Download - ECE 455 Embedded System Design
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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
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ECE 1161/2161Embedded Computer System Design 2
Embedded Communication - I
Wei Gao
Spring 2019 2
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Communication Technologies Tradeoff between data rate and communication
range
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Data rate
Communication range
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Communication Technologies Considering energy consumption
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Energy consumption
Communication range
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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
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RFID Market
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Handheld Smart ShelvesPoint of Sale
Conveyor Belt
Printers
ForkliftDock Door
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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
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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
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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
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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
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RFID Reader Hardware Design
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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
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RFID Reader Software Stack
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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
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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
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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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