Master Information Block 5G

Article from Abhijeet Kumar

Let's understand about MIB of 5G.

Technical Explanation:

The MIB is an essential part of the 5G system broadcast sent out by the gNodeB (5G base station). It's transmitted on the Physical Broadcast Channel (PBCH) within the Synchronization Signal Block (SSB). Here’s a breakdown of its technical aspects:

• Frequency and Timing: It provides fundamental details about the network such as the System Frame Number (SFN) and subcarrier spacing, which are crucial for the timing and frequency synchronization of the UE (User Equipment, like smartphones or other devices).
• System Configuration: The MIB includes information on the bandwidth and configuration of the downlink system, such as the position of reference signals (DMRS) and settings for the initial control channel (PDCCH).
• Cell Status: It also communicates essential operational status information like whether the cell is currently accessible ('not barred') and whether intra-frequency reselection is allowed. This helps the UE understand if it can connect to the cell and how it should behave regarding frequency changes.
• Decoding MIB: The UE must first decode the MIB to access more detailed system information conveyed in subsequent messages like the System Information Blocks (SIBs).

Where this message we can see in Wireshark lab

Let's understand in a fundamental way about MIB and what they do.

Think of the MIB as the "welcome mat" of a 5G network for your smartphone or other 5G devices. When your device tries to connect to a 5G network, the MIB is the first set of instructions it receives. Here's what the MIB does in simpler terms:

• Tells the Time and Place: It helps your device understand the current timing and frequency of the network. Imagine your device needs to know "when" and "where" to listen closely to understand further instructions from the network.
• Basic Rules of the Network: The MIB gives your device the basic rules about the network, like which signals to follow and how to read them. It's like getting the basic rules of a game before you start playing.

FieldDescriptionValue / SettingDetails

systemFrameNumber

• Description: This field contains the most significant part of the System Frame Number (SFN), which is used to identify the timing of the network frames over a 1024 frame period (or 10.24 seconds). SFN is essential for timing synchronization and scheduling.
• Value/Setting: 1111 00.. translates to a decimal value of 60.
• Details:Bit Length: 6 bits used to encode the value, with 2 padding bits to align to an octet boundary.3GPP Reference: Specified in 3GPP TS 38.331 and used in conjunction with TS 38.211 for physical layer procedures.

2. subCarrierSpacingCommon

• Description: Specifies the common subcarrier spacing used for the downlink across the cell, affecting how data is modulated and sent over the air.
• Value/Setting: scs30or120 (1) indicating possible spacings of 30 kHz or 120 kHz, based on the cell's configuration.
• Details:Possible Spacings: This can vary (scs15, scs30, scs60, etc.), with each step corresponding to different deployment scenarios (urban, rural, etc.).3GPP Reference: 3GPP TS 38.211 discusses the physical channels and how different spacings impact the signal structure.

3. ssb-SubcarrierOffset

• Description: The offset of the Synchronization Signal Block (SSB) from the lowest subcarrier of the common resource block in frequency domain. This ensures the UE can properly align to the network's frequency.
• Value/Setting: 0
• Details:Alignment Importance: Critical for ensuring the UE locks onto the network correctly without interference issues.3GPP Reference: Explained in 3GPP TS 38.213, which details the physical layer procedures.

4. dmrs-TypeA-Position

• Description: Specifies the mapping type of the Demodulation Reference Signals for uplink and downlink transmissions. This affects how the UE handles signal demodulation and channel quality measurements.
• Value/Setting: pos2 (0)
• Details:Channel Estimation: Essential for accurate channel state information and equalization processes.3GPP Reference: The positioning and usage are outlined in 3GPP TS 38.211.

5. pdcch-ConfigSIB1

• Description: Configuration for the initial control resource set and search space used for receiving System Information Block Type 1 (SIB1), which carries further system information.
• Value/Setting: Includes controlResourceSetZero and searchSpaceZero.
• Details:Control Resource Set: Defines specific physical resources in the downlink for control information.Search Space: Specifies where in the frequency/time grid the UE should look for control information.3GPP Reference: Configuration specifics can be found in 3GPP TS 38.213.

6. cellBarred

• Description: Indicates if the cell is barred from access by UEs, which affects whether new UEs can select or reselect to this cell.
• Value/Setting: notBarred (1) indicating the cell is accessible.
• Details:Accessibility: Ensures UE knows it can attempt to connect to this cell.3GPP Reference: Policy and usage defined in 3GPP TS 38.331.

7. intraFreqReselection

• Description: Allows or disallows the UE to autonomously reselect to another frequency within the same frequency band, critical for maintaining optimal network connectivity.
• Value/Setting: allowed (0)
• Details:Network Optimization: Important for load balancing and signal quality optimization within the network.3GPP Reference: 3GPP TS 38.331 explains the rules for reselection.

8. spare

• Description: Bits reserved for future use or to align the total bit count of the MIB to a standard size.
• Value/Setting: 00
• Details:Padding Purpose: Aligns the MIB message to a suitable size for efficient processing.3GPP Reference: General protocol structure considerations are in 3GPP TS 38.331.