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

2

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

4

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

5

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

6

Infrastructure free A-GPSGPS satellites

No or limited:Internet connectionCell phone towers

Mobile phone with assistance data

Assistance information

7

How?GPS satellites

Extract A-GPS data from one phone

Transmit it over Serval network

Inject into another phone

8

How?GPS satellites

Extract A-GPS data from one phone

Pretend to be A-GPS assistance server

Transmit assistance data to another phone

9

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

10

Conclusion

11

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?

12