• A New Simple Model for Underwater Wireless Optical Channels in the Presence of Air Bubbles

      Zedini, Emna; Oubei, Hassan M.; Kammoun, Abla; Hamdi, Mounir; Ooi, Boon S.; Alouini, Mohamed-Slim (IEEE, 2018-01-15)
      A novel statistical model is proposed to characterize turbulence-induced fading in underwater wireless optical channels in the presence of air bubbles for fresh and salty waters, based on experimental data. In this model, the channel irradiance fluctuations are characterized by the mixture Exponential-Gamma distribution. We use the expectation maximization (EM) algorithm to obtain the maximum likelihood parameter estimation of the new model. Interestingly, the proposed model is shown to provide a perfect fit with the measured data under all the channel conditions for both types of water. The major advantage of the new model is that it has a simple mathematical form making it attractive from a performance analysis point of view. Indeed, the application of the Exponential-Gamma model leads to closed-form and analytically tractable expressions for key system performance metrics such as the outage probability and the average bit-error rate.
    • 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 (IEEE, 2018-05-24)
      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.
    • Dynamic Downlink Spectrum Access for D2D-Enabled Heterogeneous Networks

      Radaydeh, Redha Mahmoud Mesleh; Al-Qahtani, Fawaz S.; Celik, Abdulkadir; Alouini, Mohamed-Slim (IEEE, 2018-01-15)
      This paper proposes new approaches for underlay device- to-device (D2D) communication in spectrum-shared het- erogeneous cellular networks. It considers devices that share downlink resources and have an enabled D2D feature to improve coverage. The mode of operation classifies devices according to their experienced base station (BS) coverage, potential to be served by BS, ability of BS to meet their quality of service (QoS), and their downlink resources occupancy. The initiation of D2D cooperation is conditioned on proposed provisional access by an active device, wherein its serving BS attempts to meet its QoS using as low number of spectrum channels as possible, while treating remaining channels for feasible D2D cooperation. Detailed formulations for the mode of operation and a proposed D2D path allocation scheme are presented under perfect and imperfect operation scenarios. The developed results are generally applicable for any performance metric and network model.
    • Supervised cognitive system: A new vision for cognitive engine design in wireless networks

      Alqerm, Ismail; Shihada, Basem (IEEE, 2018-03-19)
      Cognitive radio attracts researchers' attention recently in radio resource management due to its ability to exploit environment awareness in configuring radio system parameters. Cognitive engine (CE) is the structure known for deciding system parameters' adaptation using optimization and machine learning techniques. However, these techniques have strengths and weaknesses depending on the experienced network scenario that make one more appropriate than others. In this paper, we propose a novel design for the cognitive system called supervised cognitive system (SCS), which aims to perform radio parameters adaptation with the most appropriate CE learning technique for the encountered network scenario. To realize SCS, it is required to evaluate the performance of different CEs in different network scenarios and according to certain performance objectives. In addition, the ability to select the most appropriate CE learning technique for adaptation in the current network scenario is also a priority in our design. Therefore, SCS investigates the relationship between learning and performance improvement and it employs online learning to classify scenarios and select the most appropriate CE learning technique. The testbed implementation and evaluation results in terms of goodput, packet error rate, and spectral efficiency show that the proposed SCS achieves more than 50% in performance gain compared to the best standalone CE.
    • Terahertz communication: The opportunities of wireless technology beyond 5G

      Elayan, Hadeel; Amin, Osama; Shubair, Raed M.; Alouini, Mohamed-Slim (IEEE, 2018-05-17)
      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.
    • Joint Load Balancing and Power Allocation for Hybrid VLC/RF Networks

