ABSTRACT Reconfigurable Intelligent Surface (RIS) is emerging as a potential solution for Tera Hertz communication. It supports a re‐configurable and smart wireless environment by enhancing the signal strength and reflecting it to the desired receiver which aids in improving energy efficiency. This article presents a novel mathematical framework of a mixed integer nonlinear programming (MINLP) problem to maximize the energy efficiency (EE) of a RIS‐based multi‐user network having a multi‐antenna base station (BS). The formulated problem is a concave fractional programming problem (CFP) which is transformed into a concave program using the proposed Charnes–Cooper transformation (CCT). MINLP problems are generally NP‐hard in nature and their complexity increases with the number of users, therefore, an outer approximation algorithm (OAA) is applied which gives.

Satellite-assisted internet of things (IoT) networks have emerged as a beacon of promise, offering global coverage and uninterrupted connectivity. However, the challenges of resource allocation and task offloading in such networks are intricate due to the unique characteristics of satellite communication systems. This research’s findings enrich the landscape of energy-efficient and dependable satellite-assisted IoT networks. The paper navigates the delicate balance between energy efficiency, network throughput, and fairness in distributing resources among IoT devices. The proposed techniques, notably the Outer Approximation Algorithm (OAA), usher in seamless connectivity and resource optimization. The central challenge at hand, a concave fractional programming problem, transforms through the Charnes–Cooper transformation, presenting as a concave optimization enigma. Herein, the proposed outer approximation algorithm takes flight, navigating the intricate paths of concave optimization. The performance of the epsilon-optimal solution faces scrutiny under diverse system parameters—the constellation of IoT devices, their affiliations, fairness considerations, and the equitable distribution of resource blocks. This contribution not only enriches research but also opens doors to the boundless possibilities of satellite-assisted IoT networks.

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.

Coverage, capacity and throughput can be enhanced significantly by offering a hybrid solution consisting of microwave high power base station (HPB) underlaid millimeter wave low power base station (LPB) augmented by the downlink uplink decoupled (DU-De) user association strategy in N-tier heterogeneous networks (HetNets). However, secure user association, power and microwave and millimeter wave sub-carriers allocation employing DU-De strategy has not been investigated in the past. This work formulates mathematical models for DU-De strategy and downlink uplink coupled (DU-Co) strategy to investigate secure user association, power and sub-carrier in microwave and millimeter wave band allocation for secrecy rate maximization in N-tier HetNets. Nature of the formulated problems is complex, challenging and NP-hard. Outer approximation algorithm, with less complexity, is used to solve the formulated problems for optimal solution. Extensive simulation results in terms of secure user association and average secrecy rate show the effectiveness of DU-De strategy over DU-Co strategy in HetNets.

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.

An optimal utilization of cellular resources is ambitious target of 5thgeneration (5G) heterogeneous network (HetNet). In 4thgeneration (4G) HetNet, downlink (DL) uplink (UL) coupled access (DUCa) strategy where a mobile station (MS) is associated in DL & UL with a one base station (BS) to ensure energy efficiency (EE) and throughput maximization is a suboptimal solution. An optimal solution in term of EE and throughput is offered by novel DL and UL decoupled access (DUDa) strategy where a MS is associated in DL & UL with one or two BSs in 5G HetNet. This research work conducts performance analysis of DUCa strategy vs DUDa strategy for effective resource allocation to ensure EE in HetNet. First, EE maximization problem in term of resource allocation using DUCa and DUDa strategy in HetNet is formulated. The formulated problem belongs to a class of non-linear fractional programming problem. The formulated fractional programming problem is transformed to a concave optimization problem employing Charnes-Cooper transformation. Then outer approximation algorithm (OAA) is employed to solve the formulated concave optimization problem. Extensive simulation work is done to show the effectiveness of proposed algorithm. OAA approach gives ε-optimal solutions for multiple parameters such as MSs associated, minimum required data rate, EE and throughput in DUCa and DUDa HetNet.

Traditional downlink (DL)-uplink (UL) coupled cell association scheme is suboptimal solution for user association as most of the users are associated to a high powered macro base station (MBS) compared to low powered small base station (SBS) in heterogeneous network. This brings challenges like multiple interference issues, imbalanced user traffic load which leads to a degraded throughput in HetNet. In this paper, we investigate DL-UL decoupled cell association scheme to address these challenges and formulate a sum-rate maximization problem in terms of admission control, cell association and power allocation for MBS only, coupled and decoupled HetNet. The formulated optimization problem falls into a class of mixed integer non linear programming (MINLP) problem which is NP-hard and requires an exhaustive search to find the optimal solution. However, computational complexity of the exhaustive search increases exponentially with the increase in number of users. Therefore, an outer approximation algorithm (OAA), with less complexity, is proposed as a solution to find near optimal solution. Extensive simulations work have been done to evaluate proposed algorithm. Results show effectiveness of proposed novel decoupled cell association scheme over traditional coupled cell association scheme in terms of users associated/attached, mitigating interference, traffic offloading to address traffic imbalances and sum-rate maximization.