# Hybrid RF/VLC Network Architecture for the Internet of Things
## 2 Related Work  
A considerable amount of works on heterogenous or hybrid networks for IoT can be found in the literature. In [14], [PERSON] et al. proposed a heterogeneous architecture, but the interconnection between different technologies or the network backbone was subject to a pre-existing coverage area. In [15], [PERSON] et al. also proposed a heterogeneous IoT gateway computer appliance that provided interaction between different technologies and IP or non-IP networks. This work employed a cost-inefficient system, for example, using a computer to manage the HetNet; thus, it was not developed for low-power systems. Authors in [16; 17] proposed named data networking (NDN) to allow node identification in an IoT architecture. NDN changes the semantics of a network service from delivering the packet to a given destination address for fetching data identified by a given name. Therefore, NDN provides a solution in which the devices no longer have a network address. However, it requires several additional elements, and its integration can be compromised when multiple networks are used. The system proposed in this work provides a unique frame format for all kind of networks to achieve both routing and identification, allowing a global routing method and an identification protocol, as is required in heterogeneous systems. [PERSON] et al. designed and implemented an end-to-end solution to enhance and enable public safety communication systems [18]. The system used heterogeneous wireless communication techniques (such as WiFi) to provide an access point for end-users, and LoRa to establish ad hoc networks covering larger areas. In addition, the authors proposed a cross-layer energy-efficient routing algorithm that aimed to maximize the network lifetime. Nevertheless, as was aforementioned, WiFi networks present serious constraints in terms of energy saving. In [19], the authors proposed and evaluated an information monitoring approach based on NB-IoT and LoRa. The experiments were carried out in real scenarios, showing that the proposed system enables the achievement of wide-area information monitoring. Additionally, in [20], an LP-WAN-based architecture was proposed with the aim of monitoring the activities of Optimist Class sailboats and evaluating the performance of the LoRa protocol. Nevertheless, most works are not designed under the premises of low power, a low rate, and a long range, as the architecture proposed in this work. Both works were not capable of integrating other communication technologies of IoT, such as ZigBee and VLC. Providing IoT connectivity in remote areas is still an open challenge. [PERSON] et al. designed and tested a hybrid network combining WiFi and Public Land Mobile Networks for providing internet access in precision farming applications [21]. The authors defined an ad hoc architecture to support the aforementioned RF technologies, and proposed a simple algorithm to decide opportunistically the communication interface. Nonetheless, the authors' approach was mostly intended for monitoring applications. The use of VLC (or optical wireless communication in general) combined with RF technologies has also been considered in the literature. For instance, authors in [22] implemented an asymmetric hybrid WiFi-VLC system in which the WiFi channel was only utilized as an uplink. This work showedthat VLC downlink hotspots alleviate contention and interference on the RF channel. Furthermore, in [23], the authors proposed a hybrid WiFi-VLC system that comprised two links that can work simultaneously to provide aggregated bandwidth. One is a duplex WiFi link, while the other is an asymmetric duplex WiFi-VLC link where VLC is used as the downlink and WiFi as the uplink. It was shown that the approach was a good solution in terms of throughput. Nonetheless, in both works, the energy consumption was not evaluated, and as is well-known, WiFi network interface controllers impose serious constraints in terms of power consumption.