[USRP-users] Support with NI USRP 2954R

2017-09-01 Thread Snehasish Kar via USRP-users 
Hello


I am need to fetch GPS data and time from the on-board GPSDO in NI USRP x310. 
Is it necessary for me to sync both clock source and time source to GPSDO for 
that or without it I can directly fetch it. Please help me with an example to 
fetch GPS data from it.


BR

Snehasish

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Re: [USRP-users] Support with NI USRP 2954R

2017-09-01 Thread Marcus D. Leech via USRP-users 

On 09/01/2017 10:23 AM, Snehasish Kar via USRP-users wrote:


Hello


I am need to fetch GPS data and time from the on-board GPSDO in NI 
USRP x310. Is it necessary for me to sync both clock source and time 
source to GPSDO for that or without it I can directly fetch it. Please 
help me with an example to fetch GPS data from it.



BR

Snehasish




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If you look at the source code for query_gpsdo_sensors, you'll get good 
guidance for how to do this.


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[USRP-users] Changes in wired channel after restarting flowgraph

2017-09-01 Thread Bakshi, Arjun via USRP-users 
Hi all,


Had posted about this before, but focusing on 1 simple case here.


I'm observing a change in a wired channel every time I restart my flow graph. 
I'm using 1 USRP + WBX board, i.e. tx and rx on the same USRP. So 
time/frequency sync should not be a factor, I believe.


I simply do: start-> sleep(2)-> stop->wait->start->sleep(2) looped 10 
times, and record the rxed signal. I see that during the 2 seconds the channel 
remains constant, however after the restart the channel changes.


Any ideas on why this is happening? I was expecting to see the same channel no 
matter how many times I restart the flow or even power cycle the USRP.


Figures attached: Real and imaginary part of rxed signal, subsampled ~110 to 
fit it all in.


Thank you,


Arjun
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[USRP-users] Build question

2017-09-01 Thread Rob Kossler via USRP-users 
I have UHD installed from source using a git clone of the UHD repository.
After executing "git pull" and then "make", "make test", and "make
install", I noticed that my version had not updated when running
uhd_find_devices.  I then went back and tried "make clean" followed by the
other commands and still no luck.  Finally, I removed the build folder and
re-ran cmake and the other commands and then it was fixed.

I am wondering if I always need to remove the build directory and rerun
cmake every time I pull a few new changes?  Or, is there another way to do
this.

Thanks.
Rob
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Re: [USRP-users] Initial phase offset at TX/ DC offset and LTE

2017-09-01 Thread Edwin Li via USRP-users 
Hi AB,

Let me make a guess here. Because of the clock is not perfectly
synchronized, there is non-linearity. Therefore the channel estimator gives
multiple coefficient. Try connecting 2 USRP with the same reference clock
and pulse per second signal and see if there are still multipath.

Regards,
Edwin

Bakshi, Arjun 于2017年8月31日周四 下午3:07写道：

> Correction: The thing I mentioned about all taps being phase shifted by
> the same amount isn't always observed.
>
>
> I tried it again with the same USRP, (and 2 USRPs with a MIMO) and I still
> get different channels every time I start the flow graph.
>
>
> Identifying multiple taps: the channel estimate I get has >1 coefficient
> that is significantly greater than a noise like value.  Figure attached.
> Shows only abs(chan).
>
>
> Thank you,
>
>
> AB
> --
> *From:* Edwin Li 
> *Sent:* Wednesday, August 30, 2017 11:49:30 PM
> *To:* Bakshi, Arjun; usrp-users@lists.ettus.com
> *Subject:* Re: [USRP-users] Initial phase offset at TX/ DC offset and LTE
>
> Hi AB,
>
> I suppose you are using 2 USRPs, right? Each USRP has its own clock. These
> clocks have different phases. That's why you see a phase offset.
>
> As for the multi-tap channel, how do you identify it?
>
> Not sure how LTE eliminates the phase offset. But in my communication
> program, I use preamble for phase estimation, then use costas loop to
> eliminate the offset.
>
> Hope it helps you.
>
> Regards,
> Edwin
>
> Bakshi, Arjun via USRP-users 于2017年8月30日周三
> 下午9:09写道：
>
>> Hello everyone,
>>
>>
>> I have a setup that records the channel between a tx and rx while they
>> are connected by a wire. However I've noticed that while the channel is
>> constant over one run, when I restart the code/flow graph I get a different
>> (but still constant) channel.
>>
>>
>> Can anyone shed some light on why this is happening?
>>
>>
>> Also, I'm observing a multi-tap channel even on a wired connection. That
>> seems suspicious to me. I've however verified that my estimation code is
>> correct based on simulations. I'm using an N210 with a WBX board.
>>
>>
>> Lastly, does LTE do anything to force the same offset or eliminate random
>> offsets at the transmitting node?
>>
>>
>> I searched the srsLTE github repo and found some variable
>> tx_corr_dc_phase/gain, that suggests a fix, but I'd like some more
>> inputs on this.
>>
>>
>> github link:
>>
>>
>> https://github.com/srsLTE/srsLTE/blob/590fff9c69214b4858de2e987410f0d24ad4275c/srsue/ue.conf.example
>>
>> Thank you,
>>
>>
>> AB
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>>
>
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Re: [USRP-users] Changes in wired channel after restarting flowgraph

