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Asilomar Conference on Signals, Systems & Computers

作者： S. Mehrotra N. Chaddha R.M. Gray Information Systems Laboratory University of Stanford Stanford CA USA

We present an algorithm for performing adaptive vector quantization with memory. By using the memory between adjacent blocks which are encoded, we can take advantage of the correlation between adjacent blocks of pixels to reduce the redundancy. We use finite state vector quantization to provide the memory. To further improve the performance by exploiting nonstationarities in the image, we use variable block sizes in the encoding. This is done by using a quadtree data structure to represent an encoding based on variable block sizes. To reduce the encoding complexity, hierarchical table lookup schemes are used to replace all the full search encoders.

关键词： adaptive coding Table lookup Vector quantization Encoding Image coding Bit rate Decoding Arithmetic Information systems Laboratories

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adaptive coding and optimal speech storage in digital speech interpolation systems

Adaptive coding and optimal speech storage in digital speech...

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ACE. Proceedings of [Annual Convention and Exhibition of the IEEE In India]

作者： P.S. Tiwari K.C. Harit Department of Elecronics and Communication Engineering University of Jodhpur Jodhpur India

One of the important issue in speech interpolation is that of speech freeze-out which becomes a very serious consideration with multihop networks. The paper discusses the implementation of two such techniques namely speech storage and variable bitrate strategies with their independent and combined effects on the performance of multihop, DSI networks. The trade-off between the effective increased channel capacity and the degradation of the speech quality has also been pointed out. The basic architectural configuration of the system using multimicroprocessor system has been discussed and the potentialities of the method in accomodating newer versions of coding algorithms at desired speed of response have been included.

关键词： Speech coding adaptive coding Interpolation Detectors Channel capacity Degradation Intelligent networks Spread spectrum communication Telephony Speech processing

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adaptive coding and modulation in an OFDM-TDMA communication system

Adaptive coding and modulation in an OFDM-TDMA communication...

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IEEE Conference on Vehicular Technology (VTC)

作者： H. Rohling R. Grunheid Institute of Telecommunications Technical University of Braunschweig Germany

The capacity of a wireless communication system based on the OFDM transmission technique is analysed. The considered system, which includes a TDMA approach, is designed for mobile access to different multimedia services, such as speech, video, e-mail and file transfer. In order to support a variety of services on the one hand and to take into account the behaviour of the frequency-selective radio channel on the other hand, an adaptive allocation of modulation and coding scheme is supplied. For this purpose, an optimal combination of modulation scheme and code rate is determined in a first step. Using these results, the capacity of such a system is analysed by calculating the number of supported users within a cell and comparing these numbers to a system with fixed modulation/coding.

关键词： adaptive coding Modulation coding Speech analysis Time division multiple access OFDM modulation Electronic mail Radio spectrum management Bandwidth Videoconference Downlink

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adaptive coding in Retinal Ganglion Cells

Adaptive Coding in Retinal Ganglion Cells

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International Conference on Neural Networks and Brain (ICNNB)

作者： Xin Jin Hai-Qing Gong Pei-Ji Liang Ai-Hua Chen Departmnent of Biomedical Engineering Shanghai Jiaotong University Shanghai China Shanghai Institutes for Biological Sciences Chinese Academy and Sciences Shanghai China

Sensory systems show many aspects of adaptation. The chicken retinal ganglion cells examined in our study showed typical light adaptation and contrast adaptation. The prolonged presence of contrast or luminance stimuli reduced the firing rate of retinal ganglion cells during the adaptation phase. However, further experimental results suggest that the information about stimulation might be stored in the retinal neural network in spite of the reduction in firing rate during the adaptation process. We found that the application of background light may result in some modification for retina sensitivity, in an illumination level dependent manner. This may indicate a novel adaptive mechanism underlying the phenomena of that contrast discrimination improved when the background illumination was increased. Inspired by the physiological mechanisms, a simple and biophysically realistic model was then employed, where the spiking neuron could change their membrane properties, especially the ion channel activity, during the process of adaptation or synaptic modification. Our analyses reveal that activity-dependent regulation of membrane properties contributes to sensitivity adaptation, which may be potentially useful for neural signal detection and information processing

