Spectral and energy efficiencies of OFDMA wireless cellular networks

We study in the present paper the spectral efficiency of OFDMA cellular networks which is a classical indicator of their performance usually calculated by simulations. On the other hand, due to an increasing interest on the environmental impact of these networks, we study also their energy efficiency which may be defined as the ratio of the spectral efficiency and the consumed energy. We give an explicit expression of the signal to interference and noise power ratio (SINR) as function of the user's location. This permits to calculate easily the cell spectral efficiency, and thus to study its variations with respect to the key parameters of the network such as the cell radius, the propagation characteristics and the single link performance. We show that the energy efficiency admits a maximum for some value of the transmitted power which is finite and nonnull. Moreover, we observe that optimizing the transmitted power permits to double the energy efficiency.