The IEEE 802.11a high-speed wireless local area networking (WLAN) protocol does not specify a mechanism for dynamically altering network data rates based on changing link conditions. This thesis first presents a baseline software model of the 802.11a protocol developed using the OPNET simulation tool. The model includes both the medium access control (MAC) and physical (PHY) layers of the standard. Two data rate agility mechanisms are then proposed and analyzed using the model. An infrastructure WLAN implementation of the baseline model is first simulated under standard network conditions to verify its operational characteristics and the results are presented. The model is then used to simulate two data rate agility mechanisms, one based on the link signal- to-noise ratio (SNR) and the other based on the frame loss rate at the transmitting Station. Each technique is simulated using an infrastructure WLAN consisting of a fixed access point and a mobile workstation operating with standard network traffic loads. The results indicate that the link SNR is a better decision criterion for data rate agility than the frame loss rate. The design and methodology of this analysis provides insight into dynamic rate agility mechanisms and the criteria that may be used in developing in future 802.11 a-compliant hardware imlementations.
Published on 05/04/2019
Document details: 187 pages.
DTIC ADA390926: Modeling Data Rate Agility in the IEEE 802.11a Wireless Local Area Networking Protocol
The IEEE 802.11a high-speed wireless local area networking (WLAN) protocol does not specify a mechanism for dynamically altering network data rates based on changing link conditions. This thesis first presents a baseline software model of the 802.11a protocol developed using the OPNET simulation tool. The model includes both the medium access control (MAC) and physical (PHY) layers of the standard. Two data rate agility mechanisms are then proposed and analyzed using the model. An infrastructure WLAN implementation of the baseline model is first simulated under standard network conditions to verify its operational characteristics and the results are presented. The model is then used to simulate two data rate agility mechanisms, one based on the link signal-to-noise ratio (SNR) and the other based on the frame loss rate at the transmitting Station. Each technique is simulated using an infrastructure WLAN consisting of a fixed access point and a mobile workstation operating with standard network traffic loads. The results indicate that the link SNR is a better decision criterion for data rate agility than the frame loss rate. The design and methodology of this analysis provides insight into dynamic rate agility mechanisms and the criteria that may be used in developing in future 802.11 a-compliant hardware imlementations.
Published on 05/02/2018
Document details: 186 pages. 4 downloads.
This article is from Iranian Journal of Pharmaceutical Research : IJPR , volume 12 . Abstract Agility is the fundamental characteristic of a supply chain needed for survival in turbulent markets, where environmental forces create additional uncertainty resulting in higher risk in the supply chain management. In addition, agility helps providing the right product, at the right time to the consumer. The main goal of this research is therefore to promote supplier selection in pharmaceutical industry according to the formative basic factors. Moreover, this paper can configure its supply network to achieve the agile supply chain. The present article analyzes the supply part of supply chain based on SCOR model, used to assess agile supply chains by highlighting their specific characteristics and applicability in providing the active pharmaceutical ingredient (API). This methodology provides an analytical modeling; the model enables potential suppliers to be assessed against the multiple criteria using both quantitative and qualitative measures. In addition, for making priority of critical factors, TOPSIS algorithm has been used as a common technique of MADM model. Finally, several factors such as delivery speed, planning and reorder segmentation, trust development and material quantity adjustment are identified and prioritized as critical factors for being agile in supply of API.
Published on 10/26/2014
Document details: 186 pages. 64 downloads.
Published on 03/09/2013
Document details: 238 pages. 27 downloads.
NASA Technical Reports Server (NTRS) 20100003384: Langley Ground Facilities and Testing in the 21st Century
A strategic approach for retaining and more efficiently operating the essential Langley Ground Testing Facilities in the 21st Century is presented. This effort takes advantage of the previously completed and ongoing studies at the Agency and National levels. This integrated approach takes into consideration the overall decline in test business base within the nation and reduced utilization in each of the Langley facilities with capabilities to test in the subsonic, transonic, supersonic, and hypersonic speed regimes. The strategy accounts for capability needs to meet the Agency programmatic requirements and strategic goals and to execute test activities in the most efficient and flexible facility operating structure. The structure currently being implemented at Langley offers agility to right-size our capability and capacity from a national perspective, to accommodate the dynamic nature of the testing needs, and will address the influence of existing and emerging analytical tools for design. The paradigm for testing in the retained facilities is to efficiently and reliably provide more accurate and high-quality test results at an affordable cost to support design information needs for flight regimes where the computational capability is not adequate and to verify and validate the existing and emerging computational tools. Each of the above goals are planned to be achieved, keeping in mind the increasing small industry customer base engaged in developing unpiloted aerial vehicles and commercial space transportation systems.
Published on 11/06/2016
Document details: 15 pages. 8 downloads.
