A novel user-clustering (UC) based downlink hybrid-nonorthogonal multiple access (hybrid-NOMA) assisted heterogeneous network (HetNet) design strategy in the presence of an eavesdropper is explored to investigate the secure resource allocation beyond fifth-generation/sixth-generation (B5G/6G) wireless communications. We have formulated a secrecy rate (SR) maximization problem based on the proposed strategy subject to key performance indicators (KPIs) such as the admission of users in clusters, the association of users with the base station (BS), allocation of power to the users, and user's minimum rate requirement. This novel problem is solved to find an ε-optimal solution within ε = 10−3using the outer approximation algorithm (OAA). This paper performs an analysis of the performance of the proposed strategy and it is depicted through simulation results that the proposed strategy maximizes the SR in terms of KPIs. A performance comparison of the proposed strategy with the existing orthogonal multiple access-only (OMA-only) and nonorthogonal multiple access-only (NOMA-only) strategies is conducted, and it is identified through simulation results that the proposed strategy performs best among the existing strategies. Additionally, a comparison of the performance of the proposed strategy for HetNet and macro base station-only (MBS-only) networks is conducted, and the simulation results depicted that the proposed strategy performs better in HetNet compared to the MBS-only network.

The increasing number of mobile devices and multimedia applications demands enormous capacity that requires innovative network designs. A hybrid non-orthogonal multiple access (NOMA) scheme with user clustering has been considered a promising solution to meet the increasing demand for capacity. Successive interference cancellation (SIC) is applied to minimize interference in NOMA. Also, in addition to this, heterogeneous networks (HetNets) improve network throughput. It is necessary to find optimal resource allocation for throughput maximization. In this paper, a mixed-integer non-linear programming (MINLP) problem has formulated for throughput maximization using a hybrid NOMA scheme with user clustering in a macro base station (MBS) only network and HetNets. MINLP problems are non-deterministic polynomial time-hard (NP-hard) in general. An exhaustive search algorithm with the exponential increase in complexity with the number of users restricts it to use for the problem's solution. The throughput maximization problem is solved using an outer approximation algorithm. The proposed algorithm is evaluated with extensive simulations to show that the proposed solution is effective regarding network throughput and user association. Also, the proposed algorithm compares user admission in clusters, user association with BSs in MBS only network, and HetNets. The results clearly show that HetNet outperforms MBS only network in terms of the network throughput, the number of users admitted in clusters, and the number of users associated.

The rising number of user equipment (UE) and advanced applications in fifth-generation (5G) and beyond fifth-generation (B5G) networks need energy-efficient resource allocation. The researchers have not yet considered hybrid nonorthogonal multiple access (H-NOMA) scheme with UE clustering in heterogeneous networks (HetNets). This paper investigates downlink H-NOMA scheme with UE clustering in HetNets to maximize energy efficiency (EE). A mathematical optimization problem considers UE admission in clusters, UE association with base stations (BSs), power allocation, the minimum rate, and transmit power requirements. We have converted the formulated non-linear concave fractional programming (CFP) problem into a concave optimization problem with Charnes-Cooper transformation (CCT). An ∊-optimal outer approximation algorithm (OAA) solves the formulated problem. The effectiveness of the proposed scheme regarding EE, network throughput, UE admission, and UE association is shown with the simulation results.