4G Idle mode mobility

Idle Mode Mobility –

Reselection

The mobility in Idle mode is called reselection. The UE isn’t connected to any cell but it is listening to it in order to be able to connect to a cell when it want to perform a call, or data session. For that reason, the UE needs to be reselecting to the best cell.

There are 4 kinds of reselection that can be configured in a network: –

• Intra LTE reselection (within the same frequency);
• Inter LTE reselection (between two different frequency);
• Reselection to WCDMA (from LTE to 3G);
• Reselection to GSM/EDGE (from LTE to 2G).

How Reselection process is performed?

1. Measurements triggered: – UE is measuring the neighbor cells only when the RSRP signal level is below some threshold. The measurements trigger is based primarily on absolute priorities. In case of equal priority additional thresholds are defined. These priority levels varies from 1 to 7. 7 means the highest priority and 1 is lowest.

• Evaluate cell reselection R-Criteria: – For the reselection there are different cases depending on priorities of the neighbor frequency layers (for inter-frequency and inter-RAT).
• Execute reselection