Semiconductor science: the fourth generation

The author reviews work on quantum wires and quantum dots in the context of a generational framework. The first generation centered on the quantum physics of solids. The second generation saw the commercial and technical application of these new physical concepts. The third generation yielded the creation of man-made quantum systems and low-dimensional systems: inversion layers and quantum wells, superlattices, quantum wires, and quantum dots. The author discusses work on low-dimensional systems as a part of this progression. There is a clear connection between the work done during the first generation and the creation of new semiconductor structures, novel band structures, and the associated fundamental excitations. He also discusses the current directions in semiconductor research and speculates on the potential applications of semiconductor physics in the fourth generation     

Cognitive radio architecture evolution: annals of telecommunications

Cognitive radio research has developed dynamic radio spectrum management to enhance spectrum efficiency, e.g., as secondary users in unused TV bands. The location and user context of the mobile wireless user that regulatory bodies and lawmakers view as significant to spectrum interference policies have not been addressed as thoroughly. In addition, quality of service (QoS) provides a starting point but does not guarantee quality of experience (QoE) that depends on quality of information (QoI) which is a function of place, time, and user state in a social setting (e.g., commuting, shopping, or in need of medical assistance). This paper considers the evolution of cognitive radio architecture (CRA) from dynamic spectrum access (DSA) to QoE via an interdisciplinary perspective. Machine perception in visual, acoustic, speech, and text domains can cue the automatic detection of user state in stereotypical situations, enabling cognitive nodes and networks to select from among radio bands and modes more appropriately, thus enabling cognitive wireless networks (CWNs) to deliver higher QoE within technical policy constraints, in a way that makes cost-effective use of embedded and distributed computational intelligence. The control of networks of such cognitive radios requires advances in policy language architectures, so this paper introduces cognitive linguistics for policy languages.     

Internet tomography

Today's Internet is a massive, distributed network which continues to explode in size as e-commerce and related activities grow. The heterogeneous and largely unregulated structure of the Internet renders tasks such as dynamic routing, optimized service provision, service-level verification, and detection of anomalous/malicious behavior increasingly challenging tasks. The problem is compounded by the fact that one cannot rely on the cooperation of individual servers and routers to aid in the collection of network traffic measurements vital for these tasks. In many ways, network monitoring and inference problems bear a strong resemblance to other "inverse problems" in which key aspects of a system are not directly observable. Familiar signal processing problems such as tomographic image reconstruction, system identification, and array processing all have interesting interpretations in the networking context. This article introduces the new field of network tomography, a field which we believe will benefit greatly from the wealth of signal processing theory and algorithms     

Locating the nodes: cooperative localization in wireless sensor networks

Accurate and low-cost sensor localization is a critical requirement for the deployment of wireless sensor networks in a wide variety of applications. In cooperative localization, sensors work together in a peer-to-peer manner to make measurements and then forms a map of the network. Various application requirements influence the design of sensor localization systems. In this article, the authors describe the measurement-based statistical models useful to describe time-of-arrival (TOA), angle-of-arrival (AOA), and received-signal-strength (RSS) measurements in wireless sensor networks. Wideband and ultra-wideband (UWB) measurements, and RF and acoustic media are also discussed. Using the models, the authors have shown the calculation of a Cramer-Rao bound (CRB) on the location estimation precision possible for a given set of measurements. The article briefly surveys a large and growing body of sensor localization algorithms. This article is intended to emphasize the basic statistical signal processing background necessary to understand the state-of-the-art and to make progress in the new and largely open areas of sensor network localization research.     

Unicast-based inference of network link delay distributions with finite mixture models

Providers of high quality-of-service over telecommunication networks require accurate methods for remote measurement of link-level performance. Recent research in network tomography has demonstrated that it is possible to estimate internal link characteristics, e.g., link delays and packet losses, using unicast probing schemes in which probes are exchanged between several pairs of sites in the network. We present a new method for estimation of internal link delay distributions using the end-to-end packet pair delay statistics gathered by back-to-back packet-pair unicast probes. Our method is based on a variant of the penalized maximum likelihood expectation-maximization (PML-EM) algorithm applied to an additive finite mixture model for the link delay probability density functions. The mixture model incorporates a combination of discrete and continuous components, and we use a minimum message length (MML) penalty for selection of model order. We present results of Matlab and ns-2 simulations to illustrate the promise of our network tomography algorithm for light cross-traffic scenarios.     

