[srslte-users] RSRP based Hard Handover

[Tejas Harekrishna Sadarahalli]

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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