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Implementing Infrastructure-free Assisted-GPS
Supervisor: Paul Gardner-StephenStudent: Alexander Kotov
Master Thesis
19.09.2011
What is GPS? How does it work?
What is A-GPS?
Why? Serval Project and A-GPS
Plan and deliverables
How to measure success?
Implementing Infrastructure-free Assisted-GPS
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What is the GPS and how does it work?
GPS enabled mobile phone
GPS satellites
GPS require:
• Almanac data
• Ephemeris data
Problem:The data rate of the satellite signal is only 50 b/s !!!
3
A-GPS vs. GPS
GPS
Assisted GPS Server
Internet GPRS, EDGE, 3G, WiFi
Base station
GPS enabled mobile phone
GPS satellites
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Serval creates a WiFi mesh network of mobile phones that doesn’t require infrastructure and enables mobile communications regardless what your circumstance:
in the face of disaster, in the face of poverty, in the face of isolation, in the face of civil unrest, in the face of network black-spots.
Serval Project
Source based on data from The Serval Project, www.servalproject.org, 2011
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Knowing location is quite important in case of
disastrous situation,
Quicker location fix means less battery usage,
Serval Project use location for other services
(e.g. mapping),
It is good to know where you are!
Benefits of A-GPS in Serval Project
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Infrastructure free A-GPSGPS satellites
No or limited:Internet connectionCell phone towers
Mobile phone with assistance data
Assistance information
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How?GPS satellites
Extract A-GPS data from one phone
Transmit it over Serval network
Inject into another phone
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How?GPS satellites
Extract A-GPS data from one phone
Pretend to be A-GPS assistance server
Transmit assistance data to another phone
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How to measure success?
Wipe out any assistance data from mobile
phone
Measure TTFF
Repeat it several times
Do the same process with Serval A-GPS
assistance
Compare TTFF
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Conclusion
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A-GPS can give a faster TTFF
A-GPS is not available in Serval network
There are some ways to share assisted
data in Serval network
Thank you!
Any questions?
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