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Report
Coexistence with WiFi for a Home
Automation ZigBee product
Federico Dominguez, Abdellah Touhafi, Jelmer Tiete and
Kris Steenhaut ,Erasmus Hogeschool Brussel
Vrije Universiteit Brussel,Brussels, Belgium
Communications and Vehicular Technology in the Benelux
(SCVT), 2012 IEEE 19th Symposium on, 6-16 Nov. 2012
Adviser:
Presenter: Yu-Jhang Chen
Date: 102/12/18
Outline
1.
2.
3.
4.
5.
Introduction
Materials and Methods
Results
Discussion
Conclusion
Introduction
(1)
• Home Automation(HA):
1.
2.
3.
4.
Heating Ventilation Air Conditioning (HVAC)
automatic garage doors
intruder detection alarms
smart sensors detect temperature
Introduction
(2)
Introduction
(3)
• Tradition HA:
– Expensive
– Cabling difficulty
• Now HA:
– Cheap
– Smaller
– Offer wireless connectivity
Introduction
(4)
• HA products exploit frequencies bands :
– 433MHz, 868MHz, 900MHz, 2.4GHz
• The 2.4GHz compared with 433MHz :
– Higher data throughput
– Worldwide availability as an Industrial Scientific
Medical (ISM) band
Introduction
(5)
ZigBee:
• Advantage
– low cost SoC platforms
– High interoperability
• Defect
– WiFi, Bluetooth, Microwaves, cordless phones
interference
Materials and Methods
Window Shutter HA system:
• Content :
– Shutter motor and Remote Control (RC)
• Extra features :
– Position and error feedback
– Security
– Scalability
(1)
Materials and Methods
(2)
• The minimal
Window Shutter
HA system setup
is just a Wall RC
and a Window
Shutter. The
system can later
be expanded
with other RC
models and more
shutters
Materials and Methods
ZigBee PRO:
• Devices :
– Texas Instruments(TI) CC253x SoC
– 8051 8-bit microprocessor
– AES coprocessor
– USB controller
– CC2591 RF
(3)
Materials and Methods
Channel Allocation:
• ZigBee defines 27 channels :
– One in the 868 MHz band
– Ten in the 915 MHz band
– 16 in the 2.4 GHz band
• WiFi channels:
– Range from 1 to 13
(4)
Materials and Methods
(4)
• system uses ZigBee channel 26 and is vulnerable to
interference from WiFi channel 13
Materials and Methods
(5)
Goals of tests :
• Confirm or negate whether WiFi interference
poses a threat to the product
• Find recommendations to avoid interference
• Find a simple method to detect the presence
of disruptive interference during product
installation
Materials and Methods
(6)
• Packet Reception Rate (PRR)
− Added a test function in the firmware
− Counts all ZigBee packets flagged as test packets
− RC have the capability to send test packets in
bursts of 1000 packets per second
Materials and Methods
(7)
System Responsiveness (SR):
• Assumed that a user expected
− Response to UP, DOWN and STOP commands by
an RC , around 300ms
− response of shutter position feedback in the
embedded LCD screen on the Multi RC while the
shutter is moving
Materials and Methods
•
•
•
•
(8)
Cr is successfully executed commands
Cd is noticeable delay time
Ct is total number of commands
Fw is a weighted value for the quality of the
LCD visualization
Materials and Methods
(9)
Materials and Methods
(10)
WIFI interference:
• Constructed a lab to test the affects:
– Put in a metallic window frame to emulate
– Used a Linksys WRT54GL and D-Link DIR-615
– Used iperf to generate synthetic UDP test traffic
Materials and Methods
(11)
• X: distance of
interference source
• Y :WiFi traffic level
• C:WiFi channel
Materials and Methods
• Traffic rate Y equivalency in WiFi load
(12)
Results
(1)
• At distances below 5
meters from interference source the system is practiuzally
unreachable. The effects of interference
consistently dissipate
after 15m in all channels
Results
(2)
• SR levels of 10% or
less, where the system is completely
unresponsive,were
observed at distances of 5 meters
or less from interference source.
Results
(3)
• Even at this relatively low traffic level a small
but noticeable
degradation (around 80%) of
system responsiveness was
observed.
Discussion
(1)
Confirm:
• WiFi can create harmful interference to
ZigBee systems
• Distance to interference source and WiFi
traffic level are key variables
• Difficult to avoid the WiFi generate
interference with real traffic
Discussion
(2)
• Distance from interference source
– A distance of 5 meters can be tolerated
– 15 meters seems to be a safe distance to avoid
harmful disruption
• PRR vs. SR
– PRR can give a me accurate measure of the
expected performance
– Measuring PRR is much simpler than measuring SR
Discussion
(3)
• PRR vs. SR has
a correlation
value of 0.89.
PRR% can therefore be used
to predict the
performance
of the HA system.
Conclusion
(1)
• ZigBee can coexist with WiFi in a typical
home environment
• Precautions are taken into account
• New standards such as Wireless HD and
WiGig will not occupy the 2.4 GHz band

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