This paper proposes and optimizes a cooperative non-orthogonal multiple-access (Co-NOMA) scheme in the context of multicell visible light communications (VLC) networks, as a means to mitigate inter-cell interference in Co-NOMA-enabled systems. Consider a network with multiple VLC access points (APs), where each AP serves two users using light intensity. In each cell, the weak user (the cell edge user) can be served either directly by the VLC AP, or through the strong user that can decode the weak user's message and forward it through the radio-frequency (RF) link. The paper then considers the problem of maximizing the network throughput under quality-of-service (QoS) constraints by allocating the powers of the users' messages and APs' transmit powers, and determining the serving links of each weak user (i.e., VLC or hybrid VLC/RF). The paper solves such a non-convex problem by first finding closed form solutions of the joint users' powers and link selection for a fixed AP power allocation. The APs' transmit powers are then iteratively solved in an outer loop using the golden section method. Simulation results show how the proposed solution and scheme improve the system sum-rate and fairness as compared to conventional non-orthogonal multiple-access (NOMA) schemes.

中文翻译：

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多小区协作 NOMA 混合 VLC/RF 系统的功率分配和链路选择

本文提出并优化了多小区可见光通信 (VLC) 网络环境中的协作非正交多址 (Co-NOMA) 方案，作为减轻支持 Co-NOMA 的系统中小区间干扰的一种手段。考虑具有多个 VLC 接入点 (AP) 的网络，其中每个 AP 使用光强度为两个用户提供服务。在每个小区中，弱用户（小区边缘用户）可以直接由VLC AP服务，也可以通过强用户解码弱用户的消息并通过射频（RF）链路转发。然后，本文考虑了在服务质量 (QoS) 约束下通过分配用户消息的功率和 AP 的发射功率来最大化网络吞吐量的问题，并确定每个弱用户（即 VLC 或混合 VLC/RF）。本文通过首先找到固定 AP 功率分配的联合用户功率和链路选择的封闭形式解来解决此类非凸问题。然后使用黄金分割法在外环中迭代求解 AP 的发射功率。仿真结果表明，与传统的非正交多址 (NOMA) 方案相比，所提出的解决方案和方案如何提高系统总和率和公平性。