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Coexistence with WiFi for a Home Automation ZigBee product
• Extra features :– Position and error feedback– Security– Scalability
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
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
Materials and Methods(4)
• system uses ZigBee channel 26 and is vulnerable to interference from WiFi channel 13
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(5)
• 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(6)
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(7)
• 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(8)
Materials and Methods(9)
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(10)
• X: distance of interference source
• Y :WiFi traffic level • C:WiFi channel
Materials and Methods(11)
• Traffic rate Y equivalency in WiFi load
Materials and Methods(12)
• At distances below 5 meters from interfe-
rence source the sy- stem is practiuzally unreachable. The ef- fects of interference consistently dissipate after 15m in all chan- nels
Results(1)
• SR levels of 10% or less, where the sy-
stem is completely unresponsive,were observed at dista- nces of 5 meters or less from inter- ference source.
Results(2)
• Even at this rel- atively low traf- fic level a small but noticeable degradation (a- round 80%) of system respon- siveness was observed.
Results(3)
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(1)
• 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(2)
• PRR vs. SR has a correlation value of 0.89. PRR% can the-
refore be used to predict the performance of the HA sys- tem.
Discussion(3)
• ZigBee can coexist with WiFi in a typical home environment
• Precautions are taken into account• New standards such as Wireless HD and