| Summary: | The number of mobile devices is exponentially increasing these years. Driven by new generation wireless devices, the exponential increasing of data traffic triggers great challenge of wireless network to meet the communications requirements. Heterogeneous networks provide flexible deployments for operators to improve spectrum efficiency and increase coverage. Global warming and climate change have been a growing worldwide concern. The mobile industry is contributing to carbon dioxide emission through network operations and mobile equipments. Therefore, energy-efficient design has emerged as a promising technique in heterogeneous networks. We study the energy efficiency problem for downlink transmissions by jointly considering user association and power allocation in a two-tier heterogeneous network. The energy efficiency is maximized under certain prescribed quality-of-service requirement and maximum power limit constraint. Convex relaxation and decomposition method are employed to solve this problem. We use a convex optimization method to obtain a user association solution. A gradient-based algorithm is used to solve the power allocation problem. Then, an iterative joint user association and power allocation algorithm is proposed to maximize the downlink energy efficiency of the system. Simulation results show that the proposed algorithm has improved energy efficiency when compared with the existing schemes. === Applied Science, Faculty of === Engineering, School of (Okanagan) === Graduate
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