History

OpenBTS Frequently Asked Questions

Radio support

Does OpenBTS support the USRP2?

As of release 2.6, OpenBTS does not support the USRP2. There are no official plans to support that equipment and to our knowledge no one is doing it.

Why does OpenBTS require two RFX boards?

On of the main limiting factors of BTS performance is uplink/downlink isolation. For a full-range GSM system, we need about 160 dB of isolation. This degree of isolation does not appear possible on a single RFX board.

Can I run OpenBTS with a single RFX board instead of two?

This is possible and there are patches on the openbts-discuss (at) lists.sourceforce.net mailing list to support that and the performance is adequate for desktop development work. As of release 2.6.0, though, these patches are not in the official distribution.

Can I run OpenBTS with a WBX board?

This is possible and there are patches on the openbts-discuss (at) lists.sourceforce.net mailing list to support that. As of release 2.6.0, though, these patches are not in the official distribution.

Distributions, Servers, Software Licenses and Copyrights

What is "Kestrel Signal Processing, Inc." and what is its relationship to OpenBTS?

Kestrel Signal Processing, Inc. (KSP) is a software and signal processing consulting company in Fairfield, California. OpenBTS originated at KSP. KSP holds a blanket license for non-GPL distributions of OpenBTS and the great majority of publicly-available OpenBTS source code was written or commissioned by KSP. Any source code included in the official distribution of OpenBTS must be submitted under a contributor's license agreement (CLA) that assigns copyrights to KSP. KSP will then reassign copyrights to the FSF for any public release.

Note that the copyright-transfer requirement applies only to the core OpenBTS application, the GSM "stack". It does not apply to support applications like smqueue. Those components will be used under GPL even in commercial applications and can include any GPL-compatible components. If someone contributes GPL code to those support applications, it may also be incorporated into KSP's development trunk under GPL terms.

Do you realize that the GPLv3 patent license requirements prevent GPLv3 distributions from being used in most commercial GSM applications?

Yes. If you to use OpenBTS in a commercial application, you will probably need a non-GPLv3 license from KSP. You will still be responsible for arranging your own patent licensing for those patent-encumbered parts of the GSM specification. There are 100-200 essential patents for elements 2G GSM, depending on the feature set you intend to support.

What is the "commercial release" of OpenBTS and how does it differ from the public release?

The commercial release of OpenBTS includes features not in the public release and the GSM stack is not GPL. It is generally distributed only on KSP-provided hardware. Source code for the non-GPL components of the commercial release is available under commercial licenses.

Is OpenBTS being used in real products?

As of July 2010, not quite yet, but it is being used in the development of real products that will probably reach the market later in 2010.

Hardware, Software and Cellular Standards

Why are the transceiver and GSM stack in different applications?

Splitting the software radio transceiver and the rest of the GSM stack into two parts offers two advantages:
  1. Developers can adapt the system to other radio hardware or to their own existing demodulators without modifying the GSM stack.
  2. The transceiver and GSM stack can be licensed independently, allowing us to use GNU Radio's GPL libusrp driver with a non-GPL GSM stack.

Relationships to Other Projects

What is the relationship between OpenBTS and the rest of GNU Radio?

OpenBTS is part of the GNU Radio project and uses the same USRP hardware. However, the only part of the GNU Radio software actually used by OpenBTS is the libusrp device interface.

What is the relationship between OpenBTS and OpenBSC?

OpenBSC is an Abis-based GSM core network simulator designed for use with commercial BTS products. It is an entirely different project with an entirely different set of goals. Furthermore, the different implementation styles (C single-thread event driven versus C++ multithread dataflow) prevent direct transfer of code from one project to another. That said, the two projects often encounter identical engineering and design problems and many people who contribute in one project often follow technical discussions in the other.

What is the relationship between OpenBTS and Airprobe?

Airprobe is a GSM passive receiver and protocol analyzer. Airprobe may be useful as a debugging tool for OpenBTS developers, but it is not supported by the OpenBTS project.

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