Wang Jiayin, Wang Yafeng, Yu Jiarun
School of Information and Communication Engineering, Beijing University of Posts and Telecommunications, Beijing 100876, China.
Sensors (Basel). 2022 Feb 2;22(3):1129. doi: 10.3390/s22031129.
In this paper, we consider the optimal resource allocation problem for multiple-input multiple-output non-orthogonal multiple access (MIMO-NOMA) systems, which consists of beam-forming, user clustering and power allocation, respectively. Users can be divided into different clusters, and the users in the same cluster are served by the same beam vector. Inter-cluster orthogonality can be guaranteed based on multi-user detection (MUD). In this paper, we propose a three-step framework to solve the multi-dimensional resource allocation problem. In step 1, we propose a beam-forming algorithm for a given user cluster. Specifically, fractional transmitting power control (FTPC) is applied for intra-cluster power allocation. The considered beam-forming problem can be transformed into a non-constrained one and the limited-memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) method is applied to obtain the optimal solution. In step 2, optimal user clustering is further considered. Channel differences and correlations are both involved in the design of user clustering. By assigning different weights to the two factors, we can produce multiple candidate clustering schemes. Based on the proposed beam-forming algorithm, beam-forming can be done for each candidate clustering scheme to compare their performances. Moreover, based on the optimal user clustering and beam-forming schemes, in step 3, power allocation can be further optimized. Specifically, it can be formalized as a difference of convex (DC) programming problem, which is solved by successive convex approximation (SCA) with strong robustness. Simulations results show that the proposed scheme can effectively improve spectral efficiency (SE) and edge users' data rates.
在本文中，我们考虑多输入多输出非正交多址接入（MIMO-NOMA）系统的最优资源分配问题，该问题分别由波束赋形、用户聚类和功率分配组成。用户可以被划分为不同的簇，同一簇内的用户由相同的波束向量服务。基于多用户检测（MUD）可以保证簇间正交性。在本文中，我们提出了一个三步框架来解决多维资源分配问题。在第一步中，我们针对给定的用户簇提出了一种波束赋形算法。具体而言，分数发射功率控制（FTPC）用于簇内功率分配。所考虑的波束赋形问题可以转化为一个无约束问题，并应用有限内存布罗伊登-弗莱彻-戈德法布-沙诺（L-BFGS）方法来获得最优解。在第二步中，进一步考虑最优用户聚类。用户聚类的设计中同时涉及信道差异和相关性。通过给这两个因素赋予不同的权重，我们可以生成多个候选聚类方案。基于所提出的波束赋形算法，可以对每个候选聚类方案进行波束赋形以比较它们的性能。此外，基于最优用户聚类和波束赋形方案，在第三步中，可以进一步优化功率分配。具体而言，它可以被形式化为一个凸差（DC）规划问题，通过具有强鲁棒性的逐次凸逼近（SCA）来求解。仿真结果表明，所提出的方案可以有效提高频谱效率（SE）和边缘用户的数据速率。
