Two-tier Architecture for NB-IoT: Improving Coverage and Load Balancing

In the context of massive Machine Type Communication (mMTC), 3GPP has introduced in Release 13 the Narrowband-IoT (NB-IoT) standard, that appears particularly suitable for uplink, delay-tolerant low-rate communications. On the one hand, being compatible with the existing 4G cellular systems, and also envisioned as a primary player in next 5G, NB-IoT is developed upon the existing heterogeneous architecture, formed by several overlapping tiers (HetNets), e.g. macro and small cells. On the other hand, in order to improve coverage and connection reliability in harsh environments, NB-IoT adopts its own coverage enhancement (CE) techniques, mainly based on signal repetition procedures, thus questioning the need of low-level tiers in such new communication scenario. This paper analyzes the performance of NB-IoT in a HetNets system, taking into account its specific features, and how they combine with a multi-tier architecture. The analysis is carried out by simulation, via proper adaptation of ns-3 simulator to the NB-IoT scenario. Results show that the use of a 2-tier dedicated architecture nicely combines with the NB-IoT CE technique, boosting system efficiency and coverage, while also triggering improved load balancing.