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Weighted universal image compression

IEEE TRANSACTIONS ON IMAGE PROCESSING 1999年第10期8卷 1317-1329页

作者： Effros, M Chou, PA Gray, RM CALTECH Dept Elect Engn Pasadena CA 91125 USA Microsoft Corp Redmond WA 98052 USA Stanford Univ Dept Elect Engn Informat Syst Lab Stanford CA 94305 USA

We describe a general, coding strategy leading to a family of universal image compression systems designed to give good performance in applications where the statistics of the source to be compressed are not available at design time or vary over time or space. The basic approach considered uses a two-stage structure in which the single source code of traditional image compression systems is replaced with a family of codes designed to cover a large class of possible sources. To illustrate this approach, we consider the optimal design and use of two-stage codes containing collections of vector quantizers (weighted universal vector quantization), bit allocations for JPEG-style coding (weighted universal bit allocation), and transform codes (weighted universal transform coding). Further, we demonstrate the benefits to be gained from the inclusion of perceptual distortion measures and optimal parsing. The strategy yields two-stage codes that significantly outperform their single-stage predecessors. On a sequence of medical images, weighted universal vector quantization outperforms entropy coded vector quantization by over 9 dB, On the same data sequence, weighted universal bit allocation outperforms a JPEG-style code by over 2.5 dB. On a collection of mixed text and image data, weighted universal transform coding outperforms a single, data-optimized transform code (which gives performance almost identical to that of JPEG) by over 6 dB.

关键词： adaptive coding bit allocation clustering image compression JPEG perceptual distortion measures transform coding two-stage coding universal coding vector quantization

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Dynamic bit rate assignment in wireless CDMA data transmissions

Dynamic bit rate assignment in wireless CDMA data transmissi...

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IEEE Conference on Vehicular Technology (VTC)

作者： A. Abrardo G. Benelli G. Giambene D. Sennati Dipartimento di Ingegneria delľInformazione Università degli Studi di Siena Siena Italy

This paper compares different schemes that can be used to improve the performance of CDMA in wireless data systems. In particular, we consider a closed-loop power control scheme and an adaptive coding scheme. The comparison between these different techniques is performed in terms of mean transmission time and energy efficiency. Our aim is to show that an adaptive coding scheme can allow good performance with respect to typical power control techniques.

关键词： Bit rate Multiaccess communication Power control Base stations adaptive coding Frequency Shadow mapping Interference Fading Protection

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A flexible Reed-Solomon codec

A flexible Reed-Solomon codec

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AFRICON Conference

作者： A. du Preez F. Swarts F. Agdhasi Department of Electrical Engineering University of the Witwatersrand South Africa

We report on the implementation of a flexible Reed-Solomon codec using a field programmable gate array (FPGA) for use in a mobile communication system employing adaptive coding. The number of correctable errors can be changed in real time. A modified Euclidean algorithm is used with the number of correctable errors as an input parameter. The very high-speed integrated circuit hardware description language (VHDL) design can generate a codec for any Galois field size and field generator.

关键词： Reed-Solomon codes Codecs Field programmable gate arrays Error correction adaptive arrays Mobile communication adaptive coding High speed integrated circuits Hardware design languages Galois fields

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On the improvement of low elevation angle satellite communications impaired by tropospheric fading effects

On the improvement of low elevation angle satellite communic...

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MILCOM, Military Communications Conference

作者： J.C. Kim D.E. Schall System and Information Technology Group TRW Inc. Fairfax VA USA

Performance impairments occur on C- and Ku-band satellite communications links because of severe tropospheric fading effects when the elevation angle of the ground station is very low (<50). Two cases of satellite communications link impairment are discussed; the first is for data transmission from a high latitude ground station as found in NASA's Earth Orbiting Satellite (EOS) program. The second is for data transmission from LEO/MEO satellites at all latitudes. Experimental data shows that deep fading of satellite communications signals because of severe tropospheric absorption is as much as 27 dB during the worst summer month between a high latitude station and a geosynchronous satellite. With this amount of deep fading, if would be extremely difficult to transmit low-BER data during the summer months. The mitigation techniques proposed consist of: (a) adaptive coding by using a combination of the Reed-Solomon code, convolutional code, and interleaving, and (b), for lower orbit LEO satellites a shaped (depressed cardioid) antenna pattern. Using the same adaptive coding technique, the amount of contact time by ground stations at any latitude with LEO/MEO satellites could be increased substantially by enabling operation to very low elevation angles generally considered unusable. Using the shaped (depressed cardioid) antenna pattern, the received signal level could be maximized at very low elevation angles.

