Extended Robust \mathcal{H}_{2} and \mathcal{H}_{\infty} Filter Design for Discrete Time-Invariant Linear Systems with Polytopic Uncertainty

This paper is concerned with the problem of robust $\mathcal{H}_{2}$ and $\mathcal{H}_{\infty}$ filter design for discrete-time linear time-invariant systems with polytopic parameter uncertainties. Less conservative robust $\mathcal{H}_{2}$ and $\mathcal{H}_{\infty}$ filter design procedures are proposed in terms of single-parameter minimization problems with linear matrix inequality constraints. To this end, we generalize the filter structures available in the literature to date in such a way that the filter’s next state is built by summing the filter’s states over several samples from the past to the present. For stability of the filtering error system, the homogeneous polynomial parameter-dependent Lyapunov functions are employed. Finally, illustrative examples are given to demonstrate the merits of the proposed methods.     

Soft X-ray Absorption and Photoemission Spectroscopy Study of Cobalt-Based Thermoelectric Oxides: \hbox{Ca}_3\hbox{Co}_4\hbox{O}_9, \hbox{Ca}_3\hbox{Co}_2\hbox{O}_6, and \hbox{Bi}_{2}\hbox{Sr}_{2}\hbox{Co}_2\hbox{O}_{y}

The electronic structures of Co-based potential thermoelectric (TE) oxides, including $\hbox{Ca}_3\hbox{Co}_4\hbox{O}_9$ and $\hbox{Bi}_{2}\hbox{Sr}_{2}\hbox{Co}_2\hbox{O}_{y}$ (y = 8 + δ) single crystals and polycrystalline $\hbox{Ca}_3\hbox{Co}_2\hbox{O}_6$ , have been investigated by employing soft x-ray absorption spectroscopy (XAS) and photoemission spectroscopy (PES). Co 2p XAS measurements show that Co ions are nearly trivalent ( $\hbox{Co}^{3+}$ ) in all of these Co-based TE oxides with a small mixture of $\hbox{Co}^{4+}$ ions in $\hbox{Bi}_{2}\hbox{Sr}_{2}\hbox{Co}_2\hbox{O}_{y}$ . Valence-band PES and O 1s XAS measurements show that the occupied Co 3d states are located at the top of the valence bands and that the lowest unoccupied states have the primarily Co 3d character, respectively. These findings suggest the importance of the Co 3d electronic structures in determining TE properties of these Co-based oxides.     

WCDMA Multiclass Downlink Capacity and Interference Statistics of Cigar-Shaped Microcells in Highways

In this paper, the multiclass downlink capacity and the interference statistics of the sectors of a cigar-shaped microcells using wideband code-division multiple-access with soft handover mode are analyzed. The two-slope propagation model with log-normal shadowing is used in the analysis where a model of 8 cigar-shaped microcells is utilized. The performance of the downlink is studied for different [sector range R, standard deviation of the shadowing ( $\sigma _{1}$ and $\sigma _{2})$ and propagation exponents ( $\text{ s}_{1}$ and $\text{ s}_{2})$ ]. It is found that increasing the sector range from 500 to 1,000 m will increase the sector downlink capacity. Also, it is found that increasing the value of the propagation parameters ( $\sigma _{1}$ and $\sigma _{2})$ will reduce the downlink sector capacity. It is noticed that, the effect of changing the propagation exponent $\text{ s}_{1}$ is null while increasing the propagation exponent $\text{ s}_{2}$ will increase the downlink capacity.     

A novel image segmentation model with an edge weighting function

A variational model for image segmentation consists of a data term and a regularization term. Usually, the data term is chosen as squared $\text{ L }_{2}$ norm, and the regularization term is determined by the prior assumption. In this paper, we present a novel model in the framework of MAP (maximum a posteriori). A new iteratively reweighted $\text{ L }_{2}$ norm is used in the data term, which shares the advantages of $\text{ L }_{2}$ and mixed $\text{ L }_{21}$ norm. An edge weighting function is addressed in the regularization term, which enforces the ability to reduce the outlier effects and preserve edges. An improved region-based graph cuts algorithm is proposed to solve this model efficiently. Numerical experiments show our method can get better segmentation results, especially in terms of removing outliers and preserving edges.     

