Narrowband IoT: A Survey on Downlink and Uplink Perspectives

Narrowband-IoT (NB-IoT) is a radio access technology standardized by the 3GPP to support a large set of use cases for massive machine-type communications. Compared to human-oriented 4G technologies, NB-IoT has key design features in terms of increased coverage, enhanced power saving, and a reduced set of functionalities. These features allow for connectivity of devices in challenging positions, enabling long battery life and reducing device complexity. This article provides a detailed overview on NB-IoT, together with analysis and performance evaluation of the technology. Both uplink and downlink directions are presented, including recent updates on the support of multicast transmissions. The article summarizes the possible configurations of NB-IoT, discusses the procedures for data transmission and reception, and analyzes aspects such as latency and resource occupation. We present a performance evaluation focusing on both uplink and downlink, with the aim to understand the channel occupancy of NB-IoT for different real-life IoT use cases and cell deployments. Further analysis focuses on the impact of various radio access parameters on the capacity of NB-IoT. Finally, results focusing on a new use case for NB-IoT (i.e., firmware update of a group of devices) are presented in the form of a comparison between unicast and multicast transmission modes.