Timothy X. Brown

Jamming and sensing of encrypted wireless ad hoc networks

This paper considers the problem of an attacker disrupting an encrypted victim wireless ad hoc network through jamming. Jamming is broken down into layers and this paper focuses on jamming at the Transport/Network layer. Jamming at this layer exploits AODV and TCP protocols and is shown to be very effective in simulated and real networks when it can sense victim packet types, but the encryption is assumed to mask the entire header and contents of the packet so that only packet size, timing, and sequence is available to the attacker for sensing. A sensor is developed and tested on live data. The classification is found to be highly reliable for many packet types. The relative roles of size, timing, and sequence are discussed along with the implications for making networks more secure.

Airborne Communication Networks for Small Unmanned Aircraft Systems

This paper explores the role of meshed airborne communication networks in the operational performance of small unmanned aircraft systems. Small unmanned aircraft systems have the potential to create new applications and markets in civil domains, enable many disruptive technologies, and put considerable stress on air traffic control systems. We argue that of the existing networked communication architectures, only meshed ad hoc networking can meet the communication demands for the large number of small aircraft expected to be deployed in future. Experimental results using the heterogeneous unmanned aircraft system are presented to show that meshed airborne communication is feasible, that it extends the operational envelope of small unmanned aircraft at the expense of increased communication variability, and that net-centric operation of multiple cooperating aircraft is possible. Additionally, the ability of airborne networks of small unmanned aircraft to exploit controlled mobility to improve performance is discussed.

Cellular performance bounds via shotgun cellular systems

This paper considers two-dimensional interference-limited cellular radio systems. It introduces the shotgun cellular system that places base stations randomly and assigns channels randomly. Such systems are shown to provide lower bounds to cellular performance that are easy to compute, independent of shadow fading, and apply to a number of design scenarios. Traditional hexagonal systems provide an upper performance bound. The difference between upper and lower bounds is small under operating conditions typical in modern TDMA and CDMA cellular systems. Furthermore, in the strong shadow fading limit, the bounds converge. To give insights into the design of practical systems, several variations are explored including mobile access methods, sectorizing, channel assignments, and placement with deviations. Together these results indicate cellular performance is very robust and little is lost in making rapid minimally planned deployments.

Mobility management for personal communications systems

Using a combination of empirical data and theoretical models, this paper develops a model of user behavior for a personal communications system environment. This model is used to analyze a mobility management strategy that combines automatic updates by the users-either when they make significant moves or when they go extended periods without network interaction; multiple hysteresis in the form of dynamic registration areas and delayed updates; and a focused paging strategy that minimizes the number of pages given a constraint on the time allowed to a page. Over a range of system and user parameters, the total paging and update traffic can be kept below 1 per 2000 user seconds. The impact on the users handset is less than ten brief updates per day. The total traffic is only a factor of three more than the minimum, immobile users case.

Neural networks for switching

The author argues that a strong impetus for using neural networks is that they provide a framework for designing massively parallel machines. He notes that the highly interconnected architecture of switching networks suggests similarities to neural networks. He presents two switching applications in which neural networks can solve the problems efficiently. He shows that a computational advantage can be gained by using nonuniform time delays in the network.<<ETX>>

Potential Cognitive Radio Denial-of-Service Vulnerailities and Protection Countermeasures: A Multi-dimensional Analysis and Assessment

Cognitive radios sense spectrum activity and apply spectrum policies in order to make decisions on when and in what bands they may communicate. These activities go beyond what is done when traditional radios communicate. This paper examines the denial of service vulnerabilities that are opened by these additional activities and explores potential protection remedies that can be applied. An analysis of how vulnerable are victim cognitive radios to potential denial of service attacks is presented along different axis, namely the network architecture employed, the spectrum access technique used and the spectrum awareness model. The goal is to assist cognitive radio designers to incorporate effective security measures now in the early stages of cognitive radio development.

An analysis of unlicensed device operation in licensed broadcast service bands

Recent FCC proceedings have considered the notion of unlicensed device operation in licensed bands. Licensed users are concerned about harmful interference while unlicensed device manufacturers are concerned that harmful interference is an imprecise design concept. This paper addresses three elements to this debate. First, it advocates for an explicit model of harmful interference to be included in unlicensed device rules. Such a model provides explicit bounded protection to the licensed user while providing assurances and performance goals to the unlicensed device manufacturers. Second, it assesses several proposed methods for unlicensed devices to avoid licensed users and develops variants of each that can achieve the necessary accuracy. Third, it presents an analytic model for assessing harmful interference that not only provides quantitative analysis, but, also provides insight into how factors such as directional antennas, power control, and licensed channel avoidance strategies affect the aggregate interference. Further, it suggests that complex factors such as unlicensed device modulation schemes can be captured in a simple measurement. These ideas are applied to the notice of proposed rulemaking on unlicensed operation in the TV broadcast bands

Networking Issues for Small Unmanned Aircraft Systems

This paper explores networking issues that arise as a result of the operational requirements of future applications of small unmanned aircraft systems. Small unmanned aircraft systems have the potential to create new applications and markets in civil domains, enable many disruptive technologies, and put considerable stress on air traffic control systems. The operational requirements lead to networking requirements that are mapped to three different conceptual axes that include network connectivity, data delivery, and service discovery. The location of small UAS networking requirements and limitations along these axes has implications on the networking architectures that should be deployed. The delay-tolerant mobile ad-hoc network architecture offers the best option in terms of flexibility, reliability, robustness, and performance compared to other possibilities. This network architecture also provides the opportunity to exploit controlled mobility to improve performance when the network becomes stressed or fractured.

Adaptive call admission control under quality of service constraints: a reinforcement learning solution

We solve the adaptive call admission control (CAC) problem in multimedia networks via reinforcement learning (RL). The problem requires that network revenue be maximized while simultaneously meeting quality of service (QoS) constraints that forbid entry into certain states and use of certain actions. We show that RL provides a solution to this constrained semi-Markov decision problem and is able to earn significantly higher revenues than alternative heuristics. Unlike other model-based algorithms, RL does not require the explicit state transition models to solve the decision problems. This feature is very important if one considers large integrated service networks supporting a number of different service types, where the number of states is so large that model-based optimization algorithms are infeasible. Both packet-level and call-level QoS constraints are addressed, and both conservative and aggressive approaches to the QoS constraints are considered. Results are demonstrated on a single link and extended to routing on a multilink network.

Neural network design of a banyan network controller

The algorithm for choosing nonblocking sets of data cells from the queues can significantly affect the throughput and queuing behavior. The authors present an algorithm that is shown to have maximum throughput. This algorithm is reduced on a banyan network to a constraint satisfaction problem by using an equivalence approach. To gain the required computational speed, the massive parallelism of neural networks is used. A neural network design using multiple overlapping winner-take-all circuits is defined. This is shown to be stable and to result only in nonblocking sets of data cells. An efficient interface between the neural network and the queue is also defined. The performance of the banyan with a neural network controller is compared to a noninternal-blocking switch with various controllers. The banyan is within a factor of two of the nonblocking switch. >