# A TDMA-Based Access Protocol for Dense Networks with Moving Nodes for IoT Applications
## 2 Related Work
(2018) proposed an energy-efficient mechanism for LoRa networks based on the node's state battery; in order to save most of the energy consumed, they base the node localization on trilateration and time difference of arrival as the most common solution of a GPS could jeopardize the energy efficiency in search and rescue operations. For another form or moving nodes, the UAV, the authors in [PERSON] et al. (2018) proposed a distributed topology control algorithm based on the link budget between nodes and movement prediction techniques in a network formation where the nodes communicate via LoRa messages with the UAV nodes and the latter communicate over WiFi with the base station to propagate the messages to the backbone. Similar to the aforementioned work, in [PERSON] et al. (2018) the authors tested a node-to-UAV LoRa mesh network by applying a slotted ALOHA approach offering a robustness to network dynamic topology. In the next works, the use of LoRa in conjunction with moving nodes is presented in an effort to show the wide applicability of this technology. The authors of [PERSON] et al. (2018) designed and implemented a bicycle location-tracking system as a proof of concept for the use of low-power and wide-area network technology for IoT under various network formations. Similarly, in the work of [PERSON] et al. (2018) the authors tested the achievable transmission distance in an urban area using this time cars instead of bicycles. Again, in another use of LoRaWAN with moving nodes [PERSON] et al. (2018), the authors used moving LoRa nodes to monitor another flavor of the IoT, using floating solar panels. The authors in [PERSON] et al. (2018) propose the use of a LoRa transmitter via mobile phones for the dissemination of an emergency message in cases where the cellular network is inoperative. Under the proposed operation protocol, the nodes can operate as delay-tolerant transmitters depending either on timer expiration or the reception of different message types. It should be mentioned that the proposed algorithm is unique as it is tested in dense environments and offers different characteristics from the previous works with moving nodes. It considers a two way communication as distinct from [PERSON] et al. (2018) which does not take into account the response from the base station. The authors in [PERSON] et al. (2018) test up to 500 nodes and consider ultra-low speed nodes that do not change their spreading factor as the proposed protocol. The same applies also for [PERSON] et al. (2018), where the authors do not consider changes in the SF of the ground nodes as the data are transmitted to the base station through UAV nodes via WiFi ad hoc network. This protocol, along with the [PERSON] et al. (2018), have many common components with the proposed one but we utilize only LoRa technology for the actual data transmission and do not relay on other technologies (the use of WuR is only for orchestration and energy-saving purposes). The dense network formations tested in this work are not present in the other works that lack such escalation. Prompted from the above consideration of a delay-tolerant network in conjunction with the connectivity issues that may arise in networks with moving nodes, we present also some works that have considered IoT with the notion of opportunistic networking. In [PERSON] et al. (2018) the authors propose the use of opportunistic fog computing in hazardous and volatile situations where resources and connectivity are inherently limited. One emerging field of application for this type of fog architecture is the flying IoT and drones sector. The fog devices are referred to mainly as vehicle and mobile phone nodes.Along the same lines, in [19] the authors study the performance of the opportunistic fog network for offloading computing tasks from the IoT network.