Showing papers in "IEEE Circuits and Systems Magazine in 2008"

Wireless LAN Comes of Age: Understanding the IEEE 802.11n Amendment

Abstract: During the initial development of the IEEE 802.11n (11n) amendment for improving the throughput of wireless LANs, a lot of excitement existed surrounding the potential higher throughput (i.e., faster downloads), and increased range (distance) achievable. However, delays in the development of this standard (which began in 2003, and is still in the final draft stages) as well as vendor, customer reluctance to adopt the pre-11n offerings in the marketplace, have generally slowed interest in this next-generation technology. However, there is still much to be excited about. The latest draft of IEEE 802.11n (Draft 3.0) offers the potential of throughputs beyond 200 Mbps, based on physical layer (PHY) data rates up to 600 Mbps. This is achieved through the use of multiple transmit and receive antennas, referred to as MIMO (multiple input, multiple output). Using techniques such as spatial division multiplexing (SDM), transmitter beamforming, and space-time block coding (STBC), MIMO is used to increase dramatically throughput over single antenna systems (by two to four times) or to improve range of reception, depending on the environment. This article offers an exposition on the techniques used in IEEE 802.11n to achieve the above improvements to throughput and range. First, the current generation WLAN devices (11a/b/g) are described in terms of the benefits offered to end users. Next, the evolution of the Tin amendment is discussed, describing the main proposals given, and illustrating reasons for the delay in standardization. Then, the changes to the PHY for 11n are presented. A description of channel modeling with MIMO is shown, followed by the signal processing techniques employed, including MIMO channel estimation and detection, space-time block coding (STBC), and transmitter beamforming. Simulation results are presented which illustrate the benefits of these techniques, versus the existing a/g structures, for both throughput and range. Finally, a brief section outlining considerations for the rapid prototyping of a baseband design based on the 802.11n PHY is presented. We conclude with a discussion of the future for 11n, describing the issues addressed with Drafts 2.0 and 3.0, as well as its place in a wireless market with WiMAX and Bluetooth.

An introduction to the fractional continuous-time linear systems: the 21st century systems

Abstract: A brief introduction to the fractional continuous-time linear systems is presented. It will be done without needing a deep study of the fractional derivatives. We will show that the computation of the impulse and step responses is very similar to the classic. The main difference lies in the substitution of the exponential by the Mittag-Leffler function. We will present also the main formulae defining the fractional derivatives.

Power electronics and its applications to renewable energy in Japan

Abstract: The electric utility industry is gradually undergoing restructuring and the main paradigm shift is the introduction of the principles of competition. With the level of future demand for electricity being unclear, power market players are reluctant to commit to long-term capital investment, with the result that construction of new large-scale power plants and also transmission and distribution infrastructure is typically being avoided. At the same time, power facilities are being upgraded in response to business strategies for bringing a profit in power markets and for keeping supply reliability for customers. Under such circumstances of competitive power markets, practical use of renewable and distributed energy generation offers an attractive alternative for power supply. The advantages include a short construction cycle as the supply can be located near to the demand, being less of a burden to the existing transmission network, and contributing to prevention of global warming through clean combustion using novel energy technologies such as natural gas co-generation, natural gas micro turbines, or fuel cells. Distributed generations using renewable energy resources such as wind and solar energy are also attracting attention. Regarding practical use of renewal energy in Japan, a new set of requirements advents. The first is the development of a set of policies for promoting power generated from renewable energy. The second is to evaluate the influence of distributed generations from renewable energy on the quality and reliability of the electricity. The third is the establishment of the technology requirements for interconnection with the power grid. The fourth is the development of future energy supply networks such as Power parks, Microgrids, and Smart grids. In implementing future energy supply networks utilizing renewable energy, power electronic devices are widely used to interface some forms of renewable energy generations and energy storages to distribution networks, and their use is likely to increase remarkably in the near future. The development of these power electronics is benefiting from the rapid advancements in the capability of power semiconductor switching devices and in the progress being made in the design and control of variable-speed drives for large motors. The most diffused application of power electronic devices is to invert the DC generated from some dispersed energy resources (e.g. photo voltaic fuel cells, micro turbines and battery storages) to existing 50/60 Hz AC. Also, power electronic devices are used to decouple rotating generates from the network and so potentially increase the efficiency of the operation of the prime mover by ensuring that they operate at their most efficient speed for the range of input power. For example, power electronics are used to support variable-speed wind turbines and are also now being proposed for some forms of small hydro-generation and energy storages during transients. In this article, we will discuss the role of power electronics for renewable energy utilizations and the kinds of infrastructure that should be designed and how this should be pursued in order to maintain high reliability and quality for future energy supply networks in the restructured electricity markets.

