随机接入过程.docx

摘自 3GPP -930 Random Access Procedure The random access procedure is characterized by: - Common procedure for FDD and TDD; - One procedure irrespective of cell size; The random access procedure is performed for the following six events : - Initial access from RRC_IDLE; - RRC Connection Re-establishment procedure; - Handover; - DL data arrival during RRC_CONNECTED requiring random access procedure; - . when UL synchronisation status is“ non-synchronised ”; - UL data arrival during RRC_CONNECTED requiring random access procedure; - . when UL synchronisation status is "non-synchronised" or there are no H resources for SR available. - For positioning purpose during RRC_CONNECTED requiring random access procedure; - . when timing advance is needed for UE positioning; Furthermore, the random access procedure takes two distinct forms : - Contention based (applicable to first five events); - Non-contention based (applicable to only handover, DL data arrival and positioning). Normal DL/UL transmission can take place after the random access procedure. 10. .1 Contention based random access procedure The contention based random access procedure is outlined on Figure .1 -1 below: Figure .1 -1: Contention based Random Access Procedure The four steps of the contention based random access procedures are: 1) Random Access Preamble on RACH in uplink: - Th