In LTE does UE performs contension based RACH or contension free RACH for UE uplink sync?

Question

I don't know the complete use of CQI at eNodeB. Does it impact only downlink scheduling parameters or also considered while granting uplink resources ?

Answer 1

It is contention based RACH, In msg3 UE will send MAC-CRNTI control element to make contention resolve.

Answer 2

Both contention based and free rach are possible in case of UL unsynchronized.
If ue have UL unsynchronized and want to send data in UL then ue will perform contention based rach.

If ue is in UL unsynchronized and eNodeB want to schedule data in DL then eNodeB first send the pdcch order to ue. After getting pdcch order, ue will perform rach. This rach can be contention based or free. If eNodeB sends rach preamble in pdcch order then ue performs contention free rach otherwise ue performs contention based rach.

Answer 3

UE performs both types of RACH but one at a time depending on the scenario. In handover case it performs contention free RACH if target enodeb instructs else it go ahead with contention based RACH.