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European Conference on Microwave

作者： Francesco Barbaliscia Renzo Perfetti Fondazione Ugo Bordoni Rome Italy

First data from the propagation experiments with the Olympus satellite have been analyzed at 12.5 GHz in Rome for a 18 months period, on an event basis. The dynamic characteristics of the attenuation due to rain are examined to extract the design figures for those communication systems making use of allocation of countermeasures on a dynamic basis. A suitable preprocessing of attenuation data has been performed. The correlation of both the slope and the duration of fade events with the attenuation level have been analyzed, giving useful results for fade-countermeasure applications.

关键词： Attenuation Satellites Information filtering Information filters Data mining Rain fading Real time systems Earth Frequency diversity adaptive coding

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A self adaptive coding scheme for text and binary data

A self adaptive coding scheme for text and binary data

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IEEE Southeastcon

作者： A. Desoky T. Klein Engineering Mathematics & Computer Science University of Louisville Louisville KY USA

An effort is made to measure the amount of compression that can be accomplished using a heuristic coding algorithm. The scheme is based on the locality of the input symbols within a self-adaptive sequential list. An IBM-PC-based system has been developed for both encoding and decoding. The results using different adaptive sequential lists are presented. The test data include text files and binary files such as computer programs in executable forms and a 256-gray-levels image. Performance evaluation is discussed in terms of compression ratio, encoding time, and decoding time.< >

关键词： adaptive coding Decoding Huffman coding Encoding Frequency Data engineering Mathematics Computer science Heuristic algorithms Testing

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High compression of nuclear medicine dynamic studies

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The International Journal of Cardiac Imaging 1990年第4期5卷 261-269页

作者： Chameroy, Virginie Di Paola, Robert Inserm U-66 Institut Gustave-Roussy Villejuif cedex 94805 Rue Camille Desmoulins France

As data compression plays now an important role in the development of medical PACS, a technique has been developed for medical image sequences storage and transmission in order to obtain very high compression ratio: in dynamic nuclear medicine studies it can achieve a compression ratio as high as 100:1 without significant degradation. The implemented technique combines two methods which multiply their effects. In a first step, a principal component analysis (PCA) of the image series is performed. It extracts a limited number of principal components and their associated images. For data compression it is not necessary to perform an oblique factor analysis to estimate the so-called 'physiological functions' and their spatial distributions as in factor analysis of dynamic structures (FADS). In a second step, the principal images are compressed by means of a transform coding procedure: an adaptive block-quantization technique using the 2D discrete cosine transform (DCT) is implemented, followed by a statistical quantization method to encode the DCT coefficients. To reconstruct the principal images, an inverse DCT is applied. Then the original series is computed from the reconstructed images combined with the principal components which have been stored without any modification. The reconstructed series is compared to the original series, as well as the time activity curves generated on different regions of interest (ROI) and the factor estimates obtained using FADS performed on the two series. Method and evaluation are illustrated on an example of first pass radionuclide angiocardiography. © 1990 Kluwer Academic Publishers.

关键词： adaptive coding compression DCT dynamic studies principal component analysis

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adaptive CHANNEL/CODE MATCHING USING HIDDEN MARKOV CHAINS

ADAPTIVE CHANNEL/CODE MATCHING USING HIDDEN MARKOV CHAINS

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Asilomar Conference on Signals, Systems & Computers

作者： R.E. Pelle R.A. Scholtz Communication Sciences Institute University of Southern California Los Angeles CA USA

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A 2 ms-delay adaptive code excited linear predictive coder

A 2 ms-delay adaptive code excited linear predictive coder

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International Conference on Acoustics, Speech, and Signal Processing (ICASSP)

作者： J. Menez C. Galand M. Rosso LASSY LA CSRS 1376 Nice France IBM Thomas J. Watson Research Center Yorktown Heights NY USA IBM Laboratory La Gaude France

The technique proposed is based on a feedback adaptation of the LPC and LTP (long-term prediction) coefficients on a block basis, and on an adaptive linear code-book vector quantizer. The authors designed a 12 kb/s coding scheme with high quality, low delay, and low complexity. A 4 kb/s block protection can then be applied to ensure a robust operation at 16 kb/s. The authors give a detailed description of the backward block adapted ACELP for an operation at 12 kbps. They report quality tests including comparisons with the 32 kb/s G.721 and the 13 kb/s GSM. Finally they show that the implementation requires only 11 MIPS on a fixed point 16 bit DSP.< >

关键词： adaptive coding Feedback Linear predictive coding Vectors Delay Protection Robustness Testing GSM Digital signal processing

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Meteor burst in the post 2000 era

Meteor burst in the post 2000 era

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MILCOM, Military Communications Conference

作者： C. Marriott V. Oduol A. Ghosh B. Tailor MPB Technol. Inc. Pointe Claire Que. Canada MPB Technologies Inc. Pointe Claire QUE Canada

