Operational Considerations in Simulation and

Deployment of RFID Systems

Kin Seong Leong

Auto-ID Lab @ Adelaide

School of Electrical & Electronic Engineering

University of Adelaide

Australia

kleong@eleceng.adelaide.edu.au

Outline

• Introduction on RFID

• RFID EMC

• Sources of Error in RFID Simulation

• Others

• Conclusion

Introduction on RFID

• What is RFID?• RFID basic components:

HO STCO M PUTER

RFID REA DER RA DIO W AV ES RFID TAG SO N O BJE CTS

RE ADERAN TEN NA

Problems in RFID

• Regulations– Limited BW– Strict radiated power level

• Large Scale Deployment– Collision problem– Interrogation zone

RFID EMC

Frequency Hopping Spread Spectrum (FHSS)

RFID EMC

Listen Before Talk (LBT)

FHSS

• Example: USA FCC Title 47 Part 15.277

• 902-928MHz • maximum total radiated power of 4

W EIRP• 50 channels of 500 kHz

Listen Before Talk (1)

• Example: European ETSI 302 208• 865-868 MHz• 2 W ERP (approximately 3.2 W EIRP)• 15 sub-bands, 200 kHz wide• Only 10 sub-bands at 2W ERP

Listen Before Talk (2)

• Threshold Value for “Listen Before Talk”:

Current Situation

Sources of Simulation ErrorSources of Simulation Error

Simulation Model

Reflection, Refraction, and Diffraction

Radiation Pattern of Antenna

Simulation Result Interpretation and Analysis

Simulation Model (1)

• A simple path loss model:

(1)

• n is the environment factor.

Simulation Model (2)

• Modification to (1):

(2)

• n increases as distance increases.

Simulation Model (3)• Comparison of results:

• (2) is accurate to a certain extend but cannot take in consideration of obstacles.

Simulation Model (4)

Simulation Model (5)

Reflection, Refraction and Diffraction

• Suggested a hybrid path loss model – Using (2) together with ray tracing.– Not more than 5 rays.– Taking in consideration of obstacles

encountered along path of rays.– Reduced error between computation and

experimental results.– Infancy stage.

Radiation Pattern of Antenna

• Measured in anechoic chamber.

• Assumption:– Antennas of same model

have same radiation pattern.– Radiation pattern may

change due to surroundings.

Simulation Result Interpretation and Analysis

• Consider: The LBT threshold limit for 2 W ERP with threshold value -126 dBW. If a signal with higher power is detected in a band of interest, this band of interest cannot be used for tag interrogation.

• A sharp boundary in simulated results to represent the LBT threshold limit may not be appropriate. A boundary zone of 3dB (depending on the environment) is more suitable for interpreting simulated results.

Simulation Result Interpretation and Analysis

• Boundary zone would be more appropriate than boundary line:

Sources of Simulation ErrorSources of Simulation Error

Simulation Model

Reflection, Refraction, and Diffraction

Radiation Pattern of Antenna

Simulation Result Interpretation and Analysis

Others

Simulation of frequency channelling.

Frequency Channelling

• Transmit Mask for Dense-Interrogator Environments:(extracted from EPCglobal C1G2)

Multi Channel Simulation

• Antennas operating certain channels away from channel of interest.

Conclusion

• Identified common errors of RFID simulation and suggested ways of minimising some of these errors.

• Some errors are unavoidable, but the extent estimated from empirical measurements can be shown to be not severe.

Future Work

– A systematic way in determining n.

– A user friendly simulator.

Question?