Energy Efficiency Optimization and Resource Allocation in Wireless Communication Systems

Nowadays, energy efficiency (EE) for wireless communications is becoming a main economical and societal challenge. This thesis studies resource allocation (RA) in EE optimized wireless communication systems for various system models. The main body of this thesis consists of three parts. In the first part, EE optimization is studied in multiple input multiple output (MIMO)-orthogonal frequency-division multiplexing (OFDM) systems. Two special scenarios are considered respectively in two chapters: rate-dependent circuit power and nonlinear distortion at the high power amplifier (HPA). For the first scenario, the condition of the rate-dependent circuit power such that the global optimal EE is guaranteed to be found is given. The impact of system parameters on EE are analyzed. For the second scenario, the condition of parameters of HPA such that the rate function is concave is given. In the second part, EE maximized subcarrier allocation and precoder design are studied for downlink MIMO – orthogonal frequency-division multiple access (OFDMA) systems. Mathematical proofs to obtain the property of the EE function are provided. A condition on the subcarrier allocation and the precoder at the base station at the optimum EE is obtained and the optimality of the condition for fixed transmit power is shown. In the third part, EE maximization for relay assisted channel is studied. Two special techniques are considered respectively in two chapters: relay selection in multi-relay networks and subcarrier pairing (SP) for multi-carrier systems. For the first scenario, a relay selection method with low complexity is proposed. In the second scenario, an alternating optimization approach is adopted to solve the problem. In each subproblem, the power allocation is optimized together with subcarrier allocation and pairing at the relay.