High-rate vector quantization for detection

We investigate high-rate quantization for various detection and reconstruction loss criteria. A new distortion measure is introduced which accounts for global loss in best attainable binary hypothesis testing performance. The distortion criterion is related to the area under the receiver-operating-characteristic (ROC) curve. Specifically, motivated by Sanov's theorem, we define a performance curve as the trajectory of the pair of optimal asymptotic Type I and Type II error rates of the most powerful Neyman-Pearson test of the hypotheses. The distortion measure is then defined as the difference between the area-under-the-curve (AUC) of the optimal pre-encoded hypothesis test and the AUC of the optimal post-encoded hypothesis test. As compared to many previously introduced distortion measures for decision making, this distortion measure has the advantage of being independent of any detection thresholds or priors on the hypotheses, which are generally difficult to specify in the code design process. A high-resolution Zador-Gersho type of analysis is applied to characterize the point density and the inertial profile associated with the optimal high-rate vector quantizer. The analysis applies to a restricted class of high-rate quantizers that have bounded cells with vanishing volumes. The optimal point density is used to specify a Lloyd-type algorithm which allocates its finest resolution to regions where the gradient of the pre-encoded likelihood ratio has greatest magnitude.     

Room-Temperature Mechanical Properties and Slow Crack Growth Behavior of Mg2Si Thermoelectric Materials

Mg₂Si is of interest as a thermoelectric (TE) material in part due to its low materials cost, lack of toxic components, and low mass density. However, harvesting of waste heat subjects TE materials to a range of mechanical and thermal stresses. To understand and model the material??s response to such stresses, the mechanical properties of the TE material must be known. The Mg₂Si specimens included in this study were powder processed and then sintered via pulsed electrical current sintering. The elastic moduli (Young??s modulus, shear modulus, and Poisson??s ratio) were measured using resonant ultrasound spectroscopy, while the hardness and fracture toughness were examined using Vickers indentation. Also, the Vickers indentation crack lengths were measured as a function of time in room air to determine the susceptibility of Mg₂Si to slow crack growth.     

A low-power 72.8-GHz static frequency divider in AlInAs/InGaAs HBTtechnology

We report a 72.8-GHz fully static frequency divider in AlInAs/InGaAs HBT IC technology. The CML divider operates with a 350-mV logic swing at less than 0-dBm input power up to a maximum clock rate of 63 GHz and requires 8.6 dBm of input power at the maximum clock rate of 72.8 GHz. Power dissipation per flip-flop is 55 mW with a 3.1-V power supply. To our knowledge, this is the highest frequency of operation for a static divider in any technology. The power-delay product of 94 fJ/gate is the lowest power-delay product for a circuit operating above 50 GHz in any technology. A low-power divider on the same substrate operates at 36 GHz with 6.9 mW of dissipated power per flip-flop with a 3.1-V supply. The power delay of 24 fJ/gate is, to our knowledge, the lowest power-delay product for a static divider operating above 30 GHz in any technology. We briefly review the requirements for benchmarking a logic family and examine the historical trend of maximum clock rate in high-speed circuit technology     

The impact of publicly funded basic research: an integrative extension of Martin and Salter

This paper provides an integrative literature review of the research on the impact of the public funding of basic research, extending previous work done at the Science Policy Research Unit (SPRU), University of Sussex, East Sussex, UK. "Impact" is measured in terms of publications, patents, new drugs, employment, and new start-up companies. The primary focus of this paper is on empirical studies of the impact of biomedical research. However, a few key theoretical papers and empirical papers with a broader industrial focus are also reviewed to provide a more complete perspective. Conclusions, including an alternative view that basic research need not be public supported, and future research opportunities in this area are also discussed.     

On fast FIR filters implemented as tail-canceling IIR filters

We have developed an algorithm based on synthetic division for deriving the transfer function that cancels the tail of a given arbitrary rational (IIR) transfer function after a desired number of time steps. Our method applies to transfer functions with repeated poles, whereas previous methods of tail-subtraction cannot. We use a parallel state-variable technique with periodic refreshing to induce finite memory in order to prevent accumulation of quantization error in cases where the given transfer function has unstable modes. We present two methods for designing linear-phase truncated IIR (TIIR) filters based on antiphase filters. We explore finite-register effects for unstable modes and provide bounds on the maximum TIIR filter length. In particular, we show that for unstable systems, the available dynamic range of the registers must be three times that of the data. Considerable computational savings over conventional FIR filters are attainable for a given specification of linear-phase filter. We provide examples of filter design. We show how to generate finite-length polynomial impulse responses using TIIR filters. We list some applications of TIIR filters, including uses in digital audio and an algorithm for efficiently implementing Kay's optimal high-resolution frequency estimator