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Near Field Electromagnetic Ranging for Wireless Location

Learn about accurate distance and angle determination using low frequency near-field techniques for advanced wireless location tracking. Discover how phase monopulse and near-field antenna fields enable 3D location tracking.

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Near Field Electromagnetic Ranging for Wireless Location

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Near Filed Electromagnetic Ranging] Date Submitted: [13 July, 2004] Source: [Kazimierz “Kai” Siwiak] Company [TimeDerivative, Inc.] Address [10988 NW 14th Street, Coral Springs, FL, USA] Voice:[+1-954-937-3288], FAX: [--], E-Mail:[k.siwiak@ieee.org] Re: [ranging] Abstract: [Range determination does not require bandwidth, it can be done using near-field antenna techniques. Full 3-d location can be determined between one ‘sensor’ and one target using distance and relative angle techniques.] Purpose: [Range determination can be accomplished using many techniques involving timing of signals. Accuracies of the timing methods are related to signal bandwidth. This material is intended to inform P802.15.4a about a distance determination technique involving predictable near-field antenna fields. When combined with phase-monopulse angle determination, full 3-d location is possible ] 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. K. Siwiak, TimeDerivative, Inc.

  2. Location Using Near Field Techniques K. Siwiak, TimeDerivative, Inc. K. Siwiak, TimeDerivative, Inc.

  3. Location Doesn’t Need Bandwidth • Distance measurements do not “need” large bandwidths • Accuracies of centimeters are possible at Very Low Frequencies • “Time” is not the only parameter to carry “distance” information • Low frequency near-field techniques may be employed: Near Field EM Ranging K. Siwiak, TimeDerivative, Inc.

  4. Far field terms: 0 deg phase difference Near field terms: 90 deg phase difference Small Loop E and H Fields K. Siwiak, TimeDerivative, Inc.

  5. E and H Near Field Tracking • Electric and Magnetic fields 90 deg out of phase in the near field; in-phase far away • Phase difference varies predictably from 90 deg at antenna to 0 deg in “far” zone • Good transition region between 0.05 and 0.4 wavelengths for accurate distance tracking K. Siwiak, TimeDerivative, Inc.

  6. 90 75 H-field Phase 60 phase, degrees E-field Phase 45 30 15 Phase difference 0 distance, wavelengths 0.4 0.5 0.1 0.2 0.3 0.6 0 Basis of Near-Field Tracking Based on: “Technical Introduction to Near Field Tracking,” (Online): <http://www.q-track.com> Q-Track Corp., 2003. K. Siwiak, TimeDerivative, Inc.

  7. Range(l) TX 0.05 Beacon Locator 0.05 l Range(l) TX 0.50 Beacon Locator 0.50 l Phase Difference Yields Distance K. Siwiak, TimeDerivative, Inc.

  8. 1 0.1 Error, m 1.295 MHz system measured mean value 0.01 0.001 0 10 20 30 40 80 50 60 70 90 100 110 120 Range, m Near Field Tracking Accuracy Data Courtesy of: Q-Track Corporation K. Siwiak, TimeDerivative, Inc.

  9. Can Be Used with Phase Monopulse Techniques for Location • The relative angle f to a signal can be found by signals “a” and “b” form two closely spaced antennas “A” and “B” • Arithmetic network used to form “a+b” and “a-b” signals • The ratio (a-b)/(a+b) is proportional to angle f • Technique is called “phase monopulse” and was associated with tracking systems over the past 40 years or so • Four antennas (elevation and azimuth phase monopulse gives angle in two dimensions! K. Siwiak, TimeDerivative, Inc.

  10. Azimuth Monopulse Tracking with Near Field Ranging H-field: f found from phase monopulse on Ea , Eb emitting target “a” r found from E, H phase E-field: “b” Can do similar phase monopulse in azimuth and elevation for full three dimensional LOCATION K. Siwiak, TimeDerivative, Inc.

  11. Summary / Conclusions • The phase difference between E and H fields directly relates to distance • Phase difference in the range 0.05 to 0.4 wavelengths is suitable for accurate distance (r) measurements • Requires just a sinusoidal signal • Can be used with angle determination (in one or two planes) to get location coordinates: (r, f) K. Siwiak, TimeDerivative, Inc.

  12. Resources and Information • Q-Track: http://www.q-track.com K. Siwiak, TimeDerivative, Inc.

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