Decentralized \mathcal{L}_{2}–\mathcal{L}_{\infty} Filtering for Interconnected Markovian Jump Systems with Delays

This paper deals with the problem of decentralized $\mathcal{L}_{2}$ – $\mathcal{L}_{\infty}$ filtering for a class of interconnected (or large-scale) Markovian jump systems with constant time delays. The purpose is to present delay-dependent conditions for the existence of mode-dependent decentralized filters, which guarantees that the filtering error system is stochastically stable with a prescribed $\mathcal{L}_{2}$ – $\mathcal{L}_{\infty}$ disturbance attenuation level. Such a purpose is achieved by using a mode-dependent centralized Lyapunov functional together with the so-called Jensen’s inequality. The obtained synthesis conditions are expressed in terms of linear matrix inequalities (LMIs), which leads to a convex design method for the concerned filters. An example including numerical and simulation results is provided finally to illustrate the effectiveness of the proposed design method.     

Anisotropic Thermopower of the Kondo Insulator \hbox {CeRu}_4\hbox {Sn}_6

The intermetallic compound \(\hbox {CeRu}_4\hbox {Sn}_6\) has been tentatively classified as Kondo insulator. This class of material, especially non-cubic representatives, is not yet fully understood. Here we report thermopower measurements on single-crystalline \(\hbox {CeRu}_4\hbox {Sn}_6\) between 2 K and 650 K, along the main crystallographic directions. Large positive thermopower is observed in the directions along which the hybridization is strong and a Kondo insulating gap forms. A negative contribution to the thermopower dominates for the crystallographic \(c\) axis where hybridization is weak and metallicity prevails.     

\mathcal{H}_{\infty} Filtering for Short-Time Switched Discrete-Time Linear Systems

In this paper, the $\mathcal{H}_{\infty}$ filtering problem for a class of short-time switched discrete-time linear systems is investigated. For such systems, switching always occurs in some short interval. Since the error state may attain large unacceptable values in short-time switching intervals, besides the asymptotic stability of error dynamics, the boundedness of error state is also significant for short-time switched systems. Thus the designed filter is composed of two parts: asymptotic filter, based upon the existing results, ensures the asymptotic stability of the system during normal, relatively long interval, and finite-time filter ensures system to be finite-time bounded during the short interval of switching, which is the main concern in this paper. By introducing the concept of finite-time boundedness, the proposed filter is formulated as a set of sub-filters ensuring the error dynamics $\mathcal{H}_{\infty}$ finite-time bounded in the short switching interval. Finally, a numerical example is provided to illustrate the effectiveness of this approach.     

Design and modeling of high-resolution multibit log-domain \Delta \Sigma modulators

Log-domain Delta-Sigma ( $\Delta \Sigma$ ) modulators are attractive for implementing analog-to-digital (A/D) converters (ADCs) targeting low-power low-voltage applications. Previously reported log-domain $\Delta \Sigma$ modulators were limited to 1-bit quantization and, hence, could not benefit from the advantages associated with multibit quantization (namely, reduced in-band quantization noise, and increased modulator stability). Unlike classical $\Delta \Sigma$ modulators, directly extending a log-domain $\Delta \Sigma$ modulator with a 1-bit quantizer to a log-domain $\Delta \Sigma$ modulator with a multibit quantizer is challenging, in terms of CMOS circuit implementation. Additionally, the realization of log-domain $\Delta \Sigma$ modulators targeting high-resolution applications necessitates minimization of distortion and noise in the log-domain loop-filter. This paper discusses the challenges of multibit quantization and digital-to-analog (D/A) conversion in the log-domain, and presents a novel multibit log-domain $\Delta \Sigma$ modulator, practical for CMOS implementation. SIMULINK models of log-domain $\Delta \Sigma$ modulator circuits are proposed, and the effects of various circuit non-idealities are investigated, including the effects of log-domain compression–expansion mismatch. Furthermore, this paper proposes novel low-distortion log-domain analog blocks suitable for high-resolution analog-to-digital (A/D) conversion applications. Circuit simulation results of a proposed third-order 3-bit class AB log-domain $\Delta \Sigma$ loop-filter demonstrate 10.4-bit signal-to-noise-and-distortion-ratio (SNDR) over a 10 kHz bandwidth with a $0.84\,V_{pp}$ differential signal input, while operating from a 0.8 V supply and consuming a total power of $35.5\,\upmu \hbox {W}.$      

Effect of the stoichiometric composition of the Si(111)\sqrt {21} × \sqrt {21} -(Au, Ag) surface phase on substrate conductivity

The conductivity of a silicon substrate with a Si(111) $\sqrt {21} $ × $\sqrt {21} $ -(Au, Ag) surface phase is studied. It is found that the surface conductivity of such a substrate varies depending on the ratio of the amounts of gold and silver in the given structure. An analysis of the behavior of the Si(111) $\sqrt {21} $ × $\sqrt {21} $ -(Au, Ag) surface conductivity during silver adsorption indicates the effect of a space-charge layer in the surface region of the substrate on the measurement results.     

