Thomas G. Macdonald

Internetworking tactical MANETs

Mobile Ad-Hoc Networks (MANETS) will play a significant role in future tactical military networks. Tactical networks are required to support military operations in areas without access to a fixed network infrastructure. They are also characterized by frequent changes in network topology due to node mobility and intermittent line-of-sight (LOS) connectivity. The self-forming and self-healing nature of MANETs is therefore advantageous in a tactical military network. This is evidenced by programs such as the Joint Tactical Radio System (JTRS) and Warrior Information Network – Tactical (WIN-T), which are developing MANET capable radios and waveforms for future military operations. Most work to date addresses the challenges of networking and scalability within a MANET. The internetworking of MANETs presents a set of challenges which to date have been largely overlooked. The general assumption is that techniques and protocols currently used to interconnect fixed networks in the Internet will work equally well for MANETs. However, protocols like Border Gateway Protocol (BGP), which is widely used to interconnect autonomous networks in the Internet, may not be well suited to address the dynamics of networking between MANETs. There are a number of approaches to managing the challenges associated with internetworking MANETs, e.g. abstracting route information between MANETs, managing and updating connection points, addressing network partitions, etc. Each of these approaches offers a different balance between limiting the exchange of routing information generated by node mobility, and maintaining up-to-date routes to all nodes. The solution space can be divided into routing techniques and mobility management techniques. This paper presents simulation studies which examine the trade-offs between scalability and reachability when interconnecting tactical MANETs.

A methodology for evaluating and planning future airborne networks

Future military airborne networks is composed of a variety of different aircraft, and each of these aircraft may have a number of different communications options available. As the air force migrates to a single cohesive network, rather than a series of disparate links, it is necessary to determine the best manner in which to interconnect all the different platforms and communications links. In this paper a general methodology for determining the capacity of an airborne network is presented. This methodology applies to almost any airborne network, provides insight into the capabilities of such a network, and can act as a tool for communications planning of the network. It is shown how this methodology can be used to analyze a representative scenario.

Analysis of a polarization agile communication system

A phased array system with polarization agility for the purpose of interference rejection is evaluated. Polarization agility is defined as a system which can transmit or receive any given polarization and switch its polarization in near real time. First, the efficiency that is sacrificed to gain polarization agility with a simple interleaved dual subarray (IDS) system is quantified. Second, the interference rejection which is gained with a random-polarization-hopping technique is analyzed. Third, various approaches for processing the received signal are discussed and compared. The combined analysis provides a full picture of the true costs and benefits of employing a simplified communication system with polarization agility.

Connecting Communications Waveforms for Combat Effectiveness

Future networks, and in particular military networks, will connect numerous types of homogeneous networks, where a homogeneous network is one that uses the same communications waveform and algorithms to inter-connect all the users of the network. There are a number of challenges in inter-networking disparate waveforms including interacting with a network that does not behave in the same manner as your home network. Examples of such features are described and quantified in this paper and two architectures for connecting heterogeneous waveforms are considered. The goal of this paper is to describe the impact, interfaces, and options for inter-connecting different waveforms.

Dynamic resource allocation for satellite communications

In large multiuser systems, such as communications satellites, the dynamic allocation of resources enables the system to simultaneously maximize usable throughput and provide acceptable communications quality to all users. In this paper the dynamic allocation problem for satellite communications is discussed. We present a multiple-rate time division multiple access (TDMA) algorithm with the ability to adapt the information transfer rate per time slot as well as time slot allocation among terminals based upon traffic loads or link conditions. Simulation results comparing this algorithm with an algorithm that does not have the ability to alter the information transfer rate algorithm show significant improvement in terms of system throughput and end-to-end delay for the proposed algorithm.

Analysis of slow-frequency-hop satellite communications using ambiguity functions

Factors that designers of future satellite systems must consider include the spacing of channels, the shaping of the transmitted pulse, and the resilience of the system to errors in estimating the timing and frequency of the received signal. In this paper it is demonstrated that each of these concerns can be addressed by using an analysis based on the ambiguity function. The relationship between the system performance and the ambiguity function is derived for a slow-frequency-hop satellite link that employs QPSK modulation. To allow for closer spacing of adjacent channels a window function is applied to each transmitted signal. For a number of different pulse shapes and window functions the amount of adjacent channel interference and intersymbol interference is determined, and the effects of timing errors are demonstrated.

Coding for Slow-Frequency-Hop Transmission: Variations on a Theme of McEliece

An important theme of McEliece’s publications on slow-frequencyhop communications is that Reed-Solomon codes can protect against the effects of frequency-selective fading and partial-band interference, especially if side information is provided to the receiver. Two variations on this theme are described and the potential performance improvements are discussed. A new method is presented that permits the receiver to derive its own side information without requiring the transmitter to send side-information symbols, and Hermitian codes are evaluated as an alternative to Reed-Solomon codes for frequency-hop communications.