This paper presents a real-time, dynamic system that uses high resolution gimbals and motorized lenses with position encoders on their zoom and focus elements to “recalibrate” the system as needed to track a target. Systems that initially calibrate for a mapping between pixels of a wide field of view (FOV) master camera and the pan-tilt (PT) settings of a steerable narrow FOV slave camera assume that the target is travelling on a plane. As the target travels through the FOV of the master camera, the slave cameras PT settings are then adjusted to keep the target centered within its FOV. In this paper, we describe a system we have developed that allows both cameras to move and extract the 3D coordinates of the target. This is done with only a single initial calibration between pairs of cameras and high-resolution pan-tilt-zoom (PTZ) platforms. Using the information from the PT settings of the PTZ platform as well as the precalibrated settings from a preset zoom lens, the 3D coordinates of the target are extracted and compared to those of a laser range finder and static-dynamic camera pair accuracies.

Sensor networks that use line-of-sight (LOS) laser links can provide spatially efficient and physically secure connectivity. These features are advantageous for low-power communication networks over short distances in environments where LOS is available and where radio-frequency connectivity must be avoided because of interference, low data rates, or security problems. In order for optical wireless (OW) directional networks to provide viable short-range connectivity, the networks must provide signal coverage over an acceptable field of view and operate with efficient media access protocols to minimize random access times for the independent transmitting nodes within the network. In this paper, we present the performance of a directional media access control protocol applied to a uniquely designed OW sensor network. The protocol was implemented using vertical cavity surface-emitting lasers and microcontrollers. The results are discussed with respect to efficiency of operation and optimized performance.

Advancements in the size, weight, power and cost of gigabit per second directional wireless communication networks and technologies are enabling C 4 ISR using a backbone of unmanned autonomous systems (UAS). In this paper, we focus on the control of a set of UASs (topology) that provide mobile base stations for tactical operations. We discuss a comprehensive control architecture based on our on-going research and development, and we provide results of simulation experiments designed to investigate the effectiveness of reconfiguration of topologies that use steerable, high data rate (gigabit per second) directional beams in terms of network performance.

We have been investigating the dynamics of molecular systems as analogies for directional wireless networks. This has provided significant insight into reconfigurations of mobile wireless networks using directional point-to-point links (e. g. free-space optics or radio frequency). In this effort, we conceptualize the network as a giant molecule comprised of atoms that exert forces (attraction and repulsion) that stretch and relax the corresponding links. We monitor second-order variations of a potential energy function to gain an improved understanding of the large dimensionality of the optimized reconfiguration for network topology management. Ultimately, we envision this approach will allow for the prediction of two distinct events: 1) localized link failures and 2) catastrophic network events such as a partition. Our results show the detection of localized link failures and the availability for resource allocation more than one minute ahead of the failure (due to known events such as range and antenna blockage) with > 80% accuracy.

Active systems and raster scans are the most popular methods for achieving the pointing accuracy required to form an optical link. With advances in vision system technology, a potential extension to current methods of alignment is to use cameras to control coarse and/or fine pointing acquisition and tracking to establish covert optical communication links. The narrow beam width of an optical link requires very accurate pointing capabilities that are not achievable by low-resolution cameras. This paper focuses on analyzing the feasibility for a vision system to establish a covert optical link between two terminals.

In this paper, we present new models and algorithms for control and optimization of a class of next generation communication networks: Hierarchical Heterogeneous Wireless Networks (HHWNs), under real-world physical constraints. Two biology-inspired techniques, a Flocking Algorithm (FA) and a Particle Swarm Optimizer (PSO), are investigated in this context. Our model is based on the control framework at the physical layer presented previously by the authors. We first develop a nonconvex mathematical model for HHWNs. Second, we propose a new FA for self-organization and control of the backbone nodes in an HHWN by collecting local information from end users. Third, we employ PSO, a widely used artificial intelligence algorithm, to directly optimize the HHWN by collecting global information from the entire system. A comprehensive evaluation measurement during the optimization process is developed. In addition, the relationship between HHWN and FA and the comparison of FA and PSO are discussed, respectively. Our novel framework is examined in various dynamic scenarios. Experimental results demonstrate that FA and PSO both outperform current algorithms for the self-organization and optimization of HHWNs while showing different characteristics with respect to convergence speed and quality of solutions.

