MIB-NB Master Information Block - Narrowband

Last updated on May 1, 2023

The Master Information Block (MIB) is an essential component of the cellular network that provides information about the system parameters to the mobile devices. The MIB is periodically broadcasted by the base station, and it contains critical information like the cell identity, system bandwidth, and system frame number, which are essential for the mobile devices to synchronize with the network. The MIB is a part of the broadcast channel (BCH), which is a unidirectional downlink channel that is used for transmitting common control information to all the mobile devices within the cell.

In narrowband (NB) cellular networks like LTE-M and NB-IoT, the MIB is referred to as MIB-NB, and it differs from the MIB used in wideband (WB) cellular networks like LTE. In this article, we will discuss the MIB-NB in detail and its significance in the NB-IoT and LTE-M networks.

MIB-NB Structure

The MIB-NB is structured differently from the MIB used in the WB networks, and it contains essential information that is specific to the NB-IoT and LTE-M networks. The MIB-NB is composed of 12 octets and contains the following information:

System Frame Number (SFN) - a 10-bit field that represents the system frame number.
System Bandwidth - a 3-bit field that represents the system bandwidth.
Cell Identity (CID) - a 9-bit field that represents the cell identity.
Reserved - a 6-bit field that is reserved for future use.

The MIB-NB is broadcasted on the NB-IoT and LTE-M Physical Broadcast Channel (PBCH) once every subframe. The subframe duration in NB-IoT and LTE-M is 10 milliseconds (ms), and the MIB-NB is broadcasted once every 80 ms. The MIB-NB is transmitted using a QPSK modulation scheme in the frequency domain, and it uses a cyclic prefix of 1 symbol duration in the time domain.

SFN and System Bandwidth

The SFN is an essential parameter in the NB-IoT and LTE-M networks, and it is used to synchronize the mobile devices with the network. The SFN is a 10-bit field that represents the system frame number, and it rolls over after 1024 frames. The SFN is used by the mobile devices to synchronize with the network and to identify the timing advance required for transmitting data to the base station. The SFN is also used by the base station to schedule the uplink and downlink transmissions.

The System Bandwidth is a 3-bit field that represents the system bandwidth, and it is used by the mobile devices to determine the transmission parameters like the subcarrier spacing, modulation scheme, and channel coding rate. In NB-IoT, the available system bandwidths are 180 kHz, 1.08 MHz, and 3 MHz, while in LTE-M, the available system bandwidths are 1.4 MHz and 3 MHz.

Cell Identity

The Cell Identity (CID) is a 9-bit field that represents the cell identity, and it is used by the mobile devices to identify the cell they are connected to. The CID is unique for each cell within a given radio access technology (RAT), and it is assigned by the network operator. The CID is also used by the base station to differentiate between different cells within the same network.

MIB-NB Modulation and Coding

The MIB-NB is transmitted using a QPSK modulation scheme in the frequency domain, and it uses a cyclic prefix of 1 symbol duration in the time domain. The MIB-NB is coded using a rate-1/3 turbo coding scheme with a code rate matching scheme to adapt to different system bandwidths. The turbo coding scheme provides error correction capabilities to the MIB-NB, which ensures that the mobile devices can decode the MIB-NB accurately, even in noisy environments.

Importance of MIB-NB

The MIB-NB is a crucial component of the NB-IoT and LTE-M networks, and it provides the mobile devices with essential information required to establish a connection with the network. The MIB-NB enables the mobile devices to synchronize with the network and determine the transmission parameters required for communication. The following are some of the reasons why the MIB-NB is essential:

Synchronization: The MIB-NB provides the mobile devices with the SFN and CID, which are critical for synchronizing with the network. The SFN enables the mobile devices to align their timing with the network, while the CID identifies the cell they are connected to.
Power Efficiency: The MIB-NB is transmitted periodically on the PBCH, which ensures that the mobile devices can receive the MIB-NB with minimal power consumption. The periodic transmission of the MIB-NB enables the mobile devices to go into a low-power mode between the reception of the MIB-NB.
Network Planning: The MIB-NB provides the network operator with information about the system parameters, which can be used for network planning and optimization. The system bandwidth information provided by the MIB-NB can be used to allocate resources efficiently, while the SFN information can be used for scheduling uplink and downlink transmissions.
Security: The MIB-NB is transmitted on the PBCH, which is a unidirectional downlink channel that is not encrypted. However, the MIB-NB contains essential information required for communication with the network, and it is protected using a rate-1/3 turbo coding scheme, which provides error correction capabilities and makes it difficult for an attacker to modify the MIB-NB.

Conclusion

The Master Information Block - Narrowband (MIB-NB) is an essential component of the NB-IoT and LTE-M networks, and it provides critical information required for establishing a connection with the network. The MIB-NB contains information about the system parameters like the SFN, System Bandwidth, and CID, which are essential for synchronizing with the network and determining the transmission parameters. The MIB-NB is transmitted periodically on the PBCH using a QPSK modulation scheme and a rate-1/3 turbo coding scheme, which provides error correction capabilities. The MIB-NB is a critical component of the NB-IoT and LTE-M networks and plays a significant role in ensuring efficient and reliable communication between the mobile devices and the network.