Research On Energy Efficiency Optimization For Hybrid Power Supplied Relay Systems

With the development of mobile communications and the popularity of smart phones, global carbon emissions of wireless communication services grow so explosively that the slogan of green communication has been proposed, the goal of which is energy conservation, emission reduction and energy efficiency improvement. As an effective means for energy saving, relays can reduce the energy consumption of the source node by breaking a long range transmission into several short ones. However, the increasement of the overall energy consumption may be caused by the inherent energy consumption of the relay. The technique of energy harvesting (EH), which is very popular in recent years, can exploit and store renewable energy from the ambient environment, such as solar energy, wind energy, thermal energy, kinetic energy and salinity gradients etc.. On the one hand, energy harvesting can make use of the energy that may be wasted, which leads to zero carbon. On the other hand, due to the fluctuation of the harvested renewable energy and the uncertainty of energy arrival time, the quality of service (QoS) for long-term communication can not be guaranteed. Thus an energy harvesting and power grid coexisting relay system is designed in this research, where the source node or base station (BS) is powered by the conventional power grid to guarantee a cell-wide coverage, and the relay is powered by EH to cooperate with the source node or BS on the communication with the destination node. In addition, taking the non-ideal circuit power into consideration, i.e., the overall power consumption is the sum of the transmit power and a constant circuit power, we introduce sleep mode into the system, which has been proved an effective way to save energy with respect to the circuit power.In real-time energy harvesting and power grid coexisting relay systems, we study how to schedule the transmit power and the length of active time based on the different quantities of relay’s harvested energy in each time slot to optimize the energy efficiency and meet the given average throughput requirement. By the quasiconvex optimization theory, this thesis puts forward an energy-efficient transmission policy in real-time energy harvesting and power grid coexisting relay systems, and analyses the energy efficiency and capacity of the system under this transmission policy.In delay-tolerant energy harvesting and power grid coexisting relay systems, we study how to schedule the transmit power and the length of active time based on the different quantities of relay’s harvested energy in each time slot during a given time to optimize the energy efficiency and meet the given average throughput requirement during the given period. This thesis studies the energy-efficient transmission policies in both offline and online cases, which is determined by whether the channel state information and the energy arrival information of the relay is known before the transmission or not. Using the dynamic programming method, this thesis puts forward an energy-efficient transmission policy in delay-tolerant energy harvesting and power grid coexisting relay systems. Nonetheless, considering the computation complexity of the dynamic programming method, this thesis proposes a heuristic algorithm based on the quasiconvex property and analyses the energy efficiency and capacity of the system under this algorithm.