关键词： adaptive coding Retina Lighting Biomembranes Neural networks Neurons Mechanical factors Information analysis Signal analysis Signal detection

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adaptive coding and modulation in MIMO OFDMA systems

Adaptive coding and modulation in MIMO OFDMA systems

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IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC)

作者： Stephan Stiglmayr Johannes Klotz Martin Bossert Institute of Telecommunications and Applied Information Theory DIm University Ulm Germany

adaptive coding and modulation are well known techniques for enhancing the performance of systems transmitting over quasi-static fading channels. Especially their application in OFDM based systems promises gains in spectral efficiency. In former work we presented an efficient method for the joint optimization of code rate and modulation formats if rate-compatible punctured codewords are mapped onto sub-symbols with heterogeneous channel quality and modulation formats. In this paper, we demonstrate the application of our scheme to MIMO techniques. More specifically, we investigate non-orthogonal spatial multiplexing schemes in bit-interleaved coded OFDM systems. The techniques are evaluated within the context of the OFDMA/TDMA system designed within the EU FP6 Integrated Project WINNER.

关键词： adaptive coding Modulation coding MIMO Forward error correction Fading OFDM modulation Bit error rate Parity check codes Signal to noise ratio Proposals

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adaptive coding for high-rate direct-sequence spread spectrum

Adaptive coding for high-rate direct-sequence spread spectru...

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International Conference on Wireless Networks, Communications and Mobile Computing

作者： M.B. Pursley T.C. Royster IV Clemson University Clemson SC USA

High-rate direct-sequence (DS) spread spectrum is a modulation technique in which most or all of the spreading is provided by nonbinary data modulation. For applications to mobile ad hoc wireless networks, the limited processing gain of high-rate DS spread spectrum gives only modest protection against multiple-access or multipath interference, but increased interference rejection capability can be obtained from error-control coding. In this paper, we evaluate the performance of high-rate DS spread spectrum with turbo product codes. The utility of the Gaussian approximation for the design of adaptive coding systems is illustrated. An adaptive coding algorithm is described and its performance is compared with that of fixed-rate codes for channels with unknown propagation loss. The algorithm is based on statistics obtained in the receiver, and no external side information is employed.

关键词： adaptive coding Spread spectrum communication Multiple access interference Wireless networks Protection Product codes Gaussian approximation Performance loss Propagation losses Statistics

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adaptive coding for Information Freshness in a Two-User Broadcast Erasure Channel

Adaptive Coding for Information Freshness in a Two-User Broa...

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2019 IEEE Global Communications Conference (GLOBECOM)

作者： Songtao Feng Jing Yang School of Electrical Engineering and Computer Science The Pennsylvania State University University Park PA

ISBN: (数字)9781728109626

ISBN: (纸本)9781728109633

In this paper, we investigate the impact of coding on the Age of Information (AoI) in a two- user broadcast symbol erasure channel with feedback. We assume each update consists of K symbols and the source is able to broadcast one symbol in each time slot. Due to random channel noise, the intended symbol at each user will be erased according to an independent and identically distributed (i.i.d.) Bernoulli process. A user is able to successfully decode an update if it accumulates sufficient information and successfully decodes the K symbols of the update. Assuming perfect feedback information at the source right after the transmission of each symbol, our objective is to design an adaptive coding scheme to achieve small AoI at both users. We propose a novel coding scheme to judiciously combine symbols from different updates together, and analyze the AoI at both users. Compared with a baseline greedy scheme, the proposed adaptive coding scheme improves the AoI at the weak user by orders of magnitude without compromising the AoI at the strong user.

