Re: [Discuss-gnuradio] Saving the I/Q samples of multiple synchronized USRPs
Thanks Marcus. A quick follow-up question: Should the length of my ethernet cables (to the GigE switch from each of the USRPs that I am trying to synchronize) match so that I get time-aligned I/Q samples ? Thanks! On Mon, Jul 18, 2016 at 12:20 PM, Marcus Müller wrote: > They always align at the beginning. The file size difference is really > just because due to the nature of general purpose hardware and GNU Radio's > scheduling, there's no guarantee all blocks have written the same amount of > data when you kill the flow graph. > > Am 18. Juli 2016 17:46:13 MESZ, schrieb avinash kalyanaraman < > avinash1...@gmail.com>: >> >> Thanks Martin. >> >> Is there any particular reason why I see different file sizes for the >> former (file-sink) case? I ctrl+c the hand edited python file to stop >> sample collection. The file sinks are unbuffered. Since they are of >> different sizes, is there a way to know which samples align in time ? >> >> Thanks! >> >> On Fri, Jul 15, 2016 at 5:30 PM, Martin Braun >> wrote: >> >>> This'll work. However, the uhd_rx_cfile utility that comes with GNU >>> Radio will do that for you. >>> >>> Cheers, >>> M >>> >>> On 07/15/2016 11:33 AM, avinash kalyanaraman wrote: >>> > Hi all, >>> > >>> > I want to analyze the I/Q samples of 3 synchronized USRPs (connected to >>> > an Octoclock G). I have synchronized the USRPs according to >>> > http://files.ettus.com/manual/page_sync.html (i.e. I hand-modified the >>> > python file generated by GRC). >>> > >>> > I am feeding the output of my USRP Source block (with 3 channels and 3 >>> > motherboards) to three file sink blocks. Would this be enough to save >>> my >>> > synchronized I/Q samples ? >>> > >>> > I notice that the size of the three files (storing the I/Q samples) >>> > aren't the same after my run. >>> > >>> > Attached is also a screenshot of the GRC file. >>> > >>> > Thanks! >>> > >>> > -- >>> > Avinash >>> > >>> > >>> > ___ >>> > Discuss-gnuradio mailing list >>> > Discuss-gnuradio@gnu.org >>> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> > >>> >>> >>> ___ >>> Discuss-gnuradio mailing list >>> Discuss-gnuradio@gnu.org >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> >> >> >> > -- > Sent from my Android device with K-9 Mail. Please excuse my brevity. > -- Avinash ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] Saving the I/Q samples of multiple synchronized USRPs
Thanks Martin. Is there any particular reason why I see different file sizes for the former (file-sink) case? I ctrl+c the hand edited python file to stop sample collection. The file sinks are unbuffered. Since they are of different sizes, is there a way to know which samples align in time ? Thanks! On Fri, Jul 15, 2016 at 5:30 PM, Martin Braun wrote: > This'll work. However, the uhd_rx_cfile utility that comes with GNU > Radio will do that for you. > > Cheers, > M > > On 07/15/2016 11:33 AM, avinash kalyanaraman wrote: > > Hi all, > > > > I want to analyze the I/Q samples of 3 synchronized USRPs (connected to > > an Octoclock G). I have synchronized the USRPs according to > > http://files.ettus.com/manual/page_sync.html (i.e. I hand-modified the > > python file generated by GRC). > > > > I am feeding the output of my USRP Source block (with 3 channels and 3 > > motherboards) to three file sink blocks. Would this be enough to save my > > synchronized I/Q samples ? > > > > I notice that the size of the three files (storing the I/Q samples) > > aren't the same after my run. > > > > Attached is also a screenshot of the GRC file. > > > > Thanks! > > > > -- > > Avinash > > > > > > ___ > > Discuss-gnuradio mailing list > > Discuss-gnuradio@gnu.org > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > > ___ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > -- Avinash ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] Low transmission rate on tx_ofdm causes underflow
I wasn't getting anything through.
My USRP Sink block had an empty TSB tag name property. I didn't have a TSB
tag name = packet_len property. I started getting data across after adding
that.
On Fri, Jun 24, 2016 at 2:12 PM, Martin Braun
wrote:
> On 06/23/2016 02:42 PM, avinash kalyanaraman wrote:
> > Hi All,
> >
> > I am doing an OFDM transmission with tx_ofdm.grc and receiving it with
> > rx_ofdm.grc. I am using two USRP N210s for this.
