Re: [USRP-users] Buffer underruns on x310 when transmitting and receiving from same channel cont.

[Rob Kossler via USRP-users]

Jason,
I downloaded and compiled your program.  Here are some remarks.

   - I accidentally ran your program using UHD 3.9.LTS.  It worked fine!
   It even worked fine with Num Channels set to 2.  I then realized my mistake
   and switched to 3.10.
   - I duplicated your results using UHD 3.10.  That is, bad behavior with
   same channel for Tx/Rx and good behavior with different channels for Tx/Rx

Regarding 3.9.LTS, if this is an option for you, I would highly recommend
it. We have had issues with 3.10 and thus we only use it when necessary.
It is necessary for either working with the TwinRx daughterboard or if you
need dual 10Gbe links.  Note that a single 10Gbe link can support aggregate
300 MS/s so it can handle 2 channels at 100 MS/s.  But, it can't do 2
channels at 200 MS/s which is why you might need dual 10Gbe.

I didn't investigate whether or not I could run the example
tx_rx_loopback_to_file program successfully and if so why it succeeds while
your program fails.

Let me know if you have any questions / comments.

Rob

On Wed, Aug 30, 2017 at 7:06 PM, Jason W Zheng 
wrote:

> Hi Rob,
>
>
> Thanks for your suggestion. I tried adding set_thread_priority_safe(), but
> it didn't solve the problem.
>
>
> -Jason
> --
> *From:* Rob Kossler 
> *Sent:* Wednesday, August 30, 2017 8:02:25 AM
> *To:* Jason W Zheng
> *Cc:* usrp-users@lists.ettus.com
> *Subject:* Re: [USRP-users] Buffer underruns on x310 when transmitting
> and receiving from same channel cont.
>
> Jason,
> This is perhaps a long shot but I noticed that your code does not include
> set_thread_priority_safe() for each thread - only the main thread.  Perhaps
> adding this will help.  I realize that this does not explain why you are
> successful when not using the same channel.
>
> Also, I noticed that the example tx_rx_loopback_to_file.cpp does not
> implement this call on the Tx thread.  The Rx occurs in the main thread
> though for this example.  However, I see in "benchmark_rate.cpp" this call
> is implemented for both Tx and Rx threads.
>
> Rob
>
>
> On Thu, Aug 17, 2017 at 6:55 PM, Jason W Zheng via USRP-users <
> usrp-users@lists.ettus.com> wrote:
>
>> The last thread got a little long and kind of died, so I decided to make
>> a new thread summarizing all the findings thus far.
>>
>>
>> I'm running on an x310 across dual 10 Gigabit ethernet, outfitted with
>> twin basic tx rx daughbords. I'm running on UHD version 3.11.0. Ideally, I
>> would like two simultaneous transmit and receive streams, utilizing both
>> channels to transmit and receive. I don't want to have to use 2 x310s for 2
>> receive and transmit streams
>>
>>
>> When I transmit and receive at the same time on the same channel, I get a
>> lot of U's printed out to console signaling underflows, no matter what the
>> rate. *HOWEVER, if I transmit and receive on separate channels, say
>> tx_streamer has stream_args at channel 1 and rx_streamer has stream_args at
>> channel 0, it works just fine.*
>>
>>
>> I've attached the source code of a complete but simple program that will
>> hopefully demonstrate my problem. In this program, two threads are created:
>> a transmit thread and a receive thread. The receive thread is constantly
>> receiving data to a buffer and overwriting that buffer with new data. The
>> transmit thread is constantly transmitting 0's from a prefilled buffer.
>>
>>
>> If anyone has an x310 running across 10Gbps ethernet, can you compile and
>> run my program to test if this problem occurs not just for me?
>>
>>
>> Here's what we have already tested:
>>
>> - I'm running on a server system rocking two 12 core intel xeon
>> processors. (https://ark.intel.com/products/91767/Intel-Xeon-Processor-
>> E5-2650-v4-30M-Cache-2_20-GHz). My network card is the recommended x520
>> da2. Someone had previously suggested NUMA to be an issue, but I don't
>> think this is the case as the program works when we switch to transmitting
>> and receiving on separate channels.
>>
>>
>> - I've tested only transmitting and only receiving. We can transmit at
>> 200MS/s across both channels and we can receive at 200MS/s across both
>> channels, but we cannot transmit and receive from the same channel. This
>> suggests our network card is working properly and we can handle the high
>> rate.
>>
>>
>> - I've tried my program on UHD 3.10.2 and the problem still occurs
>>
>>
>> - I've tried setting the tx_metadata waiting 2 second before
>> transmitting. The problem still occurs.
>>
>>
>> - I've tried running the example program txrx_loopback_from_file and that
>> works for simultaneous receive and transmit, but I have no idea why.
>>
>>
>> From the last point, I'm lead to believe that I am somehow calling the
>> uhd API wrong, but I have no idea where the error is. Any help would be
>> greatly appreciated.
>>
>>
>> Thanks,
>>
>> Jason
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
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Re: [USRP-users] Performance Consistency of B200mini

[Marcus D. Leech via USRP-users]

On 08/31/2017 12:38 PM, Xingjian Chen wrote:
I found it is about 1dB difference between measurements. Please check 
the attachment file for test results I captured by my b200mini. Do you 
know how to reduce this amplitude variation? What is the cause you 
think led to this issue?

