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Patrick Bosselmann
July 4, 2006
Ray Tracing Method for System Planning and Analysis of UHF-RFID Applications With
Passive Transponders
RWTH Aachen UniversityInstitute of High Frequency TechnologyUniv. Prof. Dr.-Ing. B. Remboldhttp://www.ihf.rwth-aachen.de
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July 4, 2006 2. RFID Workshop Erlangen Slide # 2
Contents
Motivation
Ray Tracing Overview
RFID System Planning Examples
Summary
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July 4, 2006 2. RFID Workshop Erlangen Slide # 3
RFID in the UHF band using passive transponders — present status:
• Identification of consumer goods• Handling logistics of consumer goods between manufacturer and end-consumer• Suppy-chain management• Theft prevention
Motivation
Photo: METRO Group
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July 4, 2006 2. RFID Workshop Erlangen Slide # 4
Motivation
Advantages:Much faster results as compared to field tests / measurements.
Measuring wave propagation on-site is time consuming, especially when a large area is to be examined.
Same high accuracy as compared to measurements.Easily configurable: Different system constellations, such as operating frequency, transmit power, antenna configurations, orientations, mounting positions, etc., can be specified.Prediction of RFID system functionality / optimization is possible even forinfrastructures which don‘t exist yet (design / construction of new buildings etc.).
Ray tracing method for system planning:• Integration of RFID system hardware into given / new infrastructures• RFID system planning / analysis• Optimizing existing RFID systems
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July 4, 2006 2. RFID Workshop Erlangen Slide # 5
Ray Tracing Overview
General properties:• Fast, efficient simulation tool
for calculation of wavepropagation
• Flat polygon based modelling• Single or few transmitters• Few or up to thousands of
receiver positions• Ray optical approach (ap-
proximation for large objects)• Search for multipath propagation
between each transmitter andreceiver
• Result: complex channel coefficientsand deduced parameters
• Completely developed at the IHF, RWTH Aachen
outdoor example: city of Munich,3D model w/o rooftops
(source: COST 231)
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July 4, 2006 2. RFID Workshop Erlangen Slide # 6
3D Modelling
VRML model: distribution center for consumer goods, loading area
example 2
Ray tracer setup for RFID simulations:• Multipath propagation, up to 106 rays considered• Up to 15 reflections and 2 wall transmissions allowed• Found paths will be summed up with respect to correct phase information
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July 4, 2006 2. RFID Workshop Erlangen Slide # 7
RFID for logistics handling
Loading area of a distributioncenter for consumer goods:
• Modelled part of building:24 m x 20 m
• 4 docking gates for trucks, eachone having a RFID portal
• Fully 3D geometry model• Properties of obstacles (walls etc.),
such as thickness and dielectric parameters, were realistically modelled to match on-site conditions.
RFID portals
truck docking gates
large resultarea
small resultarea
Small / large result area:• An evenly spaced grid of transponder
positions (resolution 5 cm x 5 cm,height z = 75 cm) will yield 2D resultsof received tag power (in total 24.000 and 50.000 receivers resp.).
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July 4, 2006 2. RFID Workshop Erlangen Slide # 8
Simulation Parameters
Setup according to typicalRFID specifications:
• Operation frequency: 868 MHz.• Transmit power: 1 W.• Read/write unit antennas are mounted at
RFID portal constructions at height z = 75 cm.• Transponder antennas: half-wavelength
dipoles assuming different orientations.• Transponder sensitivity: -7 dBm (min. tag
power needed to operate and transmit data).• Read/write unit sensitivity: -70 dBm.• Antenna pattern of read/write units: cross-
dipole characteristics having right-handcircular polarization.
Antenna characteristics forread/write units, Gmax = 1.64
direction ofmain beam
Illustration: TI
RFID portal, mounted
with reader antennas,scanning incoming
and outgoing shipment transfer.
