Recent Submissions

  • Underwater Wireless Optical Communications Systems: from System-Level Demonstrations to Channel Modeling

    Oubei, Hassan M. (2018-06) [Dissertation]
    Advisor: Ooi, Boon S.
    Committee members: Alouini, Mohamed-Slim; Jones, Burton; Ng, Tien Khee; Cheng, Julian
    Approximately, two-thirds of earth's surface is covered by water. There is a growing interest from the military and commercial communities in having, an efficient, secure and high bandwidth underwater wireless communication (UWC) system for tactical underwater applications such as oceanography studies and offshore oil exploration. The existing acoustic and radio frequency (RF) technologies are severely limited in bandwidth because of the strong frequency dependent attenuation of sound in seawater and the high conductivity of seawater at radio frequencies, respectively. Recently, underwater wireless optical communication (UWOC) has been proposed as the best alternative or complementary solution to meet this challenge. Taking advantage of the low absorption window of seawater in blue-green (400-550 nm) regime of the electromagnetic spectrum, UWOC is expected to establish secure, efficient and high data rate communication links over short and moderate distances (< 100 m) for versatile applications such as underwater oil pipe inspection, remotely operated vehicle (ROV) and sensor networks. UWOC uses the latest gallium nitrite (GaN) visible light-emitting diode (LED) and laser diode (LD) transmitters. Although some research on LED lased UWOC is being conducted, both the military and academic 5 research communities are favoring the use of laser beams, which potentially could enhance the available bandwidth by up to three orders of magnitude. However, the underwater wireless channel is optically very challenging and difficult to predict. The propagation of laser beams in seawater is significantly affected by the harsh marine environments and suffers from severe attenuation which is a combined effect of absorption and scattering, optical turbulence, and multipath effects at high transmission rates. These limitations distort the intensity and phase structure of the optical beam leading to a decrease in signal-to-noise ratio (SNR) which ultimately degrades the performance of UWOC links by increasing the probability of error. In this dissertation, we seek to experimentally demonstrate the feasibility of short range (≤ 20 m) UWOC systems over various underwater channel water types using different modulation schemes as well as to model and describe the statistical properties of turbulence-induced fading in underwater wireless optical channels using laser beam intensity fluctuations measurements.
  • Flexible InGaN nanowire membranes for enhanced solar water splitting

    Elafandy, Rami T.; Elafandy, Rami T.; Min, Jung-Wook; Zhao, Chao; Ng, Tien Khee; Ooi, Boon S. (Optics Express, The Optical Society, 2018-05-30) [Article]
    III-Nitride nanowires (NWs) have recently emerged as potential photoelectrodes for efficient solar hydrogen generation. While InGaN NWs epitaxy over silicon is required for high crystalline quality and economic production, it leads to the formation of the notorious silicon nitride insulating interface as well as low electrical conductivity which both impede excess charge carrier dynamics and overall device performance. We tackle this issue by developing, for the first time, a substrate-free InGaN NWs membrane photoanodes, through liftoff and transfer techniques, where excess charge carriers are efficiently extracted from the InGaN NWs through a proper ohmic contact formed with a high electrical conductivity metal stack membrane. As a result, compared to conventional InGaN NWs on silicon, the fabricated free-standing flexible membranes showed a 10-fold increase in the generated photocurrent as well as a 0.8 V cathodic shift in the onset potential. Through electrochemical impedance spectroscopy, accompanied with TEM-based analysis, we further demonstrated the detailed enhancement within excess charge carrier dynamics of the photoanode membranes. This novel configuration in photoelectrodes demonstrates a novel pathway for enhancing the performance of III-nitrides photoelectrodes to accelerate their commercialization for solar water splitting.
  • Hydrothermal synthesis of p-type nanocrystalline NiO nanoplates for high response and low concentration hydrogen gas sensor application

