## 1 Introduction  
The Internet of Things (IoT) connects objects such as sensors, smart devices, appliances and other everyday items between them and with people to realize novel functionalities [1; 2; 3]. IoT applications cover a broad spectrum of domains, e.g., smart homes and smart cities [4; 5; 6; 7], smart monitoring [8; 9; 10; 11; 12], healthcare [13; 14; 15], and industrial automation [16; 17; 18; 19; 20]. The heterogeneity of the IoT scenarios results in a large spectrum of wireless communication technologies that are candidate to be adopted and fulfill the different objectives of the diverse IoT applications [21; 22]. Among them, there are short-range low-power technologies, such as Radio-Frequency IDentification (RFID) and Bluetooth Low Energy (BLE) [23; 24; 25; 26], some amendments to the IEEE 802.15.4 and the IEEE 802.11 standards for Industrial IoT [27; 28; 29; 30], cellular networks [31; 32], and Low Power Wide Area Networks (LPWANs). In particular, LPWANs are an attractive option for those IoT applications that do not need high throughput, but require to connect low-cost devices over a wide coverage range with low power consumption [33]. Thanks to their ability to connect a large number of nodes spread over wide areas, LPWANs are a suitable alternative to cellular networks and a nice complement to short-range ones [34; 35; 36; 37; 38]. One of the LPWAN standards is the Long Range Wide Area Network (LoRaWAN) [39], which on top of the Long Range (LoRa) modulation [40] defines a network architecture and a protocol stack that offer connectivity at low cost and low power consumption, mobility support, and network reconfiguration [41; 42; 43; 44; 45]. LoRaWAN is a LPWAN protocol that is gaining ground, as it supports wide communication ranges using a low-cost network infrastructure consisting of low-power devices. However, as LoRaWAN implements single-hop LoRa-based transmissions, it is not possible to set the LoRamodulation parameters so as to achieve wide coverage with relatively high bit rates. Due to this LoRaWAN limitation, a number of novel medium access strategies and routing protocols for LoRa-based networks were proposed [46; 47; 48; 49; 50]. Some of them, i.e., the ones presented in [49; 50] leverage the Software-Defined Networking (SDN) paradigm to realize priority-based traffic management and load balancing [51; 52]. Depending on the geographical region in which the LoRaWAN devices work, both the medium access strategy and the configuration of the parameters vary [53]. In particular, in Europe, according to the European Telecommunications Standards Institute (ETSI) regulations, two different channel access methods are allowed, i.e., a Pure ALOHA approach with duty-cycle limitations and a polite spectrum access method based on Listen Before Talk (LBT) Adaptive Frequency Agility (AFA). In particular, the LoRaWAN specification [39] only refers to the duty cycle limitations, while the LoRaWAN regional parameters document [53] clarifies that an LBT AFA Medium Access Control (MAC) strategy can also be adopted. Several works in the literature proposed and assessed LBT-based medium access control protocols for LoRaWAN [54; 55; 56; 57]. However, to the best of our knowledge, none of them provides an extensive performance evaluation of a LoRaWAN network in which the nodes use an LBT AFA approach and work in compliance with the ETSI regulations [59; 60]. This paper presents an assessment that provides quantitative insights on the performance that can be obtained by using LBT AFA in several scenarios by varying the number of LoRaWAN nodes and the MAC parameters. The methodology of the presented assessment is of general validity and can be useful to the network designer in the network configuration phase to properly select the MAC parameters based on the application requirements of the network under consideration. The structure of the paper is the following. Section 2 overviews related works, while Section 3 recaps the main LoRaWAN features. Section 4 describes the LBT AFA MAC protocol.