Unmanned aerial vehicles (UAVs) have acquired remarkable popularity, thanks to their variety of applications in numerous domains spanning from surveillance, health to agriculture and smart cities. UAVs are also enabler in wireless communication that has potential features such as ubiquitous and reliable connectivity, fast and easy deployment, adaptive altitude, higher chance of line of sight (LOS) propagation path, higher mobility and flexibility. There are numerous surveys that summarized these advantages for different situations and scenarios. However, none of these surveys discussed the role of UAVs in public safety communications from the energy efficiency perspective. In this paper, we review the existing literature for UAV communication with taking into account the energy consumption criteria, and propose a multi-layered network architecture incorporating UAVs for public safety communication. Future research directions are also discussed. INDEX TERMS UAV, multi-layered architecture, QoS, energy efficiency, public safety communications.

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Aggressive scaling in deep nanometer technology enables chip multiprocessor design facilitated by the communication-centric architecture provided by Network-on-Chip (NoC). At the same time, it brings considerable challenges in reliability because a fault in the network architecture severely impacts the performance of a system. To deal with these reliability challenges, this research proposed NoCGuard, a reconfigurable architecture designed to tolerate multiple permanent faults in each pipeline stage of the generic router. NoCGuard router architecture uses four highly reliable and low-cost fault-tolerant strategies. We exploited resource borrowing and double routing strategy for the routing computation stage, default winner strategy for the virtual channel allocation stage, runtime arbiter selection and default winner strategy for the switch allocation stage and multiple secondary bypass paths strategy for the crossbar stage. Unlike existing reliable router architectures, our architecture features less redundancy, more fault tolerance, and high reliability. Reliability comparison using Mean Time to Failure (MTTF) metric shows 5.53-time improvement in a lifetime and using Silicon Protection Factor (SPF), 22-time improvement, which is better than state-of-the-art reliable router architectures. Synthesis results using 15 nm and 45 nm technology library show that additional circuitry incurs an area overhead of 28.7% and 28% respectively. Latency analysis using synthetic, PARSEC and SPLASH-2 traffic shows minor increase in performance by 3.41%, 12% and 15% respectively while providing high reliability.Electronics 2020, 9, 342 2 of 22 design and has led to the evolution of on-chip interconnection network or network-on-chip (NoC) [3,4]. NoC architecture is a packet-based inter-connected network that separates communication from the computation. As it is different from the shared bus, it facilitates customization in terms of bandwidth, buffers size, and topology. It offers scalability without using long global wires. NoC infrastructure consists of routers and links that are used to deliver packets via layered protocol [5].The continuous improvement in process technology yields higher transistor density [1]. It makes transistors and links more vulnerable to different fault mechanisms [6,7]. A fault in a transistor may lead to erroneous computation. Open/short circuit in links, result in data corruption. Even single fault can paralyze the whole chip. Primarily, faults are classified into permanent and transient categories [8]. Permanent faults are also known as hard faults, apparent in the chip for a lifetime after their occurrence. They permanently affect the functionality of the chip. They are traditionally caused by open/short circuits in links, time-dependent-dielectric-breakdown (TDDB) [9], electro-migration (EM) [10], stress migration, negative-bias-temperature-instability (NBTI) [11], hot carrier injection [12] and thermal cycling [13]. On the other hand, transient faults, also known as soft errors, occur only for on...

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