    Nakate, Umesh T.; Lee, Gun Hee; Ahmad, Rafiq; Patil, Pramila; Bhopate, Dhanaji P.; Hahn, Y.B.; Yu, Y.T.; Suh, Eun-kyung (Ceramics International, Elsevier BV, 2018-05-30) [Article]
    High quality nanocrystalline NiO nanoplates were synthesized using surfactant and template free hydrothermal route. The gas sensing properties of NiO nanoplates were investigated. The nanoplates morphology of NiO with average thickness ~20 nm and diameter ~100 nm has been confirmed by FE-SEM and TEM. Crystalline quality of NiO has been studied using HRTEM and SAED techniques. Structural properties and elemental compositions have been analysed by XRD and energy dispersive spectrometer (EDS) respectively. The detailed investigation of structural parameters has been carried out. The optical properties of NiO were analyzed from UV-Visible and photoluminescence spectra. NiO nanoplates have good selectivity towards hydrogen (H2) gas. The lowest H2 response of 3% was observed at 2 ppm, whereas 90% response was noted for 100 ppm at optimized temperature of 200 °C with response time 180 s. The H2 responses as functions of different operating temperature as well as gas concentrations have been studied along with sensor stability. The hydrogen sensing mechanism was also elucidated.
  • Quantified Hole Concentration in AlGaN Nanowires for High-Performance Ultraviolet Emitters

    Zhao, Chao; Ebaid, Mohamed; Zhang, Huafan; Priante, Davide; Janjua, Bilal; Zhang, Daliang; Wei, Nini; Alhamoud, Abdullah; Shakfa, M. Khaled; Ng, Tien Khee; Ooi, Boon S. (Nanoscale, Royal Society of Chemistry (RSC), 2018-05-29) [Article]
    P-type doping in wide bandgap and new classes of ultra-wide bandgap materials has long been a scientific and engineering problem. The challenges arise from the large activation energy of dopants and high densities of dislocations in materials. We report here, a significantly enhanced p-type conduction using high-quality AlGaN nanowires. For the first time, the hole concentration in Mg-doped AlGaN nanowires is quantified. The incorporation of Mg into AlGaN was verified by correlation with photoluminescence and Raman measurements. The open-circuit potential measurements further confirmed the p-type conductivity; while Mott-Schottky experiments measured a hole concentration of 1.3×1019 cm-3. These results from photoelectrochemical measurements allow us to design prototype ultraviolet (UV) light-emitting diodes (LEDs) incorporating the AlGaN quantum-disks-in-nanowire and optimized p-type AlGaN contact layer for UV-transparency. The ~335-nm LEDs exhibited a low turn-on voltage of 5 V with a series resistance of 32 Ω, due to the efficient p-type doping of the AlGaN nanowires. The bias-dependent Raman measurements further revealed the negligible self-heating of devices. This study provides an attractive solution to evaluate electrical properties of AlGaN, which is applicable to other wide bandgap nanostructures. Our results are expected to open doors to new applications for wide and ultra-wide bandgap materials.
  • A volume integral equation solver for quantum-corrected transient analysis of scattering from plasmonic nanostructures

    Sayed, Sadeed Bin; Uysal, Ismail Enes; Bagci, Hakan; Ulku, H. Arda (2018 International Applied Computational Electromagnetics Society Symposium (ACES), IEEE, 2018-05-24) [Conference Paper]
    Quantum tunneling is observed between two nanostructures that are separated by a sub-nanometer gap. Electrons “jumping” from one structure to another create an additional current path. An auxiliary tunnel is introduced between the two structures as a support for this so that a classical electromagnetic solver can account for the effects of quantum tunneling. The dispersive permittivity of the tunnel is represented by a Drude model, whose parameters are obtained from the electron tunneling probability. The transient scattering from the connected nanostructures (i.e., nanostructures plus auxiliary tunnel) is analyzed using a time domain volume integral equation solver. Numerical results demonstrating the effect of quantum tunneling on the scattered fields are provided.
  • Biosensor for the detection of Listeria monocytogenes: emerging trends

    Soni, Dharmendra Kumar; Ahmad, Rafiq; Dubey, Suresh Kumar (Critical Reviews in Microbiology, Informa UK Limited, 2018-05-23) [Article]
    The early detection of Listeria monocytogenes (L. monocytogenes) and understanding the disease burden is of paramount interest. The failure to detect pathogenic bacteria in the food industry may have terrible consequences, and poses deleterious effects on human health. Therefore, integration of methods to detect and trace the route of pathogens along the entire food supply network might facilitate elucidation of the main contamination sources. Recent research interest has been oriented towards the development of rapid and affordable pathogen detection tools/techniques. An innovative and new approach like biosensors has been quite promising in revealing the foodborne pathogens. In spite of the existing knowledge, advanced research is still needed to substantiate the expeditious nature and sensitivity of biosensors for rapid and in situ analysis of foodborne pathogens. This review summarizes recent developments in optical, piezoelectric, cell-based, and electrochemical biosensors for Listeria sp. detection in clinical diagnostics, food analysis, and environmental monitoring, and also lists their drawbacks and advantages.
  • Over-Sampling Codebook-Based Hybrid Minimum Sum-Mean-Square-Error Precoding for Millimeter-Wave 3D-MIMO

