[Discuss-gnuradio] [ Implementing a Phase Shift block ]

[Ashish Raste]

Hi Marcus,

> I'm working on synchronising two USRPs (connected via a MIMO) and have
> calibrated the time-offset which occurs between them for a given set
> of signal generator's frequency, USRPs frequency and the sampling rate.
>
> My next step is to do a phase-compensation for one of the USRPs so
> that both are aligned in the time-domain. I read from this
> <http://www.ettus.com/content/files/kb/mimo_and_sync_with_usrp.pdf>
> document that for Phase-shifting, we need to use MRC algorithm or
> Periodic Calibration. Also I saw that a "Phase Shift" block has been
> used in that document which I guess was developed by the author who
> wrote it, as I could not find it in the GRC.
>
> I'm willing to develop one such simple phase-shift block. Can anyone
> suggest me how to approach in implementing it i.e in terms of any
> algorithm's reference that you can suggest to achieve this purpose?
>
> Note: I want my Phase-Shift block to work in real time i.e it should
> be able to adjust the phase-offset of one of the signals so that that
> signal gets aligned with the other in the time-domain.

The attached demonstrates phase-shifting using a simple complex multiply
block.

If you want to do coarser phase shifts (large multiples of 180deg), you
can use a delay block.

Presently I'm calculating the delay between two synchronised signals coming out of the USRP source (connected to a signal generator) by recording their samples and finding the offset between their first peak or zero-crossing.

Now if we want to time-align them in real-time, how can we implement a delay block that calculates the delay each time the grc flow is run and set the delay_value in the block accordingly so that they are time-aligned? i.e I don't want to record the samples rather I'd like to know how to find the delay and shift any of the two signals so that they get aligned?

Best,