Le dialogue homme- machine en langue naturelle : un défi ?

The implementation of a natural language manmachine dialogue in a data base or knowledge base query system is a difficult task. We present hereafter three different approaches to this problem : dialog modeling, exemplified through a linguistic scheme and several computational implementations ; the cooperation principles in a dialog and their associated algorithms ; and, lastly, the artificial intelligence approach based on speech acts theory and the techniques for generating and recognizing plans. We conclude by assessing the possible use of current speech processing techniques and by listing still unsolved problems.     

Quantum signal processing

In this article we present a signal processing framework that we refer to as quantum signal processing (QSP) (Eldar 2001) that is aimed at developing new or modifying existing signal processing algorithms by borrowing from the principles of quantum mechanics and some of its interesting axioms and constraints. However, in contrast to such fields as quantum computing and quantum information theory, it does not inherently depend on the physics associated with quantum mechanics. Consequently, in developing the QSP framework we are free to impose quantum mechanical constraints that we find useful and to avoid those that are not. This framework provides a unifying conceptual structure for a variety of traditional processing techniques and a precise mathematical setting for developing generalizations and extensions of algorithms, leading to a potentially useful paradigm for signal processing with applications in areas including frame theory, quantization and sampling methods, detection, parameter estimation, covariance shaping, and multiuser wireless communication systems. We present a general overview of the key elements in quantum physics that provide the basis for the QSP framework and an indication of the key results that have so far been developed within this framework. In the remainder of the article, we elaborate on the various elements in this figure.     

声表面波微压力传感器的信号调理电路设计

声表面波传感器因其独特的设计原理,具有体积小,无源无线,精度高等特点,在物理和生物领域应用广泛。针对声表面波输出频率信号采集复杂的问题,该文设计了一类信号调理电路,通过谐振选频电路稳定输出信号,并通过滤波、放大、整形将输出信号转变为方波信号,最终得到易于采集处理的频率信号。通过Multisim仿真证明,该电路有良好的信号调理能力,易集成。这为声表面波微压力传感器的信号采集和处理奠定了基础。     

智能天线技术及应用研究评述

智能天线是提高无线传输性能的一项关键技术,是无线通信领域持续的研究热点之一,其中部分研究成果已经在无线通信、雷达、电子对抗等广泛的领域获得了成功的应用,并且未来无线系统设计中会越来越多的采用智能天线技术.为此,文章首先简要回顾了有关智能天线技术的发展历史,介绍了其中主要的阵列处理算法原理,给出了基于软件无线电和FPGA/DSP等可重配置软硬件系统设计参考方案,通过一些设计实例分析了应用中的实际问题和解决途径,最后提出了有关这一技术领域未来发展的展望.     

BER Performance of Wireless BPSK Communication System in Tunnels With and Without Traffic

The bit error rate (BER) performance for high-speed personal communication service in tunnels with and without traffic is investigated. The impulse responses of tunnels for any transmitter–receiver location are computed by shooting and bouncing ray/image techniques. By using the impulse responses of these multipath channels, the BER performance of BPSK (binary phase shift keying) system with phase and timing recovery circuits are calculated. Numerical results have shown that the multipath effect by the vehicles in the tunnel is an important factor for BER performance. In addition, the effect of space diversity techniques and decision feedback equalizer on mitigating the multipath fading is also investigated.Chien-Hung Chen was born in Kaohsiung, Taiwan, Republic of China, on 8 March 1971. He received the MSEE degree from Tamkang University in 1999. He is studying for Ph.D. degree in the Department of Electrical Engineering, Tamkang University. His current research interests include indoor wireless communications and numerical techniques in electromagnetics.Chien-Ching Chiu was born in Taoyuan, Taiwan, Republic of China, on 23 January 1963. He received the BSCE degree from National Chiao Tung University, Hsinchu, Taiwan, in 1985 and MSEE and PhD degrees from National Taiwan University, Taipei, Taiwan, in 1987 and 1991, respectively. From 1987 to1989, he served in the ROC Army Force as a communication officer. In 1992 he joined the faculty of the Department of Electrical Engineering, Tamkang University, where he is now an Professor. He was a visiting scholar at the MIT and University of Illinois, Urbana from 1998 to 1999. His current research interests include microwave imaging, numerical techniques in electromagnetics and indoor wireless communications.Shi-Cheng Hung received the MSEE degree from Tamkang University in 1998. He is now a RF engineer. His current research interests include indoor wireless communications and numerical techniques in electromagnetics.Chien-Hung Lin received the MSEE degree from Tamkang University in 2001. He is now a RF engineer. His current research interests include indoor wireless communications and numerical techniques in electromagnetics.     

