July 2004 doc IEEE 802 15 05 0381

July 2004 doc. : IEEE 802. 15 -05 -0381 -02 -004 a Project: IEEE P 802. 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. 154 a] 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 P 802. 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 P 802. 15. Submission 1 Shahriar Emami, Freescale

July 2004 doc. : IEEE 802. 15 -05 -0381 -02 -004 a 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 Submission 2 Shahriar Emami, Freescale

July 2004 doc. : IEEE 802. 15 -05 -0381 -02 -004 a Sensitivity of 4 message TWR • In 4 message two way ranging (SDS-TWR) it is required that treply. A ~treply. B • Is ranging error sensitive to variation of treply. A in reference to treply. B? And to what extent? • Document IEEE-15 -05 -0002 -01 -004 a 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. Submission 3 Shahriar Emami, Freescale

July 2004 doc. : IEEE 802. 15 -05 -0381 -02 -004 a Calculated Ranges+ E* Range 10 m 20 40 60 80 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 (treply. B-treply. A)/treply. A. Submission 4 Shahriar Emami, Freescale

July 2004 doc. : IEEE 802. 15 -05 -0381 -02 -004 a Actual and Calculated Ranges Submission 5 Shahriar Emami, Freescale

July 2004 doc. : IEEE 802. 15 -05 -0381 -02 -004 a Ranging Error Ranging error at 10 m and 50 m are 15% and 3%, respectively (10 PPM) subject to 100% variation in reply time (1 ms reply time). Submission 6 Shahriar Emami, Freescale

July 2004 doc. : IEEE 802. 15 -05 -0381 -02 -004 a Actual and Calculated Ranges Submission 7 Shahriar Emami, Freescale

July 2004 doc. : IEEE 802. 15 -05 -0381 -02 -004 a Ranging Error Ranging error at 10 m and 50 m are 60% and 12%, respectively (40 PPM) subject to 100% variation in reply time (1 ms reply time Submission 8 Shahriar Emami, Freescale

July 2004 doc. : IEEE 802. 15 -05 -0381 -02 -004 a What If Reply Time Is Decreased? Submission 9 Shahriar Emami, Freescale

July 2004 doc. : IEEE 802. 15 -05 -0381 -02 -004 a What If Reply Time Is Decreased? Submission 10 Shahriar Emami, Freescale

July 2004 doc. : IEEE 802. 15 -05 -0381 -02 -004 a Summary (1) • • 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 (1 ms-0. 1 ms), ranging error and percentage ranging error also went down by up to an order of magnitude. Submission 11 Shahriar Emami, Freescale

July 2004 doc. : IEEE 802. 15 -05 -0381 -02 -004 a Summary (2) % Ranging Error Acceptable Error Minimum Range Submission Maximum Range 12 Shahriar Emami, Freescale

July 2004 doc. : IEEE 802. 15 -05 -0381 -02 -004 a Bottom Line For a given set of parameters: • PPM ( ) • Reply Time • Excess Reply Time( ) • Minimum Desired Range Calculate % ranging error If percent ranging error acceptable, you are done. • Otherwise one needs to reduce PPM, reply time, excess reply time or increase minimum range. Submission 13 Shahriar Emami, Freescale