Efficient hybrid resource allocation for uplink and downlink device-to-device underlay communication in 5G and beyond wireless networks

The device-to-device communication (D2D) concept allows direct communication between nearby devices without a base station. At the same time, cellular resources are reused. It reduces the end-to-end delay of D2D active users significantly. Most of the traditional methods consider allocating resources by downlink or uplink alone. The present study considers a novel hybrid approach for joint downlink and uplink to allocate resources, maximizing the network throughput. Further, it minimally restricts cellular and D2D pairs’ interference and ensures smooth D2D communication. The challenge is that power control and Quality of service constraints are seriously degraded by strong intra-cell and inter-cell interference due to spectrum reusability and deployment. A hybrid structure that exploits efficient resource allocation is needed to tackle this situation. The optimization problem is formulated as a mixed-integer non-linear problem that is usually NP-hard. Such a problem is divided into two stages, namely channel assignment and power allocation. The factors considered for the objective problem of resource allocation are the transmission power of the cellular user, D2D active user, base station, connection distance, and Quality of Service constraints. The proposed novel hybrid scheme can improve network throughput and improves spectrum efficiency. The numerical results imply that the hybrid method in the proposal functions efficiently and is verified by comparing it with the present joint resource allocation methods.