17 November 2018 Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Near Field Ranging Algorithm] Date Submitted: [17 August, 2004] Source: [Hans Schantz] Company [Q-Track Corporation] Address [515 Sparkman Drive; Huntsville, AL 35816] Voice:[(256) 489-0075], FAX: [Add FAX number], E-Mail:[h.schantz@q-track.com] Re: [N/A] Abstract: [This document describes a ranging algorithm for use with a near field ranging system.] Purpose: [This document is provided to assist P802.15 in evaluating near field ranging as a wireless positioning and location technology.] 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. H. Schantz, Q-Track Corporation

Near Field Ranging Algorithm 17 November 2018 Near Field Ranging Algorithm Dr. Hans Schantz The Q-Track Corporation H. Schantz, Q-Track Corporation

Introduction Near Field Ranging Basics Near Field Theory 17 November 2018 Introduction Near Field Ranging Basics Near Field Theory Dipole Model Dipole Fields Phase Relations Near Field Ranging Algorithm Accuracy Technical Implications H. Schantz, Q-Track Corporation

Near Field Ranging Basics 17 November 2018 Near Field Ranging Basics Q-Track © 2002 Close to an antenna, E & H fields are 90 degrees out of phase. Far from an antenna, E & H fields are phase synchronous (0 degree difference). H. Schantz, Q-Track Corporation

Near Field Ranging Basics 17 November 2018 Near Field Ranging Basics A near field tag or beacon transmitter sends an un-modulated sine wave. A near field locator receiver compares phase of electric and magnetic fields to determine range. Q-Track © 2002 H. Schantz, Q-Track Corporation

Near Field Ranging Basics 17 November 2018 Near Field Ranging Basics General Characteristics: Uses COTS components/no custom chips needed. Part 15 allows 100 mW TX power into < 3 m antenna (AM broadcast band ~510-1705 kHz) on unlicensed basis (§15.219). High accuracy/low complexity positioning and location technology. H. Schantz, Q-Track Corporation

Near Field Ranging Basics 17 November 2018 Near Field Ranging Basics Current Prototypes: 2-D Real Time Locating System <1 sec update rate Operates at 1.3 MHz Range ~70 m Accuracy ~ 30 cm Q-Track © 2004 H. Schantz, Q-Track Corporation

Near Field Theory Dipole Model Dipole Fields Phase Relations 17 November 2018 Near Field Theory Dipole Model Dipole Fields Phase Relations Ranging Algorithm H. Schantz, Q-Track Corporation

Near Fields: Dipole Model 17 November 2018 Near Fields: Dipole Model Dipole: equal and opposite charges Q separated a distance d. Alternatively, a small current element I with length l. H. Schantz © 2004 H. Schantz, Q-Track Corporation

Near Fields: Dipole Model 17 November 2018 Near Fields: Dipole Model Dipole moment: Note: H. Schantz © 2004 H. Schantz, Q-Track Corporation

Near Fields: Dipole Fields 17 November 2018 Near Fields: Dipole Fields Time Dependent Electric Field Time Dependent Magnetic Field H. Schantz, Q-Track Corporation

Near Fields: Phase Relations 17 November 2018 Near Fields: Phase Relations Time Dependent Electric Field E  0 yields: H. Schantz, Q-Track Corporation

Near Fields: Phase Relations 17 November 2018 Near Fields: Phase Relations Time Dependent Magnetic Field H  0 yields: H. Schantz, Q-Track Corporation

Near Fields: Phase Relations 17 November 2018 Near Fields: Phase Relations For a harmonic dipole with T(t) = sin t: Zero Crossing Relations Become: H. Schantz, Q-Track Corporation

Near Fields: Phase Relations 17 November 2018 Near Fields: Phase Relations Accounting for retardation: And inverting to solve for time yields: The E & H field phase relationships: H. Schantz, Q-Track Corporation

Near Field Ranging Algorithm 17 November 2018 Near Field Ranging Algorithm Solve for r: Df = (fE – fH) Note: transcendental in r; cannot be inverted to yield a solution in r = r(Df). Solve numerically or use look-up table. H. Schantz, Q-Track Corporation

Near Field Ranging Algorithm 17 November 2018 Near Field Ranging Algorithm Use the phase delta to find range! H. Schantz © 2004 H. Schantz, Q-Track Corporation

Accuracy Differentiate phase delta relation: 17 November 2018 Accuracy Differentiate phase delta relation: Range accuracy depends upon phase accuracy H. Schantz, Q-Track Corporation

Accuracy Phase accuracy follows from SNR. 17 November 2018 Accuracy Phase accuracy follows from SNR. Phase measurement to an accuracy Df is analogous to demodulating an M-ary phase modulation where M = 2p/Df H. Schantz, Q-Track Corporation

Accuracy Assume a P(err>Df)  0.5 is required for good ranging. 17 November 2018 Accuracy Assume a P(err>Df)  0.5 is required for good ranging. Then: SNR = 14.1641 – 9.99908 log Df Where: SNR is in dB and Df is in degrees H. Schantz, Q-Track Corporation

Accuracy Therefore: yields range error as a function of phase error. 17 November 2018 Accuracy Therefore: yields range error as a function of phase error. H. Schantz, Q-Track Corporation

Implications Propagation Timing Accuracy Narrow Band 17 November 2018 H. Schantz, Q-Track Corporation

Implications: Propagation 17 November 2018 Implications: Propagation Wavelengths of a near field system are long compared to propagation environment. No “multi-path,” instead introduce phase offsets that depend on gross features (wiring, plumbing, frame, etc.). Phase offsets relatively gradual and may be dealt with by calibration or “fingerprinting.” Low frequencies superior in propagation and penetration. H. Schantz, Q-Track Corporation

Implications: Timing Accuracy 17 November 2018 Implications: Timing Accuracy Phase is preserved in down conversion. A Df = 0.5 degree, 1.3 MHz system yields ~30 cm accuracy. Down-converted to 1 kHz baseband Df = 0.5 deg requires 1.4 s timing accuracy. Compare to ~1 ns accuracy needed for conventional time-of-flight system. H. Schantz, Q-Track Corporation

Implications: Narrow Bandwidth 17 November 2018 Implications: Narrow Bandwidth “Ultra-Narrow BandTM” approach of near field ranging allows 1000’s of channels to simultaneously co-exist. Easily co-exists between existing AM broadcast band stations. Does not interfere with other microwave services. Allows for low data rate link for ID purposes or for simple telemetry. H. Schantz, Q-Track Corporation

17 November 2018 Summary Near field ranging algorithms enable narrow band, low frequency, high precision distance measurement. Near field ranging offers a low complexity high accuracy alternative to conventional time-of-flight ranging technology. H. Schantz, Q-Track Corporation