# A Multi-Gateway Behaviour Study for Traffic-Oriented LoRaWAN Deployment
## 1 Introduction  
Nowadays, the Internet of Things (IoT) has emerged as one of the most revolutionary events of this decade. This novel trend can generally be described as an ecosystem where ubiquitous sensors connect the Internet to the physical world. The IoT can also be defined as a network of physical objects known as \"things\" with varying degrees of sensing, processing, and communication capabilities that enables these objects to collect and exchange data. The contextualization of the different usage modes of connected objects in the smart city leads us to address the need for specific and objective planning for any rigorous deployment. This approach will be decisive for conceptual adjustment purposes and guarantees a better QoS. For an environment with high-traffic demand, the very rigorous regulations of the standard and the known shortcomings of the chirp spread spectrum (CSS) [1] modulation and the Pure ALOHA protocol (P-ALOHA) increase the loss rate packets due to collisions. Hence, finding the best way to respond to these issues while minimizing the infrastructure costs (CAPEX-OPEX) is necessary.  
In the literature, several approaches recommended adding gateways (GWs) as a solution to improve the LoRaWAN QoS indicators, mainly for high-traffic situations. However, such a solution will not work in all cases since many factors need to be considered such as the packet payload size, the number of gateways to be used, the periodicity of sending data, etc. In addition, in dense networks, the degradation of network performance is proportional to the increase in the number of nodes.  
In this paper, we present a study of the factors impacting the LoRaWAN QoS in the case of the usage of multiple gateways. First, we show through simulations the role of configuration in the congestion of a LoRa gateway operating in the industrial, scientific, and medical (ISM) band EU860-870. We also show the payload size effect on the QoS of a LoRaWAN network. For this, we simulate several multi-gateway scenarios by varying the sending packet frequency, the packet payload, the number of gateways, and the number of nodes. Our results clearly show that a one-gateway network comprising a thousand nodes transmitting small-sized messages at a reduced frequency can provide better QoS than a multi-gateway network with a transmission frequency of around one message every minute per node. This first observation motivated us to study multi-gateway behaviour to plan a better traffic-oriented architecture.  
The main goal of this paper is to provide a behaviour study of the multi-gateway usage in LoRaWAN under high-traffic conditions. This study can help us to better understand the parameters that can impact network performance when increasing the number of gateways. In addition, in this study, we answer the following questions: What does adding gateways imply concerning network performance? Under which conditions can we add more gateways without losing performance quality?  
The rest of this paper is organized as follows. In Section 2, we give an overview of LoRaWAN technology fundamentals and highlight the constraints. In Section 3, the related works about using multiple gateways in a LoRaWAN are discussed. In Section 4, we provide and discuss our simulation results. Finally, in Section 5, we conclude this paper with a global overview and give some perspectives.