Energy-Aware Algorithm for Assignment of Relays in LP WAN KRZYSZTOF GROCHLA ∗ , ANNA STRZODA, RAFAŁ MARJASZ, PRZEMYSŁAW GŁOMB, and KAMIL KSIĄŻEK, Institute of Theoretical and Applied Informatics, Polish Academy of Sciences, Poland ZBIGNIEW ŁASKARZEWSKI, AIUT, Poland The Low Power Wide Area Networks allow maintaining connectivity with devices over a distance of a few kilometres. However, due to the presence of obstacles the communication range in an urban environment may be shorter, which creates multiple blind spots or areas with limited coverage. The nodes acting as relays may solve this problem by forwarding the data from other devices with poor connectivity. We propose and investigate a novel algorithm that assigns devices to the relay role while keeping the battery constraints. We deine the algorithm, describe the simulation testbed, and present performance evaluation in several scenarios, including real-life topologies of IoT networks. The proposed relay selection scheme allows increasing the lifetime of the network by selecting the relay taking into account the current battery capacity. Additionally, it outperforms a previously proposed relay selection algorithm for LP WAN, showing an average 4% decrease in transmission time and an order of magnitude lower computation complexity. CCS Concepts: • Networks → Network simulations; Network algorithms; Wireless access points, base stations and infrastructure. Additional Key Words and Phrases: LP WAN, LoRa, LoRaWAN, 2-hop, Relay-Device 1 INTRODUCTION The Low Power Wide Area Network (LPWAN) is a set of novel wireless communication technologies characterized by long-range, low cost, low throughput and low power consumption. The LP WAN technologies, such as LoRa, NB IoT or Sigfox, allow maintaining connectivity with a battery-operated device over a distance of a few kilometres for up to ten years. They are very well suited for telemetry and Smart City applications, where some actuators’ monitoring of measurements or control is needed. The Sigfox and LoRaWAN standards are the two most widely used LP WAN technologies operating in a license-free band (e.g. 868 MHz in European Union, 902-928 MHz in the US). At the same time, the cellular operators deploy the NB IoT and LTE CatM technologies which use the LTE infrastructure and typically operate in licensed bands. LoRa technology is based on chirp spread spectrum (CSS) modulation, a spread spectrum wideband technique that uses modulated linear frequency chirp pulses to encode information. This standard allows for data transmission in radio networks over a few kilometres. The LoRa modulation used together with the LoRa WAN protocol [32] deines the packet format and a star-of-stars topology forms a network in which gateways exchange messages with end devices and forward them to a central network server. ∗ All authors contributed equally to this research. Authors’ addresses: Krzysztof Grochla, kgrochla@iitis.pl; Anna Strzoda, astrzoda@iitis.pl; Rafał Marjasz, rmarjasz@iitis.pl; Przemysław Głomb, pglomb@iitis.pl; Kamil Książek, kksiazek@iitis.pl, Institute of Theoretical and Applied Informatics, Polish Academy of Sciences, Bałtycka 5, Gliwice, Poland, 44-100; Zbigniew Łaskarzewski, AIUT, Wyczółkowskiego 113, Gliwice, Poland, 44-109, Zbigniew.Laskarzewski@aiut.com. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for proit or commercial advantage and that copies bear this notice and the full citation on the irst page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior speciic permission and/or a fee. Request permissions from permissions@acm.org. © 2022 Association for Computing Machinery. 1550-4859/2022/6-ART $15.00 https://doi.org/10.1145/3544561 ACM Trans. Sensor Netw.