Thomas H. Shake

Confidentiality performance of spectral-phase-encoded optical CDMA

Enhanced security has often been cited as an important benefit of optical code-division multiple-access (O-CDMA) signaling but has seldom been analyzed in detail. This paper presents a theoretical analysis of the degree of confidentiality that can be provided by spectral-phase-encoded O-CDMA. Two eavesdropping detector structures are presented that can theoretically break the confidentiality of spectral-phase-encoded signals by detecting the code words in use by a specific user. One of them, an optical beat detector, is quantitatively analyzed to determine the probability of correctly detecting user code words. The confidentiality of user signals is shown to be vulnerable to such a detector if an eavesdropper can isolate a single user signal with a sufficiently high signal-to-noise ratio (SNR). At lower SNRs, combining multiple bits is shown to dramatically increase the probability of an eavesdropper correctly detecting user code words; even for codes long enough to strain implementation capabilities (e.g., 2048 code elements), the probability of correct detection is shown to rise from negligibly low values to virtually 100% by the combining of less than 100 transmitted bits at the eavesdroppers receiver.

Routing and rate control for coded cooperation in a satellite-terrestrial network

We address the problem of high-throughput, delay-constrained communication over a satellite-terrestrial network where terrestrial node mobility leads to intermittent links. Due to the short time-scale of link state durations, standard single-path routing protocols are disadvantaged by the delay incurred in determining that a route is unavailable and then finding a new route. Instead we focus on the approach of sending data over multiple paths simultaneously, and use random linear network coding as a distributed way of sending linearly-independent data on different paths. We present a routing and rate control protocol for coded multipath routing. This protocol specifies the fraction of offered traffic carried on each path, provides a congestion avoidance strategy to limit queueing delays in the network, and adapts quickly to time-varying connectivity. We outline our coded routing and rate-control strategy and also present simulation results from a mobile satellite-terrestrial network.

Rate Control for Network-Coded Multipath Relaying with Time-Varying Connectivity

This paper presents techniques for achieving high throughput in delay-constrained, multihop wireless communication networks with time-varying link connectivity. We develop a rate-controlled, multipath strategy using network coding, and compare its performance with that of multipath flooding and with the performance of traditional single-path strategies. These performance comparisons include both theoretical benchmarks and simulation results from cooperative relay scenarios, which incorporate different sets of link connectivity statistics that are drawn from field tests of mobile satellite communication terminals. The results indicate that with appropriate rate-control, network coding can provide throughput performance comparable to multipath flooding of the network while utilizing bandwidth nearly as efficiently as single-path routing.

A Survey of Tactically Suitable Exterior Gateway Protocols

As more IP-capable tactical MANETs are fielded, the creation of backbone-like structures through dynamic interconnection of tactical networks becomes increasingly feasible. Such interconnections hold the promise of improved connectivity and communications resilience, but also introduce policy complexity and scalability challenges. Diversity in these tactical networks in waveform, mission, security and ownership as well as scaling issues preclude flat network topologies. Exterior gateway protocols (EGPs) are traditionally used to interconnect non-aligned network domains, enabling the implementation of policy controls at network edges and enhancing scalability. This work briefly reviews some of the challenges faced by exterior gateway protocols in tactical MANETs. Existing work on EGPs that may be applicable at the tactical edge is surveyed, and the relative strengths and weaknesses of the few proposed and existing EGPs that may be suitable for use at the tactical edge are discussed.

Topology management algorithms for large-scale aerial high capacity directional networks

The U.S. Department of Defense with the Joint Aerial Layer Network (JALN) concept as well as public companies like Google with their Loon project and Facebook with their solar-powered UAV concept have all invested significant funds to develop and deploy airborne high capacity backbone systems. These systems are intended to augment ground networks in support of disaster relief, to extend Internet access to infrastructure-less areas, and to support other similar missions. They can be used to replace existing satellite backbones which typically offer low capacity and high latency connections. One of the key challenges to building an airborne backbone network is large-scale topology management of directional links in a dynamic environment. In this paper, we present several topology management algorithms for large scale airborne networks and evaluate the performance of these algorithms under various scenarios. In each case, we seek to evaluate link and path availability of each algorithm.

Defining Availability for High-Rate Data Links with Fading

Future wireless military data links are being designed to transmit packet data at rates of hundreds of Mb/s and higher. Link technologies that are liable to signal fading, such as free-space atmospheric optical technology, are also expected to gain in importance over the next decade, especially for very high-rate links. These developments require reevaluation of the traditional criteria used for determining the availability of such communications links. This paper examines some traditional criteria for defining link availability, both in the military and commercial arenas, and analyzes their shortcomings for defining link availability in future systems. New classes of error-rate-based availability definitions are presented, along with analysis showing that their characteristics are particularly suitable for the high-rate, possibly fading, data links of the future.

Quantifying the impact of routing and scheduling on throughput for wireless networks

Current evaluations of DoD tactical networking systems have left the impression of sub-optimal performance without being able to provide either a clear vision of the limits on the performance that could realistically be attained or which layers of the network algorithm are responsible for the suboptimal results. Recent advances in computing the capacity of a large MANET allow us to obtain a practical benchmark for MANET capacity performance evaluation [1]. In this paper, we quantify the impact of commonly used algorithms at the routing and the scheduling layers on the overall network throughput and compare their individual effects on overall network throughput performance. We consider the routing and the scheduling layers separately since practical MANET implementations are likely to use a layered architecture even though the joint routing and scheduling algorithm is known to be optimal. Our data shows that a good scheduling algorithm can provide potentially four times the throughput improvement of a good routing algorithm when inter-user interference conforms to an 802.11 type model.

Maximizing interconnectedness and availability in directional airborne range extension networks

Range extension via the use of small aircraft with highly directional antennas that act as relays is a topic of interest in military network technology development. Antenna elements in such designs typically have limited field-of-view (FoV), potentially making interconnectedness among communication nodes dependent on the geometry of the physical network. This paper examines a generic sectorized pod antenna design and compares the interconnectedness and link availability of these designs in representative range extension network layouts. A heuristic for determining quantitative trade-offs between link availability and node interconnectedness is developed. Results from this heuristic show that both interconnectedness and availability increase with a decreasing number of antenna sectors, and that a marginal azimuthal overlap increases average link availability substantially in two representative scenarios.

Technologies for worldwide military paging: an assessment

US warfighters must often operate in areas of the world where there is no infrastructure that will support the type of paging capability that is ubiquitous in urban areas. The US Army and Air Force have funded research and development concerning how to provide paging support for warfighters anywhere in the world. This work has included analytical studies, hardware development, and demonstrations of more than one type of system. This paper provides a review of the context and mission requirements for worldwide paging, followed by an assessment of the performance of two particular prototype implementations, a direct broadcast satcom (DBS) paging system and an unmanned air vehicle-based system. Other alternatives for supporting paging of mobile warfighters, such as commercial solutions, are also discussed.