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Odinokov Serge Flag: Public
Friday, November 07, 2003 Trolleybus
Fixed route public transport navigation
based on GSM network statistics
Report
Rubikon Apskaitos Sistemos. IT and R&D Department. Page 1 of 8
Odinokov Serge Flag: Public
Friday, November 07, 2003 Trolleybus
Contents
Preface..................................................................................................................................................3
Preparation ...........................................................................................................................................3
Test .......................................................................................................................................................3
Results ..................................................................................................................................................4
Next steps ...........................................................................................Error! Bookmark not defined.
Rubikon Apskaitos Sistemos. IT and R&D Department. Page 2 of 8
Odinokov Serge Flag: Public
Friday, November 07, 2003 Trolleybus
Preface
In year 2002 JSC “Rubikon Apskaitos Sistemos” (RAS), and Bite GSM, one of biggest GSM
network provider in Lithuania, as a part of cooperation, launch experimental project based on
RubiSafe system to identify possibilities to navigate public transport using just GSM network data.
Idea was to invent some statistical methods those can give accurate enough real time coordinates of
mobile objects without refer to GPS. Experimental phase was planned because GSM network has
complicated profile and navigation based just on GSM network data had being forecasted as, more
or less, impossible.
Staff of RAS has invented method to use so-called reference vehicle that must collect GSM
network profile periodically and then use that database to calculate real coordinates of object.
Preparation
RAS prepared one dedicated RubiSafe device that has:
- power supply from normal board voltages of public vehicles;
- GSM module, with updated software driver on RubiSafe device, that can collect some
information about GSM network;
- 12-channel GPS receiver;
- Built-in data logger was set to record GSM profile every 5 seconds.
RubiSafe system was enhanced to maintain such kind of objects.
Device was installed on one trolleybus for real time testing.
Test
Device was installed on one of trolleybuses for route 10. This route runs across Vilnius and the
city, has length about 27 km; plus route to trolleybus park one per day. RAS collected information
during one month.
Rubikon Apskaitos Sistemos. IT and R&D Department. Page 3 of 8
Odinokov Serge Flag: Public
Friday, November 07, 2003 Trolleybus
Results
GPS receiver works quite well. No problems were detected, just some disorientation during startup.
It means such equipment can work in this environment with sparkly high current/voltage noises.
On picture below you can see recorded route. It fits roads on the map completely. This route is
based on GPS receiver output.
Green dots are stops on for route 10.
Rubikon Apskaitos Sistemos. IT and R&D Department. Page 4 of 8
Odinokov Serge Flag: Public
Friday, November 07, 2003 Trolleybus
For each point device recorded current CID, LAC, TA and, additionally, data about five more
powerful base stations.
As were forecasted, GSM network profile based on CID and LAC can not give enough
information. See picture below.
Circles are cells. Numbers represent channel CID. We can see that the same cell detected on
different parts of the route. This information is not enough to recalculate coordinates.
Rubikon Apskaitos Sistemos. IT and R&D Department. Page 5 of 8
Odinokov Serge Flag: Public
Friday, November 07, 2003 Trolleybus
RAS has invented dedicated statistical function that improves normal navigation using just CID
described above by adding probability, based on other factors like TA and most powerful cells
nearby.
Results are quite optimistic. Look at pictures below.
Rubikon Apskaitos Sistemos. IT and R&D Department. Page 6 of 8
Odinokov Serge Flag: Public
Friday, November 07, 2003 Trolleybus
Blue dots are recalculated positions of trolleybus based on current GSM network profile and
statistical database. During recalculation, records dated not earlier than one hour ago were taken
into account only. It guaranties that recalculation was based on old data from previous runs, not
from current run and current coordinates. As we see, recalculated route fits real route well.
Rubikon Apskaitos Sistemos. IT and R&D Department. Page 7 of 8
Odinokov Serge Flag: Public
Friday, November 07, 2003 Trolleybus
On the next picture you can see absolute errors for some points.
Columns D/E keep errors in meters. Statistical deviations from real coordinates are 18 and 36
metersfor longitude and altitude respectfully.
This result shows that invented method can give accurate enough coordinates. Error itself can be
reduced by more frequently recording of GSM network profile. Anyway, received errors are
comparable with dimensions of trolleybus – this is quite nice in a scope of possible applications.
Benefits
1. Solution is based on existing RubiSafe system.
2. Cheaper vehicle’s devices.
3. Two-way communication with driver as a standard.
4. Statistical data can be reused in other applications because public transport covers all major
streets in a city.
5. Expansion to other cities is cheap because does not require extra hardware platforms.
Rubikon Apskaitos Sistemos. IT and R&D Department. Page 8 of 8