Formation of a Buffer Layer for Graphene on C-Face SiC{0001}

Graphene films prepared by heating the SiC $ (000\bar{1}) $ surface (the C-face of the {0001} surface) in a Si-rich environment have been studied using low-energy electron diffraction (LEED) and low-energy electron microscopy. Upon graphitization, an interface with $ \sqrt {43} \times \sqrt {43} - R \pm 7.6^\circ $ symmetry is observed by in situ LEED. After oxidation, the interface displays $ \sqrt 3 \times \sqrt 3 - R 30^\circ $ symmetry. Electron reflectivity measurements indicate that these interface structures arise from a graphene-like “buffer layer” that forms between the graphene and the SiC, similar to that observed on Si-face SiC. From a dynamical LEED structure calculation for the oxidized C-face surface, it is found to consist of a graphene layer sitting on top of a silicate (Si₂O₃) layer, with the silicate layer having the well-known structure as previously studied on bare SiC $ (000\bar{1}) $ surfaces. Based on this result, the structure of the interface prior to oxidation is discussed.     

Four-Dimensional Gallant–Lambert–Vanstone Scalar Multiplication

The GLV method of Gallant, Lambert, and Vanstone (CRYPTO 2001) computes any multiple kP of a point P of prime order n lying on an elliptic curve with a low-degree endomorphism Φ (called GLV curve) over $\mathbb{F}_{p}$ as $$kP = k_1P + k_2\varPhi(P) \quad\text{with } \max \bigl\{ |k_1|,|k_2| \bigr\} \leq C_1\sqrt{n} $$ for some explicit constant C ₁>0. Recently, Galbraith, Lin, and Scott (EUROCRYPT 2009) extended this method to all curves over $\mathbb{F}_{p^{2}}$ which are twists of curves defined over $\mathbb{F}_{p}$ . We show in this work how to merge the two approaches in order to get, for twists of any GLV curve over $\mathbb{F}_{p^{2}}$ , a four-dimensional decomposition together with fast endomorphisms Φ,Ψ over $\mathbb{F}_{p^{2}}$ acting on the group generated by a point P of prime order n, resulting in a proven decomposition for any scalar k∈[1,n] given by $$kP=k_1P+ k_2\varPhi(P)+ k_3\varPsi(P) + k_4\varPsi\varPhi(P) \quad \text{with } \max_i \bigl(|k_i| \bigr)< C_2\, n^{1/4} $$ for some explicit C ₂>0. Remarkably, taking the best C ₁,C ₂, we obtain C ₂/C ₁<412, independently of the curve, ensuring in theory an almost constant relative speedup. In practice, our experiments reveal that the use of the merged GLV–GLS approach supports a scalar multiplication that runs up to 1.5 times faster than the original GLV method. We then improve this performance even further by exploiting the Twisted Edwards model and show that curves originally slower may become extremely efficient on this model. In addition, we analyze the performance of the method on a multicore setting and describe how to efficiently protect GLV-based scalar multiplication against several side-channel attacks. Our implementations improve the state-of-the-art performance of scalar multiplication on elliptic curves over large prime characteristic fields for a variety of scenarios including side-channel protected and unprotected cases with sequential and multicore execution.     

Performance Analysis of Microwave Radio Refractivity on Radio Field Strength and Radio Horizon Distance Over Akure,Nigeria

Surface radio refractivity studies are being carried out in Akure, \((7.15^{\circ }\hbox {N}, 5.12^{\circ }\hbox {E})\) South-Western Nigeria, by in-situ measurement of atmospheric pressure, temperature, and relative humidity using Wireless Weather Station (Integrated Sensor Suit, ISS). Five years of measurement (January, 2007–December, 2011) were used to compute the surface radio refractivity and its diurnal, daily, seasonal and yearly variations are analyzed. The results were then used to compute radio horizon distance \((\hbox {R}_\mathrm{DH})\) and examine the field strength (FSV) variability. Results obtained show that the surface radio refractivity, \(\hbox {N}_\mathrm{s}\) , varies with the time of the day as well as the seasons of the year. High values of \(\hbox {N}_\mathrm{s}\) were recorded in the morning and evening hours while the values were minima around 1,500 h local time. An average value of surface radio refractivity of 364.74 N-units was obtained for this location. The annual maximum mean of FSV is 15.24 dB and the minimum is 2.20 dB. This implies that the output of a receiving antenna in Akure may generally be subject to variations not less than 2 dB in a year, but can be as high as 15 dB.     