      Obeed, Mohanad; Salhab, Anas M.; Zummo, Salam A.; Alouini, Mohamed-Slim (IEEE, 2018-01-15)
      In this paper, we propose and study a new joint load balancing (LB) and power allocation (PA) scheme for a hybrid visible light communication (VLC) and radio frequency (RF) system consisting of one RF\access point (AP) and multiple VLC\APs. An iterative algorithm is proposed to distribute the users on the APs and distribute the powers of these APs on their users. In PA subproblem, an optimization problem is formulated to allocate the power of each AP to the connected users for the total achievable data rates maximization. It is proved that the PA optimization problem is concave but not easy to tackle. Therefore, we provide a new algorithm to obtain the optimal dual variables after formulating them in terms of each other. Then, the users that are connected to the overloaded APs and receive less data rates start seeking for other APs that offer higher data rates. Users with lower data rates continue re-connecting from AP to other to balance the load only if this travel increases the summation of the achievable data rates and enhances the system fairness. The numerical results demonstrate that the proposed algorithms improve the system capacity and system fairness with fast convergence.
    • 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. (OSA, 2018-05-07)
      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.
    • 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 (OSA, 2018-05-07)
      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.
    • Intra-pulse Cavity Enhanced Measurements of Carbon Monoxide in a Rapid Compression Machine

      Nasir, Ehson Fawad; Farooq, Aamir (OSA, 2018-05-07)
      A laser absorption sensor for carbon monoxide concentration was developed for combustion studies in a rapid compression machine using a pulsed quantum cascade laser near 4.89 μm. Cavity enhancement reduced minimum detection limit down to 2.4 ppm at combustion relevant conditions. Off-axis alignment and rapid intra-pulse down-chirp resulted in effective suppression of cavity noise.
    • Thermally stable and flexible paper photosensors based on 2D BN nanosheets

      Lin, Chun-Ho; Cheng, Bin; Tsai, M. L.; Fu, Hui-chun; Luo, W.; Zhou, L. H.; Jang, S. H.; Hu, L. B.; He, Jr-Hau (IEEE, 2018-01-30)
      The market for printed and flexible electronics, key attributes for internet of things, is estimated to reach $45 billion by 2016 and paper-based electronics shows great potential to meet this increasing demand due to its popularity, flexibility, low cost, mass productivity, disposability, and ease of processing [1]. In the family of flexible electronics, solarblind deep ultraviolet (DUV) photodetectors (PDs) can be widely applied in wearable applications such as military sensing, automatization, short-range communications security and environmental detection [2]. However, conventional flexible devices made of paper and plastic substrates are expected to have thermal issues due to their poor thermal conductivity. For instance, conventional paper has a very low thermal conductivity of 0.03 W/mK as that of plastic is 0.23 W/mK. As a result, it is required to increase the thermal conductivity of the substrates used for flexible electronics. In this work, we present flexible DUV paper PDs consisting of 2D boron nitride nanosheets (BNNSs) and ID nanofibrillated celluloses (NFCs) with good detectivity (up to 8.05 × 10 cm Hz/W), fast recovery time (down to 0.393 s), great thermal stability (146 W/m K, 3-order-of-magnitude larger than conventional flexible substrates), high working temperature (up to 200 °C), excellent flexibility and bending durability (showing repeatable ON/OFF switching during 200-time bending cycles), which opens avenues to the flexible electronics.
    • Model-based fault detection algorithm for photovoltaic system monitoring

      Harrou, Fouzi; Sun, Ying; Saidi, Ahmed (IEEE, 2018-02-12)
      Reliable detection of faults in PV systems plays an important role in improving their reliability, productivity, and safety. This paper addresses the detection of faults in the direct current (DC) side of photovoltaic (PV) systems using a statistical approach. Specifically, a simulation model that mimics the theoretical performances of the inspected PV system is designed. Residuals, which are the difference between the measured and estimated output data, are used as a fault indicator. Indeed, residuals are used as the input for the Multivariate CUmulative SUM (MCUSUM) algorithm to detect potential faults. We evaluated the proposed method by using data from an actual 20 MWp grid-connected PV system located in the province of Adrar, Algeria.
    • Low Load Limit Extension for Gasoline Compression Ignition Using Negative Valve Overlap Strategy

