Fair Configuration Scheme for Random Access in NB-IoT with Multiple Coverage Enhancement Levels

Narrowband Internet of Things (NB-IoT) is a new technology developed to support low-power wide area networks (LPWAN) services. To extend its coverage and decrease its transmission power, devices in one NB-IoT cell are divided into several coverage enhancement (CE) levels with different random access configuration. This potentially results in unfair access, especially when massive number of devices in different CE levels simultaneously accessing the network. This work presents an effective strategy to configure the random access in NB-IoT to yield fair performance across CE levels. An analytical model is used to estimate the performance of each CE level and overall system performance in term of normalized throughput and average access delay. Simulation is incorporated to verify the accuracy of the model. Different practical assumptions of fair system are explored and examined in the experiment. The result shows that the analytical model is accurate under various loads. Additionally, the proposed search strategy is proven to be able to obtain the configuration which yield acceptable throughput fairly for all CE levels.