Hybrid User Grouping With Heterogeneous Devices in NOMA-Enabled IoT Networks

In this paper, we consider an uplink Internet of Things (IoT) network consisting of time-sensitive devices and throughput-sensitive devices, focusing on effective coordination between different performance requirements. To improve the spectral efficiency, Non-Orthogonal Multiple Access (NOMA) is introduced to obtain a potential performance gain by assigning the spectrum resources to different types of devices with diverse performance requirements in a coordinative and resource-sharing manner. Considering the performance diversity of heterogeneous devices, we provide two NOMA user grouping strategies: Mixed Block Strategy (MBS) and Uniform Block Strategy (UBS) which configure NOMA user groups as those consisting of different types of devices and those containing only a single type of device, respectively. Then, we propose a hybrid resource allocation protocol by switching between these two strategies. The performance of a special case with two time-sensitive devices and two throughput-sensitive devices is first optimized to evaluate the proposed strategies, and then extended to compare with traditional strategy in the multi-user scenarios. Simulation results illustrate that MBS and UBS outperform the traditional strategy, i.e., lower Age of Information (AoI) and higher throughput, and have their own advantages at different system parameters. On the basis, the hybrid protocol can further improve the system performance.