Architectures for multi-gigabit wire-linked clock and data recovery

Abstract: Clock and data recovery (CDR) architectures used in high-speed wire-linked communication receivers are often shown as PLL or DLL based topologies. However, there are many other types of CDR architectures such as phase-interpolator, oversampling and injection locked based topologies. The best choice for the CDR topology will depend on the application and the specification requirements. This paper presents an overview and comparative study of the most commonly used CDR architectures. This analysis includes the circuit structures, design challenges, major performance limitations and primary applications. Finally, the tradeoffs among the various CDR architectures are summarized.

Collective behavior coordination with predictive mechanisms

Abstract: In natural flocks/swarms, it is very appealing that low-level individual intelligence and communication can yield advanced coordinated collective behaviors such as congregation, synchronization and migration. In the past few years, the discovery of collective flocking behaviors has stimulated much interest in the study of the underlying organizing principles of abundant natural groups, which has led to dramatic advances in this emerging and active research field. Inspired by previous investigations on the predictive intelligence of animals, insects and microorganisms, we seek in this article to understand the role of predictive mechanisms in the forming and evolving of flocks/swarms by using both numerical simulations and mathematical analyses. This article reviews some basic concepts, important progress, and significant results in the current studies of collective predictive mechanisms, with emphasis on their virtues concerning consensus improvement and communication cost reduction. Due to these advantages, such predictive mechanisms have great potential to find their way into industrial applications.

The concept of time-average-frequency and mathematical analysis of flying-adder frequency synthesis architecture

Abstract: Flying-adder frequency synthesis architecture is a novel technique of generating frequency on chip. Since its invention, it has been utilized in many commercial products to cope with various difficult challenges. During the evolution of this architecture, the issues related to circuit- and system-level implementation have been studied in prior publications. However, rigorous mathematical treatment on this architecture has not been established. In this paper, we attempt to explore and understand the signal characteristics and frequency domain behavior of this architecture through mathematical analysis. In the meantime, the underlying concept associated with this architecture, time-average-frequency, is formally introduced.

Distributed sensing based on intelligent sensor networks

Abstract: Network centric approach to complex systems has been attracting a lot of attention in the recent past. With specific applications in space, military and other information enterprises, such an approach is capable of yielding autonomy at the system level. This article describes a distributed approach to information processing in sensor networks. The network architecture entails a hierarchy of capabilities, information and control, where nodes in the network are thoroughly or partially autonomous. The network also consists of slave nodes dedicated to sensing and gathering information. Individual nodes are expected to possess resources for networking and computing and presume autonomy through multi functional modules for sensory processing and situation assessment. Data association, registration and fusion are formulated into a joint process, and an expectation maximization (EM) approach is developed to solve the three problems simultaneously. A fuzzy cognitive map (FCM) is proposed to perform situation assessment, while a genetic algorithm (GA) is applied for learning, to identify an optimal structure. The distributed architecture is applied to coastal surveillance with simulations on the west coast of Canada.