Three-dimensional image generation and processing in underwateracoustic vision

Underwater exploration is becoming more and more important for many applications involving physical, biological, geological, archaeological, and industrial issues. This paper aims at surveying the up-to-date advances in acoustic acquisition systems and data processing techniques, especially focusing on three-dimensional (3-D) short-range imaging for scene reconstruction and understanding. In fact, the advent of smarter and more efficient imaging systems has allowed the generation of good quality high-resolution images and the related design of proper techniques for underwater scene understanding. The term acoustic vision is introduced to generally describe all data processing (especially image processing) methods devoted to the interpretation of a scene. Since acoustics is also used for medical applications, a short overview of the related systems for biomedical acoustic image for motion is provided. The final goal of the paper is to establish the state of-the art of the techniques and algorithms for acoustic image generation and processing, providing technical details and results for the most promising techniques, and pointing out the potential capabilities of this technology for underwater scene understanding     

一种用于移动通信的无线电多媒体DSP芯片的实现

叙述了一种用于移动通信的无线电多媒体DSP芯片的实现。开发出的WM DSP芯片既支持用于Viterbi、时间同步等的通信指令,也支持多媒体指令。这个DSP能够处理可变长数据,并且在一个周期里可以执行4个MAC。提出的DSP采用了并行处理技术,如SIMD、矢量处理和DSP结构,并且采用了无线电应用的低功耗特性。整个DSP芯片包括测试电路和各种外围设备,如DMA、总线仲裁、定时器等等。除了存储器之外总共大约有170 000个门电路,并且时钟频率达到了100 MHz。     

Coherent acoustic array processing and localization on wireless sensor networks

Advances in microelectronics, array processing, and wireless networking have motivated the analysis and design of low-cost integrated sensing, computing, and communicating nodes capable of performing various demanding collaborative space-time processing tasks. In this paper, we consider the problem of coherent acoustic sensor array processing and localization on distributed wireless sensor networks. We first introduce some basic concepts of beamforming and localization for wide-band acoustic sources. A review of various known localization algorithms based on time-delay followed by least-squares estimations as well as the maximum-likelihood method is given. Issues related to practical implementation of coherent array processing, including the need for fine-grain time synchronization, are discussed. Then we describe the implementation of a Linux-based wireless networked acoustic sensor array testbed, utilizing commercially available iPAQs with built-in microphones, codecs, and microprocessors, plus wireless Ethernet cards, to perform acoustic source localization. Various field-measured results using two localization algorithms show the effectiveness of the proposed testbed. An extensive list of references related to this work is also included.     

Increasing data rate over wireless channels

Space-time coding (STC) is a new coding/signal processing framework for wireless communication systems with multiple transmit and multiple receive antennas. This new framework has the potential of dramatically improve the capacity and data rates. In addition, this framework presents the best trade-off between spectral efficiency and power consumption. ST codes (designed so far) come in two different types. ST trellis codes offer the maximum possible diversity gain and a coding gain without any sacrifice in the transmission bandwidth. The decoding of these codes, however, would require the use of a vector form of the Viterbi decoder. Space-time block codes (STBCs) offer a much simpler may of obtaining transmit diversity without any sacrifice in bandwidth and without requiring huge decoding complexity. In fact, the structure of the STBCs is such that it allows for very simple signal processing (linear combining) for encoding/decoding, differential encoding/detection, and interference cancellation. This new signal processing framework offered by ST codes can be used to enhance the data rate and/or capacity in various wireless applications. That is the reason many of these STC ideas have already found their way to some of the current third-generation wireless systems standards     

