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Summary Heterogeneous networks (HetNets) are a practical solution for traffic offloading from a high powered base station (HBS) to a low powered base station (LBS). In the HetNets, uplink (UL)–downlink (DL) decoupled access (UDDa) strategy is an optimal solution that ensures cell association, independently, in the UL and DL. This strategy offloads HBS cell edge mobile device (MD) to the nearby LBS in the UL. However, energy‐efficient cell association for traffic offloading from HBS to LBS, relay, or device to device (D2D) in the UL employing UDDa strategy has not been explored in the past work. We formulate mathematical models which ensure energy‐efficient cell association, power allocation, and traffic offloading employing traditional UL‐DL coupled access (UDCa) and UDDa strategies in the HetNets. The formulated problems are concave fractional programming (CFP) problems. The CFP is changed to a concave optimization problem using Charnes–Cooper transformation (CCT). The transformed problems are solved using an outer approximation algorithm to obtain ϵ=10−3 optimal solution. Simulation results show the effectiveness of UDDa strategy over UDCa strategy in terms of MDs association, traffic offloading in the UL and DL, interference mitigation in the UL, data rate, and energy efficiency in the HetNets.

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Fifth‐generation (5G) heterogeneous network (HetNet) with downlink (DL) and uplink (UL) decoupled cell association strategy is a promising solution to challenges faced in fourth‐generation (4G) HetNet, ie, mitigating interference, addressing traffic imbalances, and enhanced sum‐rate. This work carries out performance analysis of 4G HetNet with DL and uplink coupled (DUCo) access scheme vs 5G HetNet with DL and UL decoupled (DUDe) access scheme employing outer approximation and heuristic algorithms. First, a mathematical model, mixed integer nonlinear programming (MINLP) problem, is formulated for DUCo access and DUDe access schemes considering cell association, addressing user traffic imbalances, mitigating interference, and sum‐rate maximization in HetNet. Then, the formulated problem is solved, employing outer approximation algorithm (OAA) to find near optimal solution. Similarly, heuristic algorithms are developed for DUCo access and DUDe access schemes considering cell association, addressing user traffic imbalances, mitigating interference, and sum‐rate maximization in HetNet. Detailed performance analysis of DUCo access and DUDe access schemes is done by comparing results employing OAA and heuristic algorithms. Simulation results have shown that proposed DUDe access scheme outperforms DUCo access scheme in HetNet in term of cell association, addressing user traffic imbalances, mitigating interference, and sum‐rate maximization.

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Fifth‐generation (5G) and future beyond fifth‐generation (B5G) networks will require immense capacity due to the high rise in the number of multimedia applications and mobile devices. The heterogeneous networks (HetNets) in 5G and B5G can increase the heterogeneity and network throughput because macro base station‐only (MBS‐only) networks cannot satisfy the drastic increase in capacity demands. Hybrid nonorthogonal multiple access (H‐NOMA) can accommodate the increasing number of multimedia applications and mobile devices in 5G and B5G. H‐NOMA in B5G can also improve spectral efficiency. Before this, the researchers had not considered user clustering with H‐NOMA in HetNets. This article investigates the user clustering with downlink H‐NOMA in HetNet to maximize the network throughput in 5G and B5G. The formulated mathematical problem optimizes the considered key performance indicators (KPIs), that is, users admission in clusters, users association with base stations, power allocation to users, and network throughput. At the same time, it also satisfies the minimum transmit power and data rate requirements of users. The formulated problem is a mixed‐integer nonlinear programming (MINLP) problem. We have proposed an ϵ$$ \epsilon $$‐optimal algorithm, that is, outer approximation algorithm (OAA) to solve the MINLP problem because the complexity of the optimal exhaustive search algorithm (ESA) increases exponentially with an increase in the number of users. H‐NOMA with user clustering in HetNet is evaluated with extensive simulations to show its effectiveness regarding network throughput in 5G and B5G. We have also considered the proposed framework in the MBS‐only network and compared its performance with HetNet. The results verify that the proposed framework in HetNet performs better than the MBS‐only network. The complexity of the ϵ$$ \epsilon $$‐optimal algorithm is calculated that gives ϵ$$ \epsilon $$‐optimal results within ϵ=10prefix−3$$ \epsilon =1{0}^{-3} $$. We have also made a complexity analysis of the proposed OAA and ESA and concluded that the complexity of the proposed OAA algorithm is less than the ESA.