Energy Efficiency Analysis For D2D Communication Underlaying Cellular Network

With the rapid development of wireless communication technology, especially the popularity of smart phones, a growing number of mobile users are attracted. How to improve the spectrum efficiency in the limited spectrum resources to make communication network gain higher transmission rates, higher reliability and higher quality has become an important subject researching wireless communication in the future. Meanwhile, with the more serious impact of global environmental problems, Green Communications also have attracted more and more attention. How to gain the maximum throughput with the lowest power consumption is a major problem we need to resolve.The short distance direct communication can effectively improve the spectrum efficiency of the system, in which device to device (D2D) communication is a classic case. Although D2D communication can effectively improve the spectrum efficiency and reduce the power consumption of D2D communication, the co-channel interference (CCI) between the D2D pair and cellular users is the serious drawback because of the frequency reusing. Considering the multi-cell environment, inter-cell interference is inevitable, especially the interference of users at the cell edge region which can cause throughput of the system even the energy efficiency of the whole system decreased. Therefore, this paper will propose two schemes to improve the energy efficiency of the system.The main contents of this paper will coordinate the CCI between D2D pair and cellular user in order to improve the throughput and performance of the system in the D2D communication underlaying cellular network. Firstly, according to the references [1-4],this paper describes the basic principle of D2D communication underlaying cellular network as well as energy efficiency analysis of single-cell cellular systems in three different modes of sharing frequency. In the single-cell cellular system, the reference [4] proposed a power allocation scheme to coordinate the interference between D2D pair and cellular user. The changes of the power of D2D pair and cellular user affect each other. It is difficult for the independent problem to find the global optimal energy efficiency. Therefore, using the non-cooperative game theory, the Nash equilibrium between D2D pair and cellular user can be found. The optimal energy efficiency of D2D pair and cellular user can be gained respectively and the global energy efficiency of the system can be improved.There is inter-cell interference in multi-cells cellular network. Although the fractional frequency reuse (FFR) can decrease the inter-cell interference, the interference of the users at the cell edge region is serious. Facing the problem, we will propose a power allocation scheme, in which the D2D pair at the cell edge region can reuse the frequency allocated to the cellular users in cell inner region and in cell outer region. Base Station (BS) knows the channel state information (CSI) in the cell, so it can find the tradeoff of D2D users and cellular user using the non-cooperative game theory. The optimal energy efficiency of D2D pair and cellular user can be gained respectively and the global energy efficiency of the system can be improved.Meanwhile, we consider the situation that the radio resource allocated a cellular user is shared by several D2D pairs. In this case, the energy efficiency of the system will be maximized ensuring energy efficiency of user whose least energy efficiency maintains at a certain level. Therefore, in this paper we will propose an analysis Algorithm of Energy Efficiency Fairness to ensure the difference of users in energy efficiency being less than a certain threshold to maximize the energy efficiency of the system.