647 research outputs found
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Error correction by means of arithmetic codes: an application to resilient image transmission
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Joint source/channel coding and MAP decoding of arithmetic codes
No full textIn this paper, a novel maximum a posteriori (MAP) estimation approach is employed for error correction of arithmetic codes with a forbidden symbol. The system is founded on the principle of joint source channel coding, which allows one to unify the arithmetic decoding and error correction tasks into a single process, with superior performance compared to traditional separated techniques. The proposed system improves the performance in terms of error correction with respect to a separated source and channel coding approach based on convolutional codes, with the additional great advantage of allowing complete flexibility in adjusting the coding rate. The proposed MAP decoder is tested in the case of image transmission across the additive white Gaussian noise channel and compared against standard forward error correction techniques in terms of performance and complexity. Both hard and soft decoding are taken into account, and excellent results in terms of packet error rate and decoded image quality are obtained
Throughput and Delay Analysis for Real-Time Applications in Ad-Hoc Cognitive Networks
No full textWe consider a simple ad-hoc cognitive scenario with two data up-links, one licensed to use the spectral resource (primary) and the other unlicensed (secondary or cognitive). It is assumed that the cognitive link accesses the channel only when the channel is sensed idle. An ON-OFF channel model is used for the primary link, where traffic statistical characteristics are taken into account. A closed-form expression for the signal-to noise-plus interference (SINR) statistics of the cognitive nodes is derived that can be used for estimating the network performance. Moreover, a M/G/1 queueing model is exploited for deriving a simple expression for the average packet delay. Finally, a MAC strategy based on a channel-and-queue aware scheduling is introduced
87. Demosthenes. Rede tegen Zenothemis, met inleiding en commentaar door A. C. Cosman. Leiden, Burgersdijk en Niermans, 1939
No full textMathieu Georges. 87. Demosthenes. Rede tegen Zenothemis, met inleiding en commentaar door A. C. Cosman. Leiden, Burgersdijk en Niermans, 1939. In: Revue des Études Grecques, tome 52, fascicule 248, Octobre-décembre 1939. p. 640
87. Demosthenes. Rede tegen Zenothemis, met inleiding en commentaar door A. C. Cosman. Leiden, Burgersdijk en Niermans, 1939
No full textMathieu Georges. 87. Demosthenes. Rede tegen Zenothemis, met inleiding en commentaar door A. C. Cosman. Leiden, Burgersdijk en Niermans, 1939. In: Revue des Études Grecques, tome 52, fascicule 248, Octobre-décembre 1939. p. 640
Bayesian population inference for effective connectivity
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. 157-169).A hierarchical model based on the Multivariate Autoregessive (MAR) process is proposed to jointly model functional neuroimaging time series collected from multiple subjects, and to characterize the distribution of MAR coefficients across the population from which those subjects were drawn. Thus, model-based inference about the interaction between brain regions, termed effective connectivity, may be generalized beyond those subjects studied. The posterior density of population- and subject-level connectivity parameters is estimated in a Variational Bayesian (VB) framework, and structural model parameters are chosen by the corresponding evidence criterion. The significance of resulting connectivity statistics are evaluated by permutation-based approximations to the null distribution. The method is demonstrated on simulated data and on actual multi-subject functional time series from electroencephalography (EEG) and functional magnetic resonance imaging (fMRI).by Eric Richard Cosman, Jr.Ph.D
Optimization of Scalable Broadcast for a Large Number of Antennas
No full textIn this paper, for a system incorporating a large number of antennas, we address the optimal space-time coding of multimedia scalable sources, which require unequal target error rates in their bitstream. First, in terms of the number of antennas, we analyze the behavior of the crossover point of the outage probability curves for the vertical Bell Laboratories space-time (V-BLAST) architecture with a linear or a maximum-likelihood receiver, and orthogonal space-time block codes (OSTBCs). We prove that, as the number of antennas increases with the transmission data rate fixed, the crossover point in outage probability monotonically decreases. This holds for any data rate employed by the system and is valid over propagation channels such as spatially correlated Rayleigh or Rician fading channels, as well as independent and identically distributed Rayleigh channels. We next show that, over such propagation channels with a large number of antennas, those analytical results can be used to simplify the computational complexity involved with the optimal space-time coding of a sequence of scalable packets, with no performance degradation. © 2016 IEEE.FALS
Optimization of Multimedia Progressive Transmission Over MIMO Channels
No full textThis paper studies the optimal transmission of multimedia progressive sources, which require unequal target error rates in their bitstream, over multiple-input-multiple-output (MIMO) channels. First, we derive the information outage probability expression of a space-time code for an arbitrarily given piecewise-linear diversity-multiplexing tradeoff (DMT) function and the conditions for the existence of a crossover point of the information outage probability curves of the space-time codes. We prove that as long as the crossover point of the outage probabilities exists, as spectral efficiency increases, the crossover point in the signal-to-noise ratio (SNR) monotonically increases, whereas that of the outage probability monotonically decreases. This analysis can be applied to any space-time code, receiver, and propagation channel with a given DMT function. As a specific example, we analyze the two-layer diagonal Bell Labs space-time architecture (D-BLAST) with a group zero-forcing receiver, the vertical BLAST (V-BLAST) with a minimum mean-square error receiver, and orthogonal space-time block codes (OSTBCs), and prove the monotonic behavior of the crossover point for those codes. Based on that, with respect to D-BLAST, V-BLAST, and OSTBC, we derive a method for the optimal space-time coding of a sequence that contains numerous progressive packets. We show that by employing the optimization method rather than exhaustive search, the computational complexity involved with optimal space-time coding can be exponentially reduced without losing any peak SNR performance. © 2015 IEEE
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