[srslte-users] RSRP based Hard Handover

[Francisco Paisana]

Hey Tejas,

You can perform new cell attachment via the cell_selection() function in
the ue rrc.cc.
Regarding your questions
1 - sure it should be implementable. However, pay attention to the CFO
between eNBs. If your eNBs are not frequency-aligned, your neighbor cell
signal strength will look lower to the UE than it actually is.
2 - if you are triggering the whole proccess from the UE, yes it should be
in the srsue/src/stack/rrc.
3 - setting the RRC to idle (via the "go_idle" flag) should be enough to
trigger a cell_selection() procedure.
4 - well the nas should be rebuilt after the successful cell selection to
another cell.

Good luck!

Regards,
Francisco

On Thu, Aug 1, 2019 at 12:34 PM Tejas Harekrishna Sadarahalli <
tsadarah at eng.ucsd.edu> wrote:

> Hi all,
>
>
> Since handover is not supported by the SRSLTE’s EPC, we are trying to
> implement an RSRP based hard handover.
>
>
> Our setup has two eNB's (eNB-A and eNB-B), one using USRP N310 and the
> other using USRP B210, on two different PC's. Both the eNB's have a shared
> EPC (being run on a third PC).
>
>
> The logic that we want to implement is as follows;
>
> - UE (USRP B200) attaches to eNB-A and the UE continuously reports RSRP.
>
>  - As we slowly move the UE away from eNB-A and towards eNB-B, the RSRP
> value starts decreasing
>
> - When the RSRP value falls below a certain threshold value (let's call it
> x dBm), it detaches from eNB-A and starts looking for new cells and
> attaches to eNB-B.
>
>
> I am currently trying to make modifications to the rrc.cc
> file in srsLTE/srsue/src/stack/rrc/, where the RSRP parameter is being
> reported.  The modifications that we made are as follows;
>
> [image: Screenshot from 2019-07-31 16-33-42.png]
>
> we call the leave connected function to ensure that the UE is in RRC IDLE
> state before it does a cell search. Then we call the run_tti function
> because the run_tti function, in turn, calls the cell selection function.
>
>
> So far, we have successfully been able to monitor the RSRP values. Where
> we have been having trouble is in the cell search and successful
> reattachment to eNB-B.
>
>
>
> Questions -
>
> 1 - Is this logic implementable using SRSLTE?
>
> 2 - Is the rrc.cc file in srsLTE/srsue/src/stack/rrc/ the correct file to
> make modifications to?
>
> 3 - If it is implementable, what function should I be invoking for cell
> search and for a successful reattachment to eNB-B?
>
> 4 - For a successful reattachment do we also need to modify an upper layer
> services such as NAS?
>
> 5 - What other things could we try to be able to implement our logic?
>
> --
> Warm Regards,
>
> *Tejas Sadarahalli*
> Communication Theory and Systems
> Electrical Engineering - Masters Student
> University of California - San Diego
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> srslte-users at lists.softwareradiosystems.com
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>
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