Multiple UAVs as relays : multi-hop single link versus multiple dual-hop links

Unmanned aerial vehicles (UAVs) have found many important applications in communications. They can serve as either aerial base stations or mobile relays to improve the quality of services. In this paper, we study the use of multiple UAVs in relaying. Considering two typical uses of multiple UAVs as relays that form either a single multi-hop link or multiple dual-hop links, we first optimize the placement the UAVs by maximizing the end-to-end signal-to-noise ratio for three useful channel models and two common relaying protocols. Based on the optimum placement, the two relaying setups are then compared in terms of outage and bit error rate. Numerical results show that the dual-hop multi-link option better than the multi-hop single link option when the air-to-ground path loss parameters depend on the UAV positions. Otherwise, the dual-hop option is only better when the source-to-destination distance small. Also, decode-and-forward UAVs provide better performances than amplify-and-forward UAVs. The investigation also reveals the effects of important system parameters on the optimum UAV positions and the relaying performances to provide useful design guidelines

Online search for UAV relay placement for free-space optical communication under shadowing

Unmanned aerial vehicle (UAV) relaying is promising to overcome the challenge of signal blockage in free-space optical (FSO) communications for users in dense urban area. Existing works on UAV relay placement are mostly based on simplified line-of-sight (LOS) channel models or probabilistic channel models, and thus fail to capture the actual LOS status of the optical communication link. By contrast, this paper studies three-dimensional (3D) online placement for a UAV to construct relay links to two ground users in deep shadow with LOS guarantees. By analyzing the properties of the UAV relay placement problem, it is found that searching on a plane that approximates the equipotential surface can achieve a good performance and complexity trade-off for a good placement of the UAV relay in 3D. Based on these insights, a two-stage online search algorithm on an equipotential plane (TOSEP) is developed for a special case where the equipotential surface turns out to be an equipotential plane. For the general case, a strategy called gradient projected online search algorithm on an approximated equipotential plane (GOSAEP) is developed, which approximates the equipotential surface with a perpendicular plane using the gradient projection method. Numerical experiments are conducted over a real-world city topology, and it is shown that the GOSAEP achieves over 95% of the performance of the exhaustive 3D search scheme within a 300-m search length

A review of relay network on UAVS for enhanced connectivity

One of the best evolution in technology breakthroughs is the Unmanned Aerial Vehicle (UAV). This aerial system is able to perform the mission in an agile environment and can reach the hard areas to perform the tasks autonomously. UAVs can be used in post-disaster situations to estimate damages, to monitor and to respond to the victims. The Ground Control Station can also provide emergency messages and ad-hoc communication to the Mobile Users of the disaster-stricken community using this network. A wireless network can also extend its communication range using UAV as a relay. Major requirements from such networks are robustness, scalability, energy efficiency and reliability. In general, UAVs are easy to deploy, have Line of Sight options and are flexible in nature. However, their 3D mobility, energy constraints, and deployment environment introduce many challenges. This paper provides a discussion of basic UAV based multi-hop relay network architecture and analyses their benefits, applications, and tradeoffs. Key design considerations and challenges are investigated finding fundamental issues and potential research directions to exploit them. Finally, analytical tools and frameworks for performance optimizations are presented

UAV sebagai Infrastruktur Jaringan Seluler pada Keadaan Darurat

Pertukaran informasi di suatu daerah bencana harus dapat bergerak lebih cepat untuk membantu proses pemulihan pasca bencana sehingga kebutuhan bagi para korban dapat dipenuhi secara efisien. Pada jalur komunikasi seluler terdapat limitasi dikarenakan dapat dipengaruhi dengan kondisi bencana seperti pemadaman listrik hingga kerusakan pada base station akibat bencana. Sehingga dibutuhkan suatu teknologi yang dapat memungkinkan adanya telekomunikasi efektif saat pasca bencana. Pada penelitian ini dirancang dua model arsitektur aerial relay node (ARN) berbasis Unmanned Aerial Vehicle (UAV). ARN digunakan untuk menyediakan jalur komunikasi pada suatu daerah bencana dengan cara meneruskan data yang diterima dari User Equipments (UEs) yang dijangkau dan diteruskan ke macro base station (MBS) terdekat dan sebaliknya. Model pertama menggunakan relay node berjenis amplify-and-forward (AF) dimana menggunakan jaringan generasi ke-4 4G LTE/LTEA pada jaringan fronthaul (ARN-MBS) dan jaringan akses (ARN-UEs). Model tersebut secara umum bekerja sebagai suatu repeater atau amplifier. Sementara untuk model kedua, ARN dengan jenis decode-and-forward (DF) bekerja sebagai seperti suatu mobile hotspot dimana digunakan 4G LTE/LTEA pada jaringan fronthaul dan wifi 802.11n pada jaringan aksesnya. Pada penelitian ini, Desa Sumbermujur dengan area seluas 16 km2 dijadikan sebagai objek penelitian. Terdapat tiga parameter utama yang akan diteliti pada kedua model tersebut yakni ketinggian optimum ARN, jarak maksimum antara ARN dengan MBS, dan yang terakhir adalah jangkauan maksimum dari ARN. Hasil dari penelitian ini didapatkan bahwa ketinggian optimum dari ARN-AF dan ARN-DF berada pada ketinggian maksimum yaitu 150 meter. Selanjutnya untuk jarak maksimum antara ARN-AF dengan MBS adalah sejauh 11 kilometer dan 8,5 kilometer untuk ARN-DF dengan MBS. Dari segi jangkauan, ARN-AF mampu menjangkau 100% objek penelitian yakni Desa Sumbermujur dengan area seluas 16 km2 sementara ARN-DF hanya mampu menjangkau 3,349% area dari Desa Sumbermujur