Stanley L. Adams

A "Near-Optimum" Multiple Path Routing Algorithm for Space-Based SDI Networks

This paper presents an adaptive routing algorithm for a mid-course, space-based SDI architecture. The goals include rapid recovery from both predictable and unpredictable outages as well as load balancing. Robust operation is critical. The routing table update algorithm is distributed, and it produces loop-free routes from periodic topology update information. In addition, multiple routes are found from source to destination nodes. This allows load splitting among these routes to achieve more effective load balancing. A heuristic is used to distribute the load among these routes. The basic algorithm also provides a mechanism to provide path diversity for added survivability. Recovery from failures detected locally occurs immediately through the use of alternate routes and an event-driven failure recovery algorithm. Simulation results are presented to demonstrate the algorithm behavior.

An adaptive link assignment algorithm for dynamically changing topologies

An algorithm is presented responsible for determining the network connectivity by finding schedules for establishing and disconnecting high-bandwidth satellite crosslinks that use directional antennas. The context is for a stressed satellite network. The algorithm is designed to recover from predictable link outages as well as massive failures. To minimize computational time complexity as well as to improve transient response, the authors use some known graph-theoretical algorithms. The algorithm is designed for robustness in stressed environments and handles multiple failures. Experimental results indicate rapid recovery and therefore utility in a dynamic environment.<<ETX>>

Time spreads incurred by multipath reflections from a random surface

The complexity of formalisms that deal with broadband acoustic channel distortions suggests temporary retrenchment to a “zeroth‐order” model that can be easily compared with experimental data. Such a model is provided by the present work, which characterizes—via a ray‐acoustic approach similar to that of J. J. Martin. [J. Acoust. Soc. Am. 47, 1303–1309 (1970)]—distortions of broadband acoustic signals reflecting from a planar surface with random roughness. The essence of the approach is to require that a ray‐path reflect specularly from each surface element. A ray arrives at a receiver if and only if the position and slope of a surface element provides the requisite specular path given the incident beam angle. In this way, the probability of reception of a ray with a given incident angle is tied to the distributions of slope and height at the reflecting surface. Whereas Martin has characterized the reflected beams angle spread, we will assess the arrival‐time spread of a pulse due to pathlength differenc...

Time spread of acoustic signals reflecting from a fixed rough boundary

The time spreading of a spherical‐wave impulse of acoustic power reflecting from a not‐too‐rough fixed boundary (such as an ocean bottom) is computed using a simple geometric‐acoustic model. In that model, a ray reflects specularly from each boundary facet, and arrives at the receiver if and only if the position and slope of the facet provide the requisite specular path. In this way, the probability of reception of a ray from a particular facet is tied to the slope distribution of the reflecting boundary (assuming the depth is constant). A general expression for time spread is derived, and computed time spreads are presented for particular source/receiver geometries. Appreciable time spreads (up to half a second) are shown for benign ocean‐boundary conditions (rms slope ≲tan 15°). Time spreads increase dramatically with rms slope, decrease with increasing range, and increase with increasing depth from source/receiver to the boundary. It is emphasized that, for broadband signals, models must be in three di...

A unified network approach to the control of survivable multimedia communication networks

A major thrust in modern military communication systems is to integrate all of the existing and future propagation media resources in a communication system with the objective of providing more reliable, survivable, enduring communication system performance in a stressed environment. An analysis of the objectives, including survivability, network throughput, and delay, to be achieved by integrating communication resources to create a multimedia network, is presented. Given the objectives of integrating resources, an architecture and a suite of algorithms are described which provide a means to use (integrate) any and all media resources, including external networks, multiple access, point-to-multipoint and multipoint-to-multipoint media. A strategy for providing integrated services over heterogeneous links, including radio links, is described. A type-of-service routing algorithm (and its associated topology update strategy) is described which individually computes routes for circuit-switched traffic and various types of packet-switched traffic.<<ETX>>

A comparison of FDD and TDD/TDMA architectures for airborne backbone network traffic

An important aspect of extending the DOD GIG into the tactical battle-space will be the development of high capacity airborne backbone IP networks. Properly designing and provisioning these networks is critically dependent on the statistical characteristics of the data flows that these networks will encounter. This paper studies the architecture of general backbone networks and airborne backbone networks through discrete event simulation methods. A network composed of FDD (frequency division duplex) links is quantitatively compared to a network composed of TDD (time division duplex) links using several criteria. Performance models for both architectures when carrying conventional and self-similar traffic were developed. The effectiveness of provisioning with open loop control was quantified as well as dynamic bandwidth allocation with closed loop control.

Optimizing Performance On Unreliable, Dynamic Networks

This paper discusses link-assignment and adaptive routing algorithms that have been developed for networks consisting of a large number of mobile nodes having directive links. We focus on the special case where data rates are large (tens of Mbits/sec) and the propagation delay between nodes may be large compared to packet transmission delay. In such circumstances, queue sizes at store-and-forward nodes can become extravagant if retransmissions are required because of lost or damaged packets. The algorithms employ techniques that provide a high probability of successful message delivery on the first transmission attempt in the unreliable network. The link-assignment algorithm builds and maintains a link topology that provides multiple node-disjoint paths between each source and destination. Decisions regarding topology changes are also based on link permanency and ability to carry the anticipated traffic load. The adaptive routing algorithm establishes routing tables for multiple independent paths that are maximally node-disjoint between all sources and destinations. Load splitting techniques are used to achieve better load balancing and also to provide a mechanism for rapid adaptation around failed links. All algorithms are distributed in the sense that each node makes independent decisions. Heuristic optimization techniques are used to reduce computation time to within affordable limits. The routing algorithm also responds well to transients in traffic loading.

A Characterization of Underwater Acoustic Channels for Communication System Design

The underwater acoustic propagation channel fluctuates with respect to both space and time. This paper presents a mathematical characterization of the propagation channel and reviews recent published experimental progagation data. The ocean ambient noise characteristics are also discussed. The underwater acoustic channel exhibits relatively rapid space-time fluctuations which impose serious constraints on the system design and performance. The channel effects on several conventional signalling schemes is calculated and the need for more sophisticated approaches is shown. The existing channel capacity results for fluctuating channels are presented and system performance predictions discussed relative to these results.

Broadband signal processing in communication systems

The broadband characteristics of the underwater acoustic propagation channel determine both the approach to communicating and the performance which can be achieved. This paper presents a detailed broadband characterization of the channel and uses this characterization to describe approaches to communication. Performance bounds are calculated and compared to channel capacity results.

Frequency spreads of broadband signals reflecting from a random surface

Extending previous time‐spread work by the present authors [J. Acoust. Soc. Am. Suppl. I 73, S11 (1983)], the frequency spreading of an acoustic signal reflecting from an ocean bottom (in the presence of source and receiver motion) is computed using a simple geometric‐acoustic model. In that model, a ray reflects specularly from each bottom facet, and arrives at the receiver if and only if the position and slope of the facet provide the requisite specular path. The model provides a connection between the expected power flux into the receiver aperture from a particular facet and the slope distribution of the bottom (assumed constant in depth). For a cw signal, the frequency spread can be computed by histogramming in Q = (f − f0)/f0 the expected relative energy from a grid of bottom facets. (Here, f0 is the frequency emitted at the source, and f is the frequency of the received signal.) The quantity Q depends only on the position of the facet, range, depth, and source and receiver velocities: it does not de...