Sensing systems with multiple sensors and operating modes warrant active management techniques to balance estimation quality and measurement costs. Existing literature shows that in the joint sensor-scheduling and state-estimation problem for HMMs, estimator optimization can be done independently of the scheduler at each time step. We investigate the special case when a MAP estimator is used, and show how the joint problem can be converted to a standard Partially Observable MarkovDecision Process (POMDP), which in turn enables us to use POMDP solvers. As this approach is highly redundant, we derive a direct solution, which exploits the separability property while still utilizing standard solvers. When compared to standard techniques, the direct algorithm provides savings by a factor of the state-space dimension. Numerical results are given for an example motivated by wildlife monitoring.

Applications such as long-term environmental monitoring and large-scale surveillance demand reliable performance from sensor nodes while operating within strict energy constraints. There is often not enough power for sensors to make measurements all of the time. In these cases, one must decide when to run each sensor. To this end, we develop a one-step optimal sensor-scheduling algorithm based on expected-utility maximization. “Utility” is an application-specific measure of the benefit from a given sensor measurement. In sensing environments that can be modeled using a hidden Markov model, selecting the appropriate combination of sensors at each time instant enables maximization of the expected utility while operating within an energy budget. For some budgets, the utility-based algorithm shows more than 300% utility gains over a constant duty-cycle scheme designed to consume the same amount of energy. These benefits are dependent on the energy budget.

The Grassmann–Taksar–Heyman algorithm is a direct algorithm for computing the steady-state distribution of an finite irreducible Markov chain. We describe our experience in implementing this algorithm on a single-instruction multiple-data parallel processor computer. Our main conclusions are that a lower-level language has a performance advantage compared to Fortran, and that data storage is the limiting factor that determines the largest problem that can be solved. As a consequence, we devote considerable attention to storing a block tridiagonal transition matrix.

This paper describes a new approach to testing that uses combinatorial designs to generate tests that cover the pairwise, triple, or n-way combinations of a system's test parameters. These are the parameters that determine the system's test scenarios. Examples are system configuration parameters, user inputs and other external events. We implemented this new method in the AETG system. The AETG system uses new combinatorial algorithms to generate test sets that cover all valid n-way parameter combinations. The size of an AETG test set grows logarithmically in the number of test parameters. This allows testers to define test models with dozens of parameters. The AETG system is used in a variety of applications for unit, system, and interoperability testing. It has generated both high-level test plans and detailed test cases. In several applications, it greatly reduced the cost of test plan development.

Software testing is expensive, tedious and time consuming. Thus, the problem of making testing more efficient and mechanical, without losing its effectiveness, is very important. The Automatic Efficient Test Generator (AETG) is a new tool that mechanically generates efficient test sets from user defined test requirements. It is based on algorithms that use ideas from statistical experimental design theory to minimize the number of tests needed for a specific level of test coverage of the input test space. The savings due to AETG are substantial when compared to exhaustive testing or other methods of testing. AETG has been used in Bellcore for screen testing, interoperability testing and for protocol conformance testing. The paper describes the current system and it constructs and reports some preliminary results obtained during initial trials.>

Results of a simulation study of the potential multiplexing gains from using variable-bit-rate encoding to multiplex video teleconferencing traffic over an asynchronous transfer mode (ATM) network are presented. Simulated traffic from several video teleconferences was fed into a buffer and multiplexed onto a higher speed output line. The study observed the cell loss resulting from buffer overflow. The spacings between the start times for the individual video conferences are found to have a large role in determining the aggregate cell-loss-rate seen by the collection of calls. After the cell-loss-rate becomes non-negligible, it grows rapidly as a function of the number of input lines. The cell losses are not distributed uniformly over time but are clustered, with the consequence that the probability that a call is loss free is much better than indicated by the cell-loss-rate.>

Results are presented of a simulation study of the potential multiplexing gains from using variable-bit-rate (VBR) encoding to multiplex video teleconferencing traffic over an asynchronous transfer mode (ATM) network. Simulated traffic from several video teleconferences is fed into a buffer and multiplexed onto a higher-speed output line. The cell loss resulting from buffer overflow is observed. The major results are as follows: (1) the spacing between cells has a large role in determining the aggregate cell loss rate seen by a collection of calls. The cell loss rate is reduced when either the frame start times are evenly spaced or cells are evenly distributed in the video frame. (2) After the cell loss rate becomes nonnegligible, it grows rapidly as a function of the number of access lines. (3) The cell losses are not distributed uniformly over time but are clustered. A consequence is that the average time between clusters of cell loss and the time to first loss is greater than if the losses were spaced uniformly. (4) A simple model is found to describe when a cluster of cell losses occurs, the duration of the cluster, and how many cells are lost in the cluster.>

A description is given of L.0, an executable specification language designed for describing communications protocols and similar reactive systems. L.0 is synchronous and rule-based. The rules are either cause-effect rules or constraints. Rules can be activated and deactivated dynamically, and several can be fired simultaneously. L.0 has modern notions of encapsulation and data sharing. Indirection, quantification, and recursive definition of modules increase its expressiveness. L.0 has been used in several development projects to design, simulate, and prototype protocols. It seems to provide a paradigm that is precise and yet can be used by designers and engineers who are not specialists in specification languages.>

The IC* project is an effort to create an environment for the design, specification, and development of complex systems such as communication protocols, parallel machines, and distributed systems. The basis of the project is the IC* model of parallel computation, in which a system is specified by a set of invariant expressions which describe its behavior in time. The features of this model include temporal and structural constraints, inherent parallelism, explicit modeling of time, nondeterministic evolution, and dynamic activation. The project also includes the construction of a parallel computer specifically designed to support the model of computation. The authors discuss the IC* model and the current user language, and describe the architecture and hardware of the prototype supercomputer built to execute IC* programs.>