How to shrink a 30ft base-station into a three-inch Raspberry Pi

One of the biggest innovations in recent years has been the Raspberry Pi platform. This $30 Linux-based computer, about the size of a credit card, is targeted at educating the next generation of software and hardware engineers in programming. Recognising its potential, we teamed up with the Raspberry Pi Foundation to launch a competition (now closed to new entrants) that challenged schoolchildren, students and programmers to use a Raspberry Pi to make the world a better place.

Meanwhile, to evaluate what the platform was capable of, our wireless experts at our Global Innovation and Technology Centre got hold of a Raspberry Pi to see if we could implement a mobile phone base-station that could run our own private mobile-phone network.

Overcoming some seriously complex obstacles along the way, we successfully managed to route voice and SMS traffic through the computer – as well as implement the GSM mobile phone standard. If you are developing your entry into the competition and are looking for inspiration – or are just interested in what can be done with this exciting new technology – please watch our video.

We shrank a 30ft base-station into a three-inch Raspberry Pi by:

• setting up our Raspberry Pi in a screened-room facility to ensure we didn’t break any laws on frequency spectrum
• hooking up the Raspberry Pi to a radio interface
• hand-optimising some of the software
• code-optimising the signal processing – we are experts in this and needed to use all our skills to get parts of the code running fast enough.

The Raspberry Pi was used to set up three pieces of software:

• OpenBTS – this implements the GSM mobile phone standard
• FreeSWITCH – this routes calls in a similar way to Skype
• our own python features – a programming script that assigns telephone numbers to colleagues.

To find out more about using off-the-shelf technologies in new product designs, please contact us now.

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