Efficiency metrics for wireless communications

Green wireless communications have received increasing attention from government, academia, and industry. However, how to define a green wireless communication system has been an open topic. In this paper, firstly, we present the definition of green efficiency of wireless links and carry out a comprehensive analysis of the efficiency metrics, e.g., the b/s/Hz spectrum efficiency, the b/s/Hz/W energy efficiency, the b/TENU power efficiency and our proposed (b·m)/s/Hz/W green efficiency of a wireless link, in particular we can prove that green efficiency is a strict convex function with respect to transmission power and distance. Secondly, by tuning the cell size with users´ QoS (quality of service) guarantee, we introduce green efficiency into a cellular network and achieve the theoretical upper bound of green efficiency for a cellular network. Finally, we present a green efficiency-based network planning method for practical environment. Simulation results show that the proposed network planning mechanism can approach the upper bound of green efficiency.