# Combined Use of LoRaWAN Medium Access Control Protocols for IoT Applications
## 1 Introduction  
The Internet of Things (IoT) paradigm is spreading across several sectors, providing connectivity between people, smart sensors, computing devices, robots, digital machines, etc. [1, 2, 3, 4]. In particular, IoT applications can be found in several domains, including smart cities and smart homes [5, 6, 7, 8], smart monitoring [9, 10, 11, 12], healthcare [13, 14], and factory automation [15, 16, 17, 18, 19]. Since IoT scenarios are highly heterogeneous and the number of IoT applications [20, 21] is steadily growing, the selection of wireless technologies capable of meeting their needs is wide, spanning low-power short-range technologies, such as RFID and Bluetooth Low Energy [22, 23, 24], high-power technologies, such as cellular networks [25], and some amendments to the IEEE 802.15.4 and IEEE 802.11 standards for Industrial IoT [26, 27, 28, 29, 30].  
As a complement of the aforementioned technologies, low power wide area networks (LPWANs) offer connectivity solutions for IoT applications that require low throughput, low power consumption, and wide coverage range using low-cost devices [31]. A very popular LPWAN standard is the Long Range Wide Area Network (LoRaWAN) [32]. LoRaWAN works on top of Long Range (LoRa) modulation [33] and defines a system architecture and protocol standards that aim to satisfy multiple key IoT requirements, such as low cost, low power, mobility support and easy network reconfiguration [34, 35].  
According to the LoRaWAN regional parameters [36], different rules are defined for both the medium access strategy and the parameter configuration, depending on the region in which the LoRaWAN devices operate. In particular, in Europe, two different uncoordinated channel access strategies [37] can be adopted, i.e., based on Pure ALOHA or on a polite spectrum access technique involving a clear channel assessment (CCA) prior totransmission. In fact, the norms imposed by the European Telecommunications Standards Institute (ETSI) allow the usage of either a duty-cycle limitation or a transmission management based on Listen Before Talk (LBT) Adaptive Frequency Agility (AFA). As discussed in [37], Pure ALOHA and LBT AFA differ in multiple aspects. As Pure ALOHA does not use any CCA mechanism, it works in an energy-efficient way under low workloads, but it may suffer from a significant number of collisions under high network traffic. In contrast, by running the CCA before starting a transmission, LBT AFA can mitigate the message loss due to overlapping transmissions, at the expense of increasing the energy consumption.  
Some works in the literature compared the medium access control (MAC) protocols supported by LoRaWAN [38; 39]. However, to our knowledge, none of them evaluated the performance obtained by combining Pure ALOHA and LBT AFA on the same LoRaWAN network when they work in accordance with the ETSI regulations [40; 41]. In contrast, this paper presents a performance assessment of a LoRaWAN network that combines the use of the two supported MAC protocols when they work in compliance with the ETSI regulations, with the aim of providing the network designer with useful information to choose the most suitable protocol to reach the desired performance metrics. The assessment is performed through simulations in realistic scenarios under different workload conditions.  
The structure of this paper is the following. Section 2 recaps the relevant literature. Section 3 outlines the main features of LoRaWAN, while Section 4 presents the MAC protocols supported by LoRaWAN. Section 5 describes the envisaged network configuration scenarios, while Section 6 addresses the performance evaluation and discusses the results obtained. Finally, Section 7 concludes the paper and outlines further research threads.