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July 4, 2006 2. RFID Workshop Erlangen Slide # 9
One-way Simulation Results„Transmitter Tag“ operation:
• Sample shipment unit consisting of paper materials at door #4• Transponder antennas vertically polarized (parallel to z axis)
One-way simulation („large result area“), received tag power [dBm]
dock #1 dock #2 dock #3 dock #4
RFID doorway
reader antenna
pallet with paper
„small result area“
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July 4, 2006 2. RFID Workshop Erlangen Slide # 10
One-way Simulation Results
dock #1 dock #2 dock #3 dock #4
RFID doorway
reader antenna
pallet with paper
dock #3
dock #4
RFID doorway
reader antenna
pallet with water
Paper vs. Water
„small result area“
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July 4, 2006 2. RFID Workshop Erlangen Slide # 11
Backscatter Simulations
Requirements for operation:
1. Is received tag power high enough for the transponder chip to operate?2. Does the reflected signal reach the reader?
Result:
• Vertically polarized tag antennas• Paper shipment unit at door #4
dock #3 dock #4
transmitterreceiver
paper
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July 4, 2006 2. RFID Workshop Erlangen Slide # 12
Backscatter Simulations (contd.)
Other tag polarizations?
• A) transponder antenna horizontallypolarized (parallel to x axis)
• B) transponder antenna horizontallypolarized (parallel to y axis)
• C) transponder antenna verticallypolarized (parallel to z axis)
• D) transponder antenna verticallypolarized (parallel to z axis)
Paper shipment unit
Water shipment unit
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July 4, 2006 2. RFID Workshop Erlangen Slide # 13
• No shipment units in these cases.• Transponder antennas vertically polarized
(parallel to z axis).
Backscatter Simulations (contd.)
Two neighboring RFID portals compared to single gate operation:
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July 4, 2006 2. RFID Workshop Erlangen Slide # 14
Simulation with docked trucks
Trucks docked at each loading gate, all gates open, no shipment units:
TXRXdock #1 dock #2 dock #3 dock #4
truck #1 truck #2 truck #3 truck #4
Vertical polarization Horizontal polarization (x axis)
TXRX
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July 4, 2006 2. RFID Workshop Erlangen Slide # 15
Backscatter with docked trucksTrucks docked at each loading gate, all gates open:• No shipment units, vertical tag polarization
dock #3 dock #4dock #2dock #1
TxRx
direction ofmain beam
dock #3 dock #4dock #2dock #1
TxRx
direction ofmain beam
dock #3 dock #4dock #2dock #1
TxRx
direction ofmain beam
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July 4, 2006 2. RFID Workshop Erlangen Slide # 16
SummaryEvaluation of shown simulations:• RFID reader sensitivity is so high that neighboring RFID installations can easily
scan transponders unintentionally. System separation in the frequency or time domain or higher spatial separation (use absorbers etc.).
• Vertically oriented transponder antennas show much better scanning results than horizontally oriented ones. Higher suppression of ground reflections and omnidirectional antenna characteristics (azimuth direction in the x-y plane) contribute to this.
• The first propagation part of backscatter operations (transmitter to tag), is more sensitive in terms of sufficient tag power supply than the reflection part. If a tag receives enough power to operatre, it is very likely that the backscattered modulation will also reach the reader. If a tag fails to be read, it is very likely that the received power at the tag location is insufficient, rather than the reflected path back to the reader is obscured.
• When docked trucks present, a significant part of RF energy enters the truck interior and tags could be scanned unintentionally. Avoid this by proper shielding of the antenna beam, re-orientation of the antenna direction or antennas with smaller HPBW.
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July 4, 2006 2. RFID Workshop Erlangen Slide # 17
Summary
RFID system planning using ray tracing:• Planning / optimizing RFID systems can be done fast and efficiently
using deterministic ray tracing.• Reduces time and costs.• Intensive testing phases and field tests can be minimized.
Outlook:• RFID system planning also on modulation / coding level.• Extend simulation capabilities for common RFID modulation schemes and
protocols.• Compare system constellations not only on physical layer (wave propagation), but
also with respect to complete system description.
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July 4, 2006 2. RFID Workshop Erlangen Slide # 18
The End
Thank you for your attention!
Questions?