Modeling the flow-level performance of hierarchical modulation in?OFDMA-based networks

Hierarchical Modulation (HM) is a means to enhance the spectral efficiency of a system by superposing, in terms of modulation, an additional stream for a given user with good radio conditions on a basic stream of a user with worse radio conditions. This, in turn, increases the throughput of the former user and hence the overall performance of the whole system. We consider, in this work, such a performance at the flow level, for a realistic dynamic setting where users come to the system and leave it after a finite duration corresponding, for instance, to the completion of a file transfer. We specifically model and quantify, both analytically and via simulations, the gain thus achieved and propose two extensions to the basic HM algorithm: a first one in which a user with bad radio conditions is also superposed on one with better radio conditions and a second one in which a user of one type is further superposed on a user of the same type as well.     

A 1.8-V operation RF CMOS transceiver for 2.4-GHz-band GFSK applications

This paper describes a single-chip RF transceiver LSI for 2.4-GHz-band Gaussian frequency shift-keying applications, such as Bluetooth. This chip uses a 0.18-/spl mu/m bulk CMOS process for lower current consumption. The LSI consists of almost all the required RF and IF building blocks: a transmit/receive antenna switch, a power amplifier, a low noise amplifier, an image rejection mixer, channel-selection filters, a limiter, a received signal strength indicator, a frequency discriminator, a voltage controlled oscillator, and a phase-locked loop synthesizer. The bandpass filter for channel selection was difficult to achieve since it operates at a low supply voltage. However, because large interference is roughly rejected at the output of the image rejection mixer and a wide-input-range bandpass filter with an optimized input bias is realized, the transceiver can operate at a supply voltage of 1.8 V. In the IF section, we adopted a circuit design using the minimum number of passive elements, resistors and capacitors, for a lower chip area of 10.2 mm/sup 2/.     

Impact of Channel Errors on Decentralized Detection Performance of Wireless Sensor Networks: A Study of Binary Modulations, Rayleigh-Fading and Nonfading Channels, and Fusion-Combiners

We provide new results on the performance of wireless sensor networks in which a number of identical sensor nodes transmit their binary decisions, regarding a binary hypothesis, to a fusion center (FC) by means of a modulation scheme. Each link between a sensor and the fusion center is modeled independent and identically distibuted (i.i.d.) either as slow Rayleigh-fading or as nonfading. The FC employs a counting rule (CR) or another combining scheme to make a final decision. Main results obtained are the following: 1) in slow fading, a) the correctness of using an average bit error rate of a link, averaged with respect to the fading distribution, for assessing the performance of a CR and b) with proper choice of threshold, on/off keying (OOK), in addition to energy saving, exhibits asymptotic (large number of sensors) performance comparable to that of FSK; and 2) for a large number of sensors, a) for slow fading and a counting rule, given a minimum sensor-to-fusion link SNR, we determine a minimum sensor decision quality, in order to achieve zero asymptotic errors and b) for Rayleigh-fading and nonfading channels and PSK (FSK) modulation, using a large deviation theory, we derive asymptotic error exponents of counting rule, maximal ratio (square law), and equal gain combiners.     

A double-gate-type static-induction thyristor

A double-gate-type static-induction thyristor (DG-SIThy) with a high blocking voltage and a high current rating has been fabricated. In this paper, a basic operational mechanism, a fabrication procedure, and the electrical characteristics of the DG-SIThy are described. In the DG-SIThy, both electron injection and hole injection are controlled by signals applied to two gale regions so that the DG-SIThy is capable of higher frequency operations than a single-gate SIThy. In the DG-SIThy, described here, both a cathode and a gate (first gate) regions have been fabricated on one side of a semiconductor wafer and both an anode and gate.(second gate) regions on another side. For realizing the DG-SIThy with a high blocking voltage and a high current rating, we have tried attentively to form a p-n junction on one side of the wafer without influencing the p-n junction on the other side, and have developed a new counter-doping technique for epitaxial growth and an improved package structure for a compression-mounted device. The DG-SIThy fabricated with these techniques has shown a for-Ward blocking voltage of 1000 V, an average current rating of 100 A, and a forward voltage drop of 1.44 V at the rated anode current. A turn-on time of 0.95 its and a turn-off time of 0.48 µs have been observed at the rated anode current and at anode voltages of 650 and 550 V, respectively. As already speculated, the DG-SIThy shows a higher switching speed and a lower forward drop than the single-gate SIThy.     

