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MILCOM, Military communications Conference

作者： J. Lee S.H. Ardalan Center for Communications and Signal Processing Department of Electrical and Computer Engineering North Carolina State University Raleigh NC USA

The interaction between echo cancellation/equalization and timing recovery is analyzed, a complete simulation of a high-speed full-duplex digital subscriber loop system is reported, and issues related to the support of multirate sampling and feedback are discussed. The simulation results suggest that the number of equalizer (EQ) training symbols must be reduced, rather than the number of echo canceler (EC) training symbols, to save total EC/EQ training time, regardless of the length of the bridged taps. The pole-zero EC performs much better than the all-zero EC. In the all-zero EC, the system needs more EQ training symbols. Fractionally spaced EC/EQ performs better than symbol rate EC/EQ when the number of EC/EQ training symbols is large. The symbol rate EC/EQ has better or equivalent performance for small number of EC/EQ training symbols, relatively large noise, and long bridged taps. The symbol rate EC/EQ reaches a performance limit however, unlike the fractionally spaced EC/EQ system, for large SNR or large training sequences.< >

关键词： Echo cancellers Equalizers Baseband DSL Sampling methods Timing jitter Circuit simulation Feedback Degradation Data communication

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The joint optimization of transmitter and receiver filters for data transmission systems using mean field annealing

The joint optimization of transmitter and receiver filters f...

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International Conference on Acoustics, Speech, and signal processing (ICASSP)

作者： R.A. Nobakht D.E. Van den Bout J.K. Townsend S.H. Ardalan Center for Communications and Signal Processing Department of Electrical and Computer Engineering North Carolina State University Raleigh NC USA

A technique is presented for finding transmitter and receiver filters for a wide class of data transmission systems which minimize the bit error rate (BER). The techniques uses Monte Carlo simulation to estimate the BER, coupled with mean field annealing (MFA) to optimize the pulse shapes. Modeling of the link can be as complex as simulation will allow, while MFA is resistant to the statistical scatter in the BER estimate from the simulation. In a complex example, MFA is coupled with Monte Carlo simulation techniques to find near optimal transmit and receive filters for a satellite communications link, taking 6 CPU hours on a DECstation 3100. The bit error rate of the link is found to be as much as three orders of magnitude lower when using the MFA-constructed optimal filters than when using filters constructed by gradient descent and simulated annealing.< >

关键词： Transmitters Filters Bit error rate Simulated annealing Data communication Couplings Pulse shaping methods Shape Scattering Satellite communication

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An improved analysis of Sigma Delta modulators with bandlimited Gaussian inputs

An improved analysis of Sigma Delta modulators with bandlimi...

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International Conference on Acoustics, Speech, and signal processing (ICASSP)

作者： J.T. Stonick S.H. Ardalan J.K. Townsend Center for Communications & Signal Processing Department of Electrical & Computer Engineering North Carolina State University Raleigh NC USA

Three results on Sigma Delta modulation are presented. First, a change of variables is presented that demonstrates that two of the parameters in a Sigma Delta modulator do not affect the system performance. Second, a successive parameterization approach is used to determine the probability density function (PDF) at the input to the quantizer of a second-order Sigma Delta modulator. Third, this calculated PDF is used to determine the minimum mean-square error linearizing gains for a second-order Sigma Delta modulator and an expression for the variance of the noise at the input to the quantizer.< >

关键词： System performance Probability density function

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Nonlinear adaptive filtering using annealed neural networks

Nonlinear adaptive filtering using annealed neural networks

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IEEE International Symposium on Circuits and Systems (ISCAS)

作者： R.A. Nobakht S.H. Ardalan D.E. van den Bout G.L. Bilbro Center for Communications and Signal Processing Department of Electrical and Computer Engineering North Carolina State University Raleigh NC USA

A technique for nonlinear adaptive filtering which combines annealed neural networks (ANNs) and conventional recursive-least-squares/fast-transversal-filter (RLS/FTF) adaptive filtering is presented. The technique can efficiently handle large-order nonlinearities with or without memory. The nonlinear channel is divided into a nonlinearity followed by a dispersive linear system. ANN is applied to obtain the coefficients of the nonlinearity, and RLS/FTF is applied to determine the weights of the dispersive linear systems. The proposed technique has better convergence properties than gradient-descent-based methods, such as those based on steepest-descent or Newton's method. The proposed technique is used to solve for the true minimum mean-squared-error estimate, as opposed to solving for an estimate which satisfies suboptimal equations. A simulation example is given which shows the superior performance of the technique compared to that of ordinary RLS/FTF and gradient-descent.< >

关键词： Adaptive filters Annealing Neural networks Resonance light scattering Dispersion Linear systems Artificial neural networks Convergence Newton method Equations

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A neural network model to configure maps for a satellite communication network

A neural network model to configure maps for a satellite com...

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[Proceedings] GLOBECOM '90: IEEE Global Telecommunications Conference and Exhibition

作者： N. Ansari Y. Chen Center for Communications and Signal Processing Department of Electrical and Computer Engineering New Jersey Institute of Technology Newark NJ USA

A self-configurable satellite communication network that can be dynamically configured to different maps, to best meet the network requirements, by means of a modified Kohonen self-organization procedure is described. The model consists of three stages. The first stage is the pattern recognition task, in which an exemplar map that best meets the current network requirements is selected. The second stage is an analysis of the discrepancy between the chosen exemplar map and the state of the network, and adaptively modifies the chosen exemplar map to conform closely to the network requirement (input data pattern) by Kohonen's self-organization procedure. On the basis of certain performance criteria, it is decided in the third stage whether a new map is generated to replace the original map. Experimental results are presented to demonstrate that the self-organization model can dynamically configure maps for a satellite communication network.< >

关键词： Neural networks Satellite communication Telecommunication traffic Traffic control Satellite broadcasting Routing Costs Communication cables Artificial satellites Satellite ground stations

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Segmentation based image coding using fractals and the human visual system

Segmentation based image coding using fractals and the human...

