Though visible-light communication (VLC) channels are contained by opaque boundaries, they present unique challenges in the development of multi-user/multi-cell scenarios. In this paper, two hybrid transmission schemes are proposed for managing multiple users in multi-cell VLC networks. The proposed schemes are based on using non-orthogonal multiple access (NOMA) in the network access points (APs), while applying zero-forcing (ZF) pre-coding to the cell edge users’ signals, which are cooperatively broadcast from the APs. The proposed approach allows a reduction of the inter-cell interference affecting the cell-edge users thanks to ZF pre-coding, while dealing with inter-user interference for cell-center users via NOMA signaling. Considering different transmission scenarios, we show the improvement in the network total achievable data rate as well as fairness, as compared to conventional NOMA. For example, for a typical scenario considered, an improvement of up to 39% in total achievable rate and up to 112% in the network fairness is achieved. The proposed approach also presents a clear advantage over the conventional ZF pre-coding, for which the maximum number of users is constrained to the number of APs.

中文翻译：

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多小区VLC网络的NOMA和ZF混合预编码传输

尽管可见光通信（VLC）通道包含在不透明的边界中，但它们在多用户/多小区方案的开发中提出了独特的挑战。在本文中，提出了两种混合传输方案来管理多小区VLC网络中的多个用户。所提出的方案基于在网络接入点（AP）中使用非正交多路访问（NOMA），同时对小区边缘用户的信号应用迫零（ZF）预编码，这些信号从AP协作广播。借助ZF预编码，所提出的方法可以减少影响小区边缘用户的小区间干扰，同时通过NOMA信令处理小区中心用户的小区间干扰。考虑到不同的传输方案，与传统的NOMA相比，我们展示了网络可达到的总数据速率以及公平性的提高。例如，对于所考虑的典型场景，可以实现最高39％的总可实现率提高和112％的网络公平性提高。所提出的方法还呈现出优于常规ZF预编码的明显优势，因为传统ZF预编码的最大用户数受限于AP的数量。