Virtual impedance control for a regional dynamic voltage restorer

A dynamic voltage restorer (DVR) can be installed in a middle-voltage (MV) power grid, to concurrently protect a cluster of sensitive loads from voltage sags. To further improve its efficiency and reduce the difficulty in its implementation, a novel control strategy for operating such a DVR as a virtual impedance in series with sensitive loads is proposed in this paper. In addition to its usual function of compensating for voltage sags, such a DVR can also operate as a virtual inductance, to function as a fault current limiter (FCL) during a downstream fault, or a virtual capacitance, to function as a series compensator (SC) to compensate the voltage loss along the feeder line during heavy load. Based on a dual-loop control design, strategies for operating a DVR as a series virtual inductance and a virtual capacitance are proposed, and methods for tuning the parameter values and a stability analysis of the whole system are presented. The feasibility and effectiveness of the proposed method are verified by simulations using the PSCAD software, and experimental results obtained using a prototype DVR are presented.     

环Zn上椭圆曲线的密钥交换协议

设n=pq,p,q为奇素数,环Z_n上的椭圆曲线E_n(a,b)的SOM密钥交换协议与QV密钥交换协议均选取E_n(a,b)上的阶为M_n=lcm{#E_p(a,b),＃E_q(a,b)}的点G作为公钥(称G为基点),并且限定其对应的E_p(a,b)和E_q(a,b)均为循环群,这就限制了这两个协议只能选择一类特殊的椭圆曲线E_n(a,b)构作密钥交换协议.本文指出,E_p(a,b)和Eq(a,b)均为循环群这一限定是不必要的.本文给出了E_n(a,b)上存在阶为M_n的点G的一个充分必要条件,并给出一个例子,其中E_p(a,b)为循环群,E_q(a,b)为非循环群,且对应的E_n(a,b)上有阶为M_n的点G.同时,本文选取E_n(a,b)上阶为lcm{n₁,m₁}的点作为基点,这里n₁,m₁分别为E_p(a,b)和E_q(a,b)的最大循环子群的阶.这样,就能够选择更多的椭圆曲线E_n(a,b),用来构作密钥交换协议(包括将两方之间的密钥交换协议扩展到三方).     

A Note on Loaded Line Synthesis (Correspondence)

The purpose of this note is to present an alternate derivation of a formula for the synthesis of a loaded line. The problem is to determine the values of the normalized susceptances a and c mounted an exact quarter-wavelength apart along a uniform line. These are arranged in the order a, c, c,. . .c, a to achieve a loaded line with a given phase shift and perfect match. In order to analyze a particular line design for standing-wave ratio and phase shift over a band of frequencies on a digital computer, it is worthwhile to know the values of the susceptances to many more decimal places than one would achieve from a simple graph.     

X波段GaN HEMT内匹配器件

自主研制的GaN HEMT,栅源泄漏电流从1E-4A量级减小到了1E-6A量级,有效提高了栅漏击穿电压,改善了器件工作特性. 采用MIS结构制作了2.5mm栅宽GaN HEMT,测试频率为8GHz,漏源电压为33V时,器件连续波输出功率为18.2W,功率增益为7.6dB,峰值功率附加效率为43.0%. 2.5mm×4 GaN HEMT内匹配器件,测试频率8GHz,连续波输出功率64.5W,功率增益7.2dB,功率附加效率39%.     

Ultra-Low-Power Interface Chip for Autonomous Capacitive Sensor Systems

Traditionally, most of the sensor interfaces must be tailored towards a specific application. This approach results in a high recurrent design cost and time to market. On the other hand, generic sensor interface design reduces the costs and offers a handy solution for multisensor applications. This paper presents a generic sensor interface chip (GSIC), which can read out a broad range of capacitive sensors. It contains capacitance-to-voltage converters, a switched-capacitor amplifier, an analog-to-digital converter, oscillators, clock generation circuits and a reference circuit. The system combines a very low-power design with a smart energy management, which adapts the current consumption according to the accuracy and speed requirements of the application. The GSIC is used in a pressure and an acceleration monitoring system. The pressure monitoring system achieves a current drain of 2.3 muA for a 10-Hz sample frequency and an 8-bit accuracy. In the acceleration monitoring system, we measured a current of 3.3 muA for a sample frequency of 10 Hz and an accuracy of 9 bits     

