Masabists: Cell IDs and Location-Based Services

// December 1st, 2007 // Dev, Mobile

Note: this was originally posted on the Masabists blog.

It was very interesting to read about the latest update to Google Maps, one of the nicest J2ME apps around at the moment, which can now find your location without GPS. My instant reaction was – “Finally! But will the operators let them continue?”

Current operator location services work by triangulating signal strength from multiple base stations, which can often give good accuracy in urban areas densely packed with cells. They carry with them a cost – low in absolute terms but sadly quite high for a lot of possible use cases – and all sort of privacy controls, which whilst clearly necessary have been a bit of a barrier to widespread adoption of Location-Based Services.

Back in I think it was 2002, Masabi had a working system to track handset location by cell IDs. Ben, being an engineer at heart, had strapped a modem unit to a Palm PDA and written an application to read out the current cell ID and plot it onto GIF maps downloaded live from StreetMap.co.uk. I distinctly remember being very impressed walking down Victoria Street towards Parliament Square in Westminster and seeing it track us across the map on this very GIF with surprising accuracy.

Consensus seems to be that Google are using a very similar system, with GPS users providing location data to map out operator’s cell IDs (something I believe explicitly mentioned). This suggests that Google haven’t purchased the location data from the operators. Why would that matter?

So how did we build up our cell location database? And if it worked, why didn’t we commercialise it? The two answers are connected – we were ramping up for a launch within certain industries which could have benefitted from a single network/limited device range service. Unfortunately – or perhaps fortunately, with hindsight – just before a major demo, the operator we were using decided to remove the cell broadcast info that had been supplying the base station OS grid reference locations (note: the cell IDs themselves did not appear to change, as I had erroneously stated earlier).

We considered some sort of effort to map cell IDs into a database, perhaps open source, but without widespread GPS ownership this was a huge task and there was no guarantee that the operators wouldn’t choose to change the IDs at any time in the future and we were not interested in trying to make commercial promises where we had no control over key components. So we put it to rest.

Some JavaME devices can access the current cell ID, as can signed Symbian apps and Windows Mobile apps; Google’s compatibility list suggests they are targeting only these devices, suggesting they are attempting something similar. I wish them luck!

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