HO , Redirection, Cell Selection and Re-Selection

What is difference between HO , Redirection, Cell Selection and Re-Selection?

Handover (HO): UE moves from one eNB to target eNB while keeping its connected state. LTE Services will be uninterrupted.

In handover procedure, target cell would be prepared and UE will latch on target cell based on the configuration sent by source enodeb to UE.

Redirection: UE changes its state from connected to Idle mode during Redirection. LTE Service will be interrupted. Meaning the Source ENB shall release the connection of the UE and will ask the UE to redirect itself onto the target ENB by indicating the carrier frequency or the cell id in the RRC connection release message. For example, During CS Fallback, the UE is redirected from LTE RRC_CONNECTED mode to (2G/3G) idle mode).

 Cell Selection: It allows a UE to search and camp on a suitable cell. Cell selection occurs during Initial cell selection (when UE switches ON),  Stored information cell selection (uses stored cell info to identify appropriate cell),  and Cell selection when leaving RRC connected mode (When UE move from RRC CONNECTED to RRC IDLE mode)

 Cell Reselection: Its Idle mode procedure and happens from idle mode to idle mode. Reselection can occue on cell within same RAT (Intra-RAT) or different RAT(Inter-RAT).

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