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:

Problems in RFID Regulations Large Scale Deployment Limited BW Strict radiated power level Large Scale Deployment Collision problem Interrogation zone

RFID EMC RFID EMC Frequency Hopping Spread Spectrum (FHSS) 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 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 Error  Simulation Model Reflection, Refraction, and Diffraction   Radiation Pattern of Antenna Simulation Result Interpretation and Analysis 

Simulation of frequency channelling. Others Simulation of frequency channelling.

Frequency Channelling Transmit Mask for Dense-Interrogator Environments: (extracted from EPCglobal C1G2) This is the transmit mask fro dense interrogator environments when frequency channelling is used. In the simulation, an easy way to simulate frequency channelling is just to reduce the signal strength accordingly. For example, channel A and channel B are side by side. An antenna is operating at channel A. If we would like to know where we can deploy another antenna using channel B, we just need to run the simulation with signal strength in channel A reduced by 30 dB.

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.

Question? Future Work A systematic way in determining n. A user friendly simulator. Question?