Mobile Network Performance and Technical Feasibility of LTE-Powered Unmanned Aerial Vehicle
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sensors Article Mobile Network Performance and Technical Feasibility of LTE-Powered Unmanned Aerial Vehicle Muhammad Aidiel Zulkifley 1 , Mehran Behjati 1 , Rosdiadee Nordin 1,* and Mohamad Shanudin Zakaria 2 1 Department of Electrical, Electronics and Systems Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, Bangi 43600, Selangor, Malaysia; aidiel.zulkifl[email protected] (M.A.Z.); [email protected] (M.B.) 2 Faculty of Information Science and Technology, Universiti Kebangsaan Malaysia, Bangi 43600, Selangor, Malaysia; [email protected] * Correspondence: [email protected]; Tel.: +60-3-89118402 Abstract: Conventional and license-free radio-controlled drone activities are limited to a line-of-sight (LoS) operational range. One of the alternatives to operate the drones beyond the visual line-of- sight (BVLoS) range is replacing the drone wireless communications system from the conventional industrial, scientific, and medical (ISM) radio band to a licensed cellular-connected system. The Long Term Evolution (LTE) technology that has been established for the terrestrial area allows command- and-control and payload communications between drone and ground station in real-time. However, with increasing height above the ground, the radio environment changes, and utilizing terrestrial cellular networks for drone communications may face new challenges. In this regard, this paper aims to develop an LTE-based control system prototype for low altitude small drones and investigate the feasibility and performance of drone cellular connectivity at different altitudes with measuring parameters such as latency, handover, and signal strength. The measurement results have shown that Citation: Zulkifley, M.A.; Behjati, M.; by increasing flight height from ground to 170 m the received signal power and the signal quality Nordin, R.; Zakaria, M.S. Mobile Network Performance and Technical levels were reduced by 20 dBm and 10 dB respectively, the downlink data rate decreased to 70%, and Feasibility of LTE-Powered latency increased up to 94 ms. It is concluded that although the existing LTE network can provide Unmanned Aerial Vehicle. Sensors a minimum requirement for drone cellular connectivity, further improvements are still needed to 2021, 21, 2848. https://doi.org/ enhance aerial coverage, eliminate interference, and reduce network latency. 10.3390/s21082848 Keywords: UAV; drone; BVLoS; wireless; cellular; 4G; LTE Academic Editor: Carlos Tavares Calafate Received: 15 February 2021 1. Introduction Accepted: 27 March 2021 Unmanned aerial vehicles (UAVs), also known as drones, are becoming increasingly Published: 18 April 2021 used in a wide variety of cases such as inspection, surveillance, package delivery, medical delivery, and agriculture [1–8]. To ensure safe operation, drones need a secure and stable Publisher’s Note: MDPI stays neutral wireless connectivity for control and command (CC) and payload communications [9]. with regard to jurisdictional claims in Conventionally, drones operate on the licensed-free industrial, scientific, and medical published maps and institutional affil- iations. (ISM) radio band (2.4 GHz) which the operational range of drones is limited to the visual line-of-sight (LoS) range [10]. To unleash drones’ potential, a beyond visual line-of-sight (BVLoS) connectivity is required to be established [11]. The cellular network has recently been considered one of the main enablers for devel- oping advanced drone use cases [12]. Cellular networks can provide wide-area, quality of Copyright: © 2021 by the authors. service (QoS), high data rate, low latency, and reliable connectivity for both terrestrial [13] Licensee MDPI, Basel, Switzerland. and drone user equipments (UEs) [14]. In addition, utilizing the existing terrestrial cellular This article is an open access article networks for drone connectivity can facilitate the drone ecosystem’s growth, without the distributed under the terms and conditions of the Creative Commons need to develop a new dedicated infrastructure for drone wireless communications [15]. Attribution (CC BY) license (https:// However, using existing cellular networks to provide connectivity to the flying drone creativecommons.org/licenses/by/ seems challenging. With an increasing height above the ground the radio environment 4.0/). Sensors 2021, 21, 2848. https://doi.org/10.3390/s21082848 https://www.mdpi.com/journal/sensors Sensors 2021, 21, x FOR PEER REVIEW 2 of 25 Sensors 2021, 21, 2848 2 of 24 and severe interference between drone UEs and terrestrial UEs [15]. changes [15], and some problems arise, such as mobility management [16] and severe Figure 1 illustrates a scenario when a low altitude small drone