A Statistical Model for the Influence of Body Dynamics on the Gain Pattern of Wearable Antennas in Off-Body Radio Channels

The goal of this paper is to address a statistical approach for modelling the influence of body dynamics on the gain pattern of wearable antennas in Body Area Networks, particularly in off-body radio channels. A dynamic model was developed based on Motion Capture data, describing a realistic human body movement. Antennas are located on 4 typical positions (i.e., Head, Chest, Arm and Leg), for which statistics of antenna orientation (i.e., average and standard deviation of elevation and azimuth angles) were calculated for 2 dynamic scenarios, i.e., Walk and Run. Based on the rotation of the antenna, the statistics of gain patterns of a wearable patch antenna operating at 2.45 GHz were calculated. The standard deviation of the change in the antenna orientation is the highest for the Arm location, reaching $19^{\circ }$ and $37^{\circ }$ for the Run scenario, for elevation and azimuth angles, respectively. For most of the scenarios, the distribution of the change in antenna orientation fits well to a Kumaraswamy distribution (using the $\chi ^2_{95\,\%}$ test). For all antenna positions and the Walk scenario, the standard deviation is $<4^{\circ }$ .     

Design of an Ultra-Wideband Microstrip Patch Antenna Suspended by Shorting Pins

Designing a compact wideband microstrip patch antenna which is composed of a folded-patch feed, a symmetric E-shaped edge and shorting pins is presented in this paper. One pin is applied in order to expand the impedance bandwidth. Two other pins are utilized to miniaturize the size of patch as well. The measured impedance bandwidth ( $\text{ VSWR}\le 2$ ) of the fabricated antenna is more than 90 % in the frequency range 3.92–10.67 GHz for ultra-wideband (UWB) applications. The antenna size is $0.438\lambda _{0}\times 0.365\lambda _{0}\times 0.170\lambda _{0}$ at its center operating frequency. Also, radiation patterns with acceptable stability within the bandwidth are obtained. In addition, the effects of some key parameters are investigated to describe the performance of the proposed design.     

Efficient Reverse Converters for 4-Moduli Sets {2^{2n-1}-1, 2^{n}, 2^{n}+1, 2^{n}-1} and {2^{2n-1}, 2^{2n-1}-1, 2^{n}+1, 2^{n}-1} Based on CRTs Algorithm

Speed and complexity of a reverse converter are two important factors that affect the performance of a residue number system. In this paper, two efficient reverse converters are proposed for the 4-moduli sets {2 \(^{2n-1}-1\) , 2 \(^{n}\) , 2 \(^{n}+1\) , 2 \(^{n}-1\) } and {2 \(^{2n-1}\) , 2 \(^{2n-1}-1\) , 2 \(^{n}+1\) , 2 \(^{n}-1\) } with 5 \(n\) -bit and 6 \(n\) -bit dynamic range, respectively. The proposed reverse converter for moduli set {2 \(^{2n-1}-1\) , 2 \(^{n}\) , 2 \(^{n}+1\) , 2 \(^{n}-1\) } has been designed based on CRT and New CRT-I algorithms and in two-level structure. Also, an efficient reverse converter for moduli set {2 \(^{2n-1}\) , 2 \(^{2n-1}-1\) , 2 \(^{n}+1\) , 2 \(^{n}-1\) } has been designed by applying New CRT-I algorithm. The proposed reverse converters are based on adders and hence can be simply implemented by VLSI circuit technology. The proposed reverse converters offer less delay and hardware cost when compared with the recently introduced reverse converters for the moduli sets {2 \(^{n}+1\) , 2 \(^{n}-1\) ,2 \(^{n}\) , 2 \(^{2n+1}-1\) } and {2 \(^{n}+1\) , 2 \(^{n}-1\) , 2 \(^{2n}\) , 2 \(^{2n+1}-1\) }.     

Elliptic Curve Discrete Logarithm Problem over Small Degree Extension Fields

In 2008 and 2009, Gaudry and Diem proposed an index calculus method for the resolution of the discrete logarithm on the group of points of an elliptic curve defined over a small degree extension field $\mathbb{F}_{q^{n}}$ . In this paper, we study a variation of this index calculus method, improving the overall asymptotic complexity when $n = \varOmega(\sqrt [3]{\log_{2} q})$ . In particular, we are able to successfully obtain relations on $E(\mathbb{F}_{q^{5}})$ , whereas the more expensive computational complexity of Gaudry and Diem’s initial algorithm makes it impractical in this case. An important ingredient of this result is a variation of Faugère’s Gröbner basis algorithm F4, which significantly speeds up the relation computation. We show how this index calculus also applies to oracle-assisted resolutions of the static Diffie–Hellman problem on these elliptic curves.     

