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1

RFID UHF

Radio Frequency

Radio frequency RFID systems usually include :

• Passive RFID’s

Mainly based on Backscatter • Active RFID’s

Based on typical wireless communications

f1

f2

Reader

(transmitter/receiver)

Tag

Ts

Ts

X

Modulator

X

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Radio Frequency

Typical Reader systems include: 1. RF Transmitter 2. RF Receiver 3. A Digital Signal Processor 4. An Antenna

Typical RF TAG systems include: 1. An Antenna 2. A chip

Typical TAG chip systems include: 1. A Voltage Harvester 2. A digital processor and a

simple transmitter

Radio Frequency

Typical Readers are moving fast to a Software Defined Radio Solution, including a digital part and a RF up-converter and RF down-converter….

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Radio Frequency

RF RFID Tags are most of the time based on electromagnetic backscatter configurations.

Backscatter is similar to radars. The TAG Antenna reflects part of an incoming electromagnetic wave back to the reader.

Electromagnetic wave are reflected by most objects that are larger than half the wavelength.

The backscatter reflection efficiency is maximized for antennas that are resonating with the incoming radar frequency.

The short wavelengths of UHF facilitate the construction of antennas with smaller dimensions and greater efficiency.

• The energy reflected from the tag is radiated into free space. A copy of this signal severely attenuated due to the free-space attenuation is received by the reader’s antenna.

• The reflected signal is returned back to the reader antenna and interpreted conveniently.

Electromagnetic Backscatter

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Far field operation

• Contrary to inductive coupling, electromagnetic backscatter operates in the far field.

• The range can be calculated based on the energy available at the transponder which is calculated using the Friis formula:

rtinTinin

eT GGr

PPGr

PGG

r

PAP

2

122

2

1224444

Backscatter RFID

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The received power can be related to the transmitted power by using the Friis formula that states:

where is the free space attenuation, and l the wavelength

UHF Electromagnetic Propagation

rtinTinin

eT GGr

PPGr

PGG

r

PAP

2

122

2

1224444

2

4

r

http://www.cdt21.com/resources/siryo3_01.asp

Electromagnetic Backscatter

• Main frequencies for backscatter are at UHF frequencies: 868 MHz (Europe) and 915 MHz (USA); and microwave frequencies: 2.5 GHz and 5.8 GHz

• The signal is modulated mainly in ASK and BPSK configurations.

• Main use for long-range systems – Distance between reader and tag > 1m

• For higher distances >15m – backscatter tag’s usually use a battery

• The tag in this situation is normally put in a stand-by mode for saving

battery time, when out of the reader range

• The battery of an active backscatter tag never provides power for the transmission of data between tag and reader. The battery is used exclusively for supply power to microchip.

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400-1000 MHz UHF RFID-Systems (UHF)

• Electromagnetic propagation • The energy collected (harvested) is related to the gain (aperture) of the

receiving antenna, which in simple terms is related to the wavelength of the received signal

• The operation range is actually dependent on the Friis formula

400-1000 MHz UHF RFID-Systems

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400-1000 MHz UHF RFID

• The range actually depends on the Friis formula and thus on:

– Transmitter (reader) power

– Energy requirements of the tags (for passive tags)

– Absorption factor of materials to which the tag is attached

– Tag size

• The smaller the tag, the smaller the energy capture area, the shorter the read range

400-1000 MHz UHF RFID Interference

• Interference can arise from electrical noise that appears in motors, florescent lights, etc Fortunately this are minimized at at UHF

• Noise from other RFID systems, mobile phones, etc.

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400-1000 MHz UHF RFID Directivity

• UHF is a frequency that can be used combined with directional antennas

• It is useful to increase gain of antennas, and thus range in a certain direction.

5.2 RFID UHF RFID Systems

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5900 MHz RFID Systems

5900 MHz RFID Systems

• 5900 MHz have been used significantly for over 10 years in transportation applications

– Rail car tracking

– Toll collection

– Vehicle access control

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• Operation based on Modulated backscatter

• 5.9 GHz systems operate in the “far field” long range systems

• These signals are attenuated and reflected by materials containing water or human tissue and are reflected by metallic objects

• Line of sight is not usually required for operations

5900 MHz RFID Systems

• Tags can be smaller than LF and UHF systems, and more efficient

• Compared to inductive systems, the UHF and microwave systems can have longer range, higher data rates, smaller antennas, more flexibility in form factors and antenna design

• Object penetration and no line-of-sight readability can be better for LF systems

5900 MHz RFID Systems

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5.850-5.925 GHz

Multi-Application

OBU

(retrofit installation)

87.5-107.9 MHz

FM sub carrier

800 to 900 MHz

Cellular Phone

1575.42 MHz

GPS Receiver

1800 to 1900 MHz

PCS Phone

Other ITS

Communications

Equipment

Multiple Bands

Two-way Radio

76-77 GHz

Collision

Avoidance Radar

2322.5-2345 MHz

for XM Radio

Satellite Radio band

909.75-921.75 MHz

Toll & Parking

OBU

(Add-on when

needed)

5900 MHz RFID Systems

• Approach: Active

• Bandwidth: 75 MHz (5.850 - 5.925 GHz)

• Modulation: QPSK OFDM (with 16QAM and 64QAM options) (BPSK

preamble)

• Channels: 7 - 10 MHz channels (optional combinations of 10 and 20 MHz

channels)

• Data Rate: 6, 9, 12, 18, 24, and 27 Mbps with 10 MHz Channels (3 Mbps

preamble)

