Cell Selection:
UE performs cell selection based on RSRP level as per 3GPP Rel 8 or consider both RSRP and RSRQ level as per 3GPP Rel9.
RSRP and RSRQ are key measures of signal level and quality for modern LTE networks. In cellular networks, when a mobile moves from cell to cell and performs cell selection/reselection and handover, it has to measure the signal strength/quality of the neighbor cells.
In LTE network, a UE measures two parameters on reference signal: RSRP (Reference Signal Received Power) and RSRQ (Reference Signal Received Quality).
Cell Reselection:
A procedure initiated by an MS to reselect a cell that provides higher quality services.
When an MS selects a cell as the serving cell ( in cell selection step ) , the MS continues to monitor BCCH carriers of
all neighboring cells in the cell frequency list indicated by the BCCH system message of
the serving cell. The MS then compares the reception level of the serving cell and that of
all BCCH carriers in the cell frequency list. When certain conditions are met,
the MS initiates cell reselection to reselect a cell that provides higher quality services.
Notes:
Scenario 1:
Cell 1 → Cell 2
under Same LAC/TAC:
- idle → idle = Cell Reselection
- connected → connected = HO
Scenario 2:
Cell 1 → Cell 2
under different LAC/TAC:
- idle → idle = Cell Reselection + RAU + TAU
- connected → connected = HO + RAU + TAU