flies above the ter- interference between drone UEs and terrestrial UEs [15]. restrial base stations (BSs).Figure Due1 illustrates to the high a scenario probability when a low of line altitude-of- smallsight drone(LoS) flies link above in higher the terres- altitudes, drone communicationstrial base stations (BSs).suffer Due from to the both high uplink probability and of line-of-sightdownlink (LoS)interferences link in higher [17]. Moreover, terrestrialaltitudes, dronenetwork communications planning sufferis optimized from both for uplink ground and downlink UEs, and interferences BS an- [17]. tennas are tilted downwardsMoreover, terrestrial to prevent network inter planning-cell interference is optimized forand ground provide UEs, andservice BS antennas for are tilted downwards to prevent inter-cell interference and provide service for ground ground UEs via antennas’UEs via antennas’ main lobes main [18]. lobes Meanw [18]. Meanwhile,hile, drones drones that that fly fly above above the the BSs BSs are are served served by the antennas’by the antennas’ sidelobes, sidelobes, which which cause cause severe severe challenges challenges forfor interference interference and and mobility mobility managementmanagement [11]. [11]. FigureFigure 1.1.Illustration Illustration of wide-area of wide wireless-area wireless connectivity connectivity for a low-altitude for a drone low with-altitude terrestrial drone cellular with networks. terrestrial cellular networks. To better understand the Long Term Evolution (LTE) network’s capability to provide wireless connectivity for low altitude small drones, the 3rd Generation Partnership Project To better understand(3GPP) conducted the Long research Term onEvolution enhanced (LTE) LTE supportnetwork for aerial’s capability vehicles [to19]. provide The primary wireless connectivitypurpose for low of that altitude study wassmall to evaluatedrones, drone the 3rd UEs’ Generation mobility performance, Partnership including Pro- the ject (3GPP) conductedhandover research (HO) procedure on enhanced and cell LTE selection. support In addition, for aerial recently vehicles theoretical [19]. research The has primary purpose ofbeen that conducted study onwas topics to suchevaluate as autonomous drone navigationUEs’ mobility [20], joint performance, trajectory and commu-in- nication design [21], energy efficiency and trajectory optimization [22,23], hybrid-duplex cluding the handoverUAV (HO) with join procedure detection [and24], 3D cell coverage selection. analysis In [addition25], and spectrum, recently sharing theoretical [26]. Among research has been theseconducted research on topics, topics channel such measurement as autonomous and modeling navigation have drawn[20], joint academic trajec- interest tory and communicationbecause of design the behavior [21], changes energy of radio efficiency channels atand high trajectory altitude and optimization their importance in [22,23], hybrid-duplexdesigning UAV reliable with communication join detection links [24], for the 3D drones’ coverage safety controlanalysis and [25], operations. and The works described in [14,15,17,27] studied the radio environment changes with spectrum sharing [26]. Among these research topics, channel measurement and modeling altitude and mobility performance of cellular-connected drones based on simulation results. have drawn academicThese interest works investigated because of drone the connectivitybehavior changes by considering of radio parameters channels such at as high signal to altitude and their importanceinterference plus in noisedesigning ratio (SINR), reliable reference communication signal received powerlinks (forRSRP the), anddrones HO under’ safety control and differentoperations. drone speeds and heights. The results show that by increasing the drone height The works describedthe probability in [14,15,17,27] of LoS communications studied linksthe increases,radio environment which results inchanges higher interference with in neighbor cells compared to terrestrial UEs. Moreover, results show how drones are altitude and mobilityserved performance by sidelobes ofof BSs’ cellular antennas-connected and reveal drones problems based of handover on simulation when drones re- move sults. These worksto investigated the BS antenna drone sidelobe connectivity nulls. However, by these cons worksidering are limitedparameters to simulation such resultsas signal to interferenceand doplus not noise fully reflect ratio the (SINR), challenges reference of real-world signal scenarios. received power (RSRP), and HO under differentThe drone works describedspeeds and in [16 height,28,29]s investigated. The results the performanceshow that ofby drone increasing cellular con- nectivity by performing field measurements. The articles analyzed the performance of the drone height the probability