Energy-Efficiency Analysis And Optimization In Green Relay Networks

The introduction of relay nodes between base stations and terminals can significantly improve the transmission quality and extend the cell coverage. On the other hand, the introduction of relay nodes in the network adds extra burden on the energy consumption expenditure of the network. Meanwhile, either the increase of the system spectral efficiency or the decrease of the system power consumption can not guarantee the improvement of the system energy efficien-cy. Therefore, it is necessary to analyze the impacts of the introduction of relay nodes in the network on the system energy efficiency performance. And it is also necessary to optimize the resource allocation such as power allocation to maximize the system energy efficiency. In order to carry out research on the energy efficiency analysis and optimization of green relay networks, this thesis will firstly establish the energy consumption model in the relay network. On the basis of the energy consumption model, this thesis will analyze the energy efficiency performance of relay networks and the impacts of the system pa-rameters on the energy efficiency performance of relay networks from the link aspect and the network aspect. Then the thesis will discuss the resource alloca-tion problem in relay networks to maximize the energy efficiency. Specifically, the main contribution of this thesis is summarized as follows:The general energy consumption model of relay network is established. The relationship between energy efficiency and spectral efficiency is analyzed. Besides the transmit power, the electronic power consumption is considered as well. The simulation shows the effect of the electronic power consumption on the relationship between energy efficiency and spectral efficiency. When the channel quality is poor, there is the chance that the received packet is in error or the quality of service for each user can not be satisfied. Extra energy con-sumed when these events occur is also taken into account. Finally, the energy efficiency metrics from the link aspect and the network aspect are proposed, respectively.Given the bit error rate, Joule per good bit for Multiple Quadrature Ampli-tude Modulation (MQAM) and Multiple Phase Shift Keying (MPSK) under ad-ditive white Gaussian noise channels and Rayleigh fading channels are derived, respectively. Simulations are carried out to analyze the impact of the system pa-rameters on Joule per good bit, including transmission distance, transmit time and diversity. The optimal constellation size is derived by simulation. The en-ergy efficiency performances of direct link and cooperative link are compared. The adaptive energy efficiency transmission strategy is proposed. Finally, the energy efficiency performance of symmetric relay networks and asymmetric relay networks are compared.To improve the network energy efficiency performance, the thesis proposes the adaptive time allocation algorithm. According to the change of the chan-nel state information, the time slot and the transmit power are allocated dy-namically to minimize the network energy consumption. The expressions of network area energy consumption for the direct transmission, equal time allo-cation and adaptive time allocation are derived, respectively. Simulation results show that the cell coverage for the adaptive time allocation relay transmission is the largest. Moreover, the location of relay nodes has no impact on the en-ergy efficiency performance of the adaptive time allocation relay transmission. But the number of relay nodes will affect the area power consumption of re-lay networks. Additionally, simulation results show that different transmission strategies can support different target spectral efficiency.In multi-cell relay networks, the impact of the combination of different number of base stations and relay nodes on the network energy efficiency is discussed. The tradeoff between the number of base stations and the number of relay nodes to satisfy the minimal area energy consumption and users’target spectral efficiency is analyzed. Simulation results demonstrate that the certain cell radius exists in the direct transmission and relay transmission to minimize the system energy consumption without the constraint of the maximum transmit power. Compared with the direct transmission, relay transmission can support the larger cell coverage. Finally, the parameters of the energy consumption model on the system energy expenditure are analyzed.The power and subcarrier allocation schemes for the multiuser downlink Orthogonal Frequency Division Multiplex Access (OFDMA) in point-to-point systems and relay systems are proposed. In the point-to-point multiuser down-link OFDMA systems, the iterative-based near-optimal algorithm with super-linear convergence is proposed based on the Dinkelbach method. In each iter-ation, the closed-form expressions for the power and subcarrier allocation are derived based on Karush-Kuhn-Tucker (KKT) and Lagrangian multipliers, re-spectively. In the multiuser downlink OFDMA relay systems, considering pro-portional fairness among users, time-averaged bits per Joule is maximized. The thesis derives the analytical solutions for the subcarrier allocation and power allocation among source and relay nodes correspondingly. Finally, simulation results validate the energy efficiency performance and convergence of the pro-posed schemes.