Maximizing energy efficiency over imperfectly known fading channel gains
In this paper, we study the issue of selecting the transmission power (energy per symbol) and power allocation between pilot and data symbols to maximize the energy efficiency (EE). We consider the system that has a slow-fading channel and employs a minimum mean square error (MMSE)-based channel estimation scheme for a pilot symbol-assisted modulation. We derive a closed-form expression for a lower bound on the channel capacity in the presence of channel estimation error, and use this lower bound to derive the energy efficiency. We then discuss optimizing transmission power and also power allocation between pilot and data symbols for maximizing the energy efficiency. At the end we present a very simple method for finding a suboptimal solution for transmission power and also the power allocation between pilot and data symbols that result in a performance very close to the optimal solution.