关键词： Satellite communication Satellite ground stations Fading Low earth orbit satellites Data communication Artificial satellites adaptive coding Cardiology Earth Observing System Absorption

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adaptive code allocation in multicode-CDMA for transmitting H.263 video

Adaptive code allocation in multicode-CDMA for transmitting ...

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IEEE Conference on Wireless Communications and Networking

作者： B. Deep Wu-Chi Feng Computer & Information Science Ohio State Uinversity Columbus OH USA Ohio State University Columbus OH US

This paper proposes a new way to incorporate H.263 video into existing voice/data code-division multiple access (CDMA) networks using a multi-code access protocol. A channel allocation policy is proposed that "shares" codes for larger I-frame video transmission and allocates a fixed number of codes for P-frame transmissions. The base station in a given cell of a CDMA network controls this allocation method, but bandwidth access distribution is based on both mobile host requests and base station forced requests. This scheme allows more efficient allocation of resources in the bandwidth-limited wireless spectrum and improves the quality of service (QoS) of video traffic over this lossy environment.

关键词： adaptive coding Multiaccess communication Base stations Quality of service Access protocols Channel allocation Force control Bandwidth Resource management Communication system traffic control

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adaptive error control for hybrid (satellite-terrestrial) networks

Adaptive error control for hybrid (satellite-terrestrial) ne...

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IEEE Conference on Wireless Communications and Networking

作者： S. Cho Broadband and Wireless Networking Laboratory School of Electrical and Computer Engineering Georgia Institute of Technology Atlanta GA USA

Hybrid satellite-terrestrial networks are becoming increasingly popular for asymmetric multimedia services such as file transfer and database services. This paper presents an adaptive error control (AEC) protocol for the hybrid network, in which the transmitter uses a combination of automatic repeat request (ARQ) over terrestrial links and forward error control (FEC) scheme with adaptive code rate over satellite links. Throughput performance shows that the proposed AEC protocol adapts to a time-variant satellite channel better than the static hybrid ARQ protocol under different satellite channel conditions.

关键词： Programmable control adaptive control Error correction Protocols Automatic repeat request Satellites Multimedia databases Transmitters Forward error correction adaptive coding

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Lexical attraction for text compression

Lexical attraction for text compression

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Data Compression Conference (DCC)

作者： J. Bach I.H. Witten Computer Science Departments Humboldt University of Berlin Germany Waikato University New Zealand

[Summary form only given]. The best methods of text compression work by conditioning each symbol's probability on its predecessors. Prior symbols establish a context that governs the probability distribution for the next one, and the actual. The next symbol is encoded with respect to this distribution. However, the best predictors for words in natural language are not necessarily their immediate predecessors. Verbs may depend on nouns, pronouns on names, closing brackets on opening ones, question marks on "wh"-words. To establish a more appropriate dependency structure, the lexical attraction of a pair of words is defined as the likelihood that they will appear (in that order) within a sentence, regardless of how far apart they are. This is estimated by counting the co-occurrences of words in the sentences of a large corpus. Then, for each sentence, an undirected (planar, acydic) graph is found that maximizes the lexical attraction between linked items, effectively reorganizing the text in the form of a low-entropy model. We encode a series of linked sentences and transmit them in the same manner as order-1 word-level PPM. To prime the lexical attraction linker, the whole document is processed to acquire the co-occurrence counts, and again to re-link the sentences. Pairs that occur twice or less are excluded from the statistics, which significantly reduces the size of the model. The encoding stage utilizes an adaptive PPM-style method. Encouraging results have been obtained using this method.

