Opportunistic Downlink User Connectivity in NOMA Enhanced NB-IoT Systems, A Semi-Matching Approach

Recently, Narrowband Internet of Things (NB-IoT) systems gained a significant focus as a promising direction for massive connectivity issues in forthcoming wireless communication systems. Thus, this paper investigates the challenge of maximizing connection density in NB-IoT networks, considering a downlink Non-Orthogonal Multiple Access (NOMA) scenario for simultaneous transmissions and efficient resource utilization. The base station assigns each device to one of the accessible Physical Resource Blocks (PRBs). This scheduling policy includes effective device clustering and optimal NOMA power assignment. We formulate this problem as finding semi-matching over a bipartite graph derived from multiple PRBs and distinct constraints, i.e., power budget, admitted PRB, interference, and quality of service constraints. Furthermore, we compared our solutions NOMA-Semi Matching 1 (NOMA-SM1) and NOMA-Semi Matching 2 (NOMA-SM2) with previous solutions. Numerical Simulations confirm that the proposed semi-matching aided approaches attain a better theoretical bound and superior performance.