A unified design of spectrum, energy, and cost efficient ultra-dense small cell networks

Spectrum, energy, and cost efficiencies will be three critical performance metrics in 5G ultra-dense green and cost-effective networks. Although research attention have been poured in optimization and tradeoff between spectrum and energy efficiencies, limited attention has been concentrated on the cost efficiency. Furthermore, there lacks a unified mathematical modeling and tradeoff investigation among spectrum, energy, and cost efficiencies. In this article, we first give a comprehensive summary of cost efficiency-related research topics, and summarize the necessary technical-economic perspective, unified design, and critical techniques towards spectrum, energy, and cost efficiencies. In particular, we first design a weighted utility function and then a general Nash-product utility function is formulated with spectral, energy and cost efficiencies into consideration. We provide the comprehensive understanding of spectrum, energy, and cost efficiencies in the unified mathematical model, and analysis results show that optimal tradeoff equilibrium solutions always exist. With these understanding and analysis, small cell deployment strategy and range expansion are identified as the most powerful techniques to approximate these optimal equilibrium solutions.