2017-09-01 Thread Edwin Li via USRP-users 
Looks like there is a random phase. Every time you start, the phase of the
clock maybe different. Hence when you plot the signal, it's going to be
different. I can observe the same random phase in my BPSK program.

Bakshi, Arjun via USRP-users 于2017年9月1日周五
下午2:48写道：

> Hi all,
>
>
> Had posted about this before, but focusing on 1 simple case here.
>
>
> I'm observing a change in a wired channel every time I restart my flow
> graph. I'm using 1 USRP + WBX board, i.e. tx and rx on the same USRP. So
> time/frequency sync should not be a factor, I believe.
>
>
> I simply do: start-> sleep(2)-> stop->wait->start->sleep(2) looped 10
> times, and record the rxed signal. I see that during the 2 seconds the
> channel remains constant, however after the restart the channel changes.
>
>
> Any ideas on why this is happening? I was expecting to see the same
> channel no matter how many times I restart the flow or even power cycle the
> USRP.
>
>
> Figures attached: Real and imaginary part of rxed signal, subsampled ~110
> to fit it all in.
>
>
> Thank you,
>
>
> Arjun
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>
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Re: [USRP-users] Changes in wired channel after restarting flowgraph

2017-09-01 Thread Bakshi, Arjun via USRP-users 
The only solution I've found is picking a center frequency that is a multiple 
of 64MHz based on this reply by Matt


http://lists.gnu.org/archive/html/discuss-gnuradio/2008-06/msg00017.html


Regards,


AB


From: Edwin Li 
Sent: Friday, September 1, 2017 6:13:03 PM
To: Bakshi, Arjun; usrp-users@lists.ettus.com
Subject: Re: [USRP-users] Changes in wired channel after restarting flowgraph

Looks like there is a random phase. Every time you start, the phase of the 
clock maybe different. Hence when you plot the signal, it's going to be 
different. I can observe the same random phase in my BPSK program.

Bakshi, Arjun via USRP-users 
mailto:usrp-users@lists.ettus.com>>于2017年9月1日周五 
下午2:48写道：

Hi all,


Had posted about this before, but focusing on 1 simple case here.


I'm observing a change in a wired channel every time I restart my flow graph. 
I'm using 1 USRP + WBX board, i.e. tx and rx on the same USRP. So 
time/frequency sync should not be a factor, I believe.


I simply do: start-> sleep(2)-> stop->wait->start->sleep(2) looped 10 
times, and record the rxed signal. I see that during the 2 seconds the channel 
remains constant, however after the restart the channel changes.


Any ideas on why this is happening? I was expecting to see the same channel no 
matter how many times I restart the flow or even power cycle the USRP.


Figures attached: Real and imaginary part of rxed signal, subsampled ~110 to 
fit it all in.


Thank you,


Arjun

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Re: [USRP-users] Changes in wired channel after restarting flowgraph

2017-09-01 Thread Bakshi, Arjun via USRP-users 
So the SBX daughter board has a phase resync feature, which I think would 
alleviate my problem. For other boards it is noted in [1] that :


"Most daughterboards use a fractional-N synthesizer ... Generally, these 
fractional- N synthesizers introduce a random phase offset after each retune 
..., this random phase offset will need to be measured and compensated for in 
software."


I'd appreciate pointers on how to do this.


