Energy-Efficient 6G Networks: A Cognitive Radio Assisted Cluster-Based Downlink Hybrid Multiple Access Approach

The rising need for better utilization of bandwidth and advance multimedia applications in future sixth-generation (6G) networks requires energy-efficient resource allocation. In this regard, cognitive radio network (CRN) can be integrated with other emerging 6G technologies. The spectrum utilization is improved using cognitive radio (CR) technology by opportunistically using unused spectrum when primary mobile components (MCs) are inactive, with primary MCs managed by the primary station (PS) and secondary MCs handled by the secondary station (SS) through spectrum sensing. In the context of emerging 6G technologies, hybrid multiple access (HMA), which combines orthogonal multiple access (OMA) and non-orthogonal multiple access (NOMA), can be implemented to enhance energy efficiency (EE). Furthermore, MC clustering can be considered to mitigate the inter-cluster interference, resulting in more energy-efficient resource allocation. In this paper, we propose a new optimization problem to explore the effectiveness of the CR-enabled cluster-based downlink HMA (CR-CDHMA) technique within a novel 6G CRN. The objective is to maximize EE while adhering to minimum quality of service (QoS) constraints and addressing issues such as false alarms and missed detections. We have converted the formulated non-linear concave fractional programming (CFP) problem into a concave optimization problem using Charnes-Cooper transformation (CCT). An e-optimal outer approximation algorithm (OAA) is presented to solve the formulated concave optimization problem. Extensive simulations demonstrate the effectiveness of the novel technique in enhancing 6G CRN's EE outperforming existing NOMA-only enabled CRN and OMA-only enabled CRN models. The e-optimal algorithm achieves results with ∊ = 10–<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>, illustrating its computational efficiency.