What version of UHD are you using?

One can expect a small amount of variability across restarts--just the 
nature of analog hardware.  But 1dB seems like more than I would expect.


Since you're using loopback, any such effect would be "amplified" 
because both the signal source and receiver are on the same hardware.


Could you repeat your tests with a laboratory signal generator or noise 
source?






 Thank you.

*From:* USRP-users  on behalf of 
Marcus D. Leech via USRP-users 

*Sent:* Monday, August 28, 2017 11:07:12 AM
*To:* usrp-users@lists.ettus.com
*Subject:* Re: [USRP-users] Performance Consistency of B200mini
On 08/28/2017 10:17 AM, Xingjian Chen via USRP-users wrote:


Hi,

How consistent is B200mini can be in terms of signal amplitude if I 
restart the board? I am sending and getting chirp pulses at the same 
time by a B200mini.  I found that if I restart the board every time 
before the loopback measurement, and comparing pulses between 
measurements, the amplitude changed more than amplitude changes in a 
single measurement. It seems the gain changed even if I have the same 
settings in controlling software. What device in the hardware of 
B200mini can lead to this variation? Thank you.





What is the magnitude of the apparent gain variability?





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

[Bakshi, Arjun via USRP-users]

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 
mailto:usrp-users@lists.ettus.com>>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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[USRP-users] How to Access a user register in fpga of X310 using UHD (3.10.2)

[Karan Suri via USRP-users]

Hello Users
I recently stumbled onto a problem. I need to implement a gain control
mechanism by left shifting bits of the received data, when the rx power is
considerably low. I need to define a settings register which controls the
shift amount, but I need to  get access to this setting register using the
C++ code.
I am using the latest stable version of uhd and it seems that there is no
proper documentation of the settings register for the X310.
It  barely talks about the peek and poke commands found in
user_settings_core_3000.hpp. But i cant find any example which relates to
this nor how to use it. Any help will be extremely appreciated.
Thanks a ton
Karan Suri
University Of Michigan
EECS - Masters
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[USRP-users] Rotating constellations and varying LOs with USRP B210 + Board Mounted GPSDO

[George Sklivanitis via USRP-users]

Hi everyone,

Has anyone noticed unstable LOs or carrier frequency offsets when using
USRP B210s with board mounted GPSDOs?

We have recently been doing field tests using GPS-disciplined oscillators
for both USRP B210s and USRP N210 and occasionally both transmitter and
receiver flowgraphs lose GPS lock, although clock reference leds in the
USRP panel are ON.

Thanks,
George
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Re: [USRP-users] Rotating constellations and varying LOs with USRP B210 + Board Mounted GPSDO

[Marcus D. Leech via USRP-users]

On 08/31/2017 10:08 PM, George Sklivanitis via USRP-users wrote:

Hi everyone,

Has anyone noticed unstable LOs or carrier frequency offsets when 
using USRP B210s with board mounted GPSDOs?


We have recently been doing field tests using GPS-disciplined 
oscillators for both USRP B210s and USRP N210 and occasionally both 
transmitter and receiver flowgraphs lose GPS lock, although clock 
reference leds in the USRP panel are ON.


Thanks,
George


Do things improve when you disable the on-board GPSDO?


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Re: [USRP-users] Distance estimation and phase continuity of LO

[Kyeong Su Shin via USRP-users]

Hello All,

Just want to note that NI 2921s use XCVR2450, which is half-duplex (cannot
rx and tx concurrently). B210s will work better, as they are full-duplex
2x2 MIMO.

Regards,
Kyeong Su Shin

On Wed, Aug 30, 2017 at 8:44 PM, Michael Don via USRP-users <
usrp-users@lists.ettus.com> wrote:

>
> USRPs can do Tx and Rx at the same time.  I did an experiment where I
> modified the FPGA image of Node 2 to send the Rx samples directly to Tx on
> a different freq., and measured the phase difference of the echo from Node
> 2 at Node 1.  I didn't measure the phase difference of the carrier, rather
> the phase difference of a FM sine signal.  Didn't play around with it too
> much, but I got an accuracy of a few meters, although for some reason I
> always had to calibrate the system to measure the processing delay.  I'd
> also be interested to see anyone else's results.
>
> -Mike
>
> On Wed, Aug 30, 2017 at 8:53 PM, Qasim Chaudhari via USRP-users <
> usrp-users@lists.ettus.com> wrote:
>
>> Hi,
>> I want to find the distance between two USRPs by sending and
>> receiving packets (or a continuous wave) in a bidirectional manner.
>>
>> Step 1: Node 1 Tx  ->  Node 2 Rx - measures phase, then switches
>> over to become Tx
>> Step 2: Node 2 Tx --> Node 1 Rx - measures phase and computes
>> distance.
>>
>>  I have two questions.
>>
>> Q1. If someone else has done/know about this kind of experiment with the
>> USRP, can you please point me towards some good reference/source/s?
>>
>> Q2. When USRP switches from Rx to Tx mode at node 2 (and more
>> importantly, from Tx to Rx mode at node 1), does it maintain phase
>> continuity of its local oscillator? (Because otherwise the phase
>> measurements become meaningless.)
>>
>> Currently, I am using NI USRP N2921 with the latest version of GNU Radio
>> but I can have access to B210s if required.
>>
>> Cheers,
>> Qasim
>>
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>>
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