王洋轩
中国电子科技集团公司第二十研究所（西安导航技术研究所）
摘要
本篇论文利用非正交多址技术（NOMA）呈现出一个在虚拟无线网（VWNs）中的功率资源分配问题。在该问题中，不同的子网分享一个基站（BS）的资源，且必须考虑每个子网的要求的子网最低传输速率来保障子网的独立性。公式下的功率资源分配问题是基于子网的独立性来实现基站发射功率最小化的目标，该优化问题为非凸优化问题且计算复杂度很高。本文利用互补几何规划，用计算量较小的迭代法将非凸的优化问题转化为凸优化形式来解决该功率资源分配问题。文末以仿真的方式阐述了在虚拟无线网中非正交多址技术（NOMA）的表现强于正交频分多址技术（OFDMA），为未来通信站点的建立提供了全新的概念。
关键词：非正交多址技术（NOMA），互补几何规划，5G，下一代无线网络，资源分配，虚拟无线网。
Abstract
In this paper, a power-efficient resource allocation problem is addressed in virtualized wireless networks (VWNs) using non-orthogonal multiple access (NOMA). In this set-up, the resources of one base station (BS) are shared among different service providers (slices), where the minimum reserved rate is considered for each slice for guaranteeing their isolation. The formulated resource allocation problem aiming to minimize the total transmit power subject to the isolation constraints is non-convex and suffers from high computational complexity. By applying complementary geometric programming (CGP) to convert the non-convex problem into the convex form, we develop an efficient iterative approach with low computational complexity to solve the proposed problem. Illustrative simulation results on the performance evaluation of VWN using OFDMA and NOMA indicate significant performance improvement in the VWN when NOMA is used. It also gives us a brand new concept about the construction of the future datalink base station.
Index term- Complementary geometric programming, NOMA, 5G, next generation wireless network, resource allocation, virtualized wireless networks.
1.背景介绍
在无线通信普遍要求高传输速率的趋势中，对于可用频段的争夺也在愈演愈烈。不仅于此，各大运营商也想尽办法减少对于无线基础设施的投资。所以，多种技术比如MIMO，虚拟化技术以及非正交多址接入技术为了下一代无线网络的铺建应运而生。无线网络虚拟化技术可谓前途无量，该技术可以使不同的运营商通过子网分组共享无线网络的物理基础设施。虚拟无线网络旨在提高频谱以及基础设施的利用率，其中最重要的问题则在于防止不同子网分组之间的有害干扰，这就是分组的独立性。为了保障每个分组的服务质量（QoS），不同形式的静待和动态资源分布被提出，这就是有效资源分布算法。
在即将到来的5G通信中，非正交多址技术（NOMA）作为一种潜在的实现手段从而近期被广泛关注。对比4G通信中的正交频分多址技术（OFDMA），NOMA技术可以使多个用户在不同的功率分配因子下共享时间和频段资源，从而增加频谱使用效率。在OFDMA中，同一时间同一频段只可分给一个用户。用户被分配到不同的子信道中，每个用户在其特定的子信道中无法被其他用户所干扰。但每个子信道只能有一个用户，当同一时间在线用户数量超过子信道数量时，后上线的用户只能排队等待造成效率下降。而NOMA利用串行码间干扰消除技术（SIC）使得多个用户共享同一时间与同一频率成为可能，NOMA在接收端采用SIC接收机来实现多用户检测。串行干扰消除技术的基本思想是采用逐级消除干扰策略，在接收信号中对用户逐个进行判决，进行幅度恢复后，将该用户信号产生的多址干扰从接收信号中减去，并对剩下的用户再次进行判决，如此循环操作，直至消除所有的多址干扰。研究显示对比OFDMA技术，NOMA技术可以使系统容量提升28%。
本文主要探讨在VWN中NOMA技术如何在功耗效率上提高网络性能。在保证每个子网容量不变的情况下，最小化VWN中的总发射功率。因为原问题为非凸优化问题且计算复杂度高，本文利用互补几何规划（CGPA）和算术几何均值不等式（AGMA）迭代将问题转化为更为高效的凸优化算法，利用CVX凸优化工具得到最终仿真。仿真结果显示NOMA在功耗效率方面强于OFDMA约45%-54%。
在第二节中主要讨论系统模型和公式的推导，第三节中解释NOMA和OFDMA的预期算法，第四节主要陈述仿真结果，第五节给出结论。
2.系统模型
假设一个单基站下行传输的系统，其中有一个分组子网的集合 ，每一个子网s（ ）有 个用户。整个系统总用户数 。为保障每个子网的独立性，
VWN中对于每一个子网s有要求的子网最低传输速率要求记为 。本文VWN中有两种传输模式：
?非正交多址技术（NOMA）整个频段为所有用户共享。
?正交频分多址技术（OFDMA）整个带宽被分为N个子信道，每个子信道同一时间只能有一个用户。
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5结论
本文探讨了在虚拟无线网络中NOMA系统对比OFDMA系统的能效表现。具体的，本文列出了一个优化问题，即以保证全部子网的最低传输速率为限制条件来得到最低总发射功率。鉴于这个优化问题非凸且计算复杂度高，本文利用CGP和AGMA近似进行迭代的算法，将每次迭代转化为凸进而求解。通过仿真结果可以看出NOMA系统的能效远高于OFDMA系统且用户数量越多越明显，且对于多个子网的支持NOMA的能效表现也强于OFDMA。如将NOMA技术用于数据链的发展，将大大减少通信站点的功耗，提升通信质量。此外，NOMA系统容量亦有所提升，同时在线用户数量多，可作为无人机蜂群的通信系统，即支持大的用户量，也支持多个子网的存在，同时还将大幅减少指挥台的功耗。
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