Ptolemy II is a component-based design and modeling environment. It has a polymorphic type system that supports both base types and structured types, such as arrays, records, and unions. This paper presents the extensions to the base type system that support structured types. In the base type system, all the types are organized into a type lattice, and type constraints in the form of inequalities can be solved efficiently over the lattice. We take a hierarchical and granular approach to add structured types to the lattice and extend the format of inequality constraints to allow arbitrary nesting of structured types. We also analyze the convergence of the constraint-solving algorithm on an infinite lattice after structured types are added. To show the application of structured types, we present two Ptolemy II models that have direct real-world background. The first one describes the workflow of a charity organization, and the second one implements part of the IEEE 802.11 specification. These models make extensive use of record and union types to represent structured information. © 2009 Wiley Periodicals, Inc.

The common belief is that a multi-hop configuration with rather small per-hop distance is the only viable energy-efficient option for wireless sensor networks. We discuss a single hop configuration, utilizing the asymmetry between lightweight sensor nodes and a more powerful "base station" and demonstrate that such a single hop configuration can actually have lower overall power consumption than a multi-hop counterpart.

In this paper we integrate the energy models of all the components of the data link layer of a wireless sensor network into a single framework, which interacts with the abstracted models of the network layer, the physical layer, and the channel. Such a framework enables intra layer and cross layer optimization. By identifying the important design parameters, it provides the venues and guidelines for energy' reduction and design improvement, as demonstrated in the paper. The validity of the models is verified using OMNET++ network simulations.

In a wireless, multi-hop sensor network, choosing transmission power levels has an important impact on energy efficiency and network lifetime. Two algorithms for dynamically adjusting transmission power level on a per-node basis are proposed here. Network lifetime, convergence speed as well as resulting network connectivity are used as figures of merit for these two algorithms. They have been evaluated in an indoor sensor environment. The network lifetime metrics of these two local algorithms are also benchmarked against power control algorithms using global information. We show that these local algorithms outperform fixed power level assignment and that the lifetime achieved by them is usually within a factor of two of globally computed solution while being scalable.

Targeted at multi-hop wireless sensor networks, a set of low power MAC design principles have been proposed, and a novel ultra-low power MAC is designed to be distributed in nature to support scalability, survivability and adaptability requirements. Simple CSMA and spread spectrum techniques are combined to trade off bandwidth and power efficiency. A distributed algorithm is used to do dynamic channel assignment. A novel wake-up radio scheme is incorporated to take advantage of new radio technologies. The notion of mobility awareness is introduced into an adaptive protocol to reduce network maintenance overhead. The resulting protocol shows much higher power efficiency for typical sensor network applications.

A two-stage adaptive multiuser detector in an additive white Gaussian noise code-division multiple-access channel is proposed and analyzed. Its first stage is an asynchronous one-shot decorrelator which in terms of computational complexity only requires inversion of K symmetric K/spl times/K matrices for all K users. In addition, the K inversions can be done in parallel, and the computed results for one user can be reused by all other users as well, resulting in a latency of only one bit, same as its synchronous counterpart. The decorrelated tentative decisions are utilized to estimate and subtract multiple-access interference in the second stage. Another novel feature of the detector is the adaptive manner in which the multiple-access interference estimates are formed, which renders prior estimation of the received signal amplitudes and the use of training sequences unnecessary. Adaptation algorithms considered include steepest descent (as well as its stochastic version), and a recursive least squares-type algorithm that offers a faster transient response and better error performance. Sufficient conditions for the receiver to achieve convergence are derived. The detector is near-far resistant, and is shown to provide substantial steady-state error performance improvement over the conventional and decorrelating detector, particularly in the presence of strong interfering signals.

A multiuser detector in an additive white Gaussian noise, code division multiple access channel is proposed and analyzed. The detector utilizes the decorrelated tentative decisions obtained in the first stage to estimate and subtract multiple access interference in the second stage. The novel feature of the detector is the adaptive manner in which the multiple access interference estimates are formed, which renders prior estimation of the received signal amplitudes unnecessary. The detector is near-far resistant, and is shown to provide substantial performance improvement over the conventional and decorrelating detector, particularly in the presence of strong interfering signals.