## 2 Related Work  
As it was mentioned in Section 1, LoRaWAN supports two kinds of random MAC protocols [61], i.e., Pure ALOHA and channel access strategies based on LBT AFA, respectively. Previous works [62; 63; 64] compared the performance of approaches based on ALOHA and that of LBT-based ones, but, differently from this work, they do not provide extensive assessments of LBT AFA with different MAC configuration parameters. Several uncoordinated MAC protocols for LoRaWAN similar to the standard ones were proposed and evaluated in the literature. In particular, some of them are based on Slotted ALOHA [65; 66], while other ones propose medium access strategies based on LBT [54; 55; 56; 57; 58; 63; 64; 67]. Table 1 provides a qualitative comparison among some of the above mentioned related works. In particular, the first row refers to the compliance with the current ETSI regulations. The second row gives the number of nodes in the considered scenarios. The third row indicates if the assessment is performed varying some MAC parameters, while the fourth row refers to the support for mobile nodes. The fifth row specifies the adopted evaluation method, i.e., analytical (an. ), simulative (sim.) or experimental (exp.). Finally, the sixth and seventh rows indicate if the message loss/delivery ratio and the delay are evaluated, respectively. The work in [62] presents a simulative performance assessment of a Pure ALOHA and an LBT AFA protocol in a LoRaWAN network with a varying number of nodes (up to 200) under different workload conditions. The comparative evaluations refer to the percentage of lost messages. The results obtained in [62] show that LBT AFA obtains better results than Pure ALOHA with higher traffic generation rate. For instance, under an exponentially distributed message generation pattern with mean between 15 s and 60 s for stationary nodes and between 5 s and 20 s for mobile nodes, LBT AFA improves the message loss ratio value by 1.40% to 2.47% on Pure ALOHA. The reason for the message loss ratio improvement is that, whenever the channel is found busy, LBT either exploits an AFA mechanism or waits for a backoff delay before retrying the transmission, thus reducing the message loss. Conversely, with Pure ALOHA each node transmits without performing any Clear Channel Assessment (CCA), i.e., without sensing the channel. As a result, a number of messages can be lost due to collisions. Under lower traffic conditions than those described before, instead, the performance of Pure ALOHA and LBT AFA are similar. The work in [54] focuses on LBT and compares four different LBT-based MAC protocols for LoRaWAN through simulations with a varying number of stationary nodes (up to 2000). The assessments presents results on the message delivery ratio, but does not provide delay results and does not deal with mobile nodes or different MAC parameters. The papers [55; 57] provide insights on the message delivery ratio and the average delays of a LoRaWAN network in which some nodes adopt ALOHA and others the LBT-based MAC protocol. The evaluation is performed considering a fixed number of stationary nodes (i.e., 300) in [57] and a variable number of stationary nodes (from 60 to 780) in [55], respectively. No assessment varying the LBT MAC parameters is made. In [56] the two MAC protocols supported by LoRaWAN are compared through simulations varying the number of nodes from 1000 to 4000. However, the considered performance metrics do not include either message loss/delivery ratio or delay and no assessments varying the LBT MAC parameters are made. The Authors of [58] present a simulative assessment of a LoRaWAN network in which the number of nodes varies from 1 to 10,000. The work evaluates the message delivery ratio comparing ALOHA with two different LBT-based protocols. The results show significantly higher message delivery ratio values than the ones obtained by all the other works in the literature discussed in this Section.