23.2 SBFD Random Access

Random access procedure in SBFD symbols is supported for all existing RACH trigger events as described in clause 9.2.6, except for the event of Request for Other SI and Early UL synchronization with an LTM candidate cell. Random access procedure in SBFD symbols is not supported in RACH associated with additional PCIs for one serving cell. For the event of RACH-based LTM cell switch, random access procedure in SBFD symbols is only supported for intra-DU case.

Both CBRA and CFRA can be supported on SBFD sub-bands. Only the 4-step RA type using SBFD RACH resources can be supported.

Two RACH configuration options are specified for SBFD RA operation in TS 38.331 [12]. A cell can configure only one SBFD RACH configuration option. This can be either: 1) A single RACH configuration that supports both non-SBFD RA operation and SBFD RA operation, or 2) A dual RACH configuration where a RACH configuration is used for non-SBFD RA operation and an additional RACH configuration is designated for SBFD RA operation, as specified in TS 38.331 [12]. An SBFD aware UE that supports the SBFD RACH configuration option configured in the cell applies the corresponding RACH configuration. Otherwise, the SBFD aware UE applies the non-SBFD RA operation.

For CFRA, an SBFD aware UE can be explicitly indicated in the PDCCH order, the (Enhanced) LTM Cell Switch Command MAC CE or dedicated RRC signalling whether to use either the first PRACH occasions or the second PRACH occasions as specified in TS 38.213 [38], for the PRACH transmission. For CBRA, the network can configure a cell specific indication in SI whether to use either the first PRACH occasions or the second PRACH occasions. If there is no cell specific indication, an SBFD aware UE selects the PRACH occasions based on an SSB RSRP threshold provided in SI. If none of cell specification indication nor SSB RSRP threshold is provided, the SBFD aware UE selects the PRACH occasions based on its implementation.

For CBRA, an SBFD aware UE is permitted to switch from the first PRACH occasions to the second PRACH occasions and vice versa during a random access procedure. However, no further switch of PRACH occasions type (the first or second PRACH occasions) is allowed in the same random access procedure.

If a fall-back from CFRA to CBRA occurs, an SBFD aware UE uses the CBRA resource associated with the same PRACH occasions type.