Iterative (turbo) expectation?maximisationbased time and frequency synchronisation for multiple-input multiple-output?orthogonal frequency-division multiplexing systems

An iterative expectation-maximisation time-frequency synchronisation algorithm joint with channel estimation for multiple-input multiple-output-orthogonal frequency-division multiplexing (OFDM) systems in frequency-selective fading channels is addressed. The receiver iterates between detection and estimation stages. For each iteration, the expectation of ODFM symbols is calculated first by using a posteriori probabilities provided by maximum a posteriori (MAP) decoder, and second, a proposed metric is maximised to obtain both frequency offset and symbol timing. The channel can be identified by means of these estimates. This algorithm can work in transmission mode, and thus, can be used to estimate the residual errors or track the change of the parameters. The performance of the proposed synchronisation approach, in terms of bit-error rate and mean-square error, is shown.     

An efficient joint channel estimation and decoding algorithm for turbo-coded space?time orthogonal frequency division multiplexing receivers

The challenging problem in the design of digital receivers of today's and future high-speed, high data-rate wireless communication systems is to implement the optimal decoding and channel estimation processes jointly in a computationally feasible way. Without realising such a critical function perfectly at receiver, the whole system will not work properly within the desired performance limits. Unfortunately, direct implementation of such optimal algorithms is not possible mainly due to their mathematically intractable and computationally prohibitive nature. A novel algorithm that reaches the performance of the optimal maximum a posteriori (MAP) algorithm with a feasible computational complexity is proposed. The algorithm makes use of a powerful statistical signal processing tool called the expectation maximisation (EM) technique. It iteratively executes the MAP joint channel estimation and decoding for space'time block-coded orthogonal frequency division multiplexing systems with turbo channel coding in the presence of unknown wireless dispersive channels. The main novelty of the work comes from the facts that the proposed algorithm estimates the channel in a non-data-aided fashion and therefore except a small number of pilot symbols required for initialisation, no training sequence is necessary. Also the approach employs a convenient representation of the discrete multipath fading channel based on the Karhunen'Loeve (KL) orthogonal expansion and finds MAP estimates of the uncorrelated KL series expansion coefficients. Based on such an expansion, no matrix inversion is required in the proposed MAP estimator. Moreover, optimal rank reduction is achieved by exploiting the optimal truncation property of the KL expansion resulting in a smaller computational load on the iterative estimation approach.     

Pulse position modulated space?time trellis coding for ultra-wideband impulse radio multiple-input multiple-output communication systems

The design of pulse position modulated (PPM) space-time trellis codes (STTC) for ultra-wideband impulse radio (UWB-IR) multiple-input multiple-output (MIMO) communication systems over slow and fast fading multipath channels is considered. First, A probability of error analysis is carried out to derive upper bounds on pairwise symbol error probability at high and low signal-to-noise ratios (SNRs). From the upper bounds, A new distance notion is introduced and novel design criteria for optimal (in error rate performance) M-ary PPM STTC are deduced for UWB. An optimal binary-PPM STTC is designed for two transmit antennas. Finally, simulation results of the UWB-IR MIMO system, using the optimal STTC, confirm significant improvement in bit-error-rate performance over the uncoded UWB-IR single-input single-output system and also over previously proposed space-time coding scheme for UWB, at higher SNR.     

M-PAM space?time trellis codes for ultra-wideband multiple-input multiple-output communications

Multiple-input multiple-output (MIMO) systems with space-time (ST) coding are desirable in ultra- wideband (UWB) communication systems to improve the error-rate performance of the UWB link. The authors have considered the design of optimal (in error-rate performance) M-ary pulse-amplitude modulated (M-PAM) ST trellis codes (STTC) for a pulse-based UWB MIMO communication system. Following the approach by Vucetic et al. for narrowband systems, the authors carry out a probability of error analysis to derive upper bounds on pairwise symbol error probability for a UWB communication system for slow fading and fast fading at both low and high signal-to-noise ratios (SNRs). The authors deduce the design criteria from the upper bounds. Based on these criteria, an optimal four-state binary-PAM STTC, for two transmit antennas, is designed by hand. Finally, simulation results of the optimal binary-PAM STTC in a UWB communication system confirm significant improvement in bit error-rate performance over previously proposed ST coding scheme for UWB, at higher transmit SNR.     

High-κ dielectrics and advanced channel concepts for Si MOSFET

With scaling of the gate length downward to increase speed and density, the gate dielectric thickness must also be reduced. However, this practice which has been in effect for many decades has reached a fundamental limitation because gate dielectric thicknesses in the range of tunneling have been reached with the SiO₂ dielectric layer for MOSFETs. Consequently, the gate dielectrics with higher dielectric constants, dubbed the “high-κ”, which allow scaling with much larger thicknesses have become active research and development topics. In this review technological issues associated with the likely high-κ materials which are under consideration as well as challenges, and solution to them, they bring about in the fabrication of Si MOSFET are discussed. Moreover, in order to squeeze more speed out of CMOS, channels for both n- and p-type MOSFET enhanced with appropriate strain and the concepts behind them are discussed succinctly. Finally, the longer term approach of replacing Si with other channel materials such as GaAs (InGaAs) for n-channel and Ge for p-channel along with technological developments of their preparation on Si and likely gate oxide developments are treated in some detail.     

