5G-NR: MIB

5G-NR: MIB

Introduction:

                   When the UE switches on, it starts listening to the SSB(PSS/SSS/PBCH) for synchronization and tried to get the system information. after the successful cell setup gNB always broadcasting the MIB according to the SSBs occasions.

MIB:

MIB (Master information block) includes the system information and always transmitted on the BCH from network to UE with a periodicity of 80 ms and repetitions made within 80 ms.

it also includes the parameters that are needed to acquire/decode the SIB1 from the cell. 

The first transmission of the MIB is scheduled in subframes defined by [TS 38.211, 7.4.3.2] and repetitions are scheduled according to the period of SSB;

It uses QPSK modulation for transmission from the network to UE It is transmitted on OFDM symbol 1,2,3.

RRC parameters of MIB:

NR PBCH under SSB:

MIB ::=                             SEQUENCE {

    systemFrameNumber                   BIT STRING (SIZE (6)),

    subCarrierSpacingCommon             ENUMERATED {scs15or60, scs30or120},

    ssb-SubcarrierOffset                INTEGER (0..15),  è offset in number of sub carrier between SSB(RB-0) and OffsetToPointA.

    dmrs-TypeA-Position                 ENUMERATED {pos2, pos3},

    pdcch-ConfigSIB1                    PDCCH-ConfigSIB1,

    cellBarred                          ENUMERATED {barred, notBarred},

    intraFreqReselection                ENUMERATED {allowed, notAllowed},

    spare                               BIT STRING (SIZE (1))

}

Description if parameters:

systemFrameNumber:

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

subCarrierSpacingCommon

Subcarrier spacing for SIB1, Msg.2/4 for initial access and broadcast SI-messages. If the UE acquires this MIB on a carrier frequency <6GHz, the value scs15or60 corresponds to 15 Khz and the value scs30or120 corresponds to 30 kHz. If the UE acquires this MIB on a carrier frequency >6GHz, the value scs15or60 corresponds to 60 Khz and the value scs30or120 corresponds to 120 kHz.

scs15or60	scs30or120
FR1	15 Khz	30 Khz
FR2	60 Khz	120 Khz

 

ssb-SubcarrierOffset

Corresponds to k_SSB (see TS 38.213 [13]), which is the frequency domain offset between SSB and the overall resource block grid in the number of subcarriers. (See 38.211).

The value range of this field maybe extended by an additional most significant bit encoded within PBCH as specified in 38.213 [13].

This field may indicate that this beam does not provide SIB1 and that there is hence no common CORESET (see TS 38.213 [13], section 13). 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 (see 38.213 [13], section 13)

dmrs-TypeA-Position

Position of (first) DM-RS for in downlink (see 38.211, section 7.4.1.1.1) and in uplink (see 38.211, section 6.4.1.1.3).

cellBarred indicates whether the cell allows UEs to camp on this cell as per specification TS 38.304

intraFreqReselection indicates if Intra frequency cell reselection is Allowed or notAllowed. It controls cell reselection to intra-frequency cells when the highest ranked cell is barred, or treated as barred by the UE as specified in TS 38.304

The call flow of MIB and SIB:

NR and LTE comparison:

Parameters	Long Term Evolution (LTE)	New Radio (NR)
Broadcast Channel	Transport – BCH	Transport – BCH
	Physical- PBCH	Physical- PBCH
Periodicity	40 ms periodicity with 10 ms re-transmission periodicity	80 ms periodicity with repetitions made within 80 ms
Channel Coding	Tail Bit Convolution encoding	Polar Coding
Modulation	QPSK Modulation	QPSK Modulation
Resource Allocation	6 RBs (72 subcarriers) in Frequency domain	It is transmitted on OFDM symbol 1,2,3.
	4 symbols of first subframe second slot symbol 0, 1, 2 and 3.	It uses 0 to 239 subcarriers number on symbol 1 & 3, whereas on symbol 2 it uses sub carried number 0 to 47 and 192 to 239