Course Project Project team forming deadline has passed Project teams will be announced soon Next step: project proposal presentation Presentation slides and one-page proposal document are

due on Jan 29 Important: include a project plan with itemized goals in

your proposal• Especially the ones for the first milestone• You will have the chance to revise further objectives at each

interim milestone• First milestone: Feb 12 and Feb 19

ECE 1161/2161 Embedded Computer System Design 2 1

ECE 1161/2161Embedded Computer System Design 2

Embedded Communication - I

Wei Gao

Spring 2019 2

Communication Technologies Tradeoff between data rate and communication

range

ECE 1161/2161 Embedded Computer System Design 2 3

Data rate

Communication range

Communication Technologies Considering energy consumption

ECE 1161/2161 Embedded Computer System Design 2 4

Energy consumption

Communication range

Radio-Frequency Identification (RFID)

Small tags Wirelessly send data when being triggered by a reader

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Radio-Frequency Identification (RFID)

Types of tags Passive

• Operational power scavenged from reader radiated power

Semi-passive• Operational power provided by battery

Active• Operational power provided by battery • Transmitter built into tag

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RFID Market

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Auto Immobilizers

Access ControlAnimal Tracking

Automated Vehicle Id

RFID Market

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Handheld Smart ShelvesPoint of Sale

Conveyor Belt

Printers

ForkliftDock Door

Radio-Frequency Identification (RFID)

Tag details

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Communication Modes Near-field: inductive coupling LF and HF frequency bands Reader generates magnetic

field• Mini transformer

Tag is powered by inductedcurrent

Tag is modulated to communicate

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N

S

TAG

Read

er

Inductive Coupling

Communication Modes Far-field: backscatter UHF and microwave bands

Tag is powered by resonance

Tag modulates backscatter by changing antenna impedance

ECE 1161/2161 Embedded Computer System Design 2 11Re

ader

TAG

Backscatter

Generic Tag Architecture

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ProtocolEngine

Receiver

Memory

Ante

nna

Write Path

D

S

G

Diode for directional transmission

Transistor for transmission control

RFID Protocols

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Class 0 Protocol Operating frequency: 3.3 MHz for data ‘1’, 2.2 MHz for data ‘0’ FSK modulation

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Class 0 Protocol Typical data stored in tag Globally unique identifier

• 96 bit EPC code

• 24 bit kill code

• 16 bit Cyclic Redundancy Check (CRC)

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Class 0 Protocol Electronic Product Code (EPC) data standard

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Class 0 Protocol Signaling

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RFID Readers Implementation challenges Must deliver enough power from RF field to power the tag

Must discriminate backscatter modulation in presence of carrier at same frequency

70db magnitude difference between transmitted and received signals

Interference between readers

Hugh volume of tag data – readers need to filter data before releasing to enterprise network

ECE 1161/2161 Embedded Computer System Design 2 18

RFID Reader Hardware Design

ECE 1161/2161 Embedded Computer System Design 2 19

Transmit path Receive Path Frequency Synthesizer Digital

RFID READERRF ModuleDAC

Hos

t Dev

ice

ADC

Crystal

Micro-Controller

AGC Filters I/QDemod

PLL

VCO

DAC Power Control

PA

Filter Coupler

Coupler

PowerDetect

Coupler

FPGA

Regulation

Baseband&

Protocol

RFID Reader Software Stack

ECE 1161/2161 Embedded Computer System Design 2 20

RFID Reader API Library

CustomApplication/

Protocol

ReaderProtocol

Application

Net

wor

km

anag

emen

t

File Systems

NetworkProtocols

High-Level Interfaces

Low-Level InterfacesO/S

Hardware

Platform API Libraries

CustomApplication/

Protocol

CustomApplication/

Protocol

Network Interface

What’s the Future Backscatter out of the reader Using other wireless signals on the air as the “helper” to

backscatter

Any wireless device can potentially become a RFID reader!• Need redesign on both the wireless device and RFID tag

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WiFi Backscatter

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WiFi signal as carrier wave

WiFi signal as carrier wave

Signal Reflection

WiFi Backscatter Key challenges At the tag: how to re-modulate the incoming signal?

• Data is encoded as absorption/reflection of incoming packets

At the WiFi reader: how to decode the difference?• WiFi packet detection

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WiFi Backscatter Limitations Low data rate

• One bit per WiFi packet

Short communication range• Helper must provide strong power

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Available RFID devices RFID tags With pre-loaded

identifiers Available at all

frequency bands

RFID readers Can be used as I/O device via USB/SPI/I2C Use the starter kit for easier access

WiFi/FM backscatter Fancy but adopt with caution

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