Insect-vision inspired collision warning vision processor for automobiles

Abstract: Vision is expected to play important roles for car safety enhancement. Imaging systems can be used to enlarging the vision field of the driver. For instance capturing and displaying views of hidden areas around the car which the driver can analyze for safer decision-making. Vision systems go a step further. They can autonomously analyze the visual information, identify dangerous situations and prompt the delivery of warning signals. For instance in case of road lane departure, if an overtaking car is in the blind spot, if an object is approaching within collision course, etc. Processing capabilities are also needed for applications viewing the car interior such as "intelligent airbag systems" that base deployment decisions on passenger features. On-line processing of visual information for car safety involves multiple sensors and views, huge amount of data per view and large frame rates. The associated computational load may be prohibitive for conventional processing architectures. Dedicated systems with embedded local processing capabilities may be needed to confront the challenges. This paper describes a dedicated sensory-processing architecture for collision warning which is inspired by insect vision. Particularly, the paper relies on the exploitation of the knowledge about the behavior of Locusta Migra- toria to develop dedicated chips and systems which are integrated into model cars as well as into a commercial car (Volvo XC90) and tested to deliver collision warnings in real traffic scenarios.

Energy-aware portable video communication system design for wildlife activity monitoring

Abstract: In this paper, we introduce our recent research and development effort on energy-efficient portable video communication system design for wildlife activity monitoring. The capability of seeing what an animal sees in the field is very important for wildlife activity monitoring and research. We design an integrated video and sensor system, called DeerCam and mount it on animals so as to collect important video and sensor data about their activities in the field. From the video and sensor data collected by DeerCam, wildlife researchers will be able to extract a wealth of scientific data for studying the behavior patterns of wildlife species and understanding the dynamic of wildlife systems. We present the system architecture of DeerCam, explain our system design goals, and discuss major design issues. One of the central challenges in DeerCam system design is energy minimization. We present a new approach for energy minimization of portable video devices: power-rate-distortion (P-R-D) analysis and optimization. We discuss various approaches to minimizing the energy consumption of DeerCam, which can be also applied to other portable video devices. Results demonstrate that, by incorporating the third dimension of power consumption into conventional rate-distortion (R-D) analysis, P-R-D analysis gives us one extra dimension of flexibility in resource allocation and energy minimization and allows us to significantly reduce energy consumption.

Some open issues associated with the new type of component: digital-to-frequency converter [Open Column]

Abstract: This paper presents seven unsolved mathematical problems which all relate to a new type of electronic component: digital-to-frequency converter. These problems are parts of the theoretical foundation of this new component. Even though theoretical in nature, these problems will have profound impact on future real electronic system design. These problems present themselves as an excellent example of demonstrating the significance of mathematical analysis in circuit design applications. They show the importance of fundamental research on directing the real world work.

On the way to plastic computation

Abstract: The development of post silicon technologies based on organic materials consolidates the possibility to realize new devices and applications with unusual properties: flexibility, lightweight, disposability. Both materials and processes play a fundamental role in this new electronic framework and have been improved continuously in the last decades. In this contribution, a new perspective will be drawn by considering a complete technology platform that lead printed organic electronics technology from the basic device and materials to a manufacturing process flow, design tools and market applications development. The final goal of the proposed approach is the manufacturing of organic circuits with sub-micron feature size at low fabrication costs with high flexibility and application versatility by using additive manufacturing processes. The identification of suitable material features and process steps and the implementation of dedicated CAD tools in a complete workflow are here reported. Moreover, the feasibility of the adopted technology is demonstrated by the design of both digital and analog circuits. Multilayered structure devices, like organic thin film transistor (OTFT), are used to design complex architectures like arithmetic logic units and nonlinear oscillators.

A Jumping Genes Paradigm: Theory, Verification and Applications

Abstract: A new evolutionary computing algorithm on the basis of "jumping genes" phenomenon is presented in this article. It emulates the gene transposition in the genome that was discovered by Nobel Laureate Dr. Barbara McClintock from her work on maize chromosome. The principle of jumping genes, adopted for evolutionary computing, is outlined and the procedures for executing the computational optimization are provided. Mathematical derivation of the schema theorem is briefly discussed, which is established to demonstrate the searching capacity of the newly proposed algorithm, in terms of convergence and diversity. The algorithm is found to be robust and provides outcomes in speed and accuracy, while the solutions are widely spread along the Pareto-optimal front when a multiobjective problem is tackled. T o further reinforce the jumping genes proposition, some typical engineering design problems are included. The obtained results have indicated that this new algorithm is indeed capable of searching multiobjective solutions including the extreme solutions at both ends of the Pareto-optimal front.