> >
> > I edited the tx_ofdm to set the transmission rate to generate 96-byted
> > packets every 10ms via : message strobe-> random pdu generator->pdu to
> > tagged stream.
> >
> >
> > However, now I am seeing an underflow ('U') which I think is because my
> > application isn't sending data fast enough to the USRP. The USRP
> > sampling rate is 512K.
>
> ...maybe not. Maybe the tagged streams are getting corrupted. Are you
> receiving anything?
>
> M
>
> > Could you please let me know how I might be able to fix this?
> >
> > Thanks!
> >
> > --
> > Avinash
> >
> >
> > ___
> > Discuss-gnuradio mailing list
> > Discuss-gnuradio@gnu.org
> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> >
>
>
> ___
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>
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[Discuss-gnuradio] Low transmission rate on tx_ofdm causes underflow
Hi All,
I am doing an OFDM transmission with tx_ofdm.grc and receiving it with
rx_ofdm.grc. I am using two USRP N210s for this.
I edited the tx_ofdm to set the transmission rate to generate 96-byted
packets every 10ms via : message strobe-> random pdu generator->pdu to
tagged stream.
However, now I am seeing an underflow ('U') which I think is because my
application isn't sending data fast enough to the USRP. The USRP sampling
rate is 512K.
Could you please let me know how I might be able to fix this?
Thanks!
--
Avinash
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Re: [Discuss-gnuradio] Re channel state information on rx_ofdm.grc
Thanks Marcus.
Following up on the rx_time format, I notice from the link that the
timestamp format is the same as uhd::time_spec_t . Therefore the timestamp
printed out on a tag is of the form: full_seconds and a fractional_seconds.
For e.g., I see: Offset: 667 Source: n/a Key: rx_time Value: {2317
0.394114}
2317 is the full second and 0.39 is the fraction of that 2317th second ?
Could you please tell me what these seconds calculated are with respect to
- i.e. 2317 seconds since when ?
When does the fraction of second roll over?
For example, I see:
Offset: 1034 Source: n/a Key: rx_time Value: {2317 1.39162}
Offset: 1035 Source: n/a Key: rx_time Value: {2318 0.393495}
What does it mean to have a fraction of 1.39 of a second ?
Thanks!
On Fri, Jun 17, 2016 at 1:12 PM, Marcus Müller
wrote:
> Hi Avinash,
>
> that's pretty much a basic OFDM question:
>
> You take the DFT of the input signal. Hence, the bins of the DFT are
> f_nyquist/l_fft spaced.
>
> Best regards,
>
> Marcus
> On 17.06.2016 17:57, avinash kalyanaraman wrote:
>
> Thanks Marcus - that helps.
>
> Could you please let me know what's the bandwidth of each sub-carrier? How
> can I calculate that and reconfigure the same?
>
>
> On Sat, Jun 18, 2016 at 12:50 AM, Marcus Müller
> wrote:
>
>> Hi Avinash,
>>
>> On 06/16/2016 03:29 PM, avinash kalyanaraman wrote:
>>
>> i) These 64 complex values (a + ib) represent the 64 sub-carriers and I
>> can get the amplitude and phase of each sub-carrier as sqrt( a^2 + b^2) and
>> arctan(b/a) respectively ?
>>
>> Yes.
>>
>>
>> ii) I see that the CSI calculation is per tag. I understand from your
>> link that the tag represents additional information/metadata attached to a
>> specific item. However, in this case, I am unsure what a tag denotes? In
>> other words, could you please tell me what a “tag” is being attached to
>> here, on which a channel estimate is calculated?
>>
>> If I remember correctly:
>> To the first sample of the "chunk" of samples that were used for
>> estimation, that is, on the first sample of the OFDM symbol.
>>
>> I do think that if you're into channel estimation, reading the source
>> code is very much worth your time, and you'll notice variable and method
>> names were chosen sensibly to make understanding what's happening easier.
>> Go for the get_chan_taps() method in ofdm_chanest_vcvc_impl.cc; you'll find
>> it in your GNU Radio source tree; be sure to use a recent version of GNU
>> Radio (3.7.7 or later).
