Energy Efficiency Based D2D Resource Allocation In LTE-A Networks

Device-to-Device(D2D)communication,direct communication between two or more devices with the regulation and coordination of base station(BS),is a promising way to improve performance of cellular networks in terms of spectral utilization,mitigation of BS load and transmit power decreases.Taking advantage of the characteristics of resource reuse between D2 D users and cellular users,this thesis investigates the resource allocation schemes to optimize energy efficiency.The major contributions of this work are summarized as follows:Conventional definition of energy efficiency in cellular networks has not considered the effect of resource reuse on power allocation.In this thesis,we redefine the definition of system energy efficiency from the perspective of resource usage,which considers both D2 D and cellular users utilizing the same spectrum resources.Furthermore,we propose a power control scheme to maximize the energy efficiency of both D2 D and cellular users.Meanwhile,a variable step length incremental iteration algorithm is proposed to improve the performance and reduce the complexity in comparison with the conventional algorithms.The proposed algorithm simultaneously searches in multiple directions and dynamically adjusts the step size to obtain the optimal power with a finite time complexity.This thesis also focus on the relay-assisted D2 D communication,an enhanced technology for the D2 D communication,which can expand network coverage,reduce energy consumption and increase network capacity.However,it is difficult to achieve better overall performance only through power control or time-frequency resource allocation,since the interference in two-hop D2 D transmission is much more complicated than that of single-hop.In this thesis,a joint resource allocation scheme is presented to optimize the energy efficiency.Firstly,a problem formulation for optimizing the energy efficiency of D2 D links is derived on the condition that the minimum rate requirements are satisfied both for cellular and D2 D users.Then,an iterative algorithm based on parametric method is proposed,which utilizes the properties of the fractional programming to transform the mixed integer nonlinear programming problem into a power control sub-problem and a time-frequency resource allocation sub-problem.In addition,the optimal transmit power and time-frequency resource reuse are obtained by the Lagrangian multiplier method and the Hungarian algorithm,respectively.The simulation results show that the proposed resource allocation schemes significantly reduce the impact of the co-channel interference due to the resource reuse,and also improvethe energy efficiency for the satisfaction of the cellular users and D2 D users with a low complexity.