[srslte-users] Frequency offsets in srsUE

[Xavier Arteaga]

Hi Philip,
I guess you are asking how to avoid carrier leakage
<https://en.wikipedia.org/wiki/Carrier_wave#Carrier_leakage>. If so, this
email will answer your question.

There are a few advanced no documented `device_args` parameters that can do
this function.

You can use the parameter `lo_freq_offset_hz` implemented here
<https://github.com/srsran/srsRAN/blob/master/lib/src/phy/rf/rf_uhd_generic.h#L175>.
To set the local oscillator frequency out of the band of interest and avoid
carrier leakage.

When tuning the LO with X300, there is a tune request
<https://github.com/srsran/srsRAN/blob/master/lib/src/phy/rf/rf_uhd_generic.h#L368>.
This provides a target RF frequency and other two frequencies: LO frequency
and DDC/DUC intermediate frequency.

By setting `lo_freq_offset_hz` the LO frequency is moved
`lo_freq_offset_hz` Hz from the target frequency while the DSP frequency is
set to an auto policy.

I recommend setting `lo_freq_offset_hz` to equal the sampling rate (i.e.
23.04e6) to make sure it is far enough from the band of interest. If you
are working with FDD, make sure TX LO frequency is not in the RX band.

Regards,
Xavier



On Tue, 24 Aug 2021 at 13:33, Philip Shaw <philip at surewavetechnology.co.uk>
wrote:

> Hi,
>
>
>
> Neel said:
>
> Hello Philip:
>
>
>
> Are you basically asking how to do offset tuning with srsRAN/srsLTE/srsUE?
>
> I'm not sure whether this is currently supported.  You should be able to
>
> have srsUE tune to a non-3GPP frequency band (which is basically the effect
>
> of using offset tuning), but I'm not sure that the srsUE PHY would be able
>
> to accommodate for that in its processing.
>
>
>
> --Neel Pandeya
>
> Hi Neel / Paul,
>
> I have a X300 with a UBX160.  I need to move the analogue BB signal away
> from DC zero Hz before it enters the X300 for ADC etc.  I can set an offset
> using the property in the config file.  I can see that the search for a
> cell is now at this offset frequency (at the analogue signal point on the
> interface between the UBX160 and X300).  I don’t have a cell to connect to
> (for testing), so the question is will srsUE connect to a cell using a
> large offset value?
>
>
>
> A offset of 1Mhz would be perfect for what we are doing.  Will the PHY
> work?  So, the system knows that the received signal is offset from zero Hz
> and is able to recover it?
>
>
>
> Thank you.
>
>
>
> Philip
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