Research On Relay-Assisted Green Communications Scheme In Heterogeneous Wireless Networks

The requirements for the next-generation wireless communication system are high transmission rate and high spectral efficiency. To achieve these requirements, 3GPP put forward the LTE-Advanced(LTE-A for short) process as further evolution of the LTE. Basing on the LTE, the LTE-A introduces the technologies of heterogeneous network(Het-Net), carrier aggregation(CA), enhanced multi-antenna and Coordinate Multi-Point(CoMP) and so on. Through deploying low-power nodes in cell edge, Het-Net technology can enhance the wireless coverage and provide mobile users flexible access to network. As a result, Het-Net technology is raising more and more focus. With the increasing of wireless communications business, the large energy consumption and CO2 emission has been a serious issue to deal with. Green communication aims at developing frameworks and protocols to jointly maximize the throughput and minimize the CO2 emissions, which means increasing the energy efficiency of wireless communications networks.In this thesis, we mainly study the Het-Net technology, including the green communication mechanism basing on relay selection. On the basis of current research, we put forward a kind of relay selection algorithm based on ant colony optimization(ACO), and the corresponding green communication mechanism based on relay selection. This communication mechanism can dynamically adjust working condition of low power nodes according to the traffic load in HWNs. Relay selection based on ant colony optimization algorithm can find global near-optimal relay arrangement scheme for multiple mobile terminals. However, the convergence speed of ACO is slow when nodes amount is big and which will result in performance loss when traffic is busy. Therefore, this thesis further puts forward an improved relay selection algorithm, namely relay selection algorithm which is based on the ant colony optimization-differential evolution(ACO-DE) hybrid algorithm. As another kind of biological algorithm, differential evolution performs better on convergence speed and stability than many other biological algorithms. Fusion of differential evolution and other biological algorithm can markedly improve the performance. Relay selection algorithm based on ACO-DE has faster and stabler searching performance, employing green communication scheme based on it in multiple cell HWNs can increase the energy efficiency remarkably.In addition to description of relay selection algorithm and theoretical analysis of green communication mechanism, this thesis also builds single cell and multiple cell heterogeneous wireless network simulation platform. We simulate the proposed green communication mechanism and compare it with traditional communication mechanism. Simulation results show that the proposed relay selection algorithm can reasonably arrange relay nodes for multi-user in heterogeneous wireless network. Communication mechanism based on the proposed relay selection algorithm can reduce the network’s overall energy consumption and improve the energy efficiency of heterogeneous wireless network.