      Vallinayagam, R.; AlRamadan, Abdullah S.; Vedharaj, S; An, Yanzhao; Sim, Jaeheon; Chang, Junseok; Johansson, Bengt (SAE International, 2018-04-03)
      Gasoline compression ignition (GCI) is widely studied for the benefits of simultaneous reduction in nitrogen oxide (NO) and soot emissions without compromising the engine efficiency. Despite this advantage, the operational range for GCI is not widely expanded, as the auto-ignition of fuel at low load condition is difficult. The present study aims to extend the low load operational limit for GCI using negative valve overlap (NVO) strategy. The engine used for the current experimentation is a single cylinder diesel engine that runs at an idle speed of 800 rpm with a compression ratio of 17.3. The engine is operated at homogeneous charge compression ignition (HCCI) and partially premixed combustion (PPC) combustion modes with the corresponding start of injection (SOI) at 180 CAD (aTDC) and 30 CAD (aTDC), respectively. In the presented work, intake air temperature is used as control parameter to maintain combustion stability at idle and low load condition, while the intake air pressure is maintained at 1 bar (ambient). The engine is equipped with variable valve cam phasers that can phase both inlet and exhaust valves from the original timing. For the maximum cam phasing range (56 CAD) at a valve lift of 0.3 mm, the maximum allowable positive valve overlap was 20 CAD. In the present study, the exhaust cam is phased to 26 CAD and 6 CAD and the corresponding NVO is noted to be 10 CAD and 30 CAD, respectively. With exhaust cam phasing adjustment, the exhaust valve is closed early to retain hot residual gases inside the cylinder. As such, the in-cylinder temperature is increased and a reduction in the required intake air temperature to control combustion phasing is possible. For a constant combustion phasing of 3 CAD (aTDC), a minimum load of indicated mean effective pressure (IMEP) = 1 bar is attained for gasoline (RON = 91) at HCCI and PPC modes. The coefficient of variance was observed to below 5% at these idle and low load conditions. At the minimum load point, the intake air temperature required dropped by 20°C and 15°C for NVO = 30 CAD at HCCI and PPC modes, respectively, when compared to NVO = 20 CAD and NVO = 10 CAD. Similarly, for the load range of IMEP = 1 to 3 bar, decrease in temperature requirement is noted for negative valve overlap cases and the translational table in terms of d (Tin)/d (NVO) is attained. However, the low load limit was extended with negative valve overlap at the expense of decreased net indicated thermal efficiency due to heat losses and reduction in gas exchange efficiency. Ultra low soot concentration and NO emission were noted at HCCI condition.
    • Enhanced machine learning scheme for energy efficient resource allocation in 5G heterogeneous cloud radio access networks

      Alqerm, Ismail; Shihada, Basem (IEEE, 2018-02-15)
      Heterogeneous cloud radio access networks (H-CRAN) is a new trend of 5G that aims to leverage the heterogeneous and cloud radio access networks advantages. Low power remote radio heads (RRHs) are exploited to provide high data rates for users with high quality of service requirements (QoS), while high power macro base stations (BSs) are deployed for coverage maintenance and low QoS users support. However, the inter-tier interference between the macro BS and RRHs and energy efficiency are critical challenges that accompany resource allocation in H-CRAN. Therefore, we propose a centralized resource allocation scheme using online learning, which guarantees interference mitigation and maximizes energy efficiency while maintaining QoS requirements for all users. To foster the performance of such scheme with a model-free learning, we consider users' priority in resource blocks (RBs) allocation and compact state representation based learning methodology to enhance the learning process. Simulation results confirm that the proposed resource allocation solution can mitigate interference, increase energy and spectral efficiencies significantly, and maintain users' QoS requirements.
    • On the analysis of human mobility model for content broadcasting in 5G networks

