The first step in 5G Standalone (SA) call processing is synchronization between UE & gNB. The synchronization process is divided into Downlink synchronization and Uplink synchronization.
Downlink synchronization precedes Uplink synchronization.
Downlink Synchronization:
– UE performs cell search for synchronization signals
– Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS) are acquired
– PSS and SSS help identify the cell and synchronize UE’s timing
Uplink Synchronization:
– Uplink synchronization achieved through RACH Process
– Random Access Channel (RACH) is used for initial uplink synchronization
– UE transmits a randomly chosen preamble via RACH
– gNB detects preamble and responds with timing adjustment
– This process aligns UE’s transmission timing with gNB for efficient communication
RRC Connection Establishment:
– Post synchronization, UE initiates Radio Resource Control (RRC) connection procedure
– UE sends RRCSetupRequest message to gNB
– gNB responds with RRCSetup message containing vital configuration details
– Configuration information facilitates UE’s access to network resources
Registration Request:
– After successful RRC connection establishment
– UE sends Registration Request message to Core Network (AMF)
– Purpose is to register with 5G network
– Message includes significant details: UE’s security credentials & UE’s network capability
