Bug 3025

Summary: A UE should not synchronize with an eNB if its RSRP is lower than -140 dBm
Product: ns-3 Reporter: Zoraze Ali <zorazeali>
Component: lteAssignee: Biljana Bojović <bbojovic>
Status: NEW ---    
Severity: enhancement CC: mmiozzo, ns-bugs
Priority: P5    
Version: ns-3-dev   
Hardware: PC   
OS: Linux   
Attachments: Example script
RSRP table

Description Zoraze Ali 2018-11-30 13:19:09 EST
Created attachment 3235 [details]
Example script


I noticed that a UE synchronizes with the eNB, i.e., read MIB and SIB1 messages even if its RSRP is below the minimum RSRP level (-140 dBm). I think it is unnecessary to synchronize with a cell whose RSRP is below -140dBm. This is also in line with the S-criterion (qRxLevMeas - qRxLevMin > 0) condition in LteUeRrc::EvaluateCellForSelection (), where qRxLevMeas is the RSRP of the cell and qRxLevMin is the minimum RSRP required to camp on a cell. 

As per table 9.1.4-1 in 3GPP TS36133 the minimum RSRP level which a UE can report is -140 dBm. I am attaching a sample script to support my point. The scenario consists of one eNB and one
UE, which is placed at 20000 m away from the eNB.

One could see that the UE RRC state transitions from:


and then from:

IDLE_WAIT_SIB1 to IDLE_CELL_SEARCH because of the cell RSRP level, which fails to fulfill the S-criterion (qRxLevMeas - qRxLevMin > 0) in LteUeRrc::EvaluateCellForSelection ().

I propose that a UE should only synchronize with a cell if its RSRP is greater than -140 dBm.

Kind regards,
Comment 1 Zoraze Ali 2018-11-30 13:21:36 EST
Created attachment 3236 [details]
RSRP table
Comment 2 Zoraze Ali 2018-11-30 13:25:56 EST
Created attachment 3237 [details]

Attached is the patch inline with my proposal.
Comment 3 Zoraze Ali 2018-11-30 13:29:33 EST
After applying the patch the UE RRC state will stay in IDLE_CELL_SEARCH until the RSRP of the cell is greater than -140 dBm.