Fast fully 3-D image reconstruction in PET using planograms

We present a method of performing fast and accurate three-dimensional (3-D) backprojection using only Fourier transform operations for line-integral data acquired by planar detector arrays in positron emission tomography. This approach is a 3-D extension of the two-dimensional (2-D) linogram technique of Edholm. By using a special choice of parameters to index a line of response (LOR) for a pair of planar detectors, rather than the conventional parameters used to index a LOR for a circular tomograph, all the LORs passing through a point in the field of view (FOV) lie on a 2-D plane in the four-dimensional (4-D) data space. Thus, backprojection of all the LORs passing through a point in the FOV corresponds to integration of a 2-D plane through the 4-D "planogram." The key step is that the integration along a set of parallel 2-D planes through the planogram, that is, backprojection of a plane of points, can be replaced by a 2-D section through the origin of the 4-D Fourier transform of the data. Backprojection can be performed as a sequence of Fourier transform operations, for faster implementation. In addition, we derive the central-section theorem for planogram format data, and also derive a reconstruction filter for both backprojection-filtering and filtered-backprojection reconstruction algorithms. With software-based Fourier transform calculations we provide preliminary comparisons of planogram backprojection to standard 3-D backprojection and demonstrate a reduction in computation time by a factor of approximately 15.     

Maximum likelihood parameter estimation of textures using aWold-decomposition based model

We present a solution to the problem of modeling, parameter estimation, and synthesis of natural textures. The texture field is assumed to be a realization of a regular homogeneous random field, which can have a mixed spectral distribution. On the basis of a 2-D Wold-like decomposition, the field is represented as a sum of a purely indeterministic component, a harmonic component, and a countable number of evanescent fields. We present a maximum-likelihood solution to the joint parameter estimation problem of these components from a single observed realization of the texture field. The proposed solution is a two-stage algorithm. In the first stage, we obtain an estimate for the number of harmonic and evanescent components in the field, and a suboptimal initial estimate for the parameters of their spectral supports. In the second stage, we refine these initial estimates by iterative maximization of the likelihood function of the observed data. By introducing appropriate parameter transformations the highly nonlinear least-squares problem that results from the maximization of the likelihood function, is transformed into a separable least-squares problem. The solution for the unknown spectral supports of the harmonic and evanescent components reduces the problem of solving for the transformed parameters of the field to a linear least squares. Solution of the transformation equations then provides a complete solution of the field-model parameter estimation problem. The Wold-based model and the resulting analysis and synthesis algorithms are applicable to a wide variety of texture types found in natural images.     

Identification of the source of an interferer by comparison with known carriers using a single satellite

We describe a method for identifying the source of a satellite interferer using a single satellite. The technique relies on the fact that the strength of a carrier signal measured at the downlink station varies with time due to a number of factors, and we use a quantum‐inspired algorithm to compute a “signature” for a signal, which captures part of the pattern of variation that is a characteristic of the uplink antenna. We define a distance measure to numerically quantify the degree of similarity between two signatures, and by computing the distances between the signature for an interfering carrier and the signatures of the known carriers being relayed by the same satellite at the same time, we can identify the antenna that the interferer originated from, if a known carrier is being relayed from it. As a proof of concept, we evaluate the performance of the technique using a simple statistical model applied to measured carrier data.     

A Binary-Weighted Switching and Reconfiguration-Based Programmable Gain Amplifier

In previous works, the authors reported on binary-weighted switching and reconfiguration techniques to design programmable gain amplifiers (PGAs) with a wide decibel (dB)-linear range, a small gain error, a wide 3-dB bandwidth, and high linearity. In this brief, two techniques are analyzed in more detail. Adopting the two techniques, a new low-voltage PGA version is proposed that offers a precise and process/temperature-insensitive gain and achieves a double dB-linear range with a small gain error while maintaining the same chip size, as compared with those of previous designs. Implemented in 0.18-mum CMOS, from the measurements, the proposed PGA shows a dB-linear gain range of 42 dB (-21 to 21 dB) with a gain error of less than plusmn 0.54 dB, a maximum input-referred third-order intercept point (IIP3) of 14 dBm, and a 3-dB bandwidth of 60 MHz at the maximum gain while consuming only 2.1 mA from a 1.5-V supply.     

Firewalls fend off invasions from the Net

Whether a computer is in a corporation, government agency, university, small business, or at home, if it is linked to a network, hackers are a risk. The first line of defense against them is a firewall, provided it is set up correctly. Firewall technology is a set of mechanisms that collectively enforce a security policy on communication traffic entering or leaving a guarded network domain. The security policy is the overall plan for protecting the domain. Embodied in hardware, software, or both, a firewall guards and isolates the domain. Broadly, firewalls attempt to maintain privacy and ensure the authenticity of data communications that pass through their domain's boundaries. Whether data is entering or leaving a domain, it is protected from eavesdropping (passive wiretapping) and change (active wiretapping). But only communication traffic entering or leaving a domain comes under the influence of firewall technology     

Flexible skew-symmetric shape model for shape representation, classification, and sampling.

