In this paper, we consider an indoor hybrid visible light communication (VLC) and radio frequency (RF) communication scenario with two-hop downlink transmission. The LED carries both data and energy in the first phase, VLC, to an energy harvester relay node, which then uses the harvested energy to re-transmit the decoded information to the RF user in the second phase, RF communication. The direct current (DC) bias and the assigned time duration for VLC transmission are taken into account as design parameters. The optimization problem is formulated to maximize the data rate with the assumption of decode-and-forward relaying for fixed receiver orientation. The non-convex optimization is split into two sub-problems and solved cyclically. It optimizes the data rate by solving two sub-problems: fixing time duration for VLC link to solve DC bias and fixing DC bias to solve time duration. The effect of random receiver orientation on the data rate is also studied, and closed-form expressions for both VLC and RF data rates are derived. The optimization is solved through an exhaustive search, and the results show that a higher data rate can be achieved by solving the joint problem of DC bias and time duration compared to solely optimizing the DC bias.

翻译：本文考虑室内混合可见光通信（VLC）与射频（RF）通信的两跳下行传输场景。在第一阶段（VLC），发光二极管（LED）同时传输数据和能量至能量采集中继节点，该节点随后利用采集的能量，在第二阶段（RF通信）将解码后的信息重新传输至RF用户。我们将直流（DC）偏置和分配给VLC传输的时间长度作为设计参数。针对固定接收机朝向的解码转发中继场景，构建了以最大化数据速率为目标的优化问题。该非凸优化问题被分解为两个子问题并循环求解：通过固定VLC链路时间长度来求解直流偏置，以及固定直流偏置来求解时间长度，从而优化数据速率。同时研究了随机接收机朝向对数据速率的影响，并推导了VLC与RF数据速率的闭式表达式。通过穷举搜索法求解优化问题，结果表明，相较于仅优化直流偏置，联合求解直流偏置与时间长度问题可获得更高的数据速率。