矢量波函数空间的电磁矢量恰当射影

提出了一种简化电磁场问题求解的新方法，将电磁场矢量的无旋场部分和无散场部分各自应用一个满足二阶方程的标量函数表示出来，然后由此分析了电磁场矢量在矢量波函数空间的恰当射影问题，并给出用一个标量格林函数构造的无散电磁场并矢格林函数。     

Mathematical Evaluation of Environmental Monitoring Estimation Error through Energy-Efficient Wireless Sensor Networks

In this paper, the estimation of a scalar field over a bidimensional scenario (e.g., the atmospheric pressure in a wide area) through a self-organizing wireless sensor network (WSN) with energy constraints is investigated. The sensor devices (denoted as nodes) are randomly distributed; they transmit samples to a supervisor by using a clustered network. This paper provides a mathematical framework to analyze the interdependent aspects of WSN communication protocol and signal processing design. Channel modelling and connectivity issues, multiple access control and routing, and the role of distributed digital signal processing (DDSP) techniques are accounted for. The possibility that nodes perform DDSP is studied through a distributed compression technique based on signal resampling. The DDSP impact on network energy efficiency is compared through a novel mathematical approach to the case where the processing is performed entirely by the supervisor. The trade-off between energy conservation (i.e., network lifetime) and estimation error is discussed and a design criterion is proposed as well. Comparison to simulation outcomes validates the model. As an example result, the required node density is found as a trade-off between estimation quality and network lifetime for different system parameters and scalar field characteristics. It is shown that both the DDSP technique and the MAC protocol choice have a relevant impact on the performance of a WSN.     

Reconstruction of Vectorial Acoustic Sources in Time-Domain Tomography

A new theory is proposed for the reconstruction of curl-free vector field, whose divergence serves as acoustic source. The theory is applied to reconstruct vector acoustic sources from the scalar acoustic signals measured on a surface enclosing the source area. It is shown that, under certain conditions, the scalar acoustic measurements can be vectorized according to the known measurement geometry and subsequently be used to reconstruct the original vector field. Theoretically, this method extends the application domain of the existing acoustic reciprocity principle from a scalar field to a vector field, indicating that the stimulating vectorial source and the transmitted acoustic pressure vector (acoustic pressure vectorized according to certain measurement geometry) are interchangeable. Computer simulation studies were conducted to evaluate the proposed theory, and the numerical results suggest that reconstruction of a vector field using the proposed theory is not sensitive to variation in the detecting distance. The present theory may be applied to magnetoacoustic tomography with magnetic induction (MAT-MI) for reconstructing current distribution from acoustic measurements. A simulation on MAT-MI shows that, compared to existing methods, the present method can give an accurate estimation on the source current distribution and a better conductivity reconstruction.     

Signal Correlation Modeling in Acoustic Vector Sensor Arrays

A vector sensor measures the scalar and vector components of the acoustic field. In a multipath channel, the sensor collects the information via multiple paths. Depending on the angle-of-arrival distribution and other channel characteristics, different types of correlation appear in a vector sensor array, which affect the array performance. In this paper, a novel statistical framework is developed which provides closed-form parametric expressions for signal correlations in vector sensor arrays. Such correlation expressions serve as useful tools for system design and performance analysis of vector sensor signal processing algorithms. They can also be used to estimate some important physical parameters of the channel such as angle spreads, mean angle of arrivals, etc.      

