Chinnadurai Sunil, Selvaprabhu Poongundran, Jeong Yongchae, Jiang Xueqin, Lee Moon Ho
Department of Electronics and Information Engineering, Chonbuk National University, Jeonju 54896, Korea.
School of Information Science and Technology, Donghua University, Shanghai 201620, China.
Sensors (Basel). 2017 Sep 18;17(9):2139. doi: 10.3390/s17092139.
In this paper, we examine the robust beamforming design to tackle the energy efficiency (EE) maximization problem in a 5G massive multiple-input multiple-output (MIMO)-non-orthogonal multiple access (NOMA) downlink system with imperfect channel state information (CSI) at the base station. A novel joint user pairing and dynamic power allocation (JUPDPA) algorithm is proposed to minimize the inter user interference and also to enhance the fairness between the users. This work assumes imperfect CSI by adding uncertainties to channel matrices with worst-case model, i.e., ellipsoidal uncertainty model (EUM). A fractional non-convex optimization problem is formulated to maximize the EE subject to the transmit power constraints and the minimum rate requirement for the cell edge user. The designed problem is difficult to solve due to its nonlinear fractional objective function. We firstly employ the properties of fractional programming to transform the non-convex problem into its equivalent parametric form. Then, an efficient iterative algorithm is proposed established on the constrained concave-convex procedure (CCCP) that solves and achieves convergence to a stationary point of the above problem. Finally, Dinkelbach's algorithm is employed to determine the maximum energy efficiency. Comprehensive numerical results illustrate that the proposed scheme attains higher worst-case energy efficiency as compared with the existing NOMA schemes and the conventional orthogonal multiple access (OMA) scheme.
在本文中，我们研究了鲁棒波束成形设计，以解决基站处具有不完美信道状态信息（CSI）的5G大规模多输入多输出（MIMO）-非正交多址接入（NOMA）下行链路系统中的能量效率（EE）最大化问题。提出了一种新颖的联合用户配对和动态功率分配（JUPDPA）算法，以最小化用户间干扰并提高用户之间的公平性。这项工作通过使用最坏情况模型（即椭球不确定性模型（EUM））向信道矩阵添加不确定性来假设不完美的CSI。制定了一个分数非凸优化问题，以在满足发射功率约束和小区边缘用户的最小速率要求的情况下最大化EE。由于其非线性分数目标函数，所设计的问题难以解决。我们首先利用分数规划的性质将非凸问题转化为其等效的参数形式。然后，基于约束凹凸过程（CCCP）提出了一种有效的迭代算法，该算法解决并收敛到上述问题的一个驻点。最后，采用丁克尔巴赫算法来确定最大能量效率。综合数值结果表明，与现有的NOMA方案和传统的正交多址接入（OMA）方案相比，所提出的方案实现了更高的最坏情况能量效率。
