November 2006

Steve Shellhammer, Qualcomm

Slide 1

doc.: IEEE 802.22-06/243r0

Submission

An ATSC Detector using Peak CombiningIEEE P802.22 Wireless RANs Date: 2006-11-13

Name Company Address Phone email Steve Shellhammer Qualcomm 5775 Morehouse Dr

San Diego, CA 92121 (858) 658-1874 Shellhammer@ieee.org

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.

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November 2006

Steve Shellhammer, Qualcomm

Slide 2

doc.: IEEE 802.22-06/243r0

Submission

Abstract• This presentation introduces an ATSC detector based

on combining peaks from the output of a correlator for the ATSC Data Field Sync pattern

• A special case of this approach is taking the maximum of the correlator output. This will be evaluated first before considering the more general case

• Probability of misdetection curves are given for the 12 preferred ATSC signal files

• The results of these curves are averaged to get an average probability of misdetection curve

• Finally, the results are averaged over the shadow fading probability density function

November 2006

Steve Shellhammer, Qualcomm

Slide 3

doc.: IEEE 802.22-06/243r0

Submission

Background

• In [1] we evaluated a technique in the 802.22 working document for ATSC signal detection

• We suggested a simpler method which actually gave better performance

• In [1] we only evaluated these methods using one ATSC signal file

• In this presentation we evaluate the simple method using the 12 preferred signal files

November 2006

Steve Shellhammer, Qualcomm

Slide 4

doc.: IEEE 802.22-06/243r0

Submission

ATSC Frame Structure

A single VSB Data Segment

The Data Field SYNC

November 2006

Steve Shellhammer, Qualcomm

Slide 5

doc.: IEEE 802.22-06/243r0

Submission

Background

• Convert the receive signal to baseband and then correlate the received baseband signal with the ATSC Field Sync pattern

1

0

)()(N

nkn nxrkp

• The correlator output is observed for one ATSC Data Field (24.2 ms)

• Use the simple test statistic,

( ( ( ))T Max Abs p k

November 2006

Steve Shellhammer, Qualcomm

Slide 6

doc.: IEEE 802.22-06/243r0

Submission

Peak Combining

• We will like to be able to combine the peaks from multiple ATSC Data Fields

• A simple approach is to effectively increase the correlator to cover multiple ATSC Data Fields

• However, there are two issues with approach– Due to clock jitter the peaks shift slightly in each Data Field

– Due to multipath the polarity of the peak can reverse

– Also, there are sometime a few peaks due to multipath

• Can we come up with a method of combining peaks from multiple ATSC Data Fields?

November 2006

Steve Shellhammer, Qualcomm

Slide 7

doc.: IEEE 802.22-06/243r0

Submission

Peak Combining

• To address the issue of polarity reversal we start by taking the absolute value of the correlator output

• The next step is to select N possible candidate peaks from each ATSC Data Field. These are the N largest peaks.

• We generate a table of peaks from each ATSC Data Field. A peak is represented by,– A peak index (the sample index starting from the beginning of that

ATSC data field)

– A peak magnitude

November 2006

Steve Shellhammer, Qualcomm

Slide 8

doc.: IEEE 802.22-06/243r0

Submission

Peak Combining – Correlator Output

ATSC Data Field 1 ATSC Data Field 2 ATSC Data Field 3

November 2006

Steve Shellhammer, Qualcomm

Slide 9

doc.: IEEE 802.22-06/243r0

Submission

Peak Combining – Absolute Value of Correlator Output

ATSC Data Field 1 ATSC Data Field 2 ATSC Data Field 3

November 2006

Steve Shellhammer, Qualcomm

Slide 10

doc.: IEEE 802.22-06/243r0

Submission

Peak Combining – Peak List

Peak Index Peak Magnitude

i1 p1

i2 p2

i3 p3

i4 p4

i5 p5

i6 p6

November 2006

Steve Shellhammer, Qualcomm

Slide 11

doc.: IEEE 802.22-06/243r0

Submission

Peak Combining – Overlay Peaks from Multiple ATSC Data Fields

Composite Peak List From ATSC Data Fields 1 through 3

November 2006

Steve Shellhammer, Qualcomm

Slide 12

doc.: IEEE 802.22-06/243r0

Submission

Combine peaks whose index fall with within a window of size M

CompositePeak List

Final Peak List

Combination of Three Peaks fromOriginal Composite Peak List

November 2006

Steve Shellhammer, Qualcomm

Slide 13

doc.: IEEE 802.22-06/243r0

Submission

Final Test Statistic

• Select the maximum magnitude of the final peak list as the test statistic

• For the case when we only process for one ATSC Data Field this is the same as the maximum of the absolute value of the correlator output

