# A Comprehensive Review of Micro UAV Charging Techniques
## 7 Simultaneous Lightwave Information and Power Transfer (SLIPT)  
Although SWIPT offers the advantage of transmitting information and power simultaneously, it can also be a source of RF pollution and interference of data transmission. One alternative method to avoid RF drawbacks is to harvest energy from lasers and LEDs. Using an optical source, it is possible to simultaneously deliver data and perform energy transfer. Exploiting an optical source to deliver power and carry information is mooted as a key technology to wirelessly recharge the batteries of UAVs, Internet-of-Things (IoT), Intelligent Internet-of-Things (IIoT) and Internet of Underwater Things (IoUT). Researchers extended this concept. naming it simultaneous light wave information and power transfer (SLIPT) [115]. Recently, SLIPT has received significant attention as an effective technique for WPT between communication terminals. It can be a cost-effective solution for wireless systems, e.g., autonomous machines such as UAVs and remote sensors. It is also very promising for aerospace, smart house, healthcare and underwater applications. The idea of SLIPT has been demonstrated in indoor IoT applications, powering of IoUT devices and UAVs [116; 117]. Recently, [PERSON] et al. [118] experimentally demonstrated SLIPT for 1 Gbps GaAs VCSEL and a photovoltaic link which is envisaged to be the paradigm for next generation backhaul connectivity. If this strategy is properly optimized, it can provide significant gains in spectral efficiency, power transfer, interference management, energy consumption and time delay. This strategy also generates a remarkable trade-off between rate and harvested energy. SLIPT is also referred to as a promising technological paradigm to unlock UAV-enabled fifth-generation (5G) and beyond backhaul communications. In [117], the authors proposed airborne radio access networks (A-RANs), which is a promising technology due to its capabilities of cost-efficient, fast and on-demand improvement of the current telecommunication infrastructure. The major issues in such networks are reliable links with ground users and energy sustainability of the aerial platforms (APs), such as UAVs, as shown in Figure 16. In this study, the authors proposed a novel approach of using SLIPS and a hybrid FSO/RF relaying protocol. The ground base station (GBS) transmits both power and information to the UAV based on the SLIPT idea, while the UAV connects with the ground users through air to ground (A2G) orthogonal RF channels. In another study [119], the authors studied a UAV-assisted multicasting system using SLIPT technology. In this proposed system, the UAV used the power splitting method to harvest wireless power and decode backhaul information over the FSO link simultaneously. In [120], the authors proposed a novel mechanism to realize energy harvesting using pulse amplitude modulation (PAM). Because SLIPT solutions revolve around time splitting (TS) and average power (AP), the authors compared this mechanism with SLIPT-TS and SLIPT-TS-AP. The presented work shows that optimization can be achieved in a simple way, which can meet the EH design requirements of the UAVs. In Table 5 different charging techniques for UAVs are shown.