Optimized query routing trees for wireless sensor networks

In order to process continuous queries over Wireless Sensor Networks (WSNs), sensors are typically organized in a Query Routing Tree (denoted as T) that provides each sensor with a path over which query results can be transmitted to the querying node. We found that current methods deployed in predominant data acquisition systems construct T in a sub-optimal manner which leads to significant waste of energy. In particular, since T is constructed in an ad hoc manner there is no guarantee that a given query workload will be distributed equally among all sensors. That leads to data collisions which represent a major source of energy waste. Additionally, current methods only provide a topological-based method, rather than a query-based method, to define the interval during which a sensing device should enable its transceiver in order to collect the query results from its children. We found that this imposes an order of magnitude increase in energy consumption. In this paper we present MicroPulse+, a novel framework for minimizing the consumption of energy during data acquisition in WSNs. MicroPulse+ continuously optimizes the operation of T by eliminating data transmission and data reception inefficiencies using a collection of in-network algorithms. In particular, MicroPulse+ introduces: (i) the Workload-Aware Routing Tree (WART) algorithm, which is established on profiling recent data acquisition activity and on identifying the bottlenecks using an in-network execution of the critical path method; and (ii) the Energy-driven Tree Construction (ETC) algorithm, which balances the workload among nodes and minimizes data collisions. We show through micro-benchmarks on the CC2420 radio chip and trace-driven experimentation with real datasets from Intel Research and UC-Berkeley that MicroPulse+ provides significant energy reductions under a variety of conditions thus prolonging the longevity of a wireless sensor network

Broadcast data organizations and client side cache

Broadcasting provides an e cient means for disseminating information in both wired and wireless setting. In this paper, we study di erent client side cache organizations for various types of multiversion data broadcast, i.e., data broadcast in which more than one value is broadcast per data item. Besides increasing the concurrency of client transactions, multiversion broadcast provides clients with the possibility of accessing multiple server states. For example, sucha functionality is essential to support applications that require access to data sequences and have limited local memory to store the previous versions, such as in the case of sensor networks. 1

Adaptive multiversion data broadcast organizations

Broadcasting provides an efficient means for disseminating information in both wired and wireless setting. In this paper, we propose a suite of broadcast organization schemes for multiversion data broadcast, i.e., data broadcast in which more than one value is broadcast per data item. Besides increasing the concurrency of client transactions, multiversion broadcast provides clients with the possibility of accessing multiple server states. For example, such a functionality is essential to support applications that require access to data sequences and have limited local memory to store the previous versions, such as in the case of sensor networks. We identify two basic multiversion organizations, namely vertical and horizontal broadcasts and propose an efficient compression scheme applicable to both. We also consider a multiversion client data cache and introduce appropriate cache replacement techniques. Finally, we propose an adaptive scheme that dynamically selects the appropriate broadcast organization based on the client access pattern. We provide performance evaluation results for both flat and broadcast disk organizations and for a variety of client query patterns

Structural Properties of GaN Films Grown by Molecular Beam Epitaxy on Singular and Vicinal 6H-SiC(0001)

Gallium nitride films are grown by plasma-assisted molecular beam epitaxy (MBE) on 6H-SiC(0001) substrates with no miscut and with 3.5 degree miscuts in both the [1 -1 0 0] and [1 1 -2 0] directions. The hydrogen-etched substrates display straight or chevron shaped steps, respectively, and the same morphology is observed on the GaN films. X-ray rocking curves display substantially reduced width for films on the vicinal substrates compared to singular substrates, for the same Ga/N flux ratio used during growth.</p

Four Current Examples of Characterization of Silicon Carbide

A description is given of the profiling of CVD grown 3C SiC on undulant (001) Si using low temperature photoluminescence (LTPL). Inelastic neutron scattering (INS) and X-ray Raman scattering (XRS) are compared for acoustical modes of 4H SiC. Schottky barrier heights are obtained for 4H and 6H SiC on different crystal faces using three different measuring techniques. Scanning electron microscopy (SEM) is used to display a variety of porous SiC morphologies achieved in n-type and p-type SiC. This paper is intended to be the introduction to the “CHARACTERIZATION” section of this volume. To serve this purpose we illustrate the subject matter with new results using four distinct experimental techniques