November 2006

Steve Shellhammer, Qualcomm

Slide 14

doc.: IEEE 802.22-06/243r0

Submission

Observations

• The actual peaks (the ones due to a correlation with the ATSC Data Field) tend to combine since they are within the window size

• The false peaks (those due to noise) tend to not combine very often since they tend to occur at different times within the field

• We do need to increase the detector threshold a bit since observing over a longer time and peak combining does result in a small increase in the test statistic due to noise only

November 2006

Steve Shellhammer, Qualcomm

Slide 15

doc.: IEEE 802.22-06/243r0

Submission

Average Probability of Misdetection

• Simulated the peak combining technique for all twelve of the preferred ATSC signal files

• Simulations for two detectors– One ATSC Data Field (already shown earlier)

– Four ATSC Data Fields

• Show the results for all twelve signal files

• Averaged the results for all twelve signal files to obtain the average probability of misdetection

November 2006

Steve Shellhammer, Qualcomm

Slide 16

doc.: IEEE 802.22-06/243r0

Submission

Probability of Misdetection Curves

November 2006

Steve Shellhammer, Qualcomm

Slide 17

doc.: IEEE 802.22-06/243r0

Submission

Probability of Misdetection Curves

November 2006

Steve Shellhammer, Qualcomm

Slide 18

doc.: IEEE 802.22-06/243r0

Submission

PMD Averaged over all 12 ATSC Data Files

November 2006

Steve Shellhammer, Qualcomm

Slide 19

doc.: IEEE 802.22-06/243r0

Submission

Average over Shadow Fading

• We can now average over the PDF of the shadow fading to obtain the average probability of misdetection at the edge of the keep-out region

• Mean signal power = -96.5 dBm [2]

• Standard deviation of the signal power = 5.5 dB [2]

• Noise Power = -95.2 dBm [2]

• Combining we get

• Average SNR = 1.3 dB

• Standard deviation of SNR = 5.5 dB

November 2006

Steve Shellhammer, Qualcomm

Slide 20

doc.: IEEE 802.22-06/243r0

Submission

Shadow Fading PDF

November 2006

Steve Shellhammer, Qualcomm

Slide 21

doc.: IEEE 802.22-06/243r0

Submission

Average PMD

• We can average the PMD functions on Slide 18 by numerically integrating over the shadow fading PDF

Number of ATSC Data Fields

PMD

1 0.05

4 0.028

November 2006

Steve Shellhammer, Qualcomm

Slide 22

doc.: IEEE 802.22-06/243r0

Submission

Conclusions• A new technique for detection of ATSC signals was

proposed utilizing the unique ATSC Data Field Sync pattern

• The results give reasonable results but do not yet reach the sensing requirements for ATSC

• Averaging over the ATSC signal files and the shadow fading gives the average probability of misdetection at the edge of the keep-out region, which is a excellent summary of a detectors performance

• The time required for detection using the ATSC Data Sync is in the tens or hundreds of ms since the pattern occurs every 24.2 ms

November 2006

Steve Shellhammer, Qualcomm

Slide 23

doc.: IEEE 802.22-06/243r0

Submission

References

1. Suhas Mathur and Steve Shellhammer, An Evaluation of the PN Sequence based detection of DTV Signals in the Draft, IEEE 802.22-06/0189r0, September 2006

2. Steve Shellhammer, Victor Tawil, Gerald Chouinard, Max Muterspaugh and Monisha Ghosh, Spectrum Sensing Simulation Model, IEEE 802.22-06/0028r10, August 2006