Adaptation of Coverage Enhancement Level Number in NB-IoT Networks

In narrowband Internet of Things (NB-IoT), a base station can define three coverage enhancement levels (CELs), each associated with a set of parameters to support a highcoverage area. The base station can set a control period for each CEL to determine the number of assignable subframes and repetitions of the data and control signals. However, certain devices may apply the parameters of a CEL that exceed their repetition requirements; therefore, the base station consumes unnecessary radio resources to deliver data to the devices. This paper investigates the CEL number adaptation problem to address this insufficiency and proposes a CEL number adaptation algorithm to determine a suitable CEL number for NB-IoT networks. Compared with the two baselines, the simulation results demonstrate that a base station with more than three CELs can use fewer subframes to satisfy the data requirements of the devices, especially when the coverage area of the base station is extended. Moreover, we found that more CELs are not necessarily better and that selecting a suitable CEL number is essential.