Thank you,


AB


[1] https://kb.ettus.com/Synchronization_and_MIMO_Capability_with_USRP_Devices


From: Bakshi, Arjun
Sent: Friday, September 1, 2017 6:29:49 PM
To: Edwin Li; usrp-users@lists.ettus.com
Subject: Re: [USRP-users] Changes in wired channel after restarting flowgraph


The only solution I've found is picking a center frequency that is a multiple 
of 64MHz based on this reply by Matt


http://lists.gnu.org/archive/html/discuss-gnuradio/2008-06/msg00017.html


Regards,


AB


From: Edwin Li 
Sent: Friday, September 1, 2017 6:13:03 PM
To: Bakshi, Arjun; usrp-users@lists.ettus.com
Subject: Re: [USRP-users] Changes in wired channel after restarting flowgraph

Looks like there is a random phase. Every time you start, the phase of the 
clock maybe different. Hence when you plot the signal, it's going to be 
different. I can observe the same random phase in my BPSK program.

Bakshi, Arjun via USRP-users 
mailto:usrp-users@lists.ettus.com>>于2017年9月1日周五 
下午2:48写道：

Hi all,


Had posted about this before, but focusing on 1 simple case here.


I'm observing a change in a wired channel every time I restart my flow graph. 
I'm using 1 USRP + WBX board, i.e. tx and rx on the same USRP. So 
time/frequency sync should not be a factor, I believe.


I simply do: start-> sleep(2)-> stop->wait->start->sleep(2) looped 10 
times, and record the rxed signal. I see that during the 2 seconds the channel 
remains constant, however after the restart the channel changes.


Any ideas on why this is happening? I was expecting to see the same channel no 
matter how many times I restart the flow or even power cycle the USRP.


Figures attached: Real and imaginary part of rxed signal, subsampled ~110 to 
fit it all in.


Thank you,


Arjun

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Re: [USRP-users] Changes in wired channel after restarting flowgraph

2017-09-01 Thread Marcus D. Leech via USRP-users 

On 09/01/2017 10:10 PM, Bakshi, Arjun via USRP-users wrote:


So the SBX daughter board has a phase resync feature, which I think 
would alleviate my problem. For other boards it is noted in [1] that :



"Most daughterboards use a fractional-N synthesizer ... Generally, 
these fractional- N synthesizers introduce a random phase offset after 
each retune ..., *this random phase offset will need to be measured 
and compensated for in software*."



I'd appreciate pointers on how to do this.


Thank you,


AB


[1] 
https://kb.ettus.com/Synchronization_and_MIMO_Capability_with_USRP_Devices



*From:* Bakshi, Arjun
*Sent:* Friday, September 1, 2017 6:29:49 PM
*To:* Edwin Li; usrp-users@lists.ettus.com
*Subject:* Re: [USRP-users] Changes in wired channel after restarting 
flowgraph


The only solution I've found is picking a center frequency that is a 
multiple of 64MHz based on this reply by Matt



http://lists.gnu.org/archive/html/discuss-gnuradio/2008-06/msg00017.html


Regards,


AB


*From:* Edwin Li 
*Sent:* Friday, September 1, 2017 6:13:03 PM
*To:* Bakshi, Arjun; usrp-users@lists.ettus.com
*Subject:* Re: [USRP-users] Changes in wired channel after restarting 
flowgraph
Looks like there is a random phase. Every time you start, the phase of 
the clock maybe different. Hence when you plot the signal, it's going 
to be different. I can observe the same random phase in my BPSK program.


Bakshi, Arjun via USRP-users > 于2017年9月1日周五 下午2:48写道：


Hi all,


Had posted about this before, but focusing on 1 simple case here.


I'm observing a change in a wired channel every time I restart my
flow graph. I'm using 1 USRP + WBX board, i.e. tx and rx on the
same USRP. So time/frequency sync should not be a factor, I believe.


I simply do: start-> sleep(2)-> stop->wait->start->sleep(2)
looped 10 times, and record the rxed signal. I see that during the
2 seconds the channel remains constant, however after the restart
the channel changes.


Any ideas on why this is happening? I was expecting to see the
same channel no matter how many times I restart the flow or even
power cycle the USRP.


Figures attached: Real and imaginary part of rxed signal,
subsampled ~110 to fit it all in.


Thank you,


Arjun

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If you expect phase consistency *across power-cycle of the hardware*, 
that won't happen.  There's no way to predict the startup behavior of 
the reference clock.


While certain very-specialized hardware might have the property that the 
startup phase of the reference clock remains predictable across 
power-cycles,

  no "general purpose" radio has that property.

Digital receiver code *MUST*, for real-world scenarios, cope with the 
fact that the TX and RX will have no tightly-predictable phase and 
frequency offsets
  from one another, particularly across power-cycles of one of them.   
That is the purpose of things like clock recovery, phase-locked loops, 
etc, in the RX

  chain.

If your algorithms assume that the participating systems are all 
"perfectly synchronized", then they aren't necessarily coping with 
real-world scenarios.





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