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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [ Ranging Accuracy of SDS-TWR Subject to Unequal Reply Times ] Date Submitted: [ July 2005 ] Source: [Shahriar Emami and Celestino A. Corral ] Company [Freescale Semiconductor, Inc] - PowerPoint PPT Presentation
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July 2004
Shahriar Emami, FreescaleSlide 1
doc.: IEEE 802.15-05-0381-01-004a
Submission
Project: IEEE P802.15 Working Group for Wireless Personal Area Networks Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)(WPANs)
Submission Title: [Ranging Accuracy of SDS-TWR Subject to Unequal Reply Times ]Date Submitted: [July 2005]Source: [Shahriar Emami and Celestino A. Corral ] Company [Freescale Semiconductor, Inc]Address [Freescale Semiconductor, Inc. 6100 Broken Sound Pkwy., N.W. Suite 1Boca Raton, FL 33487-2790]Voice:[(561) 544-4064 ]
Re: [802.154a]
Abstract: [This document addresses the performance of SDS-TWR technique]
Purpose: [To help evaluate ways to manage crystal drift]
Notice: This document has been prepared to assist the IEEE P802.15. 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 acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.
July 2004
Shahriar Emami, FreescaleSlide 2
doc.: IEEE 802.15-05-0381-01-004a
Submission
Symmetric Double Sided-Two Way Ranging (SDS -TWR)Proposed in document IEEE-15-05-0334-00-004
Device A Device B
pt unknown propagation delay
preplyB tt
pt
replyBreplyA tt pt
pt
reply time
4
replyBroundBreplyAroundAp
ttttt
roundAt
replyAroundB tt
July 2004
Shahriar Emami, FreescaleSlide 3
doc.: IEEE 802.15-05-0381-01-004a
Submission
Sensitivity of 4 message TWR
• In 4 message two way ranging (SDS-TWR) it is required that treplyA ~treplyB
• Is ranging error sensitive to variation of treplyA in reference to treplyB? And to what extent?
• Document IEEE-15-05-0002-01-004a considers differential reply times in between 2 and 20 us.
• We will compute the range and ranging error due to variations of reply time at various ranges when absolute reply time is in 0.1-1 ms range.
July 2004
Shahriar Emami, FreescaleSlide 4
doc.: IEEE 802.15-05-0381-01-004a
Submission
Calculated Ranges+
E*
Range
20 40 60 80 100
10 m 10.30 10.60 10.90 11.20 11.50
20 m 20.30 20.60 20.90 21.20 21.50
30 m 30.30 30.60 30.90 31.20 31.50
40 m 40.30 40.60 40.90 41.20 41.50
50 m 50.30 50.60 50.90 51.20 51.50
+ 10 PPM crystals are deployed and reply time is assumed to be 1 ms.
* Excess reply time of B in reference to A or 100 x (treplyB-treplyA)/treplyA .
July 2004
Shahriar Emami, FreescaleSlide 5
doc.: IEEE 802.15-05-0381-01-004a
Submission
Actual and Calculated Ranges
July 2004
Shahriar Emami, FreescaleSlide 6
doc.: IEEE 802.15-05-0381-01-004a
Submission
Ranging Error
Ranging error at 10m and 50m are 15% and 3%, respectively (10 PPM) subject to 100% variation in reply time (1ms reply time).
July 2004
Shahriar Emami, FreescaleSlide 7
doc.: IEEE 802.15-05-0381-01-004a
Submission
Actual and Calculated Ranges
July 2004
Shahriar Emami, FreescaleSlide 8
doc.: IEEE 802.15-05-0381-01-004a
Submission
Ranging Error
Ranging error at 10m and 50m are 60% and 12%, respectively (40 PPM) subject to 100% variation in reply time (1ms reply time
July 2004
Shahriar Emami, FreescaleSlide 9
doc.: IEEE 802.15-05-0381-01-004a
Submission
What If Reply Time Is Decreased?
July 2004
Shahriar Emami, FreescaleSlide 10
doc.: IEEE 802.15-05-0381-01-004a
Submission
What If Reply Time Is Decreased?
July 2004
Shahriar Emami, FreescaleSlide 11
doc.: IEEE 802.15-05-0381-01-004a
Submission
Summary
• For a given tolerable percentage error, shorter ranges determine the maximum tolerable excess reply time.
• If low PPM crystals are used, the ranging error is not significant particularly at larger distances and especially when reply time variations are held under 40%.
• On the other hand, the ranging errors for high PPM crystal devices if reply time high could are unacceptable. Other methods would have to be deployed to compensate for or correct crystal drifts
• When reply time was reduced up to an order of magnitude (1ms-0.1 ms), ranging error and percentage ranging error also went down by up to an order of magnitude.
