# A TDMA-Based Access Protocol for Dense Networks with Moving Nodes for IoT Applications
## 1 Introduction  
As the Internet of Things (IoT) continues to pave the way for innovations in network technologies, there are a number of network options on which to build smart applications for a variety of everyday life sectors. Being the major communication paradigm in this area, LoRa technology seems to fit perfectly with the IoT philosophy. Being part of the low-power wide-area network (LPWAN) technology, which provides low-cost, low-power, and wide-area coverage, needed for the ongoing era of ubiquitous computing, LoRa adds also the ease of applicability and expandability, maintaining its position among the most popular communication technologies applied for the IoT cosmos.  
Geared for IoT low traffic applications where small amounts of data are transmitted periodically, LPWAN redefines the way applications and processes are developed and established. In addition, supporting this LPWAN approach, a number of appropriate communication standards, based on the energy needs of these networks, have already achieved a level of penetration in IoT applications like city lighting, parking, utilities metering and other agriculture and industry specific uses. Among these LPWAN technologies, such as Sigfox, LoRa, NB-IoT, LTE-M, Wi-Sun, and others, LoRa has gained large popularity due to the fact that it operates in an unlicensed spectrum band, offers low deployment and operation costs without the need of a third party, and is based on a simple star topology with gateways suited for simple control and routing schemes. Apart from the aforementioned leverages, LoRa also offers high adaptability to different applications as it is highly flexible concerning the operational parameters like the SF- Spreading Factor, the coding rate, the bandwidth, the payload length and the preamble length. Configuring those parametersaccording to each application, one can balance between higher throughput or increased range achieving also different battery-life times.The sweet spot between these factors is crucial for the successful operation of the network and are application-specific.  
While in an increased number of applications, the nodes are considered stationary, moving-related applications have started to attract more and more attention. As configuration methods of optimal settings in LoRa wide-area network (LoRaWAN) specification are only present for slowly moving or stationary end nodes [1], moving nodes demand novel evaluation. While there are a number of works involving moving nodes (presented below) the majority use the same fixed high energy settings throughout the movement in order to achieve high reliability.  
Motivated by the aforementioned parameter diversity and the lack of adaptive protocols for moving nodes with LoRa technology, in this work we propose a novel way to optimize performance and reliability in highly dense networks with fast moving nodes. The proposed algorithm acts proactively and reserves an additional slot in the higher SF region for every active scheduled transmission in a way to eliminate the possibility of a lost packet. Due to the moving nature of the nodes, there should be a kind of orchestration for the different SF zones they constantly visit. Acting as a point of segregation from the typical single-node-supervision algorithms, the proposed communication protocol enables all the nodes to take part in a decentralized way.  
The reminder of this article is organized as follows. In Section 2 background and related work is presented. The proposed algorithm along with the system configuration setup are presented in Section 3. Section 4 includes the evaluation of the results along with the performance analysis and in the Section 5 we conclude this work.