Archive for USRP
The June issue of the MIT Technology Review has a short article on how to build your own cellular network (registration required). The idea of going into competition with Verizon for a few hundred dollars was just too much fun to overlook.
Far from being just a fun hack, OpenBTS’s founders Harvind Samra and David Burgess set out to design a cellular basestation that would reduce the cost of GSM service provision in rural areas and the developing world to below $1 per month per subscriber. They’ve already successfully field tested their DIY basestation at the Burning Man festival in Nevada and on the tiny island nation of Niue in the South Pacific. Now you can put your own island on the digital map for around $1,000 or so, depending on your patience and your junkbox.
OpenBTS is an open-source Unix application that uses the Universal Software Radio Peripheral (USRP) to present a GSM air interface to standard GSM handset and uses the Asterisk software PBX to connect calls. The combination of the ubiquitous GSM air interface with VoIP backhaul could form the basis of a new type of cellular network that could be deployed and operated at substantially lower cost than existing technologies in greenfields in the developing world.
OpenBTS systems draw only about 60W, which can easily be supplied by a few marine batteries in remote locations, topped up by solar panels or a small wind generator. And while the USRP hardware—which is the basis for a large number of SDR deployments—can be programmed for many waveforms other than GPS, GPS is the dominant standard worldwide—particularly in developing countries—and besides Asterisk is based on it. And Asterisk, which can run on a notebook computer, is free vs. $250,000 or so for comparable commercial infrastructure.
Your output power and antenna will clearly determine—or be determined by—the range you wish to cover. The USRP’s WBX daughterboard puts out a modest 50-100mW (17-20dBm) from 50 MHz to 1.2 GHz, which covers most international cellular bands, though 100mW won’t get you very far. Add a PA and a small array of yagis and the sky’s the limit.
There is, however, the little matter of FCC approval. For the Burning Man field test in 2008 the FCC issued Experimental Special Temporary Authorization license WD9XKN to Kestrel Signal Processing Inc., Samra and Burgess’ consulting firm. The FCC issued a second temporary license for a larger test at the 2009 Burning Man festival. Both tests proved quite successful. OpenBTS is now providing cell phone coverage to Niue’s 1,700 residents and an unknown number of tourists, using Telecom Niue for Internet backhaul. Tests are currently under way in South America and Asia.
Ready to roll your own basestation? Samra and Burgess have the Burning Man covered, but maybe you could talk the FCC into letting you cover Coachella or Austin’s South by Southwest (SXSW) music festival. You can download all the necessary software here and browse for hardware at the Kestrel OpenBTS store. You’re on your own for the batteries.
Good luck, have fun and don’t forget to call!