Positioning Analysis of Multiple Antennas in a Dense RFID Reader Environment

1
Positioning Analysis of MultipleAntennas in a
Dense RFID ReaderEnvironment

• Kin Seong Leong
• Auto-ID Lab, ADELAIDE

2
Objectives

• Investigate the art of antenna positioning.
• Minimise RFID collision problem by proper antenna
  positioning.
• Set up a convenient simulation environment in
  MATLAB.
• Provide a foundation for more advanced analysis.

3
Main Challenges in Simulation

• Simulation model
• Underlying assumptions

4
Simulation Model (The concept of free space path
loss)

• The power transfer ratio for a pair of lossless
  antennas in free space with optimum orientation
  is given by
• The factor is the free space path
  loss.

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Simulation Model 1
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Simulation Model 2

• Based on results presented by Rappaport for
  in-building path loss model
• The n is the environment factor and varies from
  place to place.
• On site measurement is required for the
  determination of n.

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Experiment

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Simulation Model

• n also changes as the distance increases. Hence
• The boundary of d 8 is based on the experiment
  results, also consistent with Rappaports
  results. However, it is an average and may change
  in some extreme environments.

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Simulation Assumptions

• Negligible reflection,
• empirically justified.
• All Antennas deployed
• have similar gain
• pattern,
• orientations may vary

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Simulation Concept

• The simulator accepts input data
• a) Location of antenna
• b) Transmit power into the antenna
• c) Antenna gain pattern
• Output of the simulator
• a) Signal strength at various locations when
  measured with a 0dBi gain antenna.

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Simulation Concept

• Example output
• One antenna located at (50,50) and both axes in
  unit of m.

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Regulations

• Listen Before Talk ETSI 302 208
• The threshold values

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Results Interpretation

• Antenna radiating 2.0 W ERP at (50,50).
• The next antenna to be placed at the side must be
  150 m away if the next antenna would want to
  radiate in the same channel.

350 m
150 m
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Results Interpretation

• Antennas radiating 2.0 W ERP at (50,50) and
  (400,50).

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Simulation Variation

• Antenna on ground
• Antenna 2m above ground is very similar to
  antenna on the ground.

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Results Interpretation

• Antenna radiating 2.0 W ERP at (50,50).
• Antenna on ground radiating 2.0 W ERP at
  (400,50).

 
Reduced


Reduced
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Frequency Channelling

• So far, all the simulations are dealing with same
  channel radiation.

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Frequency Channelling

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

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Frequency Channelling

• Both antennas operating 3 channels away from
  channel of interest.
• The black line indicates the boundary where a
  antenna can be positioned to operate in the
  channel of interest.

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Summary of Results

• Note that these results are only true when an
  isotropic 0dBi receiver antenna is used. When a
  directional antenna is used as the receiver, the
  results will be very different depending on the
  angle between the transmitting and receiving
  antenna.

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Summary of Results

• The results shown is very challenging for RFID
  deployment.
• Luckily, various policies can be adopted to
  improve the situation. These include
• a) Synchronization
• b) RF shielding
• c) Optimising reading time
• d) Optimising radiated power
• e) Sensor controlled readers

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Future Work

• A systematic way of determining n
• Changes with different environments
• A more user friendly simulator.

23

• Thank you
• Questions?