Ground vehicle mobility advances for the future combat vehicles fleet will be achieved through smaller and lighter systems with improved weapon stabilization, improved ride and agility, and reduced acoustic/IR signatures. The Iguana(trademark), a tracked vehicle concept based on a recently patented suspension and track design, could deploy to hot spots world-wide on peacekeeping and combat missions which require extra flexibility to adapt to diverse terrain, weather and threat conditions. A sophisticated sensor suite integrated with weapon systems will guarantee battlefield dominance and vehicle survivability can be enhanced with revolutionary composite armor. Hybrid electric drive will mainly enhance survivability, fuel economy, stealth, operational capability and acceleration performance. Power electronics developments will speed up the transformation from conventional gas engines to hybrid armored vehicle drive systems. This thesis presents a combat system integration process for an Iguana(trademark) based armored vehicle. It lays out steps to be taken in conceiving and developing the armored vehicle starting from the Mission Need Statement. Scenarios are used to create a context within which to define realistic operational requirements. Functional flow modeling for the interoperable reconnaissance, forward observer and anti-guerrilla version armored vehicles provides the analytical basis for defining subsystem characteristics. A particularly important operational need is for night vision sensors. The U.S. Army Night Vision & Electronic Sensors Directorate's ELIR92 and ACQUIRE computer programs are used to establish feasible Iguana(trademark) thermal night vision device performance requirements.
Published on 04/24/2018
Document details: 120 pages. 9 downloads.
Published on 01/31/2012
Document details: 134 pages. 317 downloads.
DTIC ADA639961: Bat Azimuthal Echolocation Using Interaural Level Differences: Modeling and Implementation by a VLSI-Based Hardware System
Bats have long fascinated both scientists and engineers due to their superb ability to use echolocation to fly with speed and agility through complex natural environments in complete darkness. This dissertation presents a neuromorphic VLSI circuit model of bat azimuthal echolocation. Interaural level differences (ILDs) are the cues for bat azimuthal echolocation and are also the primary cues used by other mammals to localize high frequency sounds. The fact that neurons in bats respond to short echoes by one or two spikes strongly suggests that the conventionally used firing rate is an unlikely code. The operation of first spike latency in ILD computation and transformation is investigated in a network of spiking neurons linking the lateral superior olive (LSO), dorsal nucleus of the lateral lemniscus (DNLL) and inferior colliculus IC. The results of the investigation suggest that spatially distributed first spike latencies can serve as a fast code for azimuth that can be read-out by ascending stages. With the hardware echolocation model that uses spike timing representation, we study how multiple echoes can affect bat echolocation and demonstrate that the response to multiple sounds is not a simple linear addition of the response to single sounds. By developing functional models of the bat echolocation system, we can study the efficient implementation demonstrated by nature. For example, variations among analog VLSI circuit units due to the unavoidable transistor mismatch--traditionally thought of as a hurdle to overcome--have been found beneficial in generating the desired diversity of response that is similar to their neural counterparts. This work advocates the use and design of summating and exponentially decaying synapses.
Published on 11/19/2018
Document details: 203 pages. 1 download.
DTIC ADA367954: Digital C3 Systems on the Modern Battlefield: Tactical Systems With Strategic Implications for Combined Operations
The proliferation of digital technology is having a profound impact on how ground forces are equipped, trained, conduct operations, and most importantly communicate. The combination of sensors, smart munitions and digital communications systems will provide military commanders unmatched information clarity and ability to execute missions with unprecedented speed and agility. Many suggest the process of moving from Industrial Age Forces to Information Age Forces, is actually a Revolution in Military Affairs. The combination of technology and evolving security environment will create new challenges for interoperability, and operating demands on alliances such as NATO. Several of NATO's members are aggressively developing digital command, control and communications (C3) systems. While NATO is currently pursuing initiatives to meet the interoperability requirements for systems interface, the scope of interoperability requirements will likely be beyond the mere passing of digits. The impact of digital C3 systems clearly affects interoperability across training, doctrine, communications and force structure. In order to ensure interoperability as new systems are fielded, NATO must initiate efforts now to ensure combined operations of the future are possible.
Published on 04/24/2018
Document details: 51 pages. 2 downloads.
The V-22 Osprey is the world's first production tiltrotor aircraft. Unlike any aircraft before it, the V-22 successfully blends the vertical flight capabilities of helicopters with the speed, range, altitude, and endurance of fixed-wing transports. This unique combination provides an unprecedented advantage to warfighters, allowing current missions to be executed more effectively, and new missions to be accomplished that were previously unachievable on legacy platforms. Comprehensively tested and in full rate production, the V-22 provides strategic agility, operational reach, and tactical flexibility - all in one survivable, transformational platform. Mission and Description: The V-22 Osprey Program is charged by the Department of Defense (DoD) with developing, testing, evaluating, procuring and fielding a tiltrotor Vertical/Short Takeoff and Landing (V/STOL) aircraft for Joint Service application with the Navy being the lead. The V-22 program is designed to provide an aircraft to meet the amphibious/vertical assault needs of the United States Marine Corps (USMC), the strike rescue needs of the Navy, and the special operations needs of the United States Special Operations Command (USSOCOM). The MV- 22B variant is replacing the CH-46E. The CV-22 variant provides a new capability and will augment the MC-130 in the USAF/USSOCOM inventory for special operations infiltration, exfiltration, and resupply missions.
Published on 09/02/2018
Document details: 38 pages. 46 downloads.