    Mao, Jiening; Gao, Zhen; Wu, Yongpeng; Alouini, Mohamed-Slim (IEEE Wireless Communications Letters, Institute of Electrical and Electronics Engineers (IEEE), 2018-05-23) [Article]
    Abstract: Hybrid precoding design is challenging for millimeter-wave (mmWave) massive MIMO. Most prior hybrid precoding schemes are designed to maximize the sum spectral efficiency (SSE), while seldom investigate the bit-error-rate (BER). Therefore, this letter designs an over-sampling codebook (OSC)-based hybrid minimum sum-mean-square-error (min-SMSE) precoding to optimize the BER. Specifically, given the effective baseband channel consisting of the real channel and analog precoding, we first design the digital precoder/combiner based on min-SMSE criterion to optimize the BER. To further reduce the SMSE between the transmit and receive signals, we propose an OSC-based joint analog precoder/combiner (JAPC) design. Simulation results show that the proposed scheme can achieve the better performance than its conventional counterparts.
  • Plasmonic Nanowires for Wide Wavelength Range Molecular Sensing

    Marinaro, Giovanni; Das, Gobind; Giugni, Andrea; Allione, Marco; Torre, Bruno; Candeloro, Patrizio; Kosel, Jürgen; Di Fabrizio, Enzo M. (Materials, MDPI AG, 2018-05-17) [Article]
    In this paper, we propose the use of a standing nanowires array, constituted by plasmonic active gold wires grown on iron disks, and partially immersed in a supporting alumina matrix, for surface-enhanced Raman spectroscopy applications. The galvanic process was used to fabricate nanowires in pores of anodized alumina template, making this device cost-effective. This fabrication method allows for the selection of size, diameter, and spatial arrangement of nanowires. The proposed device, thanks to a detailed design analysis, demonstrates a broadband plasmonic enhancement effect useful for many standard excitation wavelengths in the visible and NIR. The trigonal pores arrangement gives an efficiency weakly dependent on polarization. The devices, tested with 633 and 830 nm laser lines, show a significant Raman enhancement factor, up to around 6 × 10⁴, with respect to the flat gold surface, used as a reference for the measurements of the investigated molecules.
  • Using Mosaicity to Tune Thermal Transport in Polycrystalline AlN Thin Films

    Singh, Shivkant; Shervin, Shahab; Sun, Haiding; Yarali, Milad; Chen, Jie; Lin, Ronghui; Li, Kuang-Hui; Li, Xiaohang; Ryou, Jae-Hyun; Mavrokefalos, Anastassios (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2018-05-17) [Article]
    The effect of controlling the c-axis alignment (mosaicity) to the cross-plane thermal transport in textured polycrystalline aluminum nitride (AlN) thin films is experimentally and theoretically investigated. We show that by controlling the sputtering conditions we are able to deposit AlN thin films with varying c-axis grain tilt (mosaicity) from 10° to 0°. Microstructural characterization shows that the films are nearly identical in thickness and grain size, and the difference in mosaicity alters the grain interface quality. This has a significant effect to thermal transport where a thermal conductivity of 4.22 W/mK vs. 8.09 W/mK are measured for samples with tilt angles of 10° vs. 0° respectively. The modified Callaway model was used to fit the theoretical curves to the experimental results using various phonon scattering mechanisms at the grain interface. It was found that using a non-gray model gives an overview of the phonon scattering at the grain boundaries, whereas treating the grain boundary as an array of dislocation lines with varying angle relative to the heat flow, best describes the mechanism of the thermal transport. Lastly, our results show that controlling the quality of the grain interface provides a tuning knob to control thermal transport in polycrystalline materials.
  • Terahertz communication: The opportunities of wireless technology beyond 5G

    Elayan, Hadeel; Amin, Osama; Shubair, Raed M.; Alouini, Mohamed-Slim (2018 International Conference on Advanced Communication Technologies and Networking (CommNet), IEEE, 2018-05-17) [Conference Paper]
    Over the past years, carrier frequencies used for wireless communications have been increasing to meet bandwidth requirements. The engineering community witnessed the development of wide radio bands such as the millimeter-wave (mmW) frequencies to fulfill the explosive growth of mobile data demand and pave the way towards 5G networks. Other research interests have been steered towards optical wireless communication to allow higher data rates, improve physical security and avoid electromagnetic interference. Nevertheless, a paradigm change in the electromagnetic wireless world has been witnessed with the exploitation of the Terahertz (THz) frequency band (0.1–10 THz). With the dawn of THz technology, which fills the gap between radio and optical frequency ranges, ultimate promise is expected for the next generation of wireless networks. In this paper, the light is shed on a number of opportunities associated with the deployment of the THz wireless links. These opportunities offer a plethora of applications to meet the future communication requirements and satisfy the ever increasing user demand of higher data rates.
  • Contact Resistance Reduction of ZnO Thin Film Transistors (TFTs) with Saw-Shaped Electrode

