1. 17 November 2018
Project: IEEE P 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) ], FAX: [Add FAX number],
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 P in evaluating near field ranging as a wireless positioning and location technology.]
Notice: This document has been prepared to assist the IEEE P 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
H. Schantz, Q-Track Corporation

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

3. 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

4. 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

5. 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

6. 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 ~ kHz) on unlicensed basis (§15.219).
High accuracy/low complexity positioning and location technology.
H. Schantz, Q-Track Corporation

7. 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

8. 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

9. 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

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

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

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

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

14. 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

15. 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

16. 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

17. 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

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

19. 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

20. 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 = – log Df
Where:
SNR is in dB and Df is in degrees
H. Schantz, Q-Track Corporation

21. 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

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

23. 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

24. 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

25. 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

26. 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