Streamlining the Design of MEMS Devices: An Acceleration Sensor

Abstract: A synthesis and optimization process is proposed and applied to the design of a specific MEMS device, namely an acceleration sensor. The design synthesis methodology exploits the fast and accurate simulation of the SUGAR tool (based on modified modal analysis) along with the full simulation capability of ANSYS (based on the finite element method). A three degrees-of-freedom piezoresistive acceleration sensor was designed to validate the proposed design flow. During the course of design, the modified nodal analysis and the finite element methods were combined in optimizing the sensor structure. In the latter, the piezoresistance effect was employed in sensing the acceleration in three dimensions.

Leon Chua's memristor [Recognitions]

Abstract: Recounts Leon Chua's discovery of the memristor and the example Chua set for younger generations of scientists and engineers.

Moore's Law today

Abstract: The article discusses the progress of integrated electronics in terms of Gordon Moore's observation that the number of components on a single piece of silicon had doubled every year since the invention. This observation has become known as Moore's law. The contributions of device miniaturization and chip size to the increasing content of a chip were also discussed. The number of devices on a chip was found to increase faster than the chip area per pixel area.

Loop gain, input impedance and output impedance of feedback amplifiers

Abstract: Introductory treatments of feedback amplifiers commonly contain inconsistencies, or present results as universal when in fact they need qualification. Loop gain, overall gain, input impedance and output impedance are instances. A case can therefore be made for rigorous development, even in a first course, provided mathematical rigor can be combined with physical insight. A feedback factor H is first defined for ideal circumstances. The corresponding forward-path gain G has an obvious physical interpretation: the amplifier without feedback, the external source and load impedances, and the feedback network are all involved, and the form of G is such as to suggest best practice for the various feedback configurations. Stability considerations, and precise values for overall gain, sensitivity, input impedance and output impedance follow directly from GH.

Capturing device mismatch in analog and mixed-signal designs

Abstract: As feature size goes below 70 nm, process variation introduced device mismatch may cause over 40% performance variations and circuit failures especially for analog/mixed-signal designs. The location dependent correlations among devices and the large number of devices in some practical designs make it difficult to predict performance corners accurately and efficiently. This paper aims to provide an overview of possible methodologies and approaches that model and analyze device mismatch. In particular, the paper describes a new finite point device modeling technique that can speed up the analysis procedure, a new parametric reduction method and a novel Chebyshev Affine Arithmetic (CAA) based performance bound estimation approach.

The limits of light: The finite bandwidth of optical fibre [Open Column]

Abstract: Optical fibre is regularly touted as the ultimate broadband link - an "infinite"-bandwidth medium towards which all wireline communication technologies must inexorably migrate. But before describing the signal processing employed to combat dispersion in modern optical links, a little background on dispersion in optical fibres is required. The dispersion compensation techniques and the open problems facing them is discussed including speculation on the future of the field.

Apology [Plagiarism]

Abstract: The lead author (Abu Baker) of the paper entitled, "LDPC Decoder: A Cognitive Radio Perspective for NeXt Generation (XG) Communication," which appeared in the 3rd quarter issue of the IEEE Circuits and Systems Magazine, admits to having plagiarized his work from "Energy/Power Estimation for LDPC Decoders in Software Radio Systems" authored by Chia-han Lee and Wayne Wolf of Princeton University, which appeared in the IEEE-SiPS 2005 conference and in order to obfuscate the plagiarism, he made minor modifications to the original work, which he thought would make it harder to trace the material back to the source. He also inappropriately plagiarized some paragraphs from another work by Professors Ian Akyildiz, Won-Yeol Lee, Mehmet Vuran and Shantidev Mohanty, entitled "NeXt generation/dynamic spectrum access/cognitive radio wireless networks: A survey," published in Computer Networks, Vol. 50, Issue 13, September 2006, Elsevier. He acknowledges that his co-authors, Soumik Ghosh, Ashok Kumar, and Magdy Bayoumi were totally unaware of any plagiarism. Throughout the process, the VLSI research team believed that Baker's write-up showed his own work.