Jason L. Cook

Two-terminal reliability analyses for a mobile ad hoc wireless network

Reliability is one of the most important performance measures for emerging technologies. For these systems, shortcomings are often overlooked in early releases as the cutting edge technology overshadows a fragile design. Currently, the proliferation of the mobile ad hoc wireless networks (MAWN) is moving from cutting edge to commodity and thus, reliable performance will be expected. Generally, ad hoc networking is applied for the flexibility and mobility it provides. As a result, military and first responders employ this network scheme and the reliability of the network becomes paramount. To ensure reliability is achieved, one must first be able to analyze and calculate the reliability of the MAWN. This work describes the unique attributes of the MAWN and how the classical analysis of network reliability, where the network configuration is known a priori, can be adjusted to model and analyze this type of network. The methods developed acknowledge the dynamic and scalable nature of the MAWN along with its absence of infrastructure. Thus, the methods rely on a modeling approach that considers the probabilistic formation of different network configurations in a MAWN. Hence, this paper proposes reliability analysis methods that consider the effect of node mobility and the continuous changes in the networks connectivity.

Mobility and reliability modeling for a mobile ad hoc network

The mobile ad hoc wireless network (MAWN) promises to become an ever-present technology with application to a myriad of areas. This networking scheme has its roots in DoD technology, yet, the ability to measure and calculate its reliability is largely absent. This paper describes the unique attributes of the MAWN and how the classical methods for analysis of network reliability must be adjusted. The methods developed acknowledge the dynamic and scalable nature of the new networking scheme along with its absence of infrastructure and remove the need to a priori define a network configuration. The methods rely on a novel modeling approach that recognizes the effects of mobility on the formation of the networks configurations. Hence, this paper proposes a Monte Carlo simulation method that accounts for node mobility, node reliability and node performance in the networks connectivity and resultant network reliability.

Reliability analysis of cluster-based ad-hoc networks

The mobile ad-hoc wireless network (MAWN) is a new and emerging network scheme that is being employed in a variety of applications. The MAWN varies from traditional networks because it is a self-forming and dynamic network. The MAWN is free of infrastructure and, as such, only the mobile nodes comprise the network. Pairs of nodes communicate either directly or through other nodes. To do so, each node acts, in turn, as a source, destination, and relay of messages. The virtue of a MAWN is the flexibility this provides; however, the challenge for reliability analyses is also brought about by this unique feature. The variability and volatility of the MAWN configuration makes typical reliability methods (e.g. reliability block diagram) inappropriate because no single structure or configuration represents all manifestations of a MAWN. For this reason, new methods are being developed to analyze the reliability of this new networking technology. New published methods adapt to this feature by treating the configuration probabilistically or by inclusion of embedded mobility models. This paper joins both methods together and expands upon these works by modifying the problem formulation to address the reliability analysis of a cluster-based MAWN. The cluster-based MAWN is deployed in applications with constraints on networking resources such as bandwidth and energy. This paper presents the problems formulation, a discussion of applicable reliability metrics for the MAWN, and illustration of a Monte Carlo simulation method through the analysis of several example networks.

Optimal design of cluster-based ad-hoc networks using probabilistic solution discovery

The reliability of ad-hoc networks is gaining popularity in two areas: as a topic of academic interest and as a key performance parameter for defense systems employing this type of network. The ad-hoc network is dynamic and scalable and these descriptions are what attract its users. However, these descriptions are also synonymous for undefined and unpredictable when considering the impacts to the reliability of the system. The configuration of an ad-hoc network changes continuously and this fact implies that no single mathematical expression or graphical depiction can describe the system reliability-wise. Previous research has used mobility and stochastic models to address this challenge successfully. In this paper, the authors leverage the stochastic approach and build upon it a probabilistic solution discovery (PSD) algorithm to optimize the topology for a cluster-based mobile ad-hoc wireless network (MAWN). Specifically, the membership of nodes within the back-bone network or networks will be assigned in such as way as to maximize reliability subject to a constraint on cost. The constraint may also be considered as a non-monetary cost, such as weight, volume, power, or the like. When a cost is assigned to each component, a maximum cost threshold is assigned to the network, and the method is run; the result is an optimized allocation of the radios enabling back-bone network(s) to provide the most reliable network possible without exceeding the allowable cost. The method is intended for use directly as part of the architectural design process of a cluster-based MAWN to efficiently determine an optimal or near-optimal design solution. It is capable of optimizing the topology based upon all-terminal reliability (ATR), all-operating terminal reliability (AoTR), or two-terminal reliability (2TR).

Recent Research on the Reliability Analysis Methods for Mobile Ad-hoc Networks

The Mobile Ad-hoc Wireless Network (MAWN) is a network schema that does not require the infrastructure items (e.g., cellular towers) of typical networks. The flexibility this offers has led to the proliferation of this network schema. However, this unique attribute of ad-hoc networking also violates the base assumptions on which existing network reliability methods are founded. That is, that the configuration of the network is known a priori. This paper will describe methods being developed to fill the void left by existing techniques. This paper will also describe the utilization of these methods in a systems engineering construct.

