# A Multi-Gateway Behaviour Study for Traffic-Oriented LoRaWAN Deployment
## 3 Related Works  
LoRaWAN was designed for long-range and low-speed communication. It naturally displays shortcomings in responding to the challenges of current applications, requiring high data traffic. The shortcomings in this sense have also been confirmed thanks to the latest works [11; 12; 13] using effective simulation tools and considering a more realistic environment of the LoraWAN architecture. In a LoRa network, the selection of the spreading factor is position based. Nodes connect to gateways on the simple criterion of signal strength (RSSI), and spreading factors are allocated to nodes based on their distance from the gateway. LoRaWAN protocol uses the ADR mechanism to correct deficiencies at the low layer (PHY) level. This key mechanism allows terminals to dynamically change the transmission parameters of the latter according to a rate calculated on the average of the last 20 messages received by the receiver to improve the success rate of packets and reduce power consumption. The ADR mechanism has been the subject of increased research. In [14], this mechanism was highlighted as a perspective for adapting the LoRaWAN network to a traffic-oriented urban scenario. [PERSON] et al. [15] demonstrated that the ADR is best suited to a static and stable link environment and struggles in the face of network dynamics. In [13], the authors demonstrated that the ADR mechanism does not allow for obtaining significant results in the presence of congestion, which will affect the reception of the message on the uplink (UL), which is necessary for triggering this mechanism. Proposals for improved protocols of the said mechanism using simple ALOHA have been made in works such as [7] for a single-gateway network and [10] for a multi-gateway network. In [16; 17], the authors highlighted the technical perspectives at the level of the lower MAC/PHY layers and the capacity for self-adaptation of the parameters of the LoraWAN network to improve the QoS. In [18], the authors showed that increasing the number of gateways may be an obstacle given the material and regulatory constraints regarding channel occupation time and simultaneous reception. All these conclusions allow us to appreciate the contribution of the ADR to improving the quality of service of the LoRaWAN network. Although this mechanism claims to re-adapt the configuration of the terminals by modifying the parameters to maintain quality, this is not a practical solution since the development of new simulation tools with scenarios very close to reality and based on coherent mathematical models has made it possible to highlight the shortcomings of such an approach. More precisely, the implementation of the ADR in the NS-3 module has allowed for more realistic analyses of the ability of this mechanism to optimize the network. Thus,it is possible to perform a precise diagnosis and highlight the fundamental limits of the multi-gateway network. In [19], the authors showed that the use of a confirmation message (ACK) is a degrading factor for the channel due to the DC limitation of the gateways. In [6], by implementing the CSMA access method protocol as an improvement at the LoRaWAN level, the authors demonstrated a considerable reduction in the packet collision rate, which led to an improvement in the QoS. However, using this method negatively impacts power consumption for a medium-sized network. In [20], [PERSON] et al. proposed an algorithm and demonstrated that it could achieve targeted performance more than the native ADR. [PERSON] et al. [21] also demonstrated that this mechanism responds poorly to high levels of packet collision, as in the case of dense networks. In [22; 23], the authors mentioned the impact of LoRa packet size on reception success but they assumed that it was harmless to network performance. In [24], the authors argued that the packet transmission time (ToA) is an essential indicator without demonstrating and highlighting its impact on any dense network deployment planning.