electronics Article Impact of Inter-Gateway Distance on LoRaWAN Performance Bruno Citoni *, Shuja Ansari , Qammer Hussain Abbasi , Muhammad Ali Imran and Sajjad Hussain   Citation: Citoni, B.; Ansari, S.; Abbasi, Q.H.; Imran, M.A.; Hussain, S. Impact of Inter-Gateway Distance on LoRaWAN Performance. Electronics 2021, 10, 2197. https:// doi.org/10.3390/electronics10182197 Academic Editors: Jorge Navarro Ortiz, Cristina Cervelló-Pastor, Iván Vidal and Jasone Astorga Received: 29 July 2021 Accepted: 6 September 2021 Published: 8 September 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). James Watt School of Engineering, University of Glasgow, Glasgow G12 8QQ, UK; shuja.ansari@glasgow.ac.uk (S.A.); qammer.abbasi@glasgow.ac.uk (Q.H.A.); muhammad.imran@glasgow.ac.uk (M.A.I.); sajjad.hussain@glasgow.ac.uk (S.H.) * Correspondence: b.citoni.1@research.gla.ac.uk Abstract: The large-scale behaviour of LoRaWAN networks has been studied through mathematical analysis and discrete-time simulations to understand their limitations. However, current literature is not always coherent in its assumptions and network setups. This paper proposes a comprehensive analysis of the known causes of packet loss in an uplink-only LoRaWAN network: duty cycle limitations, packet collision, insufficient coverage, and saturation of a receiver’s demodulation paths. Their impact on the overall Quality of Service (QoS) for a two-gateway network is also studied. The analysis is carried out with the discrete-event network simulator NS-3 and is set up to best fit the real behaviour of devices. This approach shows that increasing gateway density is only effective as the gateways are placed at a distance. Moreover, the trade-off between different outage conditions due to the uneven distribution of spreading factors is not always beneficial, diminishing returns as networks grow denser and wider. In particular, networks operating similarly to the one analysed in this paper should specifically avoid SF11 and 12, which decrease the average overall PDR by about 7% at 10% nodes increment across all configurations. The results of this work intend to homogenise behavioural assumptions and setups of future research investigating the capability of LoRaWAN networks and provide insight on the weight of each outage condition in a varying two-gateway network. Keywords: LoRaWAN; low-power wide area network (LPWAN); Internet of Things; discrete-time simulation; stochastic geometry; uplink outage; quality of service; multi-gateway network 1. Introduction The Internet of Things (IoT) is a term that defines electronic systems with sensors and actuators which are connected wirelessly. Such a network requires a way of transfer- ring data between devices which has low power consumption, a high maximum range, and can potentially deal with a very large amount of wirelessly interconnected devices simultaneously [1]. One protocol that has gathered much attention in the past few years is LoRaWAN (Long Range WAN): a low power wide area network protocol (LPWAN) which satisfies the fundamental IoT requirements. The LoRaWAN framework is made up of two layers, the MAC layer and the PHY layer. The MAC layer, the proprietary LoRa (Long Range) technology, uses chirp spread spectrum (CSS) modulation to achieve long range communication. LoRa usually uses the licence-free, region-dependent ISM (Industrial, Scientific, and Medical) frequency bands: 863–870 MHz for Europe and 902–928 MHz for the US [2]. This makes it cheaper but also restricts the maximum achievable data rate because of regulations on available air time per device on those frequencies. This makes LoRa unsuitable for high data rate applications. LoRaWAN networks are typically organised in a star-of-stars topology where end devices (nodes) do not have a direct connection to any single gateway but broadcast to all gateways in range, as shown in Figure 1. Each gateway relays the data it receives from all nodes in range to the network server it is associated with, where identical packets are de-duplicated. No handshake is required between nodes and gateways. This is in direct contrast to Wireless Sensor Networks, which are mostly organised in a mesh topology [1,3]. Electronics 2021, 10, 2197. https://doi.org/10.3390/electronics10182197 https://www.mdpi.com/journal/electronics