System of systems reliability for multi-state systems

The proliferation of networking technologies in commercial, consumer, and industrial applications has been mirrored in the defense industry. The US Department of Defense, along with comparable organizations abroad, have adopted a network centric paradigm for emerging and future systems. This migration to an information based approach is akin to the move to Just-In-Time manufacturing. That is, both approaches seek to achieve synergies from Information rather than from bulk of material. In the JIT case, this material is the component parts or materials, and in the military SoS the material may be armor and/or ammunition. Specifically, the US military is attempting to leverage the synergies of net centricity in order to obtain a more mobile and lighter fighting fleet that retains the same lethality and survivability by shedding armor and ammo in favor of information (radios and computers). In previous years, this author has presented papers on network reliability [1] and multi-state reliability [2] to the RAMS. In this years paper, the notion of multi-state reliability is combined with the ad-hoc network reliability methods. This integrated model provides the ability to measure, in capacity terms the reliability of a SoS level by considering the networks state (connectivity) temporally and the interactions and contributions of its elements. Specifically, this paper describes a mathematical construct for simulating the capacity of general functions including lethality, mobility, survivability, reconnaissance, and supportability based upon traditional probabilistic measures of reliability. Next, the paper will describe a new method to combine those platform capabilities to an aggregate SoS level capability that is dependent on the connectivity between those nodes and the resultant synergies realized due to said connectivity.

Detecting failure precursors in BGA solder joints

A failure precursor is a measurable parameter which provides an indication of impending failure. By detecting changes in these precursors, deviation of the system from its healthy state can be detected early and unanticipated failures can be avoided. The case study illustrates the use of Multivariate State Estimation Technique (MSET) and Sequential Probability Ratio Test (SPRT) to detect the onset of failure in Ball Grid Arrays (BGA) subjected to Accelerated Temperature Cycling (ATC) tests. The residuals from MSET show a shift in their distribution as they degrade; SPRT detects the anomalous behavior (degradation) in the interconnects. The time to detection of anomalies was found to be earlier than the time to failure of the BGA interconnects, providing a prognostic distance. Hence the change in resistance of the BGA can be used as a precursor to failure.

Reliability for cluster-based Ad-hoc Networks

The Mobile Ad-hoc Wireless Network (MAWN) is a new and emerging network scheme that is being employed in a variety of applications. The MAWN varies from traditional networks because it is a self-forming and dynamic network. The MAWN is free of infrastructure and as such only the mobile nodes comprise the network. Nodes communicate either directly or through other nodes. To do so each node acts as source, destination, and relay. The virtue of a MAWN is the flexibility this provides however the challenge for reliability analyses is also brought about by this unique feature. The variability and volatility of the MAWNs configuration makes typical reliability methods (e.g. reliability block diagram) inappropriate because no single structure or configuration represents all manifestations of a MAWN. For this reason, new methods are being developed to analyze the reliability of this new networking technology. New published methods adapt to this feature by treating the configuration probabilistically or by inclusion of mobility models. This paper expands upon these works by modifying the problem formulation to utilize a Monte Carlo simulation technique for the reliability analysis of a cluster-based MAWN. The cluster-based MAWN is deployed in applications with constraints or limits on the networking resources such as bandwidth and energy. This paper presents the problems formulation, a discussion of applicable reliability metrics for the MAWN, and illustration of the method through the analysis of several example networks. Within this paper, a new and innovative use of the general MC simulation approach will be described that allows the practitioner to quickly approximate the reliability of a MAWN and understand the interactions of the characteristics that describe the MAWN; namely node reliability, node mobility, and transport (cluster) layer design. This paper is a follow on from one presented at RAMS 2007.

Multi-state reliability requirements for complex systems

Few complex systems exhibit a binary set of states, that is only simple systems are limited to the basic states of operational and failed. Complex systems and Systems of Systems (SoS) take on multiple degraded states between the fully operational and fully failed extremes. However, reliability requirements often lack the necessary information to adequately allocate multi-state reliability to the sub-systems and components. Specifically, the criticality of functional failures is not defined in the requirements phase but rather, it is done just prior to test. A proposed requirements generation and allocation method is presented to enable more robust requirement sets specific to multi-state systems and SoS which in turn enables more effective and efficient design for reliability practices.

Capacitated Reliability for Ad-hoc Networks

Ad-hoc networking is used because of its malleable topology. The absence of infrastructure allows for the hasty deployment and redeployment of a network. No preparation of the coverage area is needed because things like transmission towers or communication wire lines are not necessary. It is this distinctive attribute of ad-hoc networking that does not conform to the base assumption on which all current network reliability methods are founded; that connectivity is known a priori. The proliferation of ad-hoc networking warrants new network reliability methods that may be applied to analyze them. This paper describes the unique characteristics of ad-hoc networks, presents current research on ad-hoc networks, and presents a new method for approximating the reliability of an ad-hoc network which is capacity constrained