    Park, Woojin; Shaikh, Sohail F.; Min, Jungwook; Lee, Sang Kyung; Lee, Byoung Hun; Hussain, Muhammad Mustafa (Nanotechnology, IOP Publishing, 2018-05-15) [Article]
    We report a saw-shaped electrode architecture ZnO thin film transistor (TFT) for effectively increase channel width. Such a saw-shaped electrode has ~2 times longer contact line at the contact metal/ZnO channel junction. We experimentally observed an enhancement in the output drive current by 50% and reduction in the contact resistance by over 50%, when compared to a typical shaped electrode ZnO TFT consuming the same chip area. This performance enhancement is attributed to extension of channel width. This technique can contribute to device performance enhancement and especially reduction in the contact resistance which is a serious challenge.
  • Asymptotic Performance Analysis of Two-Way Relaying FSO Networks with Nonzero Boresight Pointing Errors Over Double-Generalized Gamma Fading Channels

    Yang, Liang; Alouini, Mohamed-Slim; Ansari, Imran Shafique (IEEE Transactions on Vehicular Technology, Institute of Electrical and Electronics Engineers (IEEE), 2018-05-07) [Article]
    In this correspondence, an asymptotic performance analysis for two-way relaying free-space optical (FSO) communication systems with nonzero boresight pointing errors over double-generalized gamma fading channels is presented. Assuming amplify-and-forward (AF) relaying, two nodes having the FSO ability can communicate with each other through the optical links. With this setup, an approximate cumulative distribution function (CDF) expression for the overall signal-to-noise ratio (SNR) is presented. With this statistic distribution, we derive the asymptotic analytical results for the outage probability and average bit error rate. Furthermore, we provide the asymptotic average capacity analysis for high SNR by using the momentsbased method.
  • Enhanced performance of 450 nm GaN laser diodes with an optical feedback for high bit-rate visible light communication

    Shamim, Md. Hosne Mobarok; Shemis, Mohamed; Shen, Chao; Oubei, Hassan M.; Ng, Tien Khee; Ooi, Boon S.; Khan, Mohammed Zahed Mustafa (Conference on Lasers and Electro-Optics, OSA, 2018-05-07) [Conference Paper]
    First report on significant performance improvement of 450 nm blue edge-emitting laser in terms of optical linewidth (~6.5 times), modulation bandwidth (~16%) and SMSR (~7.4 times) by employing self-injection locking scheme.
  • X-ray created metamaterials: applications to metal-free structural colors with full chromaticity spectrum and 80 nm spatial resolution

    Bonifazi, Marcella; Mazzone, Valerio; Fratalocchi, Andrea (Conference on Lasers and Electro-Optics, OSA, 2018-05-07) [Conference Paper]
    We created new types of metamaterials by hard X-rays possessing high fluency. We discuss applications in structural colors that show full spectrum of Cyan, Yellow, Magenta, Black (CYMK), realized in transparent dielectrics with 80 nm resolution.
  • Ti/TaN Bilayer for Efficient Injection and Reliable AlGaN Nanowires LEDs

    Priante, Davide; Janjua, Bilal; Prabaswara, Aditya; Subedi, Ram Chandra; Elafandy, Rami T.; Lopatin, Sergei; Anjum, Dalaver H.; Zhao, Chao; Ng, Tien Khee; Ooi, Boon S. (Conference on Lasers and Electro-Optics, OSA, 2018-05-07) [Conference Paper]
    Reliable operation of UV AlGaN-based nanowires-LED at high injection current was realized by incorporating a Ti-pre-orienting/TaN-diffusion-barrier bilayer, thus enhancing external quantum efficiency, and resolving the existing device degradation issue in group-III-nanowires-on-silicon devices.
  • 375-nm ultraviolet-laser based non-line-of-sight underwater optical communication