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International Conference on Acoustics, Speech, and signal processing (ICASSP)

作者： J. Jang S.A. Rajala Department of Electrical and Computer Engineering Center for Communication and Signal Processing North Carolina State University Raleigh NC USA

A new segmentation-based image coding technique which performs segmentation based on roughness of textural regions and on properties of the human visual system (HVS) is presented. The image is segmented into texturally homogeneous region with respect to the degree of roughness as perceived by the HVS. The fractal dimension is used to measure the roughness of the textural regions. The segmentation is accomplished by thresholding the fractal dimension so that textural regions are classified into several classes. Three texture classes are chosen: perceived constant intensity, smooth texture, and rough texture. An image coding system with high compression and good image quality is achieved by developing an efficient coding technique for each texture class.< >

关键词： Image segmentation Image coding Fractals Humans Visual system Image quality

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A COMPARATIVE STUDY OF QUADRATURE SAMPLING AND DIRECT SAMPLING OF BANDPASS signalS

A COMPARATIVE STUDY OF QUADRATURE SAMPLING AND DIRECT SAMPLI...

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International Conference on signal processing(ICSP’90)

作者： Chung H.Lu Danmei Chang Ray Chapel Department of Electrical Engineering Center for Communications and Signal Processing Research New Jersey Institute of Technology University Heights NewarkNew Jersey 07102USA

Various techniques have been studied for the sampling of bandpass *** this paper,we present a comparative study of quadrature sampling and direct sampling of bandpass ***,both schemes provide efficient sampling of a bandpass signal at a minimum data rate and at the same time demultiplex the in-phase and quadrature components. In reality,imperfect circuit parameters lead to nonideal sampling, resulting in quadrature *** form relations for quadrature interference for quadrature sampling and direct sampling are derived and *** analysis shows that quadrature interference is inversely proportional to the variance of sampling phase jittering.

关键词： A COMPARATIVE STUDY OF QUADRATURE SAMPLING AND DIRECT SAMPLING OF BANDPASS signalS

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BIT-SERIAL VLSI IMPLEMENTATION OF VECTOR QUANTIZER FOR REAL-TIME IMAGE-CODING

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IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS 1989年第10期36卷 1281-1290页

作者： RAMAMOORTHY, PA POTU, B TRAN, T Signal Processing and Communications Group Department of Electrical and Computer Engineering University of Cincinnati Cincinnati OH USA

A practical high-throughput architecture and its implementation for real-time coding of television-quality signals are presented. The architecture is directed toward the implementation of multistage vector quantization (VQ), as the authors\' simulation results show that the latter is more suitable for real-time coding. However, the implementation is suitable for both single-stage and multistage VQ. The functional blocks of the VQ encoder system have been designed and implemented in VLSI technology. The VQ encoding scheme designed has an encoding delay of 25 clock cycles and is independent of the codebook size.

关键词： ARCHITECTURE time coding Building construction signal quality clock cycle real-time coding multistage vector quantization vector quantization encoding Vector quantization

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ESTIMATION OF MULTIPATH CHANNEL RESPONSE IN FREQUENCY SELECTIVE CHANNELS

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IEEE JOURNAL ON SELECTED AREAS IN communications 1989年第1期7卷 12-19页

作者： HATZINAKOS, D NIKIAS, CL Communications and Digital Signal Processing (CDSP) Department of Electrical and Computer Engineering Northeastern University Boston MA USA

A novel discrete-time method is proposed for estimating the impulse response of a frequency-selective digitally modulated communication channel. The received signal is first demodulated and sampled and then the fourth-order cumulants of the resulting discrete-time sequence are estimated. The method estimates the channel impulse response from the complex cepstrum of the aforementioned fourth-order cumulants (i.e. tricepstrum). The method depends only on the second- and fourth-order statistics of the transmitted sequence and is capable of reconstructing nonminimum-phase impulse responses. Monte Carlo simulation results demonstrate the effectiveness of the method, its low sensitivity to observation noise, and its improved performance in terms of probability of error or the reconstructed transmitted sequence.< >

关键词： Frequency estimation Multipath channels signal processing algorithms Decision feedback equalizers Working environment noise Intersymbol interference Data communication Adaptive equalizers Fading Maximum likelihood estimation

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Primitive-based teleconference image coding technique

Primitive-based teleconference image coding technique

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International Conference on Acoustics, Speech, and signal processing (ICASSP)

作者： A.M. Alattar S.A. Rajala Department of Electrical and Computer Engineering Center for Communications and Signal Processing North Carolina State University Raleigh NC USA

An image coding technique with the capability of producing good image quality at a compression ratio over 1000:1 is described. The main idea is to break the image into complicated primitives using a priori knowledge. Usually these primitives are not coded and transmitted, but are matched to a previously created database, and the necessary information about the best match is coded and transmitted. This information is used at the receiver to retrieve a replica of the original primitive from a duplicate database. The primitives are assembled as in computer animation to produce a faithful reconstruction of the original image. The proposed technique allow real-time transmission of video signals over low-bit-rate channels (less than 64 kb/s). The application of this technique to teleconference and picture phone images is discussed.< >

关键词： Teleconferencing Image coding Image segmentation Image databases Head Mouth signal processing Image quality Information retrieval Assembly

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