In this paper, we study the secrecy performance of non-orthogonal multiple access (NOMA) enabled visible light communication (VLC) broadcast channels in the presence of an active eavesdropper (Eve). The considered VLC system consists of multiple separately distributed light-emitting diodes arrays and multiple randomly located users (UEs) in an indoor room. User clustering is conducted to reduce the implementation complexity of successive interference cancellations. Two cooperative precoding strategies based on zero-forcing (ZF) and maximum ratio transmission (MRT) are designed using the effective channel of each cluster. Based on each precoding strategy, a sum secrecy rate maximization problem is developed to obtain the near-optimal power allocation (PA) to strengthen UEs’ confidential transmission and degrade Eve’s reception under minimum secrecy rate requirement, peak amplitude, non-negativity, and power constraints. To tackle the challenging non-convex problem for each precoding strategy, equivalent transformations and arithmetic-geometric mean approximation are conducted to convert the original problem into a series of geometric programming (GP) problems. Based on the reformulated problems, iterative algorithms are proposed to obtain near-optimal solutions by solving the GP problems through successive convex approximations. The convergence and complexity analysis of the proposed algorithms are studied. Simulation results show that the sum security performance of the proposed PA approach outperforms conventional PA approaches in both ZF-based and MRT-based precoder schemes. The effectiveness of applying NOMA compared with the orthogonal multiple access-based scheme is also validated for the proposed system.

中文翻译：

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采用协作预编码设计的 NOMA 辅助多用户可见光通信广播网络的安全传输


在本文中，我们研究了在主动窃听者 (Eve) 存在的情况下启用非正交多址 (NOMA) 的可见光通信 (VLC) 广播信道的保密性能。所考虑的 VLC 系统由多个独立分布的发光二极管阵列和室内房间中多个随机分布的用户 (UE) 组成。进行用户聚类是为了降低连续干扰消除的实现复杂度。利用每个簇的有效信道设计了两种基于迫零（ZF）和最大比传输（MRT）的协作预编码策略。基于每种预编码策略，开发了总保密率最大化问题，以获得接近最优的功率分配（PA），以在最小保密率要求、峰值幅度、非负性和功率下增强 UE 的保密传输并降低 Eve 的接收性能限制。为了解决每种预编码策略具有挑战性的非凸问题，进行了等价变换和算术几何均值逼近，将原始问题转换为一系列几何规划（GP）问题。基于重新表述的问题，提出了迭代算法，通过连续凸逼近求解 GP 问题来获得接近最优解。研究了所提出算法的收敛性和复杂性分析。仿真结果表明，在基于 ZF 和基于 MRT 的预编码器方案中，所提出的 PA 方法的总安全性能优于传统的 PA 方法。与基于正交多址的方案相比，应用 NOMA 的有效性也针对所提出的系统进行了验证。