Research On Energy Efficient Resource Management And Transmission Scheme In The Wireless Relay Network

As the wireless communication data traffic increases rapidly, dense deployment and complex transmission technologies are required in future wireless networks, leading to increasing network energy consumption and operation cost for operators. On the other hand, energy consumption in wireless networks results in a large amount of greenhouse gas emission, which is harmful to environment protection and sustential development. Therefore, it is significant to investigate energy efficient wireless transmission technologies to reduce the network energy consumption. Cooperative relay transmission plays an important role in system capapbility enhancement and network coverage expansion. Recently, relaying has been widely studied and adopted by international standardization organizations. Reasonable resource management and transmission scheme design in the relay network can effectively improve the network energy efficiency, contribute to the solvement of the network energy consumption issues and provde new opportunity to realize green communications.This dissertation summarizes the research work the author accomplished on energy efficient resource management and transmission in relay networks. The research work is finacially supported by National Key Technology R&D Program of China:"IMT-Advanced Oriented Cross Layer Optimization Technologies"(2010ZX03003-001-01); The Fundamental Research Funds for the Central Universities:"Research on Energy Efficient Transmission Technology in the Relay Network".Taking one-way and two-way relay networks into account, the dissertation mainly focuses on energy efficient resource management and transmission in the network, including:relay selection and power allocation, multi-antenna relay precoding technology, cooperative ARQ, and develops related algorithms to acheive energy efficiency optimization. The main research work and achievements of this dissertation are as follows:(1) The related theory and wireless transmission technologies for enengy efficient transmission in the wireless network are analyzed. Existing research on energy efficient transmission issues in the relay network are summarized, including relay selection and power allocation, multi-antenna precoding and cooperative ARQ. The main research questions and challenges are also pointed out.(2) Research on energy efficient relay selection and power allocation scheme while satisfying QoS requirement of bidirectional users. Considering the asymmetric characteristic of bidirectional traffic in the one-way and two-way relay network, the weighted enenrgy efficiency of the system is first modeled as the objective and the optimal power allocation results are given using KKT conditions. Then, the optimal transmission mode and the best relay are selected in MAC layer, using cross layer theory. The proposed bidirectional traffic based transmission scheme can effectively reduce the network energy consumption while satisfying the QoS requirement for users. Furthermore, the impact of the signaling exchange overhead due to cross layer transmission and the optimal relay position on the network energy efficiency are discussed, which can be the reference for practical energy efficient relay network deployment.(3) Research on joint power allocation and beamforming transmission scheme in multi-antenna relay networks. In multi-antenna one-way and two-way relay networks, the average transmission data rate and bit error probablity requirement of birectional traffic are first converted into MSE limitations, and the energy consumption model is set up. By converting the non-convex objective problem into several convex sub-problems and employing Lagrange multiplier methods, the close form expressions of the power allocation and beamforming results for each node are given. Simulations demonstrate that in both one-way and two-way relay networks, the proposed power allocation and beamforming algorithm can improve the energy efficiency of the network effectively while guaranteeing the speed of convergence. The research can provide theory basis for the usage of energy efficiency multi-antenna relay networks.(4) Research on the energy efficiency of cooperative ARQ transmission. In the one-way relay network, the redundant circuit energy consumption and latency caused by retransmissions are introduced into the energy consumption per bit transmitted model. Adopting exhaustive search methods, the optimal instantaneous transmission rate and power are found. The impact of the maximum retransmission number on the tradeoff between circuit energy and tranmission energy consumption, the tradeoff between latency limitation and system energy consumption, are demonstrated through Monte Carlo simulation. Based on the results, energy efficient transmission parameters are discussed. In the two-way relay network, the relationship between system energy efficiency and throughput of ARQ transmission is investigated. By modeling the state transfer process of the relay as a Markov chain and analyzing the transition probability between different states, the throughput and the energy consumption of the network are derived. The tradeoff between the throughput and energy efficiency are discussed using the results of numerical simulations. It is shown that in cooperative ARQ transmission, the energy consumption can be reduce by jointly optimizing the parameters, such as the maximum ARQ retransmission number, transmission data rate and transmit power, etc.