Vertically aligned carbon nanotube (VACNT) arrays have been reported to be the "blackest" material fabricated to date. They also have a thermal conductivity parallel to the VACNT axis that is much larger than their thermal conductivity perpendicular to the axis. Even so, because of their large length-to-radius ratio, they can be assumed to have the same temperature in any cross section that is perpendicular to the tube axis. Consequently, a pulsed-laser irradiated VACNT array is a candidate to produce fast thermal emissions from the face of a VACNT array grown on a high thermal conductivity substrate. This can be represented as a one-dimensional thermal conductivity problem, where the proximal end of the carbon nanotubes (CNTs) jumps in temperature when irradiated with a pulsed laser, and the tubes then cool by thermal conduction down their axis to their distal end on a substrate where the temperature is fixed. We have measured and calculated analytically the time-dependent infrared (IR) emission from a range of VACNT arrays with different tube lengths grown on aluminum-nitride (AlN) and silicon-dioxide-silicon (SiO2/Si) substrates. In a parallel effort to characterize their "blackness," we measured the spectral reflectance and emissivity and single-wavelength bidirectional reflectance distribution functions (BRDFs) of these arrays and found these optical characteristics compare well to ideal blackbody behavior. Shorter CNTs exhibit faster cooling than longer nanotubes, and the effective axial conductivity has been determined by comparison between experimental IR signatures and theoretical modeling of expected temperature distributions. Our key finding is that VACNT arrays can act as very fast on-off blackbody sources, which can be useful in many applications requiring such a source.

Even though advances in wireless technology have yielded lower power consumption, higher data rates, and numerous other improvements, the ability to develop a proactive strategy towards handling degradations and failures in directional wireless networks has evaded the research community. In this paper, we introduce a methodology using an analogy to molecular systems in which a directional wireless network utilizing free space optical (FSO) or RF links is modeled as a molecule whose links can grow/retract similarly to bonds. A normal mode analysis (NMA) is performed to identify link instabilities (degradations and failures) and an N-dimensional potential energy surface (PES) is derived with respect to network and environmental parameters to aide in the detection of when a new topology is available ahead of the topology computation stage. Together, the NMA and PES form a basis for a proactive network methodology aimed at improving performance in directional wireless networks.

Directional wireless networks (DWNs) using free space optical (FSO) and RF transmissions provide wireless backbone support for mobile communications in dynamic environments. The heterogeneous and dynamic nature of such networks challenges their robustness and requires self-organization mechanisms to assure end-to-end broadband connectivity. We have developed a framework to provide prediction and control strategies for assured network operation. We draw an analogy between a set of interconnected communication nodes and a molecule in which the bonds between atoms are representative of the links in the equivalent network. The dynamics of the network, and its optimization, can be analyzed by the methods of molecular dynamics. Links are modeled as bonds described by potential energy functions, such as the Morse potential, and a global description of the stability of the network can be obtained by a normal mode analysis (NMA). Effective “forces” act on nodes, which include the effects of power control, link length, and channel characteristics. A molecular re-arrangement or fragmentation occurs because this reduces the potential energy. In the same way a network can undergo topological reconfiguration, and an adaptive control strategy can be used to release, retain or reconfigure communication links for network performance optimization. Simulation results show the effectiveness of our self-organized control mechanism, where the physical topology reorganizes to maximize the number of source to destination communicating pairs. NMA of a network suffering degradation shows a correlation between anomalous eigenvalue behavior of the Hessian matrix describing the network and the improvement of network performance that can be achieved by topology change.

Free-space optical (FSO) systems are known for providing data rates much higher than RF based systems, however their narrow beams require a method to keep the transceivers precisely aligned. To date, most systems have used a combination of coarse pointing platforms and fast steering mirrors tied to a feedback loop based on received optical power to accomplish this. This method can encounter problems if the alignment of one of the transceivers is disrupted or obstructed. In this paper, we present an approach to mitigating this problem using a low data-rate, omni-directional RF network that disseminates pointing commands to all platforms in the network, thereby if the main FSO channels are disrupted, the network can recover faster than a purely received signal strength (RSS) based approach. Utilizing custommade high precision direct drive servo pan-tilt platforms coupled with position and orientation sensors, we can calculate the appropriate pointing angles for all the transceiver platforms, which are then relayed over the control network. We present theoretical calculations regarding the required performance specifications of the control network and pan-tiltplatforms. Experimental results are then presented for a link where one transceiver is mounted on a coarse vibration platform to simulate disturbances in a real network.