    Sun, Xiaobin; Cai, Wenqi; Alkhazragi, Omar; Ooi, Ee-Ning; He, Hongsen; Chaaban, Anas; Shen, Chao; Oubei, Hassan M.; Khan, Mohammed Zahed Mustafa; Ng, Tien Khee; Alouini, Mohamed-Slim; Ooi, Boon S. (Optics Express, The Optical Society, 2018-05-04) [Article]
    For circumventing the alignment requirement of line-of-sight (LOS) underwater wireless optical communication (UWOC), we demonstrated a non-line-of-sight (NLOS) UWOC link adequately enhanced using ultraviolet (UV) 375-nm laser. Path loss was chosen as a figure-of-merit for link performance in this investigation, which considers the effects of geometries, water turbidity, and transmission wavelength. The experiments suggest that path loss decreases with smaller azimuth angles, higher water turbidity, and shorter wavelength due in part to enhanced scattering utilizing 375-nm radiation. We highlighted that it is feasible to extend the current findings for long distance NLOS UWOC link in turbid water, such as harbor water.
  • Polarization-induced hole doping in N-polar III-nitride LED grown by metalorganic chemical vapor deposition

    Yan, Long; Zhang, Yuantao; Han, Xu; Deng, Gaoqiang; Li, Pengchong; Yu, Ye; Chen, Liang; Li, Xiaohang; Song, Junfeng (Applied Physics Letters, AIP Publishing, 2018-05-03) [Article]
    Polarization-induced doping has been shown to be effective for wide-bandgap III-nitrides. In this work, we demonstrated a significantly enhanced hole concentration via linearly grading an N-polar AlxGa1-xN (x = 0–0.3) layer grown by metal-organic chemical vapor deposition. The hole concentration increased by ∼17 times compared to that of N-polar p-GaN at 300 K. The fitting results of temperature-dependent hole concentration indicated that the holes in the graded p-AlGaN layer comprised both polarization-induced and thermally activated ones. By optimizing the growth conditions, the hole concentration was further increased to 9.0 × 1017 cm−3 in the graded AlGaN layer. The N-polar blue-violet light-emitting device with the graded p-AlGaN shows stronger electroluminescence than the one with the conventional p-GaN. The study indicates the potential of the polarization doping technique in high-performance N-polar light-emitting devices.
  • Estimation Methods for Infinite-Dimensional Systems Applied to the Hemodynamic Response in the Brain

    Belkhatir, Zehor (2018-05) [Dissertation]
    Advisor: Laleg-Kirati, Taous-Meriem
    Committee members: Shamma, Jeff S.; Alouini, Mohamed-Slim; Magistretti, Pierre J.; Bamieh, Bassam
    Infinite-Dimensional Systems (IDSs) which have been made possible by recent advances in mathematical and computational tools can be used to model complex real phenomena. However, due to physical, economic, or stringent non-invasive constraints on real systems, the underlying characteristics for mathematical models in general (and IDSs in particular) are often missing or subject to uncertainty. Therefore, developing efficient estimation techniques to extract missing pieces of information from available measurements is essential. The human brain is an example of IDSs with severe constraints on information collection from controlled experiments and invasive sensors. Investigating the intriguing modeling potential of the brain is, in fact, the main motivation for this work. Here, we will characterize the hemodynamic behavior of the brain using functional magnetic resonance imaging data. In this regard, we propose efficient estimation methods for two classes of IDSs, namely Partial Differential Equations (PDEs) and Fractional Differential Equations (FDEs). This work is divided into two parts. The first part addresses the joint estimation problem of the state, parameters, and input for a coupled second-order hyperbolic PDE and an infinite-dimensional ordinary differential equation using sampled-in-space measurements. Two estimation techniques are proposed: a Kalman-based algorithm that relies on a reduced finite-dimensional model of the IDS, and an infinite-dimensional adaptive estimator whose convergence proof is based on the Lyapunov approach. We study and discuss the identifiability of the unknown variables for both cases. The second part contributes to the development of estimation methods for FDEs where major challenges arise in estimating fractional differentiation orders and non-smooth pointwise inputs. First, we propose a fractional high-order sliding mode observer to jointly estimate the pseudo-state and input of commensurate FDEs. Second, we propose a modulating function-based algorithm for the joint estimation of the parameters and fractional differentiation orders of non-commensurate FDEs. Sufficient conditions ensuring the local convergence of the proposed algorithm are provided. Subsequently, we extend the latter technique to estimate smooth and non-smooth pointwise inputs. The performance of the proposed estimation techniques is illustrated on a neurovascular-hemodynamic response model. However, the formulations are efficiently generic to be applied to a wide set of additional applications.
  • System on Package (SoP) Millimeter Wave Filters for 5G Applications