A Novel Haar Wavelet-Based BPSK OFDM System Robust to Spectral Null Channels and with Reduced PAPR

Orthogonal frequency-division multiplexing (OFDM) has lately gained a great deal of attention and is considered as a strong candidate for many next-generation wireless communication systems. However, OFDM is very sensitive to nonlinear effects due to the high peak-to-average power ratio (PAPR) owned by the transmitted signals and does not show robustness to spectral null channels. This paper proposes a novel BPSK OFDM system based on Haar wavelet transformation. The Haar wavelet transformation operates decomposition over the data symbol sequence after binary-to-complex mapping shows that half of the data symbols are zeros and the rest are either ${\sqrt{2}}$ or ${-\sqrt{2}}$ . Then, we have the PAPR reduced by ${10\log_{10} 2\approx 3}$ ?dB at most, compared with the conventional OFDM system. We also propose a novel decoding algorithm for the proposed OFDM system to show robustness to spectral null channels, and derive the bit error rate (BER) performance in theory from unbalanced QPSK modulation. Finally, we compare BER performance of our proposed OFDM with the conventional OFDM over different channels to show the excellent performance of our proposed OFDM system.     

A 4-bit CMOS phase shifter for millimeter-wave phased arrays

A 4-bit active phase shifter for millimeter-wave phased arrays is presented in this brief. The proposed phase shifter has achieved a phase-shifting range of $360^{\circ }$ with a $22.5^{\circ }$ resolution over 40 to 50-GHz. Thanks to the careful dimension designs of digitally controlled gain stage in the programmable weighted combiner, the active phase shifter achieves root-mean-square phase and gain errors of $5^{\circ }$ and 1.25-dB at 45-GHz, respectively. The measurement results also show that the input and output return losses are better than 7-dB from 40 to 50-GHz. The whole chip dissipates only 10.7-mA from 1.2-V supply excluding output driven buffer.     

A New Linearized CCII-Based Fully Differential CMOS Transconductor Used for \hbox {G}_\mathrm{m}-C Active Filters Implementation

The paper presents a new linearized, of high performance, fully differential transconductor, based on class AB second generation current conveyor (CCII) in CMOS technology. The proposed circuit is composed by two positive CCII cells connected in series and a common mode feedback loop. Unlike other CMOS circuits on the basis of CCII reported in the literature, the proposed transconductor cell allows to obtain a higher transconductance value, an improved linearity and operates at high frequency for a 3.3 V supply voltage. As an application, the new transconductor cell in CMOS technology is used for designing a 4th order differential $\hbox {G}_\mathrm{m}$ -C low-pass filters in different approximations (Butterworth and Chebyshev) operating up to 300 MHz cut-off frequency. The simulations performed in 130 nm CMOS process confirm the theoretical results.     

A 5 GHZ CMOS Power VCO with Novel Frequency-Modulation for RF Transmitter

A 5 GHz transformer-feedback power oscillator with novel frequency modulation (FM) up to 10 MHz is presented in this paper. The novel FM is achieved by a CMOS transistor between transformer and ground, which is designed for varying the equivalent inductance and mutual inductance of the transformer and shows no DC connection with the oscillation circuit. The major frequency tuning is realized by the variable capacitor which is controlled by a phase lock loop. The RF VCO with 210 MHz tuning range operates in class-E mode to achieve a cost-effective transmitter, which demonstrates a high DC-to-RF conversion efficiency of 39 %. A RF power of 15.1 dBm and phase noise better than \(-\) 109 dBc/Hz @ 100 kHz from the central frequency of 5.5 GHz is obtained with the biasing conditions V \(_\mathrm{ds}\) = 1.8 V and V \(_\mathrm{gs}\) = 0.65 V. The VCO also demonstrates an ultra-low voltage operation capability: with V \(_\mathrm{ds}\) = V \(_\mathrm{gs}\) = 0.6 V and DC power consumption of 9 mW, the output power is 4.5 dBm and the phase noise better than \(-\) 93 dBc/Hz @ 100 kHz. The die size of the transformer-feedback power oscillator is only \(0.4\times 0.6\) mm \(^{2}\) .