Joint Optimization Of Link Parameters In A D2D Underlaid Uplink Cellular System

Compared with the traditional cellular communications,D2 D communication allows mobile users which are close with each other to connect directly without going through the base station and the core network.Due to this feature,D2 D communication can help save system power and spectrum resources,and thus becomes one of the key technologies of 5G and B5 G systems.For a D2D-underlaid cellular system,how to properly allocate channel resources and transmit power to mobile users and reduce co-channel interference is a key issue.This dissertation considers a D2D-underlaid cellular system,and aims to solve several problems,e.g.,maximizing the weighted sum spectral efficiency as well as energy efficiency of D2 D users,maximizing the sum secrecy rate of cellular users,etc.by jointly optimizing the parameters of both cellular and D2 D links.The main work of this dissertation can be summarized as follows.Chapter 2 considers two problems,i.e.,maximizing the weighted sum spectrum efficiency of D2 D users,and maximizing the weighted sum energy efficiency of D2 D users.To increase the spectral efficiency,D2 D users are allowed to reuse all the uplink cellular subchannels.The main work of this chapter is: 1)Since the channel assignment variables are discrete,the considered problems are mixed integer programming.To make the problems more tractable,both the problems are divided into two sub-problems.The first subproblem aims to optimize the channel allocation and power of cellular users when the transmit power of D2 D users is fixed,and the second subproblem aims to optimize the transmit power of D2 D users for determined channel allocation and power of cellular users.The first subproblem can be transformed to an assignment problem and optimally solved,while the second subproblem is non-convex.2)To solve the second subproblem,an alternative algorithm is proposed.Simulation results show that the proposed algorithm can effectively improve the spectrum and energy efficiency of D2 D underlaid cellular systems,and its performance is better than existing algorithms.Chapter 3 investigates the robust transmission design of a multi-cell D2 D underlaid cellular network with imperfect CSI.The main work of this chapter is: 1)The bounded model is adopted to characterize the CSI impairment and the aim is to maximize the worst-case sum rate of the system.It is first shown that the worst-case SINR of each D2 D link can be obtained directly,while that of cellular links cannot be similarly found since the channel estimation error vectors of cellular links are coupled in the SINR expressions.2)To solve the nonconvex problem,the objective function of the original problem is replaced with its lower bound,and the resulted problem is decomposed into multiple SDP subproblems which are convex and have computationally efficient solutions.An iterative algorithm is then proposed to obtain a suboptimal solution.3)Simulation results show that D2 D communication can significantly increase the performance of the conventional cellular systems while causing tolerable interference to cellular users.In addition,the proposed algorithm outperforms the conventional non-robust transmission design greatly in terms of network spectral efficiency.Chapter 4 aims to maximize the sum secrecy rate of all cellular users in a D2 D underlaid cellular system.The main work of this chapter is: 1)It is proven that in the optimal case,each cellular user either keeps inactive or transmits their signal in the maximum power.2)To investigate the potential of D2 D communication in improving network security,the conventional network without D2 D users is first considered.It is shown that the problem of maximizing the sum secrecy rate of cellular users for this special case can be transformed to an assignment problem and optimally solved.3)Then,the normal D2 D underlaid network is considered.Since the joint optimization of resource block allocation,CU-DU matching and power control is a mixed integer programming,the problem is difficult to handle.Hence,the resource block assignment process is first conducted by ignoring D2 D communication,and an iterative algorithm is then proposed to solve the remaining problem.4)Simulation results show that the sum secrecy rate of CUs can be greatly increased by D2 D communication,and compared with the existing schemes,a better secrecy performance can be obtained by the proposed algorithms.Chapter 5 aims to maximize the sum secrecy rate of all cellular and D2 D users.The main work of this chapter is: 1)This problem is intractable due to the non-negative and logarithm operators and the fractional SINR expressions in the objective function.In order to cope with these challenges,this chapter first simplifies the original problem by relaxing the non-negative operator in secrecy rate and then propose an alternative algorithm to solve the remaining problem.2)The proposed algorithm removes the logarithm operation by introducing auxiliary functions and handles the fractional SINR by applying an extended parametric algorithm.Simulation results show that both the sum secrecy rate and positive secrecy rate ratio of cellular users can be effectively increased by introducing underlaid D2 D pairs,and compared with existing methods,the proposed algorithm can obtain a better system secrecy performance.