TINA showcase: Passive RFID

The INtelligentAirport

Multiservice RF Infrastructure with Passive Tag Location Capability

Richard Penty, S Sabesan, Michael Crisp, Ian WhiteCambridge University Engineering Department

http://www.epsrc.ac.uk/


• Unreliable coveragefrom outdoor cells

• Dedicated indoor capacity

• Fewer RF transceivers needed compared to distributed radios

• Analogue links may be coax cable (<100 m) or fibre (>100 m)

• Wideband versions can carry all required baseband and radio services

In-Building Coverage/Distributed Antenna System


Distributed Antenna Network Performance

3 Antennas

(m)

(m)

Single Antenna

-10 -5 0 5 10-10

-5

0

5

10

(m)(m

)

3 Antennas

Thro

ughp

ut (M

bps)

-10 -5 0 5 10-10

-5

0

5

10

2

4

6

8

10

12

14

16


Adding Sensing to Communications DAS

• Passive UHF RFID allows very low cost tags to be used for object detection at ranges up to 10 m

• Increasing demands for mobile data bandwidth is driving down cell sizes, requiring closer antenna spacing.

Can RFID be added as an additional service on RoF DAS allowing a shared infrastructure?

Can RFID leverage similar power requirement reductions to we have shown with communications services?


Why RFID over Fibre in Airports?

• RFID is considered cheaper than bar code readers

• But <100% read rate reliability means critical reading for e.g. baggage is compromised

• Only two airports internationally implement RFID for baggage handling

• Within TINA we’ve tried to improve read success rate over a wider area

• Airport applications, particularly if security sensitive, really do need ~ 100% success rate

• Will allow tagging of other items e.g. passengers

• Late passengers contribute to 10% of all delays in UK• Extremely expensive for airline business models• Different airlines would use passenger location information in different ways!

• Security

• Tagging of passenger, along with video, would reveal suspicious behaviour• Monitoring of security areas


AU1

Tag

Rx Tx

AU3Rx Tx

AU2

TxRx

Zinwave H

ub

AU1

AU1

AU1

Tag

RFID Tx

RFID Rx

DA

S

Processing

Aim to show improvement in RFID read rate/accuracy

and reduction in nulls

Improved Tag Detection with DAS


Demonstration of Error Free Operation Usinga Commercial RFID System

-1 -0.5 0 0.5 1

0

2

4

6

8

10

12

14

16

18

20

X (m)

Y (m

)

Rx (-1, 0)

Tx (1, 0)

(1.25, 9.75) Tx

Rx (1, 19)

Tx (-1, 19)

Rx(1.25, 11.75)

AU1

AU2

AU3

19 x 2 m area. +31 dBm EIRP output power, UK frequency band


Improving Read Rate and Accuracy - Intel R1000

Command-Begin Packet

Antenna-Begin Packet

Inventory-Cycle-Begin Packet

Inventory-Round-Begin Packet

Inventory-Response Packet

Inventory-Round-End Packet

Inventory-Cycle-End Packet

Antenna-End Packet

Command-End Packet

DAS Settings

Intel R1000 Firmware

Intel Transceiver R1000

Intel R1000

PC

Intel Transceiver Interface(executing on PC)

USB Interface

(executing on ARM7)

SSB Interface

Serial InterfaceARM7

Micro controller

DAS Settings

Intel R1000 supports host side applications (Intel Transceiver interface). The transceiver interface includes a C/C++ functional interface to talk to the firmware module using USB communication.

When an inventory is performed using the transceiver interface, it returns data from the Intel firmware in a sequential of packets.

Phase is varied when it returns the inventory-round-begin packet which indicates the beginning of a an inventory round on an antenna.


DAS RFID System

Tx

AU1

Tag

Rx Tx

AU3Rx Tx

AU2Rx

AU3

AU2

AU1

Alien Tag

Zinwave H

ub

Intel R1000 Firmware

Intel Transceiver R1000

Intel R1000

TagAlien TagTagAlien

TagTagAlien TagTagAlien

TagD

AS

Processing


Enhanced Read Rate/Accuracyusing R1000 Reader System

80 Alien Higgs2 tags are placed at a height of 2 m in a 50 cm grid interval over a 10 m x 4 m area.

AU3

AU1

AU2

The conventional RFID system takes 1.7s to read 62 tags out of 80 (77.5% accuracy) - read rate of 36 tags/sec.

The R1000 system takes 1.2s to read all tags (100% accuracy),- read rate of 67 tags/sec


Providing Location in optical DAS RFID system

Now we can read a tag (quickly) over a large area, we have lost the location accuracy of an RFID “portal” – can we somehow improve the accuracy

Estimating the location of passive UHF RFID tag is a major challenge due to the narrow bandwidth available.

The most common techniques are based on RSSI location algorithms. - However, multi-path effects, fading and nulls result in the RSSI being only a weak function of range.

By using an optical DAS with multiple antennas, we can reduce the degree of fading in the field of view- and thus significantly improve the accuracy of RSSI location techniques.


Passive UHF RFID RTLS

Pillar

Location Algorithm• The area is first mapped by recording the

combined RSSI from all the AUs and the RSSI of each AU

• Measurements are repeated five times at each grid point and the AU with the highest number of successful reads is identified.

• Location is then estimated by finding the closest match of:

• the three antenna RSSI• the RSSI from the mostly likely

closest antenna • the probability that the antenna is

closest to the tag from the mapped data set.

• A maximum likelihood weighting is applied to the mapped data.


Demonstration of Enhanced Location Accuracy

Optimised DAS

Random Commercial RFID Reader

Mean error 1.9 m 4.6 m 4.1 mStandard deviation 1.0 m 3.6 m 2.1 m

Error Distribution

0

5

10

15

20

25

30

0.5 1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5

Error (m)

Per

cent

age

(%)

Triple antenna DAS

Random

Commercial RFID Reader


Demonstration of Enhanced Location Accuracy

100% location estimations using the DAS has less than 4.2 m error compared to only 55% and 40% from the commercial RFID reader and the random algorithm respectively.

0 1 2 3 4 5 6 7 8 9 100

0.2

0.4

0.6

0.8

1

Error (m)

CD

F

Error distribution

Triple antenna DASRandomCommercial RFID Reader


Tracking/Location System GUI

We intend to use the current system as a test bed to develop new algorithms.


Application Software Integration with Hong Kong-TINA Project

Intel R1000

CambridgeSoftware

MySQLDatabase

HK-TINASoftware


Demonstrator

Passive RFID over DAS demonstrator exhibiting

• Large passive RFID field of view

• 100% read accuracy using DAS to reduce fading

• Enhanced read rate (67 tags/second)

• RSSI based location with 1.9 m mean error

• Integration with HK TINA software demonstrators

Business

TINA showcase: Passive RFID