UmTRX integration with OpenBTS

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Thomas Tsou thomastsou at gmail.com
Mon Jun 18 00:17:52 UTC 2012


On Sun, Jun 17, 2012 at 4:21 AM, Alexander Chemeris
<alexander.chemeris at gmail.com> wrote:
> Alternatively I recommend you to use this image which is tested and
> known to work fine (either bin for usrp_n2xx_net_burner.py or bit for
> JTAG):
> http://code.google.com/p/umtrx/downloads/detail?name=u2plus_umtrx-20120424.bin
> http://code.google.com/p/umtrx/downloads/detail?name=u2plus_umtrx-20120424.bit

Ok. With this FPGA image and the following initialization sequence, I
get signal. OpenBTS output is pretty clean as shown in the attachment.
Note that I halved the GSM symbol rate because for some strange
reason, I was not able to run OpenBTS with two samples-per-symbol,
though I was able to send a tone with tx_waveforms at the same sample
rate.

So this is 'slow' GSM at 135 kHz, but the point was to get sampling
above Nyquist to capture any distortion from the device and not
OpenBTS itself. There is noticeable IQ imbalance, but I guess that is
just uncorrected. Also, please ignore the failure messages on our test
equipment (we have a converter spec issue).

Is there a similar sequence to enable Rx?

  Thomas

> Looks like it is not correctly initialized. Try using the same
> initialization sequence as I do:
>
> ./umtrx_lms.py --lms 1 --lms-init
> ./umtrx_lms.py --lms 1 --lms-tx-enable 1
> #./umtrx_lms.py --lms 1 --lms-rx-enable 1
> # Select 0.75MHz LPF
> ./umtrx_lms.py --lms 1 --reg 0x34 --data 0x3e
> ./umtrx_lms.py --lms 1 --pll-ref-clock 26e6 --lpf-bandwidth-code 0x0f
> --lms-auto-calibration
> # Manual DC calibration
> ./umtrx_lms.py --lms 1 --reg 0x42 --data 0x71
> ./umtrx_lms.py --lms 1 --reg 0x43 --data 0x89
> ../build/utils/uhd_cal_tx_dc_offset --compl_i 0.001 --compl_q 0
> # Tuning
> ./umtrx_lms.py --lms 1 --lms-tx-pll-tune 925e6
> ./umtrx_lms.py --lms 1 --lms-pa-on 2
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