Narrowband IoT (NB-IoT) is a 3GPP Release 13 feature that reuses various principles and building blocks of the LTE physical layer and higher protocol layers and defines a new Cat-NB1 UE. The standard leverages a mobile operator's existing LTE base stations permitting rapid time-to-market. NB-IoT has been designed to offer extended coverage compared to traditional networks through the use of an ultra-narrow bandwidth of only 180 kHz.
In comparison to a conventional LTE deployment, NB-IoT offers an additional 20 dB of link budget, equating to roughly ten times the coverage of a normal base station. NB-IoT finds its place as a long range, very low data rate service for low cost, non-real-time applications. The downside of using thin channel sizes is a significant limitation to data throughput. Cat-NB1 devices are limited to data rates of 26 kb/s DL and 62 kb/s UL.
NB-IoT is currently the most widely deployed IoT / LPWAN technology due to the ability for mobile network operators to deploy the technology without the installation of new infrastructure.
NB-IoT Implementation
NB-IoT can be deployed in three modes:
- Within an existing LTE channel by utilising existing resource blocks
- Utilising the unused resource blocks within a LTE carrier’s guard-band
- As a standalone service, utilising an entirely separate carrier.
NB-IoT can improve UL capacity for users in bad coverage areas through single tone transmissions. New physical layer signals and channels, such as synchronisation signals and physical random access channel, are designed to meet the demanding requirement of extended coverage and ultra low device complexity. Higher protocols, signalling, and physical-layer processing requirements are greatly simplified in order to reduce UE power consumption and complexity, and consequently device cost.
3GPP proposed to the ITU-R that NB-IoT should be integrating the technologies as part of the 5G specifications, given that both technologies satisfy the 5G LPWA requirement. 5G New Radio (NR) was designed to support diverse deployment models, spectrum usage and device capabilities. One of the deployment scenarios that is supported from the start of 5G NR work in 3GPP is to allow LTE-M and NB-IoT transmissions to be placed directly into a 5G NR frequency band.
Introducing Cat-NB2
With the publishing of 3GPP Release 14 in 2018 came an additional UE category, Cat-NB2. The new device category expanded DL transport block size from 680 bits to 2536 bits, and UL from 1000 bits to 2536 bits. The larger TBS increased data rates to 127 kb/s DL and 159 kb/s UL.
3GPP Release 14 added several further enhancements, including a lower power class (14 dBm) to support applications with smaller batteries, enhanced mobility, improved positioning accuracy, and multicast.