In recent years a renewed interest has been shown in the possibility of using meteor burst links in tactical communications, both for networking and covert operations. Some of the applications that recent performance improvements would permit are evaluated. In evaluating the feasibility of a meteor burst implementation, certain technical and physical limitations are addressed. For the success of these applications, interoperability with other communication systems is necessary. The level of interoperability with other media, and the standards necessary to assure this interoperability are examined. Methods of minimizing and combating jamming are proposed. Meteor burst systems can be used in a large number of applications within a tactical environment. The principal disadvantage of the meteor burst medium is the problem of interference to other spectrum users from the probe end, and the interference from other users at the receiver end. The low throughput characteristic of meteor burst compares with some of the channel capacities used in other systems. Interoperability with other networks or communications links is relatively easy if certain straightforward protocols and standards are established.< >

关键词： Frequency Throughput Automatic repeat request Protocols Signal processing algorithms Communication systems adaptive coding Jamming Reflection Radio communication

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Hybrid-ARQ Reed-Solomon coding in an adaptive rate system

Hybrid-ARQ Reed-Solomon coding in an adaptive rate system

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IEEE International Conference on Communications (ICC)

作者： S.B. Wicker School of Electrical Engineering Georgia Institute of Technology Atlanta GA USA

The performance of a channel estimation procedure based on retransmission statistics is examined for a two-state channel. Throughput performance is derived from the ability of the estimation mechanism to determine which of the two states the channel is in at any given moment. The throughput analysis is then used to derive a simple rule for maximizing throughput through careful selection of the code set. The performance of Reed-Solomon codes in type-I hybrid-ARQ protocols is considered. The tradeoff between throughput and reliability is derived for the general case and plotted for several specific examples. An example is presented in which a pair of Reed-Solomon codes is used in an adaptive rate coding system on a two-state channel.< >

关键词： Reed-Solomon codes adaptive systems Protocols Statistics Transmitters Throughput Probability adaptive coding Error correction codes Frequency

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Spatial domain decomposition for coding image sequences

Spatial domain decomposition for coding image sequences

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Multidimensional Signal Processing Workshop

作者： R.J. Clarke P.J. Cordell Department of Electronic and Electrical Engineering Heriot-Watt University Edinburgh UK

Summary form only given. A spatial technique for the efficient adaptive coding of image sequences at low data rates is reported. The technique has the advantage of simple implementation for real-time operation and allows the matching of coding resolution to variations in image detail. The basis of the technique is a recursive quadtree division of image frames into successively smaller and smaller blocks until the original picture detail can be adequately represented by a bilinear interpolation from the four block corner points. At this point subdivision ceases and information is transmitted about the structure of the quadtree division and any new corner points needed for interpolation (for most blocks, some corner points will have already been coded to reconstruct previous blocks). Initial problems with the application of the algorithm to an image sequence derived from the effects of noise causing random failure of the threshold test and errors in corner point values, which are then spread over the whole block by the reconstruction interpolation. Methods of counteracting these effects as well as techniques for optimizing the quantization of sample values, particularly in the case of the processing of small blocks, have been developed.< >

关键词： Image coding Image sequences Interpolation Image reconstruction adaptive coding Spatial resolution Image resolution Testing Optimization methods Quantization

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Low bitrate coding for storage of ID photos

Low bitrate coding for storage of ID photos

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Southern African Conference on Communications and Signal Processing (COMSIG)

作者： T. Weyers J.J.D. Van Schalkwyk Department of Electronic and Computer Engineering University of Pretoria Pretoria South Africa

The application of suboptimal runlength codes to two-tone ID photos is discussed. Standard and vertical predictive run-length-coding techniques are examined. Huffman coding of the results is reviewed. Computation of thresholds, edge detection, and pattern recognition are employed to enhance the images. A 256*256-pixel picture, quantized to 64 grey levels, was scaled down to two levels, employing a histogram averaging algorithm to determine the most effective threshold. Suboptimal vertical adaptive coding was implemented to minimize digital storage space. The bit rate was reduced to 0.145 b/pel on average with a deviation of sigma =0.01722. Image enhancement was artificially produced by superimposing the eyes from the edge detection sequence onto the two-tone picture. Pattern recognition was employed to detect the nose, thus creating a lower bound for the algorithm searching for the eyeline while defining a natural axial line through the facial image.< >

关键词： Bit rate Image edge detection Pattern recognition Huffman coding Histograms adaptive coding Image enhancement Eyes Face detection Nose

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An analysis of convolutional coding for land mobile channels

An analysis of convolutional coding for land mobile channels

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IEEE Conference on Vehicular Technology (VTC)

作者： F. Gagnon D. Haccoun C. Leung Department of Electrical Engineering Ecole Polytechnique de Montréal Montreal QUE Canada Dept. of Electr. Eng. Ecole Polytech. de Montreal Que. Canada

The performance of convolutional coding is analyzed with reference to a land mobile radio channel. A two-state channel model is developed to determine the performance as a function of the probability of occurrence and duration of the fades. Using computer simulation, the relationship that exists between the Doppler frequency, the amount of diversity, the interleaving depth, and the bit error rate is shown. coding is shown to provide a significant gain if the fades are relatively short. Using a feedback channel, an adaptive coding strategy uses punctured and repeated convolutional codes to achieve a variable-rate coding scheme. This adaptive coding strategy yields an appreciable coding gain even when long fades are present.< >

关键词： Convolutional codes Convolution Land mobile radio adaptive coding Frequency shift keying Performance analysis Computer simulation Bit error rate Vehicles Error correction

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