User Fairness in NOMA-HetNet Using Optimized Power Allocation and Time Slotting

Abstract

Exponential growth in number of users with diverse data rate requirements has lead to the heterogeneity of traditional cellular networks. To support massive number of users, nonorthogonal multiple access (NOMA) has emerged as a promising solution to achieve increased number of connections and higher spectral gains as compared to orthogonal multiple access (OMA). However, studies show that weak users (WU) and strong users (SU) served using NOMA (referred as NOMA-group) experience different throughputs. In a NOMA group, an SU achieves higher throughput than a WU. Further, as the number of users in a NOMA group increases, due to superposition of signal of multiple users in NOMA, the intra-group interference dominates, thereby reducing throughput of the WUs. This article proposes novel time slotting (TS) techniques that aims at user fairness amongst the users by increasing the throughput of WUs, especially when the number of users increases in a NOMA group. The power allocation coefficients and the time slot duration for the proposed TS techniques are optimized to satisfy the minimum throughput of each user in a NOMA group while maximizing the throughput of WUs. The fairness between the users is measured by calculating both quality of service fairness and quality of experience fairness experienced by the user. It is observed that the proposed TS technique improves the fairness measures significantly. Furthermore, energy efficiency (EE) is also calculated for the TS techniques using the optimized power allocation coefficients and time duration. The numerical results suggest improvement in the EE of the system along with enhancing user fairness amongst the users.