Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

1. 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] Address [Freescale Semiconductor, Inc. 6100 Broken Sound Pkwy., N.W. Suite 1 Boca 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. Shahriar Emami, Freescale

2. Symmetric Double Sided-Two Way Ranging (SDS -TWR)Proposed in document IEEE-15-05-0334-00-004 Device B Device A unknown propagation delay reply time Shahriar Emami, Freescale

3. 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 small variations in reply times (up to 2%). • We will compute the range and ranging error due to larger variations of reply time at various ranges. Shahriar Emami, Freescale

4. Calculated Ranges+ + 10 PPM crystals are deployed. * Excess reply time of B in reference to A or 100 x (treplyB-treplyA)/treplyA . Shahriar Emami, Freescale

5. Actual and Calculated Ranges Shahriar Emami, Freescale

6. Ranging Error Shahriar Emami, Freescale

7. Actual and Calculated Ranges Shahriar Emami, Freescale

8. Ranging Error Shahriar Emami, Freescale

9. Summary • For a given tolerable percentage error, shorter ranges determine the maximum tolerable reply time variation. • Ranging error at 10m and 50m are 3% and 16%, respectively (10 PPM) subject to 100% variation in reply time. • Ranging error at 10m and 50m are 11% and 60%, respectively (40 PPM) subject to 100% variation in reply time. • To limit the ranging error to 6%, reply time variation should be kept under 40% and 10% for 10 ppm and 40 PPM crystals, respectively. • 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 are unacceptable if the reply time variations exceeds teens. Other methods would have to be deployed to compensate for or correct crystal drifts. Shahriar Emami, Freescale