Robert Nichols

Gain scheduling for H-infinity controllers: a flight control example

A new approach to gain scheduling linear dynamic controllers is illustrated for a pitch-axis autopilot design problem. In this application the linear controllers are designed at distinct operating conditions by H/sup infinity / methods. The gain scheduling procedure uses particular features of both the linear dynamic controllers and the controller configuration to remove so-called hidden coupling terms that can occur in scheduled controllers. Potential performance improvement is demonstrated by comparing simulation results to those for a naive gain scheduled controller that ignores the coupling terms. >

Protocol adaptation in hybrid RF/optical wireless networks

One of the major challenges in network-centric warfare is the ability to connect nodes with very high-capacity links. For example, sensor data dissemination is fundamental to network-centric warfare and yet it may overwhelm many available RF communication links. Free-space optical communications (FSOC) has the potential to meet this emerging military need by offering dramatic increases in bandwidth. This technology is not without significant technical challenges such as acquisition/tracking and mitigating the effects of propagation, so multi-band hybrid capabilities are likely to be needed. This diversity of systems provides a degree of robustness that is required for the assured ability to communicate in military operations. This paper will examine protocols and technical approaches for hybrid RF/optical tactical wireless networks

DTN-based free-space optical and directional RF networks

With the growth in demand for capacity from users in wireless networks and the scarcity of available RF spectrum, directional networks are expected to provide effective solutions. Directional RF antennas offer increased capacity over omni-directional antenna networks and some emerging highly-directional networks like free-space optical communication (FSOC) systems will be an important part of future networking infrastructures. The ability to construct and manage an optical network has challenges such as topology control involving the scheduling of pointing, acquisition and tracking events. In many of these directional systems, especially in FSOC where links may be fragile, this will result in an intermittently-connected network, though of tremendous capacity on a per-link basis. This paper establishes delay (or disruption) tolerant networking (DTN) algorithms for such networks and evaluates these new algorithms with mobility, communications constraints, network traffic loads and quality of service (QoS) provisions.

Blue Force Tracking Network Modeling and Simulation

Blue force tracking (BFT) has become a critical capability for the military. It involves communicating situational awareness (SA) and command & control (C2) information among highly dispersed battlefield units in a dynamic environment BFT was used during operation Iraqi freedom (OIF) for coordinating operations within the joint services and with allies and resulted in reduced causalities due to enhanced SA. The Armys current BFT system is a program of record C2/SA system known as Force XXI Battle Command Brigade and Below (FBCB2). It consists of a terrestrial line-of-sight (LOS) system and a commercial L-band satellite- based beyond-line-of-sight (BLOS) system known as FBCB2-BFT. About 6000 BLOS BFT devices were fielded during OIF. The Army is projecting its worldwide FBCB2-BFT fielding needs to exceed 100,000 devices over the next 5 years. The information exchange requirements per user are also expected to increase. At issue is the ability of the current FBCB2 architecture to support the projected BFT needs. This paper will discuss an Army G-3/G-6 sponsored study to investigate the BFT communications and coverage needs in the 2015 timeframe. It will focus on the network modeling and simulation aspects of the study using OPNET

Advanced communications networking concepts for the National Airspace System

This paper presents terminal-area and en-route communications networking concepts that aim to help meet future aviation requirements. Future aviation applications, combined with increasing air traffic density and aging and antiquated systems, will significantly change the National Airspace System (NAS) and result in a need to develop and adopt new communications technologies. An architectural study for flight information services (FIS) performed by The Johns Hopkins University Applied Physics Laboratory (JHU/APL), which considered both near-term and long-term technologies including terrestrial line-of-sight (LOS) systems, satellite communications (SATCOM) beyond LOS (BLOS) systems, and hybrid architectures which seek to use both types of systems, revealed that there are no existing or envisioned communications solutions that are well-suited for the application in all cases. Furthermore, studies of the terminal area reveal that there is a lack of near-term technologies that can address all requirements. This paper presents a vision of an Internet-like NAS networking architecture, and then presents mobile ad-hoc network (MANET) and wireless local area network (WLAN) concepts that could provide significantly improved networking both in the en-route and terminal areas

Communications network architectures for the army future combat system and objective force

A key element of the USA armys transformation is the future combat system and objective force (FCS/OF). The FCS/OF will operate as a cohesive, mobile, lethal, survivable, and sustainable land combat force capable of rapid deployment and immediate employment upon arrival and able to defeat threats in the 2010-2025 timeframe. This is to be achieved through network-centric operations wherein the force is realized through the network. In this paper we consider three echelons of the objective force, the FCS at the lowest level, above which resides the unit of action and the unit of employment. A communications network architecture study has been conducted to determine how the mobile nodes of the FCS/OF network may be best configured to realize this force. The study has examined a number of potential architectural topologies and the performance that can be expected from each. Trade studies were conducted to assess the relative merit of various technologies to the FCS/OF network on the basis of measures of performance such as capacity, connectivity, coverage, protection, and scalability. The result is a recommended communications architecture that will most readily achieve the goals of the FCS/OF. A flat architecture at the lowest echelons exploits mobile ad hoc networking with directional antennas for terrestrial communications. Range extension is realized through relays of various forms including unmanned aerial vehicle and satellite communications. Unit of action communications are organized into subnetworks with relay to lower and higher echelons, as well as joint and coalition forces. The unit of employment network enables command and control on-the-move and reachback to continental USA and external forces.

Traffic predictions for tactical wideband communications

The joint tactical radio system (JTRS) wideband networking waveform (WNW) will be a fundamental new capability for a variety of tactical users. In future U.S. marine corps (USMC) operations, the WNW will be the backbone network for the tactical users with other waveforms used in the lower tiers. Performance of the WNW will need to be stringent to ensure connectivity with adequate quality of service. A study has been conducted to determine the performance of this system in USMC scenarios. This work has included an assessment of traffic loads on the network and modeling and simulation to determine the performance of the WNW in various USMC scenarios. This paper focuses on the methodology for traffic prediction which is a key need for DoD to conduct rigorous networking engineering.

A fast algorithm for optimal satellite spot beam pointing

An optimal algorithm for pointing a steerable satellite spot beam is described. The optimality criterion considered is maximization of the number of Earth terminals covered. The computation time of the algorithm has been compared with a brute force algorithm through a series of Monte Carlo trials.

Nonlinear Scheduling Approach for H-Infinity/Mu-Synthesis Controllers

A recently-developed technique for gain scheduling is illustrated by application to an autopilot design problem for a pitch-axis model of a highly-maneuverable missle. Using H-Infinity designs at widely-spaced operating conditions, we develop a nonlinear gain-scheduled controller that achieves closed-loop specifications throughout the operating range. Various theoretical issues that arise are discussed in terms of the design example.

Communications capacity analysis for multiple-beam processing satellites

This paper analytically compares the communications capacity of various satellite payload architectures against a fixed quality of service (QoS) metric which is connection blocking probability. The effectiveness of the payload architectures is dependent on the payload switching technique, multiple access scheme, and the number of satellite antenna beams utilized. The payloads considered are an on-board circuit switch and an on-board asynchronous transfer mode (ATM) switch. It is shown that a demand assigned multiple access scheme (DAMA) with an on-board ATM switch provides the best performance in terms of communications payload resource utilization. It is also shown that DAMA with a circuit-switched payload provides efficient performance if the number of satellite beams employed is small. Finally, it is shown that the degree of DAMA resource sharing allowed in the system strongly influences resource utilization performance. The sensitivity of these results to key system parameters is determined and further work in this area is proposed.