Merging VLIW and vector processing techniques for a simple,high-performance processor architecture

This paper proposes a new processor architecture called VVSHP for accelerating data-parallel applications, which are growing in importance and demanding increased performance from hardware. VVSHP merges VLIW and vector processing techniques for a simple, high-performance processor architecture. One key point of VVSHP is the execution of multiple scalar instructions within VLIW and vector instructions on unified parallel execution datapaths. Another key point is to reduce the complexity of VVSHP by designing a two-part register file: (1) shared scalar–vector part with eight-read/four-write ports 64×32-bit registers (64 scalar or 16×4 vector registers) for storing scalar/vector data and (2) vector part with two-read/one-write ports 48 vector-registers, each stores 4×32-bit vector data. Moreover, processing vector data with lengths varying from 1 to 256 represents a key point for reducing the loop overheads. VVSHP can issue up to four scalar/vector operations in each cycle for parallel processing a set of operands and producing up to four results to be written back into VVSHP register file. However, it cannot issue more than one memory operation at a time, which loads/stores 128-bit scalar/vector data from/to data memory. The design of our proposed VVSHP processor is implemented using VHDL targeting the Xilinx FPGA Virtex-5 and its performance is evaluated.     

An efficient finite-element formulation without spurious modes foranisotropic waveguides

A numerically efficient finite-element formulation is presented for the analysis of lossless, inhomogeneously loaded, anisotropic waveguides of arbitrary shape. The electromagnetic field is described either by the three components of a magnetic vector potential and an electric scalar potential or by the three components of an electric vector potential and a magnetic scalar potential. The uniqueness of the potentials is ensured by the incorporation of the Coulomb gauge and by proper boundary conditions. Owing to the implementation of the solenoidality condition for the vector potential even in the case of zero wavenumber, no spurious modes appear. Variation expressions suited to the finite-element method are formulated in terms of the potentials. Standard finite-element techniques are employed for the numerical solution, leading to a generalized eigenvalue problem with symmetric, sparse matrices. This is solved by means of the bisection method with the sparsity of the matrices fully utilized. Dielectric- and ferrite-loaded waveguides with closed and open boundaries and including both isotropic and anisotropic materials are presented as examples     

软件无线电技术综述

软件无线电是最近几年提出的一种实现无线电通信的体系结构,被认为是继模拟通信、数字通信之后的第三代无线电通信技术。在无线电应用领域,软件无线电已经成为一个重要的研究课题。特别是在信息成为主导市场竞争优胜劣汰、军事斗争成败等重大问题的关键因素后,软件无线电技术作为一种有利于技术体制改革创新、有利于提高信息处理能力的关键技术,已经得到了飞速的发展。介绍了软件无线电的基本概念、功能结构、关键技术等问题,同时阐述了软件无线电的应用和发展前景。     

An Introduction to Convex Optimization for Communications and Signal Processing

Convex optimization methods are widely used in the design and analysis of communication systems and signal processing algorithms. This tutorial surveys some of recent progress in this area. The tutorial contains two parts. The first part gives a survey of basic concepts and main techniques in convex optimization. Special emphasis is placed on a class of conic optimization problems, including second-order cone programming and semidefinite programming. The second half of the survey gives several examples of the application of conic programming to communication problems. We give an interpretation of Lagrangian duality in a multiuser multi-antenna communication problem; we illustrate the role of semidefinite relaxation in multiuser detection problems; we review methods to formulate robust optimization problems via second-order cone programming techniques.     

正交频分复用技术原理及应用

正交频分复用(OFDM)由于它在无线通信中的成功应用,近年来备受关注.本文介绍了正交频分复用技术的基本原理、相关技术、优缺点以及在无线通信系统中的应用.指出了OFDM技术将是宽带无线接入系统和下一代移动通信系统的核心技术.     

空时传输预处理技术

首先分析了一维通信信号处理的局限,然后给出空时信号处理的概念、特点和主要技术内容,在此基础上,探讨了空时传输预处理技术。重点对空时预RAKE、空时联合传输、预编码和预均衡等关键技术友其应用进行了系统总结和阐述,对发展新一代宽带无线通信系统和标准具有重要作用。