30 Dec
2013
30 Dec
'13
12:44 p.m.
Hi,
I don't use the method of hardware modification. That can do synchronization
promisingly, sure. I know this scheme couple of months ago, and good to know it works
pretty well from you.
My thought is doing the compensation by software according to a common source over the air
instead of over the hardware.
Do you think it is doable? And what would be the bottleneck according to your experience?
Any possibility to tune the hardware by software after we estimate the synchronization
error in frequency and timing?
BR
Jiao xianjun
-----Original Message-----
From: "Sdr Guru" <sdrguru1(a)gmail.com>
Sent: 2013/12/30 19:01
To: "Jiao Xianjun" <putaoshu(a)gmail.com>
Cc: "osmocom-sdr(a)lists.osmocom.org" <osmocom-sdr(a)lists.osmocom.org>
Subject: Re: How to get IQ samples from multiple rtl-sdr dongles in asynchronized manner?
Hi
Are you using a common clock?
http://kaira.sgo.fi/2013/09/16-dual-channel-coherent-digital.html
I've modified some of the RTL dongles, played with GNURadio and Octave.
The results are promising, sample level correlation (2.4M/10, FM radio signal).
On Mon, Dec 30, 2013 at 9:38 AM, Jiao Xianjun <putaoshu(a)gmail.com> wrote:
Hi guys,
For the multiple dongles synchronization in signal level instead of bits/packets level, I
setup a working repo in github, and write a initial demo framework. See below:
https://github.com/JiaoXianjun/multi-rtl-sdr-udp-relay.git
You may find information and instruction of demo quickly by reading the README.
My initial purpose is performing in-fly calibration for multiple dongles according to some
pre-known signal (GSM, ADS-B?) to let them work together coherently.
An ideal scheme may be that we should generate a very narrow band and very week signal in
(or just located at the edge of) target working band of dongles, and perform the software
in-fly calibration in background (or driver level). This would be user friendly.
Cheap (8USD+PP), simple, computer-controlled and legal FM band "marker"
http://blog.palosaari.fi/2013/08/naked-hardware-12-usb-audio-transmitter.ht…
I know it is far from final state currently, and many things are not clear yet (See TODO).
But please join me if you also think this is a good idea. Just check out the demo and run
it to have a look.
Testing it and I'll let you know.
Currently I just test the demo in Ubuntu-Linux.
BR
Jiao Xianjun
On Mon, Sep 2, 2013 at 8:23 PM, Sylvain AZARIAN <sylvain.azarian(a)gmail.com> wrote:
Thanks.
sylvain
2013/9/2 Sdr Guru <sdrguru1(a)gmail.com>
The second way, use MLAT enabled dump1090
https://github.com/antirez/dump1090/pull/23
http://www.satsignal.eu/raspberry-pi/dump1090.html
On Sun, Aug 25, 2013 at 4:13 PM, Jiao Xianjun <putaoshu(a)gmail.com> wrote:
Hi,
I want to use multiple rtl-sdr dongles to do some multi-antenna experiments.
Is it possible to read IQ samples from multiple rtl-sdr dongles in a synchronized manner?
I already have a glance at dump1090 codes, which is a project using rtl-sdr to decode
aircraft broadcasting ADS-B messages in 1090MHz.
Seems that I should use rtlsdr_read_async() instead of rtlsdr_read_sync(), because that if
rtlsdr_read_sync() is used, I have to call it multiple times sequentially. That looks not
synchronized.
But rtlsdr_read_async() function only accept one rtl-sdr device as input parameter, and it
will be blocked after it is called. So seems that it also can't be used for my purpose
directly.
Also welcome any opinion on how to improve rtl-sdr lib/driver to support this feature.
Thank you.
BR
Jiao Xianjun
30 Dec
30 Dec
4:09 p.m.
New subject: How to get IQ samples from multiple rtl-sdr dongles in asynchronized manner?
Hello Jiao,
My thought is doing the compensation by software
according
to a common source over the air instead of over the hardware.
Do you think it is doable?
Yes. This is most certainly possible. The same thing was done long
ago in radio astronomy. Two big telescopes on different continents
made recordings aiming at a coomon direction in the sky. By
evaluating the recordings they could make interferometry.
http://en.wikipedia.org/wiki/Very-long-baseline_interferometry
This is a very interesting approach for the future.