关键词： Encoding Probability distribution Natural languages Couplings Statistical distributions Decoding Costs Mutual information adaptive coding Computer science

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adaptive code acquisition using a GO-CFAR processor in DS/CDMA systems

Adaptive code acquisition using a GO-CFAR processor in DS/CD...

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IEEE Region 10 International Conference TENCON

作者： Hong Gil Kim Iickho Song Sun Yong Kim Jung Hoon Lee Suk Chan Kim Department of Electrical Engineering Korea Advanced Institute of Science and Technology Daejeon South Korea Department of Electronics Engineering Hallym University Chuncheon Kangwon South Korea

We propose to use a greatest of (GO) CFAR processor for PN code acquisition in DS/CDMA systems. We compare the single-dwell scheme without the verification mode using the GO CFAR processor with that using the cell averaging (CA) and order statistics (OS) CFAR processors. From the simulation results, we can observe that the DS/CDMA systems with the GO CFAR processor has better performance than those with the CA and OS CFAR processors at abrupt change of the variance.

关键词： adaptive coding Multiaccess communication Additive white noise Gaussian noise Signal to noise ratio Detectors Interference Radar detection AWGN Noise generators

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A hybrid compression method based on region separation for synthetic and natural compound images

A hybrid compression method based on region separation for s...

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IEEE International Conference on Image Processing

作者： T. Mogi Hypermedia Research Center Sanyo Electric Company Limited Japan

This paper presents a hybrid compression method for a compound image including characters, graphics, and photos. Such kind of image is popular as Web contents or TV game images. We use usually JPEG to compress it, but the DCT compression like JPEG causes strong mosquito distortion around the contours of characters or graphics because of their strong edge intensity. Therefore we need high quality and low bitrate coding scheme for the compound image. Our hybrid compression method is based on region separation and adaptive coding. This method separates synthetic image region and natural image region according to each features, i.e., edge intensity and color deviation. Then our method encodes synthetic region by runlength coding, and natural region by JPEG respectively from the viewpoint of visual quality and coding efficiency. Our hybrid compression method provides good performance for the compound images compared with JPEG. This method can remarkably reduce mosquito distortion around the contours of character or graphics. Experimental results show +5 to +10 dB improvement of the SNR over JPEG.

关键词： Image coding Transform coding Graphics Discrete cosine transforms Frequency Shape Bit rate adaptive coding Radio spectrum management Quantization

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Spatio-temporal coding for wireless communication

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IEEE TRANSACTIONS ON COMMUNICATIONS 1998年第3期46卷 357-366页

作者： Raleigh, GG Cioffi, JM Clar Wireless Inc Belmont CA 94002 USA Stanford Univ Dept Elect Engn Stanford CA 94305 USA Amati Commun Corp San Jose CA 95124 USA

Multipath signal propagation has long been viewed as an impairment to reliable communication in wireless channels, This paper shows that the presence of multipath greatly improves achievable data rate if the appropriate communication structure is employed, A compact model is developed for the multiple-input multiple-output (MIMO) dispersive spatially selective wireless communication channel, The multivariate information capacity is analyzed, For high signal-to-noise ratio (SNR) conditions, the MIMO channel can exhibit a capacity slope in bits per decibel of power increase that is proportional to the minimum of the number multipath components, the number of input antennas, or the number of output antennas, This desirable result is contrasted with the lower capacity slope of the well-studied case with multiple antennas at only one side of the radio link, A spatio-temporal vector-coding (STVC) communication structure is suggested as a means for achieving MIMO channel capacity. The complexity of STVC motivates a more practical reduced-complexity discrete matrix multitone (DMMT) space-frequency coding approach. Both of these structures are shown to be asymptotically optimum, An adaptive-lattice trellis-coding technique is suggested as a method for coding across the space and frequency dimensions that exist in the DMMT channel. Experimental examples that support the theoretical results are presented.

关键词： adaptive arrays adaptive coding adaptive modulation antenna arrays broad-band communication channel coding digital modulation information rates MIMO systems multipath channels

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