A current trend in the evolution of mobile communication networks consists in integrating Non-Terrestrial Networks (NTN) with the Terrestrial ones. One option to implement the NTN part of this hybrid architecture using Unmanned Aerial Vehicles (UAV) that relay the uplink radio signals through optical wireless backhaul links. A good choice for the radio uplink waveform is conventional SC-FDMA, which mitigates the PAPR and enables a longer battery lifetime at the transmitter side. For the optical backhaul link, which is based on low-cost Visible Light Communication (VLC) technology, a non-orthogonal implementation of SC-FDMA is proposed. By doing so, it is possible to improve the end-to-end throughput by reducing the communication bandwidth (to make it fit the LED frequency response), mitigate the effect of light reflections, and increase the energy efficiency in the backhaul link. Since VLC relies on non-coherent IM/DD, the non-orthogonal SC-FDMA waveform must rotate the phase of the IDFT subcarriers, in order to obtain real-valued signal samples at the output. Two strategies for relaying the data in the UAV node are evaluated, namely: Detect-and-Forward and Decode-and-Forward. The first one recovers the modulation part (i.e. partial regeneration), whereas the second one regenerates the transmitted message up to the bit level (i.e., total regeneration). This paper studies the combination of relaying strategy and NB-IoT Modulation and Coding Scheme (MCS) that maximizes the end-to-end throughput at different UAV altitudes.

移动通信网络发展的当前趋势在于将非地面网络 (NTN) 与地面网络集成。一种使用无人机 (UAV) 来实现这种混合架构的 NTN 部分的选项，无人机通过光学无线回程链路中继上行链路无线电信号。无线电上行链路波形的一个不错的选择是传统的 SC-FDMA，它可以减轻 PAPR 并在发射器侧实现更长的电池寿命。对于基于低成本可见光通信（VLC）技术的光回程链路，提出了一种SC-FDMA的非正交实现方案。通过这样做，可以通过降低通信带宽（使其适合 LED 频率响应）来提高端到端吞吐量，减轻光反射的影响，并提高回程链路的能源效率。由于 VLC 依赖于非相干 IM/DD，非正交 SC-FDMA 波形必须旋转 IDFT 子载波的相位，以便在输出端获得实值信号样本。评估了在无人机节点中中继数据的两种策略，即：检测转发和解码转发。第一个恢复调制部分（即部分再生），而第二个将传输的消息再生到比特级别（即全部再生）。本文研究了中继策略与 NB-IoT 调制和编码方案 (MCS) 的结合，以最大限度地提高不同无人机高度下的端到端吞吐量。