关键词： Encoding adaptive coding Switches Measurement Servers Optimization Energy harvesting

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adaptive coding strategies for beamforming ad hoc networks

Adaptive coding strategies for beamforming ad hoc networks

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MILCOM, Military Communications Conference

作者： D. Hoang R.A. Iltis Department of Electrical and Computer Engineering University of California Santa Barbara CA USA

The application of beamforming to mobile ad hoc networks has been studied extensively. It has been shown that a simple transmit beamforming protocol may yield better performance than a traditional four-way handshake protocol. However, for a data packet of moderate size (around 10/sup 4/ bits), obtaining a reasonable packet error rate in fast fading requires an average uncoded bit error rate of 10/sup -5/. This is impractical in most radio networks and especially in the ad hoc case. Therefore the use of error correcting codes is required. Furthermore, to fully take advantage of the channel capacity, an adaptation coding scheme with variable code rate is usually required. The choice of the variable rate coding scheme and MAC protocol has been addressed recently as a cross-layer design problem. However, most variable rate coding methods choose the rate in a heuristic manner. In this paper we introduce a procedure to calculate an appropriate code rate for an ad hoc network employing both transmit and receive beamforming under a basic access (CSMA/CA) protocol. Though the method can be applied to CSMA networks with or without beamforming, due to the limited space of the space, in this paper we only present the detail calculation for the beamforming case. Simulation results show that the new combination of variable-rate coding and beamforming improves network throughput significantly.

关键词： adaptive coding Array signal processing Ad hoc networks Access protocols Multiaccess communication Mobile ad hoc networks Error analysis Fading Bit error rate Radio network

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A convolutional spiking neural network with adaptive coding for motor imagery classification

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NEUROCOMPUTING 2023年第1期549卷

作者： Liao, Xiaojian Wu, Yuli Wang, Zi Wang, Deheng Zhang, Hongmiao Soochow Univ Sch Mech & Elect Engn Jiangsu Prov Key Lab Adv Robot Suzhou 215000 Peoples R China Shanghai Univ Tradit Chinese Med Sch Basic Med Sci Shanghai 201203 Peoples R China

Motor imagery (MI) signal classification is crucial for brain-computer interfaces (BCI). The third-generation neural network, spiking neural network (SNN), has rich neurodynamic properties in the spa-tiotemporal domain, and therefore it is more suitable for processing EEG signals. However, the feature extraction capability of the SNN previously applied to MI signal classification is limited by its structure, and the model's classification accuracy is not comparable to the state-of-the-art algorithms. In this paper, we propose a spiking neural network model called SCNet, which combines the feature extraction capa-bility of CNN with the biological interpretability of SNN, making the model structurally closer to the bio-logical neuronal dynamical system and improving the classification accuracy. SCNet reduces information loss by adaptive coding with learnability and solves the training difficulties of spiking neural networks by surrogate gradient learning. We evaluated the performance of the proposed SCNet on three typically rep-resentative motor imagery datasets. The validation shows that the model outperforms state-of-the-art SNN-based MI classification methods and various ANN and machine learning methods. The experimental results demonstrate the generality and effectiveness of the proposed motor imagery EEG signal classifi-cation model. Better classification results can be obtained by designing a well-structured spiking neural network.& COPY;2023 Elsevier B.V. All rights reserved.

关键词： Spiking neural network Motor imagery adaptive coding

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adaptive coding in fading channels

Adaptive coding in fading channels

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AFRICON Conference

作者： C. Mitchell F. Swarts F. Aghdasi Department of Electrical Engineering University of the Witwatersrand South Africa Department of Electrical Engineering University of Pretoria South Africa

The use of an adaptive forward error control coding scheme is investigated on Rayleigh fading channels typically encountered in mobile communications systems. A predictive algorithm is used to estimate the fading intensity on the channel and this estimate is used to predict the code parameters. It is found that the use of the proposed scheme leads to an improvement in both the bit error rate performance and the throughput of the system.

关键词： adaptive coding Fading Programmable control adaptive control Error correction Mobile communication Prediction algorithms Rayleigh channels Bit error rate Throughput

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