>>
>>
>> iii) Please let me know what is the unit of rx_time ? Seconds?
>> Offset: 76 Source: n/a Key: rx_time Value: {7 0.303}
>> Offset: 77 Source: n/a Key: rx_time Value: {7 0.399}
>>
>> http://gnuradio.org/doc/doxygen/page_uhd.html
>>
>> look for "timestamp" on that page.
>>
>> Best regards,
>> Marcus
>>
>
>
>
> --
> Avinash
>
>
>
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[Discuss-gnuradio] Control the transmission rate of TX_OFDM.grc
Hi All, I am doing an OFDM transmission with tx_ofdm.grc and receiving it with rx_ofdm.grc. I am using the Random Source of the tx_ofdm unmodified. I want to be able to control the packet transmission rate - for e.g. 10 packets every 100ms. How can I modify the grc to be able to do this ? Thanks! -- Avinash ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] Re channel state information on rx_ofdm.grc
Thanks Marcus - that helps.
Could you please let me know what's the bandwidth of each sub-carrier? How
can I calculate that and reconfigure the same?
On Sat, Jun 18, 2016 at 12:50 AM, Marcus Müller
wrote:
> Hi Avinash,
>
> On 06/16/2016 03:29 PM, avinash kalyanaraman wrote:
>
> i) These 64 complex values (a + ib) represent the 64 sub-carriers and I
> can get the amplitude and phase of each sub-carrier as sqrt( a^2 + b^2) and
> arctan(b/a) respectively ?
>
> Yes.
>
>
> ii) I see that the CSI calculation is per tag. I understand from your link
> that the tag represents additional information/metadata attached to a
> specific item. However, in this case, I am unsure what a tag denotes? In
> other words, could you please tell me what a “tag” is being attached to
> here, on which a channel estimate is calculated?
>
> If I remember correctly:
> To the first sample of the "chunk" of samples that were used for
> estimation, that is, on the first sample of the OFDM symbol.
>
> I do think that if you're into channel estimation, reading the source code
> is very much worth your time, and you'll notice variable and method names
> were chosen sensibly to make understanding what's happening easier. Go for
> the get_chan_taps() method in ofdm_chanest_vcvc_impl.cc; you'll find it in
> your GNU Radio source tree; be sure to use a recent version of GNU Radio
> (3.7.7 or later).
>
>
> iii) Please let me know what is the unit of rx_time ? Seconds?
> Offset: 76 Source: n/a Key: rx_time Value: {7 0.303}
> Offset: 77 Source: n/a Key: rx_time Value: {7 0.399}
>
> http://gnuradio.org/doc/doxygen/page_uhd.html
>
> look for "timestamp" on that page.
>
> Best regards,
> Marcus
>
--
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Re: [Discuss-gnuradio] Re channel state information on rx_ofdm.grc
Hi Marcus,
Thanks for the email. I connected the debug tag to OFDM Channel Estimation
and noted that the ofdm_sync_chan_taps key has 64 complex values.
Could you please confirm the following two things ?
i) These 64 complex values (a + ib) represent the 64 sub-carriers and I can
get the amplitude and phase of each sub-carrier as sqrt( a^2 + b^2) and
arctan(b/a) respectively ?
ii) I see that the CSI calculation is per tag. I understand from your link
that the tag represents additional information/metadata attached to a
specific item. However, in this case, I am unsure what a tag denotes? In
other words, could you please tell me what a “tag” is being attached to
here, on which a channel estimate is calculated?
iii) Please let me know what is the unit of rx_time ? Seconds?
Offset: 76 Source: n/a Key: rx_time Value: {7 0.303}
Offset: 77 Source: n/a Key: rx_time Value: {7 0.399}
Thanks for your help,
Avinash
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[Discuss-gnuradio] Re channel state information on rx_ofdm.grc
Hello all, Could you please let me know how I can get channel-frequency response (like channel state information (CSI) ) for an OFDM transmission? I am looking at rx_ofdm.grc to capture the phase and amplitude at each of the 64 sub-carriers. Would connecting the OFDM Channel Estimation Block of the HeaderStream to a FileSink such that item_size is fft_size* gr.sizeof_gr_complex , give me enough information to capture the CSI ? What would be the granularity of the aforementioned calculation? I transmit using tx_ofdm.grc. Please let me know. Thanks! -- Avinash ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
