Resource allocation for energy efficiency optimization in uplink-downlink decoupled 5G heterogeneous networks

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 epsilon=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.