MIB : Master Information Block

Master Information Block

Direction: gnB=> UE

Signalling Radio Bearer: N/A

RLC-SAP: TM

Logical Channel: BCCH

Transport Channel: BCH

The MASTER INFORMATION BLOCK (MIB) includes a limited number of most essential and most frequently transmitted parameters that are needed to acquire other information from the cell. The MIB is transmitted on BCH while all other SYSTEM INFORMATION messages are transmitted on DL-SCH

The MIB is always transmitted on the BCH with a periodicity of 80ms and repetitions within 80ms.
It includes parameters that are needed to acquire SIB1 from the cell.
The first transmission of the MIB is scheduled in subframes as defined, and repetitions are scheduled according to the period of the SSB.

The Master information Block (MIB) is transmitted using BCCH logical channel, the BCH transport channel and the PBCH Physical Channel
The MIB & SIB1 are known as” Minimum system information ” because these parameters are the basic parameters which is important for initial access and acquiring any other system information block

MIB		Bits
systemFrameNumber	BIT STRING	6
subCarrierSpacingCommon	scs15or60, scs30or120	1
ssb-SubcarrierOffset	0..15	4
dmrs-TypeA-Position	pos2, pos3	1
pdcch-ConfigSIB1	Control resourcesetzero	4
cellBarred	barred, notBarred	1
intraFreqReselection	allowed, notAllowed	1
Spare	BIT STRING	1
pdcch-ConfigSIB1	Search space zero	4

Actions upon reception of the MIB:

Upon receiving the MIB the UE shall:

1> store the acquired MIB;

1> if the UE is in RRC_IDLE or in RRC_INACTIVE, or if the UE is in RRC_CONNECTED while T311 is running:

2> if the cellBarred in the acquired MIB is set to barred:

3> consider the cell as barred in accordance with TS 38.304 [20];

3> if intraFreqReselection is set to notAllowed:

4> consider cell re-selection to other cells on the same frequency as the barred cell as not allowed, as specified in TS 38.304 [20].

3> else:

4> consider cell re-selection to other cells on the same frequency as the barred cell as allowed, as specified in TS 38.304 [20].

2> else:

3> apply the received systemFrameNumber, pdcch-ConfigSIB1, subCarrierSpacingCommon, ssb-

SubcarrierOffset and dmrs-TypeA-Position.

systemFrameNumber :

The 6 most significant bits (MSB) of the 10-bit System Frame Number (SFN). The 4 LSB of the SFN are conveyed in the PBCH transport block as part of channel coding (i.e. outside the MIB encoding),

subCarrierSpacingCommon :

one: Subcarrier spacing for SIB1, Msg.2/4 for initial access, paging and broadcast SI-messages. If the UE acquires this MIB on an FR1 carrier frequency, the value scs15or60 corresponds to 15 kHz and the value scs30or120 corresponds to 30 kHz.

Tow: Subcarrier spacing for SIB1, Msg.2/4 for initial access, paging and broadcast SI-messages. If the UE acquires this MIB on an FR1 carrier frequency, the value scs15or60 corresponds to 15 kHz and the value scs30or120 corresponds to 30 kHz.

ssb-SubcarrierOffset

Corresponds to kSSB which is the frequency domain offset between SSB and the overall resource block grid in number of subcarriers. The value range of this field may be extended by an additional most significant bit encoded within PBCH.

This field may indicate that this cell does not provide SIB1 and that there is hence no CORESET#0 configured in MIB ). In this case, the field pdcch-ConfigSIB1 may indicate the frequency positions, where the UE may (not) find a SS/PBCH with a control resource set and search space for SIB1.

pdcch-ConfigSIB1 :

Determines a common ControlResourceSet (CORESET), a common search space and necessary PDCCH parameters. If the field ssb-SubcarrierOffset indicates that SIB1 is absent, the field pdcch-ConfigSIB1 indicates the frequency positions where the UE may find SS/PBCH block with SIB1 or the frequency range where the network does not provide SS/PBCH block with SIB1.