Abstract
The continuous increase in the energy consumption of wireless networks has led to extensive research and development into “green communications”. Towards this objective, this thesis aims at introducing a novel technique for maximizing the energy efficiency of wireless networks both in the uplink and downlink channels, whilst satisfying other system targets such as rate-fairness and quality of service. More specifically, this thesis focuses on: 1) evaluating the energy efficiency of the uplink channel and locating the optimal operating points based on different optimality measures using average energy efficiency contours, 2) obtaining energy efficiency contours for the downlink channel and highlighting the fundamental difference between energy-efficient design in the uplink and downlink channels, 3) investigating the weighted average energy efficiency of the uplink channel, where users are prioritized based on different criteria such as channel gain and available battery, 4) employing a realistic linear power model in the downlink channel to define the total power consumed at the base station, encompassing circuit and processing power, amplifier efficiency and transmit power, 5) highlighting the trade-off between energy efficiency and spectral efficiency using energy efficiency contours. Our results show that in the case of the uplink channel, maximum energy efficiency is achieved by allowing all users within one cell to transmit by employing a successive interference cancellation receiver. Additionally, allocating higher weights to the users with stronger channel gains sacrifices the rate-fairness but also significantly improves the energy efficiency of the system. In the case of the downlink channel, maximum energy efficiency is achieved by only transmitting to the user with the higher channel gain, by employing superposition coding. By increasing the number of active users in the system, the network energy efficiency increases. On the other hand, increasing the cell radius decreases the system energy efficiency.