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Thursday, April 05, 2007

Geo-locking femtocells

Interesting to see that this femto from Samsung has a GPS device in it, which is used to "geo lock" it to an operator's licenced territory.

I presume this is particularly relevant for countries like the US where there are regional operators. For markets elsewhere with nationwide licences, I guess that the IP address of the broadband connection should be sufficient to ensure customers don't put the device in a suitcase and try & plug it in somewhere the provider isn't permitted to operate.

Interesting to see the real-world practicalities starting to come out, though. I suspect there's going to be a range of issues around security/authentication for femtocells that are only now being recognised.


Anonymous said...

Dean - a GPS in a femto - which is designed to sit INDOORS! Don't believe all the press releases you get!

Dean Bubley said...

GPS can work indoors. And also in this case the femto isn't as power-constrained as a battery-powered device, and can therefore keep monitoring GPS signals 24x7. Could be some form of assisted GPS too, I guess.

Anonymous said...


Several points.

First, you are absolutely correct: secirity, authentication, provisioning are all critical - and are there are a number of "subtle but important" issues. Making sure that subscribers to a "home service" do not just put the femto in a suitcase for freecalls all the time are a good example.

As such, most carriers and OEMs are planning on such "geo-locking" in their systems.

Secondly, GPS is a possibility. Indoor coverage is not too bad: especially as you only need "slow" tracking (the house is unlikely to move down a motorway: any movement is a worry). That said, coverage in US is probably better than, say, Korean towerblocks.

However, there are alternatives. One of the obvious is just locking the femto to a specific DSLAM or CMTS: if it is moved you must call the carrier to reset it. (Yes, I know this opens up a load of other issues... We are back to "subtle but important - and good examples of why creating a scalable service is much more than just building a modem!).

Finally, though, is a different point. Basestations need very accurate timing: a few parts-per-billion, accurate over the life of the BS. In normal use that is from a stratum clock locked over PDH (T1 link), a rubidium OCXO -- or a "proper" GPS timing reference. There are a number of ways of doing this - but if you can rely on coverage (see above, reasonable in USA), then why not kill two birds with one stone?

Rupert Baines, picoChip