How to get IQ samples from multiple rtl-sdr dongles in a synchronized manner?

Jiao Xianjun putaoshu at gmail.com
Mon Aug 26 02:49:58 UTC 2013


computer has become more powerful than our imagination. According to my
experiences, order of Msps correlation operation can be done in real time
by using state of art computer.
Instead of cross correlation, we can also transmit a training sequence (for
example spread code, m sequence, barker sequence, M sequence, ZC sequence,
etc.) to do synchronization and sampling/frequency correlation.


On Sun, Aug 25, 2013 at 11:30 PM, Sylvain AZARIAN <sylvain.azarian at gmail.com
> wrote:

> Another issue you'll have is to start both dongles simultaneously...
> with the sampling rate you'll have on the dongles this becomes quite
> tricky : you get blocks of samples from both dongles but you have no idea
> of how many samples they are shifted in time. One way to solve this is to
> search for cross correlation between channels, but this is not very easy in
> realtime. This can be done by post-processing offline.
> I thaught of this a while ago, using a pin diode or something equivalent
> to shortcut both inputs to ground to find an easy way to have the synchro
> between channels but did not try it yet
>
> sylvain
>
>
> 2013/8/25 Jiao Xianjun <putaoshu at gmail.com>
>
>> basically you are right.
>> But there is signal processing algorithm to track two dongles
>> sampling/oscillator error separately and compensate them separately. Thus
>> we can get them synchronized finally after signal processing algorithm.
>>
>> What I need actually is that how to get two streams of sample from two
>> dongles.
>>
>> Actually I notice that in dump1090 it put rtlsdr_read_async in a new
>> created background thread, then there is a possibility that I create two
>> thread to operate two dongles. But in this method, there should be some
>> mechanisms to synchronize two threads. It is complicated.
>>
>> Anyone has simpler solution?
>>
>> Thank you.
>>
>>
>>
>> On Sun, Aug 25, 2013 at 9:49 PM, Thierry Leconte <
>> thierry.leconte at laposte.net> wrote:
>>
>>> Le 25/08/2013 15:13, Jiao Xianjun a écrit :
>>>
>>>  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?
>>>>
>>>>  Each dongle have its own clock, so it will never be synchronized at
>>> the sample level.
>>>
>>>
>>>
>>
>
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