UmTRX integration with OpenBTS

[Thomas Tsou]

On Sun, Jun 10, 2012 at 10:05 AM, Alexander Chemeris
<alexander.chemeris at gmail.com> wrote:
> 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.

If the load drops down and the signal transmits, I wouldn't worry
about it for now. The likely condition is that there is a offset
between the initial arriving timestamp and the expected timestamp.
Because the receive timestamps drive the transceiver, the receiver may
run at 100% until the timestamp and expected value align. If OpenBTS
transmits consistently, then the system is in sync.

>> 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).

Signals look great!

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

Yes, check for RACH bursts. The bursts will probably get rejected if
they arrive at GSM core due to timing offset, but that is an easy fix.

Have you verified reception of a receive test signal?

  Thomas