A Modelling Approach for the Narrowband IoT (NB-IoT) Physical (PHY) Layer Performance

Abstract

Although the Narrowband Internet of Things (NB-IoT) is tightly connected and integrated with cellular networks such as the Long Term Evolution (LTE), it remains an independent radio interface technology. Therefore, it is important to understand its specific requirements by providing a systematic mathematical model of its physical (PHY) layer. This article begins by systematically and numerically describing the PHY layer of the NB- IoT technology, its applications and the context of its deployment. The article then presents a mathematical modelling of the NB- IoT operations mode as this is key for modelling its PHY layer. This is followed by a clear and concise mathematical modelling of the NB-IoT down-link (DL) by elucidating the fundamental differences with the ones of the LTE. This modelling study goes further by providing a comprehensive model and analysis of the data rate against energy efficiency dilemma as an identified problem for the PHY design of the NB- IoT. This analysis is performed theoretically but also tested by means of computer simulation. The obtained results demonstrate that the contribution of the NB- IoT to the LTE in terms of energy consumption is less significant in the inband deployment compared to the guard band and standalone bands. However, the in-band deployment is expected to reduce the LTE's channel capacity more than the other deployment modes. In terms of network scalability, the obtained results further show that the data rate and energy efficiency of the network are reduced affected by the increase in the number of devices within a cell. These modelled network performances of the NB-IoT sufficiently demonstrate that in order to enable a licensed Massive IoT network, there is a need for developing novel PHY layer techniques (modulation, channel coding etc.) capable to efficiently scale the NB-IoT network while maintaining acceptable data rate and low energy consumption.