THE READER COLLISION PROBLEM IN RFID SYSTEMS

1
THE READER COLLISION PROBLEM IN RFID SYSTEMS
Kin Seong Leong Auto-ID Lab _at_ Adelaide School of
Electrical Electronic Engineering University of
Adelaide Australia kleong_at_eleceng.adelaide.edu.au
2
Introduction on RFID

• What is RFID?
• RFID basic components

3
Reader Collision Problem

• Definition
• Interrogation signal from a reader jams a reply
  of a tag to another reader
• EPCglobal Class 1 Generation 2
• Using frequency hopping
• Our Focus
• In-Channel Collision
• Listen Before Talk

4
In-Channel Collision

• Path loss of path 1 and path 2,
• tag antenna gain, and tag efficiency loss
• (b) Path loss of path 3

5
Theoretical Background(1)
Free Space Path Loss
For 915 MHz, at 1 m away, PL 31.6 dB
6
Theoretical Background(2)
In-Building Path Loss
d0 arbitrary reference distance n
environment factor
7
Our Model
Propose piece-wise linear model based on
Rappaport experiment result.
8
Our Model Equations
9
Our Experiment Results
Distance of Separation Between Antennae, d/m
Approximately
Model
10
Calculation Results
11
Some Recommendations
Proper Readers Arrangement (Reduce in-channel
collision)
12
More Recommendations

• (Reduce in-channel collision)
• Reducing the power output.
• Use of external sensors.
• The use of RF opaque or RF absorbing materials

13
Listen Before TalkIntroduction

• From ETSI 302 208
• (European RFID Regulation)
• Prior to Transmission, the interrogator must
  listen for the presence of another signal within
  its intended sub-band of transmission. The listen
  time shall comprise a fixed period of 5 ms plus a
  random time of 0 ms to 5 ms in 11 steps. If the
  sub-band is free the random time shall be set to
  0 ms.

14
Listen Before TalkLimits
15
Recommendation
Readers Synchronisation (to fulfil LBT)
16
Case Study

• Warehouse Depot in Europe
• ETSI EN 302 208
• 865 to 868 MHz
• 15 sub-bands, 200 kHz wide
• Only 10 sub-bands at 2W ERP
• EPCglobal Class 1 Generation 2
• Interrogator transmissions are located in
  even-numbered channels
• Tag backscatter located in odd-numbered channels

17
Synchronised LBT in Warehouse
Sub-band 2 Sub-band 4 Sub-band 6
Sub-band 8 Sub-band 10
18
Missing Truck 3
19
Limitations/ Challenges

• Model is just an approximation.
• On-site measurement is needed for value n.
• Case study yet to be tested in real life.

20
Conclusion