Terminology » LTE » LTE-NB and NB-IoT: Understanding MIB and SIB Information Blocks

LTE-NB and NB-IoT: Understanding MIB and SIB Information Blocks

lte nb-iot mib sib information block

This page describes MIB (Master Information Block) and SIBs (System Information Blocks) in LTE-NB or NB-IoT. It covers functions and contents of MIB-NB, SIB1-NB, SIB2-NB, SIB3-NB, SIB4-NB, SIB5-NB, SIB14-NB and SIB16-NB.

Introduction

3GPP has been working on three different IoT standards viz. LTE-M, EC-GSM and NB-LTE.

NB (Narrowband) IoT is proposed as LPWAN (Low Power Wide Area Network) technology. The NB-IoT has been developed specifically to improve indoor coverage, lower cost, longer battery life and to support a large number of connected devices. It is deployed in three scenarios viz. standalone, guard band and in-band.

MIB | Master Information Block

  • The NPBCH is used to provide NB-IoT MIB which delivers essential information for the NB-IoT device in order to operate in the network.
  • After acquiring PCID, the device knows the NRS placement within a resource block. It can thus demodulate and decode NPBCH, which carries MIB-MB.
  • A MIB-NB is encoded to an NPBCH code block, consisting of eight CSBs. NPBCH is transmitted in subframe 0, and each NPBCH subframe carries a CSB. A CSB is repeated in eight consecutive NPBCH subframes.

SIB | System Information Block

  • SIB1-NB: The scheduling information of SIB1-NB carried in MIB-NB describes the TBS (208, 328, 440, or 680 bits) and number of repetitions (4, 8, or 16) used for SIB1-NB transmissions. With such information, the device knows how to receive SIB1-NB. A SIB1-NB TB is carried in eight SIB1-NB subframes, mapped to subframe 4 in every other frame during 16 frames. These 16 frames are repeated 4, 8, or 16 times. The repetitions are evenly spread over the SIB1-NB transmission interval, which is defined as 256 frames, i.e., 2.56 s.
  • After reading the SI scheduling information in SIB1-NB, the device is ready to acquire the full set of SI messages. SIBs 2, 3, 4, 5, 14, 16 are periodically broadcasted during specific time-domain windows known as the SI windows.

Table of SIB and MIB contents

The following table mentions contents or fields carried in SIB and MIB information blocks in LTE-NB IoT system.

MIB or SIBDescription
MIB-NBFollowing information is decoded from MIB-NB by the device:
  • Operation mode (stand-alone, in-band, guard-band)
  • In case of in-band and guard-band, the frequency raster offset (±2.5, ±7.5 kHz)
  • Four MSBs of the SFN
  • Two LSBs of the H-SFN
  • Information about SIB1-NB scheduling
  • SI value tag, which is essentially a version number of the SI. It is common for all SIBs except for System Information Block Type 14 (SIB14-NB) and System Information Block Type 16 (SIB16-NB)
  • Access barring (AB) information
SIB1-NBHyperframe information, network information such as PLMN, tracking area and cell identities, access barring status, thresholds for evaluating cell suitability, valid subframe bitmap and scheduling information regarding other System Information Blocks.
SIB2-NBRadio resource configuration (RRC) information for all physical channels that is common for all devices.
SIB3-NBCell reselection information that is common for intrafrequency and interfrequency cell reselection. It further provides additional information specific to intrafrequency cell reselection such as cell suitability related information.
SIB4-NBNeighboring cell-related information, e.g., cell identities, relevant only for intrafrequency cell reselection.
SIB5-NBNeighboring cell-related information, e.g., cell identities and cell suitability-related information, relevant only for interfrequency cell reselection.
SIB14-NBAccess class barring information per PLMN. Contains a specific flag for barring of a specific access class, It also indicates barring of exception reporting.
SIB16-NBInformation related to GPS time and Coordinated Universal Time (UTC).