only input This implies that the test statistic can approach zero even for a noise only input signal This results in false alarms. The detector threshold ‘c’ cannot be calibrated for a given false alarm probability p FA.

6. doc.: IEEE 802.22-06/xxxxr0 Submission September 2006 Suhas Mathur, Qualcomm Inc.Slide 6 Test Statistic with Noise-only Input The Correlator Output for Noise-only Input The test statistic shows false peaks

7. doc.: IEEE 802.22-06/xxxxr0 Submission September 2006 Suhas Mathur, Qualcomm Inc.Slide 7 Test Statistic with DTV Signal plus Noise (SNR = 0 dB) Output of the correlator over the duration of one ATSC field. The peak indicated the position of the PN sequence The Test Statistic still shows false peaks

8. doc.: IEEE 802.22-06/xxxxr0 Submission September 2006 Suhas Mathur, Qualcomm Inc.Slide 8 A simple ‘fix’ Take absolute value of the correlator output before feeding as input to the detector. The mean no longer tends to zero

9. doc.: IEEE 802.22-06/xxxxr0 Submission September 2006 Suhas Mathur, Qualcomm Inc.Slide 9 Modified Test Statistic with Noise-only Input Absolute value of the correlator output with Noise-only input The Test Statistic no longer shows excessively large peaks

10. doc.: IEEE 802.22-06/xxxxr0 Submission September 2006 Suhas Mathur, Qualcomm Inc.Slide 10 Modified Test Statistic with DTV Signal plus Noise (SNR = 0 dB) Output of the correlator over the duration of one ATSC field. The peak indicated the position of the PN sequence The peak in the Test Statistic occurs at PN sequence

11. doc.: IEEE 802.22-06/xxxxr0 Submission September 2006 Suhas Mathur, Qualcomm Inc.Slide 11 Performance of Modified Detector We picked  = 0.99 The value of the threshold ‘c’ was chosen based on 10% false alarm rate with only noise as input to the detector. Simulated signal WAS_38_34_05312000_OPT

12. doc.: IEEE 802.22-06/xxxxr0 Submission September 2006 Suhas Mathur, Qualcomm Inc.Slide 12 Simpler Test Statistic Process the output of the correlator –Take the absolute value –Select the largest value as the test statistic

13. doc.: IEEE 802.22-06/xxxxr0 Submission September 2006 Suhas Mathur, Qualcomm Inc.Slide 13 Picking the max of the correlator output Simulated signal WAS_38_34_05312000_OPT

14. doc.: IEEE 802.22-06/xxxxr0 Submission September 2006 Suhas Mathur, Qualcomm Inc.Slide 14 References [1]IEEE P802.22™/D0.1, Draft Standard for Wireless Regional Area Networks Part 22: Cognitive Wireless RAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Policies and procedures for operation in the TV Bands, Version 0.1, May 2006