An anisotropic viscoelastoplastic model for composites—sensitivity analysis and parameter estimation

Because of their potential in achieving many performance enhancements, composite material systems (e.g. fiber-reinforced composites) are presently called upon to operate under wide range of stresses, temperatures, and loading rates. This in turn requires the development of general material models to capture the significant effects of anisotropy on both elastic and inelastic responses. The starting point in the present contribution is the development of a class of such viscoplastic models. Furthermore, a number of robust, computationally efficient, algorithms are also presented for the development of an overall strategy to estimate the material parameters characterizing these complex models; i.e. rate-dependent plastic flow, non-linear kinematic hardening, thermal/static recovery, anisotropic viscoelastic and viscoplastic flow. The entire procedure is automated through an integrated software namely, COnstitutive Material PARameter Estimator, COMPARE, to enable the determination of an ‘optimum’ set of material parameters by minimizing the errors between the experimental test data and the predicted response. The key ingredients of COMPARE are (i) primal analysis, (ii) sensitivity analysis, (iii) a gradient-based optimization problem and a (iv) graphical user interface. The estimation of the material parameters is cast as a minimum-error, weighted multi-objective, non-linear optimization problem with constraints. Detailed derivations of the direct differentiation sensitivity expressions are presented. In addition, numerical comparisons of the sensitivities obtained by the more traditional finite difference approaches are given to assess accuracy. Results generated by applying the developed algorithms for anisotropic, strain-controlled tensile (with comparison to typical experimental data) and constant-stress creep tests are presented to demonstrate the ability of the present models to accurately capture time-dependent anisotropic material behavior.     

A method for identifying customer orientations and requirements for product–service systems design

For manufacturers, developing product–service systems (PSSs) is getting more important because of the trends of servitisation and creating social value. A PSS is a social system where multiple actors mutually provide products and services. A PSS design, therefore, must take into account various actors as customers. However, existing methods provide an insufficient solution as to how various customers should be handled in an analysis to identify and accommodate various customer preferences and requirements. To tackle this issue, this article proposes a new method of identifying customers’ orientations and requirements for PSS design. The proposed method employs a combination of topic analysis, persona and scenario approaches. The effectiveness of the method is demonstrated with its application to an urban development case. Through the demonstration, its practical benefits are concluded as follows: consistent and logical results of requirement analysis and insights into a new market for manufacturers.     

Why do we need numerical methods for constrained fermion systems?

Approximative methods such as perturbation theory, mean-field caluclations or variational treatments are not reliable for many strongly interacting fermion models. Numerical methods are thus essential in the investigation of these strongly correlated fermion systems. A strong Coulomb repulsion present in these systems can often be replaced by a constraint to no-double occupancy, leading to an effective model for the low-energy excitations. These constrained systems are often easier to investigate. We review the exact algorithms mainly used to simulate constrained fermion systems, exact diagonalization, quantum Carlo and the quantum transfer matrix algorithm (QTM). We report on a new improved QTM algorithm, obtained by a combination of the QTM with the recently developed look-ahead Lanczos algorithm for non-hermitian matrices. These methods give reliable results and can answer many open questions in the field of strongly correlated electron systems.     

Glass integrated optics circuit for 1.48/1.55- and 1.30/1.55-µm-wavelength division multiplexing and 1/8 splitting

We demonstrate the integration, in a single glass substrate, of a 1.48/1.55-μm-wavelength multiplexer and a 1.30/1.55-μm-wavelength multiplexer followed by a 1/8 splitter by using potassium- and silver-double-ion-exchange processes. The wavelength multiplexers are based on nonsymmetric three-port Mach-Zehnder interferometers, and symmetrical Y junctions are used for achromatic splitting. The facet-to-facet excess loss in both the 1.48/1.55-μm multiplexer and in the integrated 1.30/1.55-μ m multiplexer and 1/8 splitter is less than 2.7 dB. The device can be used, in connection with an erbium-doped fiber, in future wavelength division multiplexing subscriber networks in which amplification is needed in the 1.55-μm-wavelength region.     

So, you want to be a systems biologist? Determinants for creating graduate curricula in systems biology

Systems biology is uniquely situated at the interface of computing, mathematics, engineering and the biological sciences. This positioning creates unique challenges and opportunities over other interdisciplinary studies when developing academic curricula. Integrative systems biology attempts to span the field from observation to innovation, and thus requires successful students to gain skills from mining to manipulation. The authors outline examples of graduate program structures, as well as curricular aspects and assessment metrics that can be customised around the environmental niche of the academic institution towards the formalisation of effective educational opportunities in systems biology. Some of this material was presented at the 2009 Foundations of Systems Biology in Engineering (FOSBE 2009) Conference in Denver, August 2009.     