      Lau, Chun Pong; Alabbasi, Abdulrahman; Shihada, Basem (IEEE, 2018-02-15)
      Today's mobile service providers aim at ensuring end-to-end performance guarantees. Hence, ensuring an efficient content delivery to end users is highly required. Currently, transmitting popular contents in modern mobile networks rely on unicast transmission. This result into a huge underutilization of the wireless bandwidth. The urban scale mobility of users is beneficial for mobile networks to allocate radio resources spatially and temporally for broadcasting contents. In this paper, we conduct a comprehensive analysis on a human activity/mobility model and the content broadcasting system in 5G mobile networks. The objective of this work is to describe how human daily activities could improve the content broadcasting efficiency. We achieve the objective by analyzing the transition probabilities of a user traveling over several places according to the change of states of daily human activities. Using a reallife simulation, we demonstrate the relationship between the human mobility and the optimization objective of the content broadcasting system.
    • Energy-Aware Sensor Networks via Sensor Selection and Power Allocation

      Niyazi, Lama B.; Chaaban, Anas; Dahrouj, Hayssam; Al-Naffouri, Tareq Y.; Alouini, Mohamed-Slim (IEEE, 2018-02-12)
      Finite energy reserves and the irreplaceable nature of nodes in battery-driven wireless sensor networks (WSNs) motivate energy-aware network operation. This paper considers energy-efficiency in a WSN by investigating the problem of minimizing the power consumption consisting of both radiated and circuit power of sensor nodes, so as to determine an optimal set of active sensors and corresponding transmit powers. To solve such a mixed discrete and continuous problem, the paper proposes various sensor selection and power allocation algorithms of low complexity. Simulation results show an appreciable improvement in their performance over a system in which no selection strategy is applied, with a slight gap from derived lower bounds. The results further yield insights into the relationship between the number of activated sensors and its effect on total power in different regimes of operation, based on which recommendations are made for which strategies to use in the different regimes.
    • Energy Harvesting in Heterogeneous Networks with Hybrid Powered Communication Systems

      Alsharoa, Ahmad; Celik, Abdulkadir; Kamal, Ahmed E. (IEEE, 2018-02-12)
      In this paper, we investigate an energy efficient and energy harvesting (EH) system model in heterogeneous networks (HetNets) where all base stations (BSS) are equipped to harvest energy from renewable energy sources. We consider a hybrid power supply of green (renewable) and traditional micro-grid, such that traditional micro-grid is not exploited as long as the BSS can meet their power demands from harvested and stored green energy. Therefore, our goal is to minimize the networkwide energy consumption subject to users' certain quality of service and BSS' power consumption constraints. As a result of binary BS sleeping status and user-cell association variables, proposed is formulated as a binary linear programming (BLP) problem. A green communication algorithm based on binary particle swarm optimization is implemented to solve the problem with low complexity time.
    • 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 (OSA, 2018-05-07)
      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.
    • Standardized Gasoline Compression Ignition Fuels Matrix

      Badra, Jihad; Bakor, Radwan; AlRamadan, Abdullah; Almansour, Mohammed; Sim, Jaeheon; Ahmed, Ahfaz; Viollet, Yoann; Chang, Junseok (SAE International, 2018-04-03)
      Direct injection compression ignition engines running on gasoline-like fuels have been considered an attractive alternative to traditional spark ignition and diesel engines. The compression and lean combustion mode eliminates throttle losses yielding higher thermodynamic efficiencies and the better mixing of fuel/air due to the longer ignition delay times of the gasoline-like fuels allows better emission performance such as nitric oxides (NOx) and particulate matter (PM). These gasoline-like fuels which usually have lower octane compared to market gasoline have been identified as a viable option for the gasoline compression ignition (GCI) engine applications due to its lower reactivity and lighter evaporation compared to diesel. The properties, specifications and sources of these GCI fuels are not fully understood yet because this technology is relatively new. In this work, a GCI fuel matrix is being developed based on the significance of certain physical and chemical properties in GCI engine operation. Those properties were chosen to be density, temperature at 90 volume % evaporation (T90) or final boiling point (FBP) and research octane number (RON) and the ranges of these properties were determined from the data reported in literature. These proposed fuels were theoretically formulated, while applying realistic constraints, using species present in real refinery streams. Finally, three-dimensional (3D) engine computational fluid dynamics (CFD) simulations were performed using the proposed GCI fuels and the similarities and differences were highlighted.
    • LightFD: A Lightweight Flow Detection Mechanism for Traffic Grooming in Optical Wireless DCNs