    Showail, Jameel (2018-05) [Thesis]
    Advisor: Shamim, Atif
    Committee members: Salama, Khaled N.; Anthopoulos, Thomas D.
    Bandpass filters are an essential component of wireless communication systems that only transmits frequencies corresponding to the communication band and rejects all other frequencies. As the deployment of 5G draws nearer, first deployments are expected in 2020 [1], the need for viable filters at the new frequency bands becomes more imminent. Size and performance are two critical considerations for a filter that will be used in emerging mobile communication applications. The high frequency of 5G communication, 28 GHz as opposed to sub 6 GHz for nearly all previous communication protocols, means that previously utilized lumped component based solutions cannot be implemented since they are ill-suited for mm-wave applications. The focus of this work is the miniaturization of a high-performance filter. The Substrate Integrated Waveguide (SIW) is a high performance and promising structure and Low Temperature Co-Fired Ceramic (LTCC) is a high-performance material that both can operate at higher frequencies than the technologies used for previous telecommunication generations. To miniaturize the structure, a compact folded four-cavity SIW filter is designed, implemented and tested. The feeding structure is integrated into the filter to exploit the System on Package (SoP) attributes of LTCC and further reduce the total area of the filter individually and holistically when looking at the final integrated system. Two unique three dimensional (3D) integrated SoP LTCC two-stage SIW single cavity filters and one unique four-cavity filter all with embedded planar resonators are designed, fabricated and tested. The embedded resonators create a two-stage effect in a single cavity filter. The better single cavity design provides a 15% fractional bandwidth at a center frequency of 28.12 GHz, and with an insertion loss of -0.53 dB. The fabricated four-cavity filter has a 3-dB bandwidth of .98GHz centered at 27.465 GHz, and with an insertion loss of -2.66 dB. The designs presented highlight some of the previously leveraged advantages of SoP designs while also including additions of embedded planar resonators to feed the SIW cavity. The integration of both elements realizes a compact and high-performance filter that is well suited for future mm-wave applications including 5G.
  • Collision Analysis at 60-GHz mmWave Mesh Networks: The Case With Blockage and Shadowing

    Lyu, Kangjia (2018-05) [Thesis]
    Advisor: Alouini, Mohamed-Slim
    Committee members: Rezki, Zouheir; Kammoun, Abla; Shihada, Basem
    This thesis can be viewed as two parts. The first part focuses on performance analysis of millimeter wave (mmWave) communications. We investigate how the interference behaves in the outdoor mesh network operating at 60-GHz when block age and shadowing are present using the probability of collision as a metric, under both the protocol model and the physical model. In contrast with results reported in mmWave mesh networks at 60-GHz that advocates that interference has only a marginal effect, our results show that for a short-range link of 100 m, the collision probability gets considerably larger (beyond 0.1) at the signal-to-interference-plus-noise ratio (SINR) of interest (for example, the reference value is chosen as 15 dB for uncoded quadrature phase shift keying (QPSK)). Compensation or compromise should be made in order to maintain a low probability of collision, either by reducing transmitter node density which is to the detriment of the network connectivity, or by switching to a compact linear antenna array with more at-top elements, which places more stringent requirements in device integration techniques. The second part of this thesis focuses on finding the optimal unmanned aerial vehicle (UAV) deployment in the sense that it can maximize over specific network connectivity. We have introduced a connectivity measure based on the commonly used network connectivity metric, which is refered to as global soft connectivity. This measure can be easily extended to account for different propagation models, such as Rayleigh fading and Nakagami fading. It can also be modified to incorporate the link state probability and beam alignment errors in highly directional networks. As can be shown, under the line-of-sight (LOS) and Rayleigh fading assumptions, the optimization regarding the global soft connectivity can be expressed as a weighted sum of the square of link distances between the nodes within the network, namely the ground-to-ground links, the UAV-to-UAV links and the ground-to-UAV links. This can be shown to be a quadratically constrained quadratic program (QCQP) problem with non-convex constraints. We have also extended our global connectivity to other types of connectivity criteria: network k-section connectivity and k-connectivity. In all the three cases, we have proposed a heuristic and straightforward way of finding the suboptimal UAV locations. The simulation results have shown that all these methods can improve our network connectivity considerably, which can achieve a gain of up to 30% for a five UAV scenario.

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