Skewness of shape data often arises in applications (e.g., medical image analysis) and is usually overlooked in statistical shape models. In such cases, a Gaussian assumption is unrealistic and a formulation of a general shape model which accounts for skewness is in order. In this paper, we present a novel statistical method for shape modeling, which we refer to as the flexible skew-symmetric shape model (FSSM). The model is sufficiently flexible to accommodate a departure from Gaussianity of the data and is fairly general to learn a "mean shape" (template), with a potential for classification and random generation of new realizations of a given shape. Robustness to skewness results from deriving the FSSM from an extended class of flexible skew-symmetric distributions. In addition, we demonstrate that the model allows us to extract principal curves in a point cloud. The idea is to view a shape as a realization of a spatial random process and to subsequently learn a shape distribution which captures the inherent variability of realizations, provided they remain, with high probability, within a certain neighborhood range around a mean. Specifically, given shape realizations, FSSM is formulated as a joint bimodal distribution of angle and distance from the centroid of an aggregate of random points. Mean shape is recovered from the modes of the distribution, while the maximum likelihood criterion is employed for classification.     

Efficient computation of unique input/output sequences in finitestate machines

This paper makes two contributions toward computing unique input/output (UIO) sequences in finite-state machines. Our first contribution is to compute all UIO sequences of minimal lengths in a finite-state machine. Our second contribution is to present a generally efficient algorithm to compute a UIO sequence for each state, if it exists. We begin by defining a path vector, vector perturbation, and UIO tree. The perturbation process allows us to construct the complete UIO tree for a machine. Each sequence of input/output from the initial vector of a UIO tree to a singleton vector represents a UIO sequence. Next, we define the idea of an inference rule that allows us to infer UIO sequences of a number of states from the UIO sequence of some state. That is, for a large class of machines, it is possible to compute UIO sequences for all possible states from a small set of initial UIOs. We give a modified depth-first algorithm, called the hybrid approach, that computes a partial UIO tree, called an essential subtree, from which UIO sequences of all possible states can be inferred. Using the concept of projection machines, we show that sometimes it is unnecessary to construct even a partial subtree. We prove that if a machine remains strongly connected after deleting all the converging transitions, then all of the states have UIO sequences. To demonstrate the effectiveness of our approach, we develop a tool to perform experiments using both small and large machines     

Perspectives on special issues [From the Editor]

The special issues of IEEE Signal Processing Magazine (SPM) provide a forum wherein a collection of tutorials, concentrated on a specific topic, span the entire field and expose a wide-ranging segment of readers in the signal processing community to a thorough overview of the topic. The presentation of complementary tutorials, focused on a particular area in signal processing and aimed at a broad technical audience, is a unique feature of this publication. The wide exposure of selected topics to a large audience makes the special issues in SPM a top venue to educate and raise the prominence of important disciplines in signal processing.     

多路径环境下电信流量模型研究

在下一代通信网络中,一个终端可同时拥有多个网络接口,在一对源、目的终端间存在多条可用路径。这为网络通信提供了一种全新的思路,即利用多条路径并发进行数据传输。针对多路径传输出现的问题,文章为多路径传输建立了流量模型,分析了多路径传输流媒体的优势,提出了＂流体带宽＂和＂流体调度＂的概念,并引入网络流理论计算了多路径环境下的目标流量。     

A mathematical theory of antenna arrays with randomly spaced elements

Various probabilistic properties of a large antenna array with randomly spaced elements have been studied. It is found that for almost all cases of practical interest the required number of elements is closely related to the desired sidelobe level and is almost independent of the aperture dimension, the resolution (or the beamwidth) depends mainly on the aperture dimension, and the directive gain is proportional to the number of elements used if the average spacing is large. As a consequence the number of elements required is considerably less than that with uniform spacings. Starting with a given number of elements and a given aperture size, it is possible to improve the resolution by a factor of ten, a hundred, or more by spreading these elements over a larger aperture with little risk in obtaining a much higher sidelobe level and a lower directive gain. In fact, this method offers a solution which is optimum in a certain statistical sense, i.e., all sidelobes are of equal level with equal probability. In addition, this analysis also gives a simple estimate of the sidelobe level of most nonuniformly spaced antenna arrays. In a number of such arrays studied by various investigators with high speed computers, the agreement found is remarkable.