# Combined Use of LoRaWAN Medium Access Control Protocols for IoT Applications
## 2 Related Work  
LPWANs are capable of connecting a large number of devices distributed in wide areas and, for this reason, represent a promising option to replace or complement traditional cellular and short-range wireless technologies [42; 43; 44]. Among LPWANs, the LoRaWAN standard is emerging thanks to its interesting features that offer wide communication ranges with a low-cost network infrastructure that includes low-power devices.  
LoRaWAN supports single-hop LoRa-based transmissions. Consequently, LoRaWAN cannot, at the same time, achieve a wide coverage range and a relatively high bit rate by setting the LoRa modulation parameters. For this reason, several works propose novel medium access strategies and routing protocols for LoRa-based networks [45; 46; 47; 48; 49]. Among them, the proposals in [48; 49] exploit the Software-Defined Networking (SDN) paradigm to implement priority-based traffic management mechanisms and load balancing algorithms [50; 51; 52; 53].  
Furthermore, LoRaWAN only supports random MAC protocols, and therefore cannot provide real-time flows with bounded delays. For this reason, several works in the literature deal with the proposal and evaluation of alternative MAC protocols to LoRaWAN ones. For example, the works in [54; 55; 56] propose centralized MAC protocols for LoRa-based networks that are capable of supporting real-time communications through a Time Division Multiple Access (TDMA) channel access method.  
The previously described works introduce multiple extensions to the LoRaWAN standard and often build directly on the LoRa physical layer. As a result, they require custom software implementation on LoRaWAN commercial-off-the-shelf (COTS) devices.  
LoRaWAN supports uncoordinated channel access strategies based on Pure ALOHA or LBT AFA. Several state-of-the-art works deal with simple random MAC protocols (similar to standard ones) for LoRaWAN, such as Slotted ALOHA [57; 58] or other protocols based on LBT [59; 60], providing comparisons [61].  
The work in [38] summarizes the restrictions that the ETSI norms impose on some timing parameters and presents a comparative performance evaluation of Pure ALOHA and LBT AFA. The aim of [38] is to compare the packet-loss ratio obtained by each protocol through different simulations on the same network. Conversely, this work investigates the combined use of the two MAC protocols in the same LoRaWAN network, that is, in the simulation, some of the end-devices adopt Pure ALOHA and the others adopt LBT AFA. The aim here is to provide quantitative information on which protocol an end-device shall use to meet the requirements of its traffic flows. Furthermore, differently from the work in [38], here, we evaluate multiple performance metrics, i.e., the packet loss ratio, the packet discard ratio, the end-to-end delay, and the energy consumption ratio per transmission.  
A performance evaluation of a LoRaWAN network in which both protocols, i.e., the Pure ALOHA and LBT, are adopted is addressed in [39; 62]. However, none of them takes into account the limitations imposed by the ETSI norms defined in [40; 41]. On the contrary, this paper addresses a performance assessment of a LoRaWAN network in which both the devices that use ALOHA-based and the devices that use LBT-based MAC protocols work in accordance with the ETSI norms. In particular, this paper discusses the results obtained through simulations in realistic scenarios under different workloads and provides useful information about the performance of the two MAC protocols. In this way, the network designer can choose the MAC protocol that is more suitable to achieve the desired performance.