      Al-Ghadhban, Amer; Celik, Abdulkadir; Shihada, Basem; Alouini, Mohamed-Slim (IEEE, 2018-05-05)
      State of the art wireless technologies have recently shown a great potential for enabling re-configurable data center network (DCN) topologies by augmenting the cabling complexity and link inflexibility of traditional wired data centers (DCs). In this paper, we propose an optical traffic grooming (TG) method for mice flows (MFs) and elephant flows (EFs) in wireless DCNs which are interconnected with wavelength division multiplexing (WDM) capable free-space optical (FSO) links. Since handling the bandwidth-hungry EFs along with delay-sensitive MFs over the same network resources have undesirable consequences, proposed TG policy handles MFs and EFs over distinctive network resources. MFs/EFs destined to the same rack are groomed into larger rack-to-rack MF/EF flows over dedicated lightpaths whose routes and capacities are jointly determined in a load balancing manner. Performance evaluations of proposed TG policy show a significant throughput improvement thanks to efficient bandwidth utilization of the WDM-FSO links. As MFs and EFs are needed to be separated, proposed TG requires expeditious flow detection mechanisms which can immediately classify EFs with very high accuracy. Since these cannot be met by existing packet-sampling and port-mirroring based solutions, we propose a fast and lightweight in-network flow detection (LightFD) mechanism with perfect accuracy. LightFD is designed as a module on the Virtual-Switch/Hypervisor, which detects EFs based on acknowledgment sequence number of flow packets. Emulation results show that LightFD can provide up to 500 times faster detection speeds than the sampling-based methods with %100 detection precision. We also demonstrate that the EF detection speed has a considerable impact on achievable EF throughput.
    • Auto-Ignition and Spray Characteristics of n-Heptane and iso-Octane Fuels in Ignition Quality Tester

      Jaasim, Mohammed; Elhagrasy, Ayman; Sarathy, Mani; Chung, Suk-Ho; Im, Hong G. (SAE International, 2018-04-04)
      Numerical simulations were conducted to systematically assess the effects of different spray models on the ignition delay predictions and compared with experimental measurements obtained at the KAUST ignition quality tester (IQT) facility. The influence of physical properties and chemical kinetics over the ignition delay time is also investigated. The IQT experiments provided the pressure traces as the main observables, which are not sufficient to obtain a detailed understanding of physical (breakup, evaporation) and chemical (reactivity) processes associated with auto-ignition. A three-dimensional computational fluid dynamics (CFD) code, CONVERGE™, was used to capture the detailed fluid/spray dynamics and chemical characteristics within the IQT configuration. The Reynolds-averaged Navier-Stokes (RANS) turbulence with multi-zone chemistry sub-models was adopted with a reduced chemical kinetic mechanism for n-heptane and iso-octane. The emphasis was on the assessment of two common spray breakup models, namely the Kelvin-Helmholtz/Rayleigh-Taylor (KH-RT) and linearized instability sheet atomization (LISA) models, in terms of their influence on auto-ignition predictions. Two spray models resulted in different local mixing, and their influence in the prediction of auto-ignition was investigated. The relative importance of physical ignition delay, characterized by spray evaporation and mixing processes, in the overall ignition behavior for the two different fuels were examined. The results provided an improved understanding of the essential contribution of physical and chemical processes that are critical in describing the IQT auto-ignition event at different pressure and temperature conditions, and allowed a systematic way to distinguish between the physical and chemical ignition delay times.