9.1 Second system information broadcast channel

25.3003GPPGeneral descriptionRelease 17Stage 2TSUniversal Terrestrial Radio Access Network (UTRAN)

In order to increase system information capacity (see TR 25.704 [7]) a second system information broadcast channel on SCCPCH can be configured, in addition to the system information broadcast channel on PCCPCH.

The second system information broadcast channel is mapped to a separate SCCPCH, which is different from the SCCPCH used for paging and FACH/CTCH, as depicted in Figure 9.1-1.

Figure 9.1-1: Channel mapping of system information broadcast channel and second system information broadcast channel.

The UE should be able to monitor at least two SCCPCHs simultaneously, but the UE may skip reading the second system information broadcast channel during CTCH occasions in Idle mode and CELL_PCH/URA_PCH state. When HS-DSCH in CELL_FACH is used, a UE supporting second system information broadcast channel monitors the corresponding SCCPCH while listening to HS-DSCH.

REL-12 and later SIBs are introduced on both the system information broadcast channel as well as the second system information broadcast channel. Pre-REL-12 SIBs may be broadcasted on the second system information broadcast channel in addition to the system information broadcast channel. Any SIB type may be scheduled simultaneously on system information broadcast channel and second system information broadcast channel provided that the content is the same.

Most of the existing principles and procedures for system information reading are retained for the second system information broadcast channel. To reduce the latency to acquire the system information on both system information broadcast channel and second system information broadcast channel, the UE acquires the system information on both channels simultaneously. The simultaneous acquisition of system information on both system information broadcast channel and second system information broadcast channel is depicted in Figure 9.1-2.

Figure 9.1-2: System information acquisition on system information broadcast channel and second system information broadcast channel.

When the SB3 value tag in PAGING TYPE 1 or SYSTEM INFORMATION CHANGE INDICATION (SICI) message is updated the UE supporting second system information broadcast channel is required to re-acquire the system information on the second system information broadcast channel. When the SB3 value tag is updated, but the MIB value tag is not, the UE supporting second system information broadcast channel is only required to re-acquire the system information on the second system information broadcast channel.

The scheduling block 3 (SB3) contains the scheduling information for the system information on the second system information broadcast channel. This scheduling information uses the SFN of the PCCPCH.

The SB3 is broadcasted with a pre-defined offset (40 ms) from the start of the frame containing the MIB, as depicted in the Figure 9.1-3. The MIB on BCH mapped on PCCPCH contains the channelization code of the second system information broadcast channel, the repetition interval of SB3 and the number of segments of SB3. The remaining configuration parameters of the second system information broadcast channel are pre-defined.

Figure 9.1-3: SB3 pre-defined offset from the start of the frame containing the MIB.