The control of topologies and the management of mobility can enable assured end-to-end connectivity and coverage in next generation mobile wireless networks. Previously we have investigated how analogies from physics and biology aid in control and prediction in backbones in hierarchical heterogeneous wireless networks (HHWNs). In this molecular-inspired approach, we employ molecular-based systems to investigate the prediction of link degradation leading to a self-diagnosing ability within the network in the subsequent evolutions of its (re)configuration or topology. By modeling the network as a set of convex (connected) and non-convex (non-connected) springs the network entity can be thought of as a giant molecule. The analysis of the network evolution will follow molecular dynamics and the contribution of each backbone node's movement can be defined as a consequence (positive or negative) on the overall health of the network and its available connectivity. The preliminary results show promise towards the assessment of link degradation and network evolution as it relates to end-to-end broadband connectivity (topology).

We have been looking at the properties of physical configurations that occur in nature in order to characterize, predict, and control network robustness in dynamic communication networks. Our framework is based on the definition of a potential energy function to characterize robustness in communication networks and the study of first- and second-order variations of the potential energy to provide prediction and control strategies for network-performance optimization. This paper describes novel investigations within this framework that draw from molecular system dynamics. The Morse potential, which governs the energy stored in bonds within molecules, is considered for the characterization of the potential energy of communication links in the presence of physical constraints such as the power available at the transmitters in a network. The inclusion of the Morse potential translates into improved control strategies, where forces on network nodes drive the release, retention, or reconfiguration of communication links based on their role within the network architecture. The performance of the proposed approach is measured in terms of the number of source-to-destination connections that have an end-to-end communications path. Simulation results show the effectiveness of our control mechanism, where the physical topology reorganizes to maximize the number of source-to-destination communicating pairs. The algorithms developed are completely distributed, show constant time complexity and produce optimal solutions from local interactions, thus preserving the system's self-organizing capability.

This paper presents a new model and algorithm for slef-organization and control of a class of next generation communication networks: hierarchical heterogeneous wireless networks (HHWNs), under real world physical constraints. A nature inspired flocking algorithm (FA) is investigated in this context. Our model is based on the control framework at the physical layer presented previously by the authors, where network robustness is characterized in terms of the system's potential energy, and control mechanisms are designed to minimize potential energy for optimized network performance. We first focus on the modeling of HHWNs under real world physical constraints. Second, we propose a new FA for self-organization and control of the backbone nodes in an HHWN by collecting local information from end users. Our algorithm is examined in our built simulation platform that supports various dynamic scenarios. Experimental results demonstrate that FA outperforms current algorithms for the self-organization and optimization of HHWN under real world physical constraints.

Directional wireless networks using FSO and RF transmissions provide wireless backbone support for mobile communications in dynamic environments. The heterogeneous and dynamic nature of such networks challenges their robustness and requires self-organization mechanisms to assure end-to-end broadband connectivity. We developed a framework based on the definition of a potential energy function to characterize robustness in communication networks and the study of first and second order variations of the potential energy to provide prediction and control strategies for network performance optimization. In this paper, we present non-convex molecular potentials such as the Morse Potential, used to describe the potential energy of bonds within molecules, for the characterization of communication links in the presence of physical constraints such as the power available at the network nodes. The inclusion of the Morse Potential translates into adaptive control strategies where forces on network nodes drive the release, retention or reconfiguration of communication links for network performance optimization. Simulation results show the effectiveness of our self-organized control mechanism, where the physical topology reorganizes to maximize the number of source to destination communicating pairs. Molecular Normal Mode Analysis (NMA) techniques for assessing network performance degradation in dynamic networks are also presented. Preliminary results show correlation between peaks in the eigenvalues of the Hessian of the network potential and network degradation.

Free space optical (FSO) sensor networks using direct line of light (LOS) laser links can provide spatially efficient and physically secure connectivity. The data rates can range from bits/s to hundreds of Mb/s with the complete optical transceiver system consuming power in the tens of mW. These features are advantageous for low-power communication networks over short distances in environments where LOS is available, and where radio frequency connectivity must be avoided because of interference or security problems. The range of links in FSO networks is limited by power requirements and angular coverage. In order for FSO directional networks to provide viable short-range connectivity, the networks must provide signal coverage over a wide field of view and operate with efficient media access protocols to minimize random access times for the independent transmitting nodes within the network. In this paper, the system design of a FSO sensor network is presented. The system includes a network of small, low power (mW), integrated systems, or "motes," that transmit data optically to a central " cluster head," which controls the network traffic of all the motes and can relay data to another cluster head in a series of multi-hops to achieve data communication over longer distances. To provide wide field of view signal coverage, each cluster head is equipped with multiple vertical cavity surface emitting lasers oriented in different directions and controlled to diverge at 10 degrees. To implement the proper media access controls, a properly designed master-slave network connecting multiple motes to a cluster head was developed and implemented. The network can handle multiple access from all motes within each cluster head's field of view, as well as set up a directional network backbone between multiple cluster heads, so that signals collected from a mote can be relayed through other cluster heads, until the signal is delivered to its destination. This paper presents the network architecture and optical communication system hardware of our FSO sensor network, and some experimental performance results of our multiple access protocol attempting to resolve channel contention between 10 motes and a cluster head.

