UmTRX integration with OpenBTS

historical

Hi Thomas,

On Sun, Jun 10, 2012 at 4:58 AM, Thomas Tsou <thomastsou at gmail.com> wrote:
> On Sat, Jun 9, 2012 at 9:30 AM, Alexander Chemeris
> <alexander.chemeris at gmail.com> wrote:
>> Hi Thomas,
>>
>> If we get a UmTRX to you, could you make OpenBTS to run with it
>> quickly, like before the end of the month? No matter how hackish the
>> solution would be. We just need a way to start testing the hardware
>> performance in a more real situation. Then we could target a cleaner
>> solution.
>>
>> To recap - right now we could transmit on a single channel, and
>> receive on both channels, but the control of LMS chips is done by an
>> external python script. I.e. to tune and set bandwidth, gain, etc you
>> have to run this script before claiming a device with UHD.
>
> FYI, I was finishing plans to attend the openhere festival in Dublin
> at the end of the month. That is in two weeks.

Oh, that's great! So hopefully see you there!
Andrey Sviyazov is going to be there as well.

> What is the state of OpenBTS integration right now?

OpenBTS starts with this change:

diff --git a/Transceiver52M/UHDDevice.cpp b/Transceiver52M/UHDDevice.cpp
index d4ba580..4baf824 100644
--- a/Transceiver52M/UHDDevice.cpp
+++ b/Transceiver52M/UHDDevice.cpp
@@ -48,7 +48,8 @@

     tx_ampl           - Transmit amplitude must be between 0 and 1.0
 */
-const double master_clk_rt = 52e6;
+//const double master_clk_rt = 52e6;
+const double master_clk_rt = 13e6;
 const size_t smpl_buf_sz = (1 << 20);
 const float tx_ampl = .3;

But the behavior is a bit strange - when I start OpenBTS transceiver
starts to consume 100% of CPU and doesn't transmit. After a while (a
minute or so) CPU usage drops and I start seeing a signal at the UmTRX
output. I had no time to look into this deeply.

> Can you transmit a beacon signal?

Yes. I could see the network with a phone. Signal hound pictures:
1) umtrx-openbts-spectrum.PNG - spectrum, generated by OpenBTS.
2) umtrx-openbts-timeslots.PNG - the same, but with zero span.
3) "GMSK VGA1 -5, VGA2 18, channel power 750kHz.PNG" and
"Tx_GMSK#6(hot)_240412.png" are spectrum of a pure continuous GMSK
signal, transmitted with UmTRX (captured by me and Andrey Sviyazov).

> If UmTRX can support tuning, gain, and full duplex
> streaming with the existing UHD timestamp interface, then it shouldn't
> take long for OpenBTS.

Great!

Actually I should just try to run it - may be it will work right away? :)

> I can use any reasonable sample rate for testing.

FYI: We use 13MHz

> Is the external python script in a repository?

Yes.
https://github.com/chemeris/UHD-Fairwaves/blob/fairwaves/umtrx-dboard/host/utils/umtrx_lms.py

Not everything is implemented, but it's easy to amend it.

-- 
Regards,
Alexander Chemeris.
CEO, Fairwaves LLC / ООО УмРадио
http://fairwaves.ru
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