IDLE mobility in LTE?

Question

Is it possible to have mobility in IDLE mode if so please provide some pointers?

Comments

Yes it is possible and difficult to describe here in detail so I suggest you take a look at 36.304 for LTE idle mobility, for GERAN see 45.008, and for 3G check 25.304.

Answer 1

When we talk about "Idle" mode mobility, it mean track an UE when it doesn't have RRC connection with an eNodeB. When UE is in ECM-IDLE or RRC-IDLE, it's location can't be tracked at the cell level granularity.

In LTE, the geographical location is divided into cell(s) and tracking area(s). One tracking may consist of a number of cell(s). MME is the node which maintains UE's location at the granularity of tracking area when an UE is in ECM-DILE or we can say when there is no radio connection between UE and eNodeB. So there are two possibilities may occurs:

1. Down link data is coming: In that case, SGW informs to MME and MME initiates paging for that UE.
2. UE's tracking area is changed due to its mobility: UE is moved to new tracking area to it's mobility.