Networking for Wireless Sensors
in the UCI@Home energy project
Jonathan Chu
Computer Science, UCI
Mentor: Professor David Kirkby
SURF-IT
July 27, 2010
Overview
• Group Interdisciplinary project to design,
assemble, and integrate energy measuring
devices into homes
• Determine whether immediate feedback on
energy patterns can change a subject’s
behavior and reduce wasteful activities
• Collaboration between physics and social
science departments
Broadcast Storm Problem in Wireless
Networks
• Our wireless network is a self configuring
network of devices connected by wireless links
• Problem occurs during flooding when a host
receiver must take in multiple packets from
different transmitters simultaneously. Packets
will block each other and cause packet loss.
• Time Division Multiple Access (TDMA)
methodology could be used to assign time
slots to specified receivers on the same
channel
Time Synchronization
• Transmitter and receivers should be
synchronized as accurately as possible for
scanning channels
For our purposes, accuracy
within +/- 1 millisecond was
sufficient
RF Scanner
• To measure electromagnetic interference in
rooms
• Electromagnetic interference can be caused by
radio signals, wifi signals, phone, microwave,
etc..
• Program in software, the Nordic nRF24L01+
transciever
Implementation
• Had to understand and program wireless
protocols at the lowest, most complex level of
the OSI architecture, the Physical Layer
OSI Model
7. Application Layer
6. Presentation Layer
5. Session Layer
4. Transport Layer
3. Network Layer
2. Data Link Layer
1. Physical Layer
2.4x GHz Band
Nordic Transceiver broadcasting at 2.450 GHz band
Laptop wireless 802.11g
Signature of a Laptop’s wireless signal at WLAN channel 1
Centered at 2.412 GHz with a .022 GHz band
Channel Scanning
• Graph of Amplitude over Time for each frequency
• Scans from 2.400 to 2.500 GHz, in increments of .01GHz with 1 second
for each increment,
Home Microwave Interference
Your home microwave can cause interference at
around 2.45 GHz
Testing range of Nordic nRF24L01+
• Test packet loss between 2 nRF24L01+ for varying distances
• The greater the distance, the greater the packet loss rate
• Random noise causes data to vary
Repeater
• How to improve range?
• Place device between hub and leaf to repeat
packets from each other.
Repeater
• Pros: Seemed to be fairly effective in
increasing range of wireless devices, quick and
easy solution
• Cons: additional hardware required, costs,
• Alternative: In a network with multiple nodes
connected to each other, nodes themselves
can act as repeaters; these are called mesh
networks
• Many different types of mesh network
protocols can be used
Wireless Bootloader
• System used was AVR Atmega328p + Nordic
nRF24L01+ transciever
• Normally, each device must be manually
programmed by STK500v1 protocal via ICSP
header; updating firmware is pain
• Have been and still am working on wireless
bootloader, extremely difficult, bootloader
must be below 4K, on air timing cannot
disrupt baudrate, every packet must make it
through, detailed protocol implementation
Acknowledgements
• Professor and mentor David Kirkby
SURF-IT program organizers
• Calit2 (Stuart Ross, Shellie Nazarenus, Anna
Spitzer)
• UROP (Said Shokair)