**1. Introduction**

Urban growth has been boosted in recent decades due both to economic factors and to political, social, and health trends. However, this growth brings with it problems in such different areas as waste management, mobility, scarcity of natural resources, noise and air pollution, and more.Air pollution, for example, is an environmental problem that can cause several diseases in humans and damage to both the environment and animals, with transportation and industry being the main sources of pollutants in the atmosphere [1].

Smart Cities are emerging as an alternative that can enable applications to deal with several problems associated with urban centers. Smart Cities are urban scenarios using Information, Technology, and Communications (ITC) to improve infrastructure and the quality of citizens' lives. Strongly linked with the concepts of the Internet of Things (IoT) and Wireless Sensor Networks (WSN), Smart Cities provide means to carry out acquisition, transmission, and processing of data to make more effective tools available for facing the challenges of the urban environment [2,3].

A WSN is comprised of several wireless sensor nodes distributed in a large area to perform control and monitoring tasks and to share sensor data with each other in order to solve specific problems [4].

**Citation:** Medeiros, D.d.F.; Souza, C.P.d.; Carvalho, F.B.S.d.; Lopes, W.T.A. Energy-Saving Routing Protocols for Smart Cities. *Energies* **2022**, *15*, 7382. https://doi.org/ 10.3390/en15197382

Academic Editors: Antonio Cano-Ortega, Francisco Sánchez-Sutil and Aurora Gil-de-Castro

Received: 29 July 2022 Accepted: 19 September 2022 Published: 8 October 2022

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**Copyright:** © 2022 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/).

To deploy a WSN, several stages are needed, including the development of sensors, which depends on the application, number of sensors, network topology, communication technology, and routing protocol. It is worth mentioning that the routing protocol is critical in any WSN design and that its performance needs to be evaluated for different scenarios and applications.

Computer simulations are an important design tool for evaluating routing protocols in high-density WSNs, thereby reducing costs and saving time during implementation. Simulations can support the choice of a particular routing protocol and help in evaluating new protocols, mainly in scenarios subjected to unfavorable conditions, such those in which device failure is highly probable.

Another important stage in WSN implementation is the wireless communication technology used by the network. Many of the main wireless communication technologies adopted in IoT and WSN applications are based on Low-Power Wide-Area Networks (LPWAN), 3G/4G/5G cellular networks, or ZigBee. LPWANs have gained importance compared to the others thanks to relevant characteristics such as low power consumption and transmission over long distances. Among LPWAN technologies, LoRa (Long Range) is being widely used worldwide, as it can achieve ranges up to 15 km in urban areas with a very low power consumption [5,6].

In this context, the main objective of this paper is to implement and evaluate the performance of routing protocols for the establishment of LoRa-based WSN applications. To this end, we chose the Cupcarbon network simulator, which was developed specifically for Smart Cities and IoT scenario, to evaluate the performance of different routing protocols in terms of data package delivery rate, average jitter, average end-to-end delay, throughput, and load consumption of battery power. In addition, we propose a novel tool for determining node ranges using the Egli propagation model inside the Cupcarbon simulator. In this paper, we consider the widely used WSN routing protocols Ad Hoc On-Demand Distance Vector (AODV), Dynamic Source Routing (DSR), and Distance Vector Routing (DVR). Additionally, a novel routing protocol based on radio power adjustment (RPA) is proposed as means of energy saving.

The rest of this paper is organized as follows. In Section 2, details about LoRa technology and routing protocols for WSN are presented. The Cupcarbon simulator and the Egli propagation loss model are highlighted within the methodology considered in this work. Simulation results are presented and evaluated in Section 3, then and the conclusions and next steps in the research derived from this paper are discussed in Section 4.
