[srslte-users] Frequency offsets in srsUE
Philip Shaw
philip at surewavetechnology.co.uk
Mon Aug 30 15:28:27 UTC 2021
Hi
All I am trying to do is to move the wanted baseband signal away from zero DC as we have some custom hardware we are working on that has magnetic components that only pass higher frequencies.
500khz to 1mhz should be enough.
Will this work just by setting the configuration file offset?
Many thanks
Philip
Sent from my Galaxy
-------- Original message --------
From: Andre Puschmann <andre at srs.io>
Date: 30/08/2021 13:59 (GMT+00:00)
To: Philip Shaw <philip at surewavetechnology.co.uk>, Xavier Arteaga <xavier at srs.io>
Cc: srslte-users at lists.softwareradiosystems.com
Subject: Re: [srslte-users] Frequency offsets in srsUE
Hey,
On 30/8/21 14:17, Philip Shaw wrote:
> Hi
>
> Thank you for this, so if I set, say, 1mhz offset in srsUE config file,
> you don't believe if will work?
we are talking about two different things here.
Setting a 1mhz offset in the config file will basically just tune the RF
frontend by 1mhz. This will work with any offset. And you can manually
calibrate the offset such that it matches the transmitter offset as
close as possible. But this will never be perfect, it only serves to
bring the actual CFO into a range where the fractional estimator can
detect and correct it.
Hope that helps.
Best
Andre
>
> Many thanks
>
> Philip
>
>
>
> Sent from my Galaxy
>
>
>
> -------- Original message --------
> From: Andre Puschmann <andre at srs.io>
> Date: 30/08/2021 09:54 (GMT+00:00)
> To: Philip Shaw <philip at surewavetechnology.co.uk>, Xavier Arteaga
> <xavier at srs.io>
> Cc: srslte-users at lists.softwareradiosystems.com
> Subject: Re: [srslte-users] Frequency offsets in srsUE
>
> Hey,
>
> On 24/8/21 15:20, Philip Shaw wrote:
>> 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 in the
>> baseband (at the analogue signal point on the interface between the
>> UBX160 and X300)
>>
>> Will srsUE handle this?
>
> Yes, srsUE will compensate any fractional CFO of up to half the
> subcarrier-spacing, i.e. for LTE this is 15khz/2=7.5kHz
>
> Thanks
> Andre
>
>
>>
>> Regards
>>
>> Philip
>>
>> *From:*Xavier Arteaga <xavier at srs.io>
>> *Sent:* 24 August 2021 14:15
>> *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,
>>
>> 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
>> <mailto:philip at surewavetechnology.co.uk
> <mailto: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 <mailto:xavier at srs.io <mailto:xavier at srs.io>>>
>> *Sent:* 24 August 2021 13:06
>> *To:* Philip Shaw <philip at surewavetechnology.co.uk
>> <mailto:philip at surewavetechnology.co.uk
> <mailto:philip at surewavetechnology.co.uk>>>
>> *Cc:* srslte-users at lists.softwareradiosystems.com
>> <mailto:srslte-users at lists.softwareradiosystems.com
> <mailto: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
> <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
> <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
> <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
>> <mailto:philip at surewavetechnology.co.uk
> <mailto: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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>
> --
> Andre Puschmann
>
> Software Radio Systems (SRS)
> https://www.srs.io <https://www.srs.io>
> andre at srs.io
>
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--
Andre Puschmann
Software Radio Systems (SRS)
https://www.srs.io
andre at srs.io
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