Daniel D. Deavours

The Mobius modeling tool

Despite the development of many modeling formalisms and model solution methods, most tool implementations support only a single formalism. Furthermore, models expressed in the chosen formalism cannot be combined with models expressed in other formalisms. This monolithic approach both limits the usefulness of such tools to practitioners, and hampers modeling research, since it is difficult to compare new and existing formalisms and solvers. This paper describes the method that a new modeling tool, called Mobius, uses to eliminate these limitations. Mobius provides an infrastructure to support multiple interacting formalisms and solvers, and is extensible in that new formalisms anal solvers can, be added to the tool without changing those already implemented. Mobius provides this capability through the use of an abstract functional interface, which provides a formalism-independent interface to models. This allows models expressed in multiple formalisms to interact with each other, and with multiple solvers.

Evaluation of the State of Passive UHF RFID: An Experimental Approach

In this paper, we identify the state of the technical capability of passive UHF RFID tags and readers using a simple, empirical, experimental approach. This paper does not focus on theoretical capabilities of RFID systems in ideal environments, but rather a pragmatic evaluation of the state of commercially available ISO 18000-6c systems and identifying areas where there are opportunities for improvements in the technology. We examine the free-space read distance of tags by readers, near-metal read distance, near-water read distance, frequency-dependence of read distance in those environments, near-field read distance in those environments, read speeds, and a determination of forward or reverse channel limits.

Möbius: An Extensible Tool for Performance and Dependability Modeling

Mobius is a system-level performance and dependability modeling tool. Mobius makes validation of large dependability models possible by supporting many different model solution methods as well as model specification in multiple modeling formalisms.

An Efficient Disk-Based Tool for Solving Very Large Markov Models

Very large Markov models often result when modeling realistic computer systems and networks. We describe a new tool for solving large Markov models on a typical engineering workstation. This tool does not require any special properties or a particular structure in the model, and it requires only slightly more memory than what is necessary to hold the solution vector itself. It uses a disk to hold the state-transition-rate matrix, a variant of block Gauss-Seidel as the iterative solution method, and an innovative implementation that involves two parallel processes: the first process retrieves portions of the iteration matrix from disk, and the second process does repeated computation on small portions of the matrix. We demonstrate its use on two realistic models: a Kanban manufacturing system and the Courier protocol stack, which have up to 10 million states and about 100 million nonzero entries. The tool can solve the models efficiently on a workstation with 128 Mbytes of memory and 4 Gbytes of disk.

On-the-fly solution techniques for stochastic Petri nets and extensions

High level modeling representations, such as stochastic Petri nets, frequently generate very large state spaces and corresponding state transition rate matrices. We propose a new steady state solution approach that avoids explicit storing of the matrix in memory. This method does not impose any structural restrictions on the model, uses Gauss Seidel and variants as the numerical solver, and uses less memory than current state of the art solvers. An implementation of these ideas shows that one can realistically solve very large, general models in relatively little memory.

RFID tag antenna based temperature sensing in the frequency domain

The efficiency of cold supply chain operations can be improved with pervasive temperature sensing. In this paper, we investigate the design of a low-cost, single-use RFID based temperature threshold sensor that is capable of relating the violation of a temperature threshold to a shift in the optimal operating frequency at which the tag antenna is well matched to the tag IC. This shift is detectable by commercial UHF RFID readers operating in the 902–928 MHz frequency band. We will illustrate how state change information is preserved using a nonelectric memory mechanism that works even in the absence of reader transmitted power. We demonstrate that the sensor works reliably for a read distance of over 3 m and in noisy environments.

An efficient disk-based tool for solving large Markov models

Very large Markov models often result when modeling realistic computer systems and networks. We describe a new tool for solving large Markov models on a typical engineering workstation. This tool does not require any special properties or a particular structure in the model, and it requires only slightly more memory than what is necessary to hold the solution vector itself. It uses a disk to hold the state-transition-rate matrix, a variant of block Gauss-Seidel as the iterative solution method, and an innovative implementation that involves two parallel processes: the first process retrieves portions of the iteration matrix from disk, and the second process does repeated computation on small portions of the matrix. We demonstrate its use on two realistic models: a Kanban manufacturing system and the Courier protocol stack, which have up to 10 million states and about 100 million nonzero entries. The tool can solve the models efficiently on a workstation with 128 Mbytes of memory and 4 Gbytes of disk.

A circularly polarized planar antenna modified for passive UHF RFID

The majority of RFID tags are linearly polarized dipole antennas, but a few use a planar, dual-dipole antenna that facilitates circular polarization, but requires a three-terminal IC. In this paper, we present a novel way to achieve circular polarization with a planar antenna using a two-terminal IC. We present an intuitive methodology for design, and perform experiments that validate circular polarization. The results show that the tag exhibits strong circular polarization, but the precise axial ratio of the tag remains uncertain due to lack of precision in the experimental system.

Analysis and design of wideband passive UHF RFID tags using a circuit model

The great majority of commercial UHF RFID tags are based on dipole antennas using a modification of a T-match as a matching circuit. The literature contains examples of wideband matching, but provides little insight as to how wideband behavior is achieved. Here, we present a simple circuit-based theory to describe the antenna, matching circuit, and IC behavior; we present an approach for developing an impeding matching strategy to maximize bandwidth; and we present a concrete example and analysis using a method of moments (MoM) numerical solver. The results show very good agreement with theory.

Mobius: framework and atomic models

This paper gives an overview of the Mobius framework, and gives a formal specification for defining atomic models within the framework. The framework is designed to be capable of incorporating multiple modeling formalisms, including atomic models (e.g, SPNs), composition formalisms (e.g., Replicate/Join), measure specification formalisms, connection formalisms, and solvers. We focus on atomic models, which are composed of actions, state variables, and properties. We argue that these are sufficient to specify a large number of atomic model formalisms in the Mobius framework. The framework serves as a basis for the Mobius tool.