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Sun, 01 Aug 2010
TCH Support for OsmocomBB

I started to implement Layer-1 support in OsmocomBB for traffic channels. Its not yet ready and in a rather crude state but I hope to clean it up in the next few days so that it can be released.

During testing I used a nice feature of my HP8922 GSM Testset: It can continuously generate Full-Rate TCH speech traffic on a timeslot without the need for any signalling. You can even connect an external audio source like a CD player and "broadcast" your own content. And while it is in this mode, the HP8922 can also receive speech traffic and you can hear it on its built-in loudspeaker.

The benefit of this for getting the Layer-1 code on the phone right is that you can concentrate on TCH receiving and transmitting without having to care about signalling. You just "tune" to the right ARFCN and timeslot (I don't use hopping during testing) and see that you get your code running.

I guess that having this special mode (setting an ARFCN and timeslot and "listen" to the TCH) in the phone can be quite useful for debugging non-hopping, non-encrypted, single ARFCN cells like OpenBSC and OpenBTS.

[ /gsm | permanent link ]

Microsoft Research and SDR

I wasn't aware of it, but Microsoft Research is doing SDR (Software Defined Radio): Sora.

Their approach is interesting, all the raw samples are transferred between the PC memory and the ADC/DAC of the Radio Front-end by a PCIe card and all the signal processing is done by the CPU of a PC. There is no DDC (Digital Down Converter) or DUC (Digital Up Converter) in an FPGA involved. They already implemented 802.11a/b/g and an LTE receiver this way.

The price of the hardware does not sound too expensive. The software only runs on Windows and I have not yet checked the license terms in detail.

I could imagine that combining this approach with the power of a GPU can be quite interesting.

[ /sdr | permanent link ]