• (or 6, 9, 12, 18, 24, 36, 48, and 54 Mbps with 20 MHz Channel option) (6

Mbps preamble)

• Max Tx Pwr: 28.8 dBm (at the antenna input)

• RSU EIRP: Nominal 0 - 33 dBm (1 mW - 2 W) / Max. 44.8 dBm (30 W)

• OBU EIRP: Nominal 0 - 20 dBm (1 - 100 mW) / Max. 44.8 dBm (30 W)

• RSU and OBU Sensitivity: - 82 dBm (QPSK) / - 65 dBm (64QAM)

• C/I: 4 - 6 dB (for QPSK @ 10-4 BER coded) / 16 - 17 dB (for 64QAM @

10-4 BER coded)

• Band Sharing Strategy - Frequency Coordination. Selection of alternate

channels for adjacent zones. Use CSMA to prevent interference between

users in the channel.

5900 MHz RFID Systems

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SPECTRUM USED

DATA RATE

COVERAGE

ALLOCATION STATUS

INTERFERENCE

POTENTIAL

MAXIMUM RANGE

MINIMUM SEPARATION

CHANNEL CAPACITY

POWER (Downlink)

POWER (Uplink)

12 MHz (909.75 to 921.75 MHz)

0.5 Mbps

One communication zone at a time

No protection

Many 900 MHz Phones,

Many Rail Car AEI Readers,

Many Spread Spectrum Devices,

Wind Profile Radars

300 ft (at required- 30 dBm sensitivity)

1500 ft (except where carefully planned)

1 to 2 channels

Nominally less than 40 dBm (10 W)

Nominally less than 6 dBm (< 4mW)

75 MHz

6 Mbps - 27 Mbps

Overlapping communication zones

Primary Status (high protection)

Sparsely located Military Radars,

Very Sparsely located Satellite

Uplinks

1000 m (~ 3000 ft)

50 ft (on small zone channels)

7 channels

Nominally less than 33 dBm (2 W)*

Nominally less than 33 dBm (2 W)*

902 - 928 MHz Band PARAMETERS 5850 - 5925 MHz Band

RED – Substantial Limitation

GREEN – Substantial Advantage

5900 MHz RFID Systems

Range (ft)

10

00

12

00

14

00

16

00

18

00

20

00

22

00

24

00

26

00

28

00

30

00

32

00

34

00

36

00

20

0

40

0

60

0

80

0

Data

Rate

(Mb

ps)

33

30

27

24

21

18

12

9

6

3

0

~

~

0.5 Mbps

902 - 928 MHz Band Performance Envelope

5850 - 5925 MHz Band

Performance Envelope

Emergency Vehicle Services Safety Message Services

Data Transfer and

Internet Access Services

Toll and Payment Services

(Approximate)

5900 MHz RFID Systems

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• PUBLIC SAFETY and PRIVATE APPLICATIONS share the band

• INTEROPERABILITY

• LICENSED OPERATION

• PUBLIC SAFETY INSTALLATION PRIORITY

• NON-MUTUAL EXCLUSIVITY FOR PRIVATE INSTALLATIONS

• LIMITED RANGE FOR PRIVATE OPERATIONS

• FREQUENCY COORDINATOR USED TO ASSIGN LICENSES

5900 MHz RFID Systems

5.850-5.925 GHz

Multi-Application

OBU

(connected to the IDB)

5.850-5.925 GHz

Multi-Application

OBU

(360 deg horizontal pattern)

The multi-application OBUs use a 360 deg. horizontal pattern for all applications.

909.75-921.75 MHz

Toll & Parking

OBU

(360 deg horizontal pattern)

5900 MHz RFID Systems

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Traffic Signal

Traffic Signal

Traffic Signal - Green

Traffic Signal- Red

COLLISION

ANIMATION

FOLLOWS

TYPICAL INTERSECTION

Traffic Signal

Traffic Signal

Traffic Signal - Green

Traffic Signal- Red

NO COLLISION AVOIDANCE SYSTEM IN OPERATION

ANIMATION

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EMERGENCY VEHICLE APPROACH WARNING

VEHICLE

FRONT

EMERG.

VEHICLE

REAR

EMERG.

Note 1: The Emergency OBU transmits a warning to

ALERT other vehicles that it is coming.

In-Vehicle

Displays and

Annunciations

Traffic Signal

Traffic Signal

Emergency

Vehicle

Not to Scale

up to 1000 m (3281

ft)

OBUs on Control Ch

Emergency Vehicle

Approach Warning

Communication Zone

VEHICLE

LEFT

EMERG.

VEHICLE

RIGHT

EMERG.

ANIMATION

FOLLOWS

5.2 DSRC – DEDICATED SHORT RANGE COMMUNICATION

EMERGENCY VEHICLE APPROACH WARNING

VEHICLE

FRONT

EMERG.

VEHICLE

REAR

EMERG.

Note 1: The Emergency OBU transmits a warning to

ALERT other vehicles that it is coming.

In-Vehicle

Displays and

Annunciations

Traffic Signal

Traffic Signal

Emergency

Vehicle

Not to Scale

up to 1000 m (3281

ft)

OBUs on Control Ch

Emergency Vehicle

Approach Warning

Communication Zone

VEHICLE

LEFT

EMERG.

VEHICLE

RIGHT

EMERG. ANIMATION

5.2 DSRC – DEDICATED SHORT RANGE COMMUNICATION