Maximum a posteriori estimation

About: Maximum a posteriori estimation is a research topic. Over the lifetime, 7486 publications have been published within this topic receiving 222291 citations. The topic is also known as: Maximum a posteriori, MAP & maximum a posteriori probability.

Wideband Spectrum Sensing for Cognitive Radios With Correlated Subband Occupancy

Abstract: In this letter, we consider wideband spectrum sensing in the presence of correlation between the occupancies of frequency subbands. We begin by formulating the maximum a posteriori (MAP) estimator of channel occupancy based on measurements from multiple frequency subbands. Since the MAP estimator's complexity grows exponentially with the number of subbands, we propose an alternative structure, in which the subband energy measurements are linearly combined according to a minimum mean-square error (MMSE) criterion to form a sufficient statistic for binary detection in each subband. Through analysis and numerical simulations, we show that the proposed frequency-coupled detector can significantly outperform the traditional decoupled one.

Conditionally Gaussian Hypermodels for Cerebral Source Localization

Abstract: Bayesian modeling and analysis of the MEG and EEG modalities provide a flexible framework for introducing prior information complementary to the measured data. This prior information is often qualitative in nature, making the translation of the available information into a computational model a challenging task. We propose a generalized gamma family of hyperpriors which allows the impressed currents to be focal and we advocate a fast and efficient iterative algorithm, the Iterative Alternating Sequential (IAS) algorithm for computing maximum a posteriori (MAP) estimates. Furthermore, we show that for particular choices of the scalar parameters specifying the hyperprior, the algorithm effectively approximates popular regularization strategies such as the Minimum Current Estimate and the Minimum Support Estimate. The connection between priorconditioning and adaptive regularization methods is also pointed out. The posterior densities are explored by means of a Markov Chain Monte Carlo (MCMC) strategy suitable for this family of hypermodels. The computed experiments suggest that the known preference of regularization methods for superficial sources over deep sources is a property of the MAP estimators only, and that estimation of the posterior mean in the hierarchical model is better adapted for localizing deep sources.

Robust Low-Dose CT Sinogram Preprocessing via Exploiting Noise-Generating Mechanism

Abstract: Computed tomography (CT) image recovery from low-mAs acquisitions without adequate treatment is always severely degraded due to a number of physical factors. In this paper, we formulate the low-dose CT sinogram preprocessing as a standard maximum a posteriori (MAP) estimation, which takes full consideration of the statistical properties of the two intrinsic noise sources in low-dose CT, i.e., the X-ray photon statistics and the electronic noise background. In addition, instead of using a general image prior as found in the traditional sinogram recovery models, we design a new prior formulation to more rationally encode the piecewise-linear configurations underlying a sinogram than previously used ones, like the TV prior term. As compared with the previous methods, especially the MAP-based ones, both the likelihood/loss and prior/regularization terms in the proposed model are ameliorated in a more accurate manner and better comply with the statistical essence of the generation mechanism of a practical sinogram. We further construct an efficient alternating direction method of multipliers algorithm to solve the proposed MAP framework. Experiments on simulated and real low-dose CT data demonstrate the superiority of the proposed method according to both visual inspection and comprehensive quantitative performance evaluation.

Moving Region Segmentation From Compressed Video Using Global Motion Estimation and Markov Random Fields

Abstract: In this paper, we propose an unsupervised segmentation algorithm for extracting moving regions from compressed video using global motion estimation (GME) and Markov random field (MRF) classification. First, motion vectors (MVs) are compensated from global motion and quantized into several representative classes, from which MRF priors are estimated. Then, a coarse segmentation map of the MV field is obtained using a maximum a posteriori estimate of the MRF label process. Finally, the boundaries of segmented moving regions are refined using color and edge information. The algorithm has been validated on a number of test sequences, and experimental results are provided to demonstrate its advantages over state-of-the-art methods.

Task adaptation using MAP estimation in N-gram language modeling

Abstract: Describes a method of task adaptation in N-gram language modeling for accurately estimating the N-gram statistics from the small amount of data of the target task. Assuming a task-independent N-gram to be a-priori knowledge, the N-gram is adapted to a target task by MAP (maximum a-posteriori probability) estimation. Experimental results showed that the perplexities of the task-adapted models were 15% (trigram) and 24% (bigram) lower than those of the task-independent model, and that the perplexity reduction of the adaptation went up to a maximum of 39% when the amount of text data in the adapted task was very small.