With several dongles that have some signals in common it
will be possible to synchronize in software.
One of the common signals could be a GPS diciplined frequency
standard that the software could use to provide extreme
frequency stability on the processed signals from all the dongles.
Once syncronization is arranged one could use the multi-channel
antenna for interference suppression and to improve S/N of any
desired signal.
And what would be the bottleneck according to your
experience?
There is a lot of code that has to be written, but
I do not think there is any bottleneck to worry about
in hardware
Any possibility to tune the hardware by software after
we
estimate the synchronization error in frequency and timing?
The entire passband of
the dongles will be coherent.
You can tune to any frequency within the passband and also
evaluate several frequencies at the same time.
In case one wants to change the center frequency one would
loose synchronization and one would have to restart the
synchronization procedure.
SDR has just begun. Most of the interesting things have
not yet been done:-)
Regards
Leif / SM5BSZ
2 Jan
2 Jan
1:09 p.m.
New subject: How to get IQ samples from multiple rtl-sdr dongles in asynchronized manner?
Good to know that. Actually I also notice that radio astronomy is
attracting more and more signla processing researchers to work on it. Some
conference, such as ICASSP, envn setup a dedicate session on radio
astronomy. There is a radio astronomy called "DOME" are carrying on, which
involves computation on massive data and signal processing algorithm.
You have notice the problem that re-tuning will casue lossing
synchronization. That's also the problem I considered.
Because we always want the rtl-sdr work in the band we are interested, but
unfortunatelly in that band there maybe no any pre-known reference signal
for us to do synchronization. So a possible solution maybe make a beacon,
which can generate ultra-narrow-band or ultra-low-power signal in the
target band to help us do the on-line calibration. Any better ideas to
avoid this dedicate beacon?
On Mon, Dec 30, 2013 at 11:09 PM, Leif Asbrink <leif(a)sm5bsz.com> wrote:
Hello Jiao,
My thought is doing the compensation by software
according
to a common source over the air instead of over the hardware.
Do you think it is doable?
Yes. This is most certainly possible. The same thing was done long
ago in radio astronomy. Two big telescopes on different continents
made recordings aiming at a coomon direction in the sky. By
evaluating the recordings they could make interferometry.
http://en.wikipedia.org/wiki/Very-long-baseline_interferometry
This is a very interesting approach for the future.
With several dongles that have some signals in common it
will be possible to synchronize in software.
One of the common signals could be a GPS diciplined frequency
standard that the software could use to provide extreme
frequency stability on the processed signals from all the dongles.
Once syncronization is arranged one could use the multi-channel
antenna for interference suppression and to improve S/N of any
desired signal.
And what would be the bottleneck according to
your experience?
There is a lot of code that has to be written, but
I do not think there is any bottleneck to worry about
in hardware
Any possibility to tune the hardware by software
after we
estimate the synchronization error in frequency and timing?
The entire passband of
the dongles will be coherent.
You can tune to any frequency within the passband and also
evaluate several frequencies at the same time.
In case one wants to change the center frequency one would
loose synchronization and one would have to restart the
synchronization procedure.
SDR has just begun. Most of the interesting things have
not yet been done:-)
Regards
Leif / SM5BSZ
7:23 p.m.
New subject: How to get IQ samples from multiple rtl-sdr dongles in asynchronized manner?
On Thu, 2 Jan 2014 20:09:56 +0800
Jiao Xianjun <putaoshu(a)gmail.com> wrote:
Because we always want the rtl-sdr work in the band we
are interested, but
unfortunatelly in that band there maybe no any pre-known reference signal
for us to do synchronization. So a possible solution maybe make a beacon,
which can generate ultra-narrow-band or ultra-low-power signal in the
target band to help us do the on-line calibration. Any better ideas to
avoid this dedicate beacon?
To add a beacon is a very good idea. It can be placed
near the band
edge where S/N is not so good due to aliasing so it would not disturb
signals of interest. By having very good frequency accuracy on the
beacon one can synchronize all the dongles to get very high stability
and accuracy:-)
- leif -
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days inactive
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Leif Asbrink