Accurate modeling of indoor multiple-input multiple-output (MIMO) channels is an important prerequisite for multi-antenna system design. In this paper, a new model for indoor MIMO channels is proposed, and a closed-fo...
详细信息
Accurate modeling of indoor multiple-input multiple-output (MIMO) channels is an important prerequisite for multi-antenna system design. In this paper, a new model for indoor MIMO channels is proposed, and a closed-form expression for the spatio-temporal cross-correlation function between any two subchannels is derived. This new analytical correlation expression includes many key physical parameters of interest such as mean angle-of-departure at the transmitter and mean angle-of-arrival at the receiver, the associated angle spreads, the distance between transmitter and receiver, etc. in a compact form. Comparison of this model with channel correlations and capacity, using the collected indoor MIMO data, exhibits the utility of the model.
We describe an algorithm to estimate and track slow changes in power spectral density (PSD) of nonstationary pressure signals. The algorithm is based on a Kalman filter that adaptively generates an estimate of the aut...
详细信息
We describe an algorithm to estimate and track slow changes in power spectral density (PSD) of nonstationary pressure signals. The algorithm is based on a Kalman filter that adaptively generates an estimate of the autoregressive model parameters at each time instant. The algorithm exhibits superior PSD tracking performance in nonstationary pressure signals than classical nonparametric methodologies, and does not assume a piecewise stationary model of the data. Furthermore, it provides better time-frequency resolution, and is robust to model mismatches. We demonstrate its usefulness by a sample application involving PSD estimation and tracking of short records of simulated pressure waveforms. This algorithm is intended for applications were the PSD must be estimated and tracked during short transient periods, possibly after clinical interventions.
Automatic segmentation of brain tissues is crucial to many medical imaging applications. We use a multi-resolution analysis and a power transform to extend the well-known Gaussian mixture model expectation maximizatio...
详细信息
Automatic segmentation of brain tissues is crucial to many medical imaging applications. We use a multi-resolution analysis and a power transform to extend the well-known Gaussian mixture model expectation maximization based algorithm for segmentation of white matter, gray matter, and cerebrospinal fluid from T1-weighted magnetic resonance images (MRI) of the brain. Experimental results with near 4000 synthetic and real images are included. The results illustrate that the proposed method outperforms six existing methods.
Magnetic resonance spectroscopic imaging (MRSI) is a non-invasive technique for assessing biochemical fingerprint of tissue composition. The need to differentiate between normal and abnormal tissues and determine type...
详细信息
Magnetic resonance spectroscopic imaging (MRSI) is a non-invasive technique for assessing biochemical fingerprint of tissue composition. The need to differentiate between normal and abnormal tissues and determine type of abnormality before biopsy or surgery motivated development and application of MRSI. There are several technical reasons that make the brain easier than other organs to be examined with MRSI. This work presents our proposed methods and results for the analysis of the brain spectra of patients with three tumor types (malignant glioma, astrocytoma, and oligodendroglioma). After extracting features from MRSI data using wavelet and wavelet packets, we use artificial neural networks to determine the abnormal spectra and the type of abnormality. We evaluated the proposed methods using clinical and simulated MRSI data and biopsy results. The MRSI analysis results were correct 97% of the time when classifying the spectra of the clinical MRSI data into normal tissue, tumor, and radiation necrosis. They were correct 72% and 83% of the time when determining tumor types using the clinical and simulated MRSI data, respectively.
In this paper, a new frequency offset compensation scheme for up link of multicarrier code-division multiple access (MC-CDMA) systems is proposed. The proposed scheme exploits guard interval (GI) information embedded ...
详细信息
Accurate identification of a DNA sequence depends on the ability to precisely track the time varying signal baseline in all parts of the electrophoretic trace. We propose a statistical learning formulation of the sign...
Accurate identification of a DNA sequence depends on the ability to precisely track the time varying signal baseline in all parts of the electrophoretic trace. We propose a statistical learning formulation of the signal background estimation problem that can be solved using an Expectation-Maximization type algorithm. We also present an alternative method for estimating the background level of a signal in small size windows based on a recursive histogram computation. Both background estimation algorithms introduced here can be combined with regression methods in order to track slow and fast baseline changes occurring in different regions of a DNA chromatogram. Accurate baseline tracking improves cluster separation and thus contributes to the reduction in classification errors when the Bayesian EM (BEM) base-calling system, developed in our group (Pereira et al., Discrete Applied Mathematics, 2000), is employed to decide how many bases are “hidden” in every base-call event pattern extracted from the chromatogram.
It is known that long-term memory motion estimation can bring a significant coding gain to a video coding system. In this paper, a fast algorithm for long-term memory motion estimation is presented. The proposed algor...
详细信息
It is known that long-term memory motion estimation can bring a significant coding gain to a video coding system. In this paper, a fast algorithm for long-term memory motion estimation is presented. The proposed algorithm attempts to track the direction of the best long-term motion vector in a frame-by-frame manner from the most recent reference frame to the oldest reference frame. Nine direction patterns for the direction tracking are used and the search locations of the long-term memory motion estimation are adaptively selected according to the chosen direction pattern. Simulation results demonstrate that the proposed algorithms can speed up long-term motion estimation by more than 40 times.
Fast block motion estimation algorithms are needed for real-time implementations of video coding standards due to the high computational complexity of the full-search algorithm for block motion estimation. In this pap...
详细信息
Fast block motion estimation algorithms are needed for real-time implementations of video coding standards due to the high computational complexity of the full-search algorithm for block motion estimation. In this paper, an algorithm using 8-bit partial sums of 16 luminance values for a fast block motion estimation is proposed. The technique of using the partial sums is employed to reduce the computational complexity of not only the full-search algorithm but also some of the fast block motion estimation algorithms while maintaining their accuracy. Furthermore, it is shown that the byte-type data-parallelism on an SIMD architecture can be utilized to access and process these partial sums concurrently to accelerate the process of motion estimation. Simulation results are presented to demonstrate that the use of the partial sums can accelerate the execution of the full-search, three-step search, and four-step search algorithms on an SIMD architecture significantly.
Due to the high computational requirement of the full-search algorithm for block motion estimation, fast block motion estimation algorithms are needed for real-time implementations of the video coding standards. Recen...
详细信息
Due to the high computational requirement of the full-search algorithm for block motion estimation, fast block motion estimation algorithms are needed for real-time implementations of the video coding standards. Recently, a three-step search algorithm for block motion estimation has been proposed in the literature. In this paper, a fast three-step search algorithm is proposed to further reduce the computational complexity of the three-step search algorithm with no loss of accuracy. By using a multilevel vector partial sums and lower bounds in the proposed algorithm, a large number of possible candidate motion vectors are discarded while still retaining the optimal motion vector of the three-step search algorithm. It is shown that not all the levels of partial sums and lower bounds are needed. A method to select these vector partial sums and lower bounds are also presented. Simulations of the proposed algorithm are carried out for various benchmark video sequences and the results demonstrate that the new algorithm can reduce the computational complexity of the three-step search algorithm by 20 to 60 percent with no loss of accuracy.
暂无评论