[USRP-users] MIMO bug?

Dan Sego bubbadoradar at gmail.com
Mon Dec 29 20:36:32 EST 2014


It turns out that after specifically mapping both N200 daughter boards with
set_rx_subdev_spec(uhd::usrp::subdev_spec_t("A:0"), 0) and ("A:0"),1), the
global settings only work for set_rx_rate. The gain commands and the
antenna selection ("TX/RX") and frequency (tuning) had to be made
explicitly to each channel.

What I was seeing was leakage on the slave (which tracked the slave device
when I switched master/slave).

cheers, and Happy New Year! Dan



On Mon, Dec 29, 2014 at 1:57 PM, Marcus D. Leech <mleech at ripnet.com> wrote:

>  On 12/29/2014 04:54 PM, Dan Sego wrote:
>
>  Thank you for the reply, I hope your holiday was a good one.
>
>  I should have noted that I do query the motherboards for gain after the
> code has completed sampling. Results echo the initial read back after gains
> are set.
>
>  As to the GR, no I haven't. Looked at that approach originally and
> passed as the learning curve looked longer than C++, and I didn't know
> C++.......
>
>  I had considered the gain question but the only control is on the HMC472
> attenuator and 6 dB (coarse) and 3.5 dB (fine) in the ADC (if I have the
> correct model number - ADS62P45 and family and which is not a user control
> state I suspect). So at 10 dB gain attempted (21.5 dB attenuation) on the
> master,slave attenuator and ADC defaulting at/to 0 dB gain combines to
> yield ~20 dB of channel offset (slave relative to master and this presumes
> that the ADC gains are both set in the master). Otherwise, it looks like
> fixed gain in the remainder of the cascade (the ADA493X and differential
> driver for the ADC, MGA82563), have I missed something?
>
>  The fact that it is always the slave suggests a driver to me.
>
>  I haven't yet run over a range of gain settings in MIMO. I'll try that
> and report back. I'll also try an older UHD release.
>
>  Cheers, and thanks again. Dan
>
> There's a variable attenuator in the WBX RX chain, independent of the
> motherboard.
>
> Putting a simple thing together in GRC would be five minutes work, just to
> confirm sanity:
>
> UHD-source-with-2-channels------>2 FFT sinks.
>
>
>
>
> On Mon, Dec 29, 2014 at 1:05 PM, Marcus D. Leech via USRP-users <
> usrp-users at lists.ettus.com> wrote:
>
>>   On 12/29/2014 12:09 PM, Dan Sego via USRP-users wrote:
>>
>>   Good morning to the list.
>>
>>  I have 2 N200 r4 units with WBX daughter cards operating with the
>> following Win32; Microsoft Visual C++ version 10.0; Boost_105400;
>> UHD_003.008.000-release. One unit has an internal GPSDO.
>>
>>  In MIMO operation (via the MIMO cable). The slave unit experiences an
>> unexplained 25 dB of attenuation relative to the master. This change does
>> not follow the hardware: that is it tracks the slave.
>>
>>  I am using US HDTV as probing signal: tuning to 575 MHz with fc32
>> formatted data sampled as 12.5 MCSPS per unit. The code operated
>> successfully performing data capture to file (though does have the windows
>> prompt upon completion to terminate). An example run screen capture is
>> pasted below: the collection operation involves continuous sampling saving
>> contiguous packets (28) and skipping 50 for a approximate burst sampling
>> rate of 25 Hz.
>>
>>  Win32; Microsoft Visual C++ version 10.0; Boost_105400;
>> UHD_003.008.000-release
>>
>> -- Opening a USRP2/N-Series device...
>> -- Current recv frame size: 1472 bytes
>> -- Current send frame size: 1472 bytes
>> -- Creating WSA UDP transport for 192.168.10.3:49156
>> -- Creating WSA UDP transport for 192.168.10.3:49158
>> -- Creating WSA UDP transport for 192.168.10.3:49157
>> -- Creating WSA UDP transport for 192.168.10.3:49159
>> -- Detecting internal GPSDO.... Found an internal GPSDO
>> -- Creating WSA UDP transport for 192.168.10.2:49156
>> -- Creating WSA UDP transport for 192.168.10.2:49158
>> -- Creating WSA UDP transport for 192.168.10.2:49157
>> -- Creating WSA UDP transport for 192.168.10.2:49159
>> -- Setting references to the internal GPSDO
>> -- Initializing time to the internal GPSDO
>> Using Devices: Multi USRP:
>>   Device: USRP2 / N-Series Device
>>   Mboard 0: N200r4
>>   Mboard 1: N200r4
>>   RX Channel: 0
>>     RX DSP: 0
>>     RX Dboard: A
>>     RX Subdev: WBXv3 RX+GDB
>>   RX Channel: 1
>>     RX DSP: 0
>>     RX Dboard: A
>>     RX Subdev: WBXv3 RX+GDB
>>   TX Channel: 0
>>     TX DSP: 0
>>     TX Dboard: A
>>     TX Subdev: WBXv3 TX+GDB
>>   TX Channel: 1
>>     TX DSP: 0
>>     TX Dboard: A
>>     TX Subdev: WBXv3 TX+GDB
>>
>> Actual RX Rate Master: 12.500000 Msps...
>>
>> Actual RX Rate Slave: 12.500000 Msps...
>>
>> Actual Gain Master: 10.000000 dB...
>>
>> Actual Gain Slave: 10.000000 dB...
>>
>> GPS lock status: locked
>> GPS epoch time: 1419183071 seconds
>> -- Successfully tuned to 575.000000 MHz
>> --
>> -- Successfully tuned to 575.000000 MHz
>> --
>> Checking LO Lock Master LO: locked...
>> Checking LO Lock Slave LO: locked...
>> Checking MIMO Lock MIMO: locked...
>>
>> sample time first packet2.3000003
>>
>> full seconds2.3000003
>>
>>
>> sample time first packet2.34068534
>>
>> full seconds2.34068534
>>
>>
>> Done!
>>
>>
>>  I have measured the channel signals of the units individually
>> and configured for MIMO. Examples of the individual measurements (power
>> spectra and mean noise power and total signal power are summarized in slide
>> 1 attached. All runs were made at 10 dB of gain. Both units were
>> individually exercised from 0 to 30 dB of gain to have side-by-side
>> responses (indeed one unit is 5 dB less sensitive which track over gain and
>> both have distinctive and repeatable gain responses using identical log
>> periodic antennas and matched length coax).
>>
>>  Slide 2 has the MIMO results in both possible configurations.
>>
>>  Has anyone encountered this? Any suggestions?
>>
>>  regards, Dan Sego
>>
>>
>> _______________________________________________
>> USRP-users mailing listUSRP-users at lists.ettus.comhttp://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>
>>  The only thing I can think of is that the slave gain isn't being set,
>> despite the messages shown to the contrary.
>>
>> Have you tried a GR flow-graph to experiment with this case?
>>
>>
>>
>> --
>> Marcus Leech
>> Principal Investigator
>> Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org
>>
>>
>> _______________________________________________
>> USRP-users mailing list
>> USRP-users at lists.ettus.com
>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>
>>
>
>
> --
> Marcus Leech
> Principal Investigator
> Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org
>
>
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