A novel driver with adjustable frequency and phase for traveling‐wave type ultrasonic motor

Abstract

This paper describes the design of a traveling‐wave ultrasonic motor (TWUSM) drive circuit, intended to simultaneously employ both driving frequency and phase modulation control. The operating principles and a detailed analysis of the proposed driving circuit, consisting of voltage‐controlled oscillator (VCO), voltage‐controlled phase‐shifter circuit and non‐resonant power amplifier converter, are introduced. To drive the USM effectively, a two‐phase power amplifier converter using non‐resonant output was designed to provide a balanced two‐phase voltage source. Two‐phase output driving voltages could be maintained at the same peak voltage value as the driving frequency under varying phase‐modulation processes. Detailed experimental results are provided to demonstrate the effectiveness of the proposed driving circuit.     

Measurements of radio channels and bit error rate estimation of IEEE802.16 standard in semi-rural environment at three frequencies in the 2?6 GHz frequency band

Simultaneous measurements with 10 MHz bandwidth at 2.5, 3.5 and 5.8 GHz were performed in a rural/semi-rural environment in the UK. The measurements were processed to generate power delay profiles to estimate the root mean square delay spread of the channel. The frequency range of the orthogonal frequency division multiplexing (OFDM) symbol bandwidth that has dropped below a predefined level, termed herein as average fade bandwidth, and the corresponding level crossing are employed to quantify the severity of frequency selectivity. The channel data were used to estimate the bit error rate, for the 256 carrier-OFDM IEEE802.16 standard using a frequency domain channel simulator especially designed for the study. It was found that the performance of quasi-stationary wireless broadband systems depends mainly upon the frequency selectivity and the channel coding rate with 1/2 rate coding giving a superior performance to 3/4 rate coding. Puncturing was found to weaken the capability of forward error correction coding in the presence of series of deep fades in the channel transfer function.     

Stability criteria for neutral systems with time‐varying delays and nonlinear uncertainties

Abstract

The asymptotic stability problem for a class of neutral systems with time‐varying delays and nonlinear uncertainties is investigated in this paper. LMI‐based delay‐dependent criteria are proposed to guarantee the asymptotic stability of the considered systems. New Lyapunov‐Krasovskii functional and Leibniz‐Newton formulae are used to find the delay‐dependent stability results. Finally, some numerical examples are illustrated to show the improved results from using this method.     

Uncertain process–based reliability and maintenance modeling for systems under mutually dependent degradation and shock processes

For the systems that experience competing failure processes, an uncertain process–based degradation model is developed to describe the systems. The competing degradation process is composed of internal continuous degradation and external shocks, and the mutual dependence between them is considered. When the magnitude of the internal degradation exceeds the threshold, the soft failure occurs. While for the shock processes involving the randomness and the subjective information, we adopt the uncertain random renewal reward process to characterize it. Hard failure occurs when the damage of the shock process exceeds the strength threshold of the system. By using the belief reliability metric, the reliability of the degraded system is defined as the chance measure that neither soft failure nor hard failure occurs. And the effect of the degradation-shock dependence on the system reliability is performed by the parametric studies. Then the proposed degradation model is introduced into the preventive maintenance strategy to minimize the average maintenance cost. Using the microelectromechanical systems as an example, the effectiveness of the constructed degradation model and maintenance strategy is illustrated, and the proposed model can characterize the system degradation process in a superior way to the stochastic process model. These methods can be applied to other similar degraded systems and provide support for maintenance decisions.     

Thin-film nano- and micro-electromechanical systems – the basis of contemporary and future pressure sensors for rocket and aviation engineering

Ways of improving information converters are considered, in particular, primary information converters (sensors). Problems are described that arise during the use of sensors in space rocket and aviation engineering. Designs are presented for thin-film nano- and micro-electromechanical systems that are the basis of contemporary and future tensoresistive pressure sensors. Areas of research are determined with the aim of minimizing the effect of critical destabilizing factors (temperature, vibration) within these systems and pressure sensors based upon them.     

On δ-record observations: asymptotic rates for the counting process and elements of maximum likelihood estimation

Given a sequence of random variables {X _n ,n≥1} and δ∈ℝ, an observation X _n is a δ-record if X _n >max {X ₁,…,X _n−1}+δ. We obtain, for δ≤0, weak and strong laws of large numbers for the counting process of δ-records among the first n observations from a sequence of independent identically distributed random variables, with common distribution F, possibly discontinuous. We provide examples of our results in the context of common probability distributions. Finally, we show how δ-records can be used for maximum likelihood estimation.     

Effects of pressure sensitivity on the η factor and the J integral estimation for compact tension specimens

In this paper, the effects of pressure-sensitive yielding on the factor and the J integral estimation for compact tension specimens are investigated. The analytical expressions for and J for pressure-insensitive von Mises materials are generalized to pressure-sensitive Drucker-Prager materials using a lower bound approach. The factor as a function of the pressure sensitivity and the normalized crack depth for compact tension specimens is derived under plane stress and plane strain conditions. The numerical results indicate that the factor decreases as the pressure sensitivity increases. The effects are more pronounced under plane strain conditions than under plane stress conditions. However, the effects of the pressure sensitivity on are found to be mild in general. For rigid perfectly-plastic materials, the J estimation for pressure-sensitive materials is also reduced to a simple expression of the tensile yield stress times the crack tip opening displacement as for the von Mises materials.