How Enb resolves contention resoultion in Rach procedure?

Question

At handover time target ENB will give rach preamble to UE. Is it necessary that target ENB is to be sink with source ENB. How UE will do contention free rach when both or not in sink? Is their any case Contention free rach will fail?

Answer 1

Two UEs may send same rach preamble at the same time and frequency domain and both can receive RACH response with uplink grant. In this situation, both the UEs will send "RRC Connection Request" message to eNodeB but only one of them or none of them will be handled by eNodeB. The UE for which RRC connection request is handled by eNodeB, it receives contention resolution message (same as RRC connection Request) message from eNodeB. This is the way RACH contention resolution gets resolved.

Comments

Will you tell on what basis one of the UE will be accepted by eNB

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It depends which of the RRC connection request message is decoded successfully. Both RRC connection request or one of them may be corrupted.