[srslte-users] Frequency offsets in srsUE

[Xavier Arteaga]

Hi Philip,
What about using custom frequencies?

You can set the srsenb and srsue to operate in any frequency independently
of the EARFCN.

For the UE:
  --rat.eutra.dl_freq arg (=-1)         Downlink Frequency (if positive
overrides EARFCN)
  --rat.eutra.ul_freq arg (=-1)         Uplink Frequency (if positive
overrides EARFCN)

For the eNb:
  --rf.dl_freq arg (=-1)         Downlink Frequency (if positive  overrides
EARFCN)
  --rf.ul_freq arg (=-1)         Uplink Frequency (if positive
overrides EARFCN)

Regards,
Xavier


On Tue, 24 Aug 2021 at 15:06, Philip Shaw <philip at surewavetechnology.co.uk>
wrote:

> Xavier,
>
>
>
> We are adding some analogue hardware that has a lower frequency cut off.
> It does not work to DC.
>
>
>
> The idea is to move the Baseband signal away from zero Hz.
>
>
>
> I hope this helps.
>
>
>
> Regards
>
>
>
> Philip
>
>
>
> *From:* Xavier Arteaga <xavier at srs.io>
> *Sent:* 24 August 2021 13:06
> *To:* Philip Shaw <philip at surewavetechnology.co.uk>
> *Cc:* srslte-users at lists.softwareradiosystems.com
> *Subject:* Re: [srslte-users] Frequency offsets in srsUE
>
>
>
> 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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>
>
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