•Random Access can be triggered by:
• PDCCH order (i.e., handover)
• UE MAC sublayer (i.e., initial access)
•Two types of Random Access:
• Synchronized:
– The PDCCH order or RRC optionally indicate a Random Access Preamble and PRACH resource
– When Random Access Preamble and PRACH resource are explicitly signaled, it is contention free
• Unsynchronized
– UE selects a Random Access Preamble and PRACH resource
Select one of the two groups of Random Access Preambles configured by RRC
Randomly select a Random Access Preamble within the selected group
Contention resolution is needed
E-UTRA Random Access
More information can be found in TS36.321 Section 5.1.