Free space optical (FSO) links for indoor sensor networks can provide data rates that can range from bits/s to hundreds of Mb/s. In addition, they offer physical security, and in contrast with omnidirectional RF networks, they avoid interference with other electronic systems. These features are advantageous for communication over short distances in fixed infrastructure sensor networks. In this paper the system architecture for a fixed infrastructure FSO sensor network is presented. The system includes a network of small, low power (mW), sensor systems, or "motes," that transmit data optically to a central "cluster head," which controls the network traffic of all the motes and can aggregate the sensor information. The cluster head is designed with multiple vertical cavity surface emitting lasers oriented in different directions and controlled to diverge at 12º in order to provide signal coverage over a wide field of view. Both the cluster head and motes form a local area network. Our system design focuses on low-power wireless motes that can maintain successful communication over distances up to a few meters without having to use stringent optical alignment techniques, and our network design focuses on controlling mote sleep cycles for energy efficiency. This paper presents the design as well as the experimental link and optical communications performance of a prototype FSO-based sensor network.

Requirements for increasingly complex, scalable, and dynamic wireless networks, which provide assured end-to-end broadband connectivity in a wide range of scenarios, have been emerging. In this context, we have been investigating wireless technologies that provide extremely high data rates through the use of narrow-beam free space optical (FSO) and/or radio-frequency (RF) point-to-point links. The use of directional wireless communications to form flexible backbone networks, which provide broadband connectivity to capacity- limited wireless networks or hosts using omnidirectional transmission, promises to circumvent the scalability limitations of traditional flat wireless networks. We have been investigating backbones of base stations, in which topologies and mobility can be controlled for purposes of assured communications. We refer to these as Directional Mobile Ad Hoc Networks (DMANET). Our work considers the use of topology control to assure robust end-to-end broadband connectivity in heterogeneous and dynamic environments. Topology control is defined as the autonomous network capability to dynamically reconfigure its physical topology. In the case of directional wireless backbone (DWB) networks, the physical topology can be reconfigured through: Autonomous 1) Topology Reconfiguration (ATR): dynamic redirection of point-to-point links using heuristic algorithms for creating new topologies and pointing, acquisition and tracking of links. Topology reconfiguration algorithms, which compute minimum energy configurations by determining optimal link assignments between backbone nodes, are presented. The pointing, acquisition and tracking (PAT) process needed to physically redirect point-to-point links is also addressed. 2) Mobility Control (MC): dynamic reposition and "morphing" of backbone nodes. In this model, communication links define physical interactions between network nodes. Control mechanisms are designed to mimic physical systems' natural reaction to external excitations, which drive the network topology to minimum energy configurations Using both ATR and MC, networks are completely selforganizing. They can autonomously adapt their physical topology to maximize coverage to terminals or hosts while maintaining robust backbone connectivity. In this paper, we present the design, implementation and evaluation of our novel approaches to autonomous reconfiguration and control.

Free space optical (FSO) links for sensor networks can provide data rates that can range from bits/s to hundreds of Mb/s. In addition, FSO links using blue-green lasers or light emitting diodes can provide underwater communication over distances of tens of meters. Compared to acoustic technology, optical communication provides larger bandwidths, faster propagation speeds, and reduced multipath fading effects. These features make FSO an attractive medium for undersea communications, as compared to present day acoustic technology. In this paper the system design, implementation, and evaluation of a prototype FSO sensor network are presented. The system includes a network of small, low power (mW), integrated systems, or “motes,” that transmit data optically to a central “cluster head,” which controls the network traffic of all the motes and can relay data to another cluster head in a series of multi-hops to achieve data communication over longer distances. The devices are designed with multiple narrow-beam transmitters oriented in different directions to provide signal coverage over a wide field of view. This paper presents the system design and media access controls of our prototype FSO-based sensor network that can be tailored to fit underwater sensor networking applications