32 research outputs found
Signal-Aligned Network Coding in K-User MIMO Interference Channels with Limited Receiver Cooperation
In this paper, we propose a signal-aligned network coding (SNC) scheme for
K-user time-varying multiple-input multiple-output (MIMO) interference channels
with limited receiver cooperation. We assume that the receivers are connected
to a central processor via wired cooperation links with individual limited
capacities. Our SNC scheme determines the precoding matrices of the
transmitters so that the transmitted signals are aligned at each receiver. The
aligned signals are then decoded into noiseless integer combinations of
messages, also known as network-coded messages, by physical-layer network
coding. The key idea of our scheme is to ensure that independent integer
combinations of messages can be decoded at the receivers. Hence the central
processor can recover the original messages of the transmitters by solving the
linearly independent equations. We prove that our SNC scheme achieves full
degrees of freedom (DoF) by utilizing signal alignment and physical-layer
network coding. Simulation results show that our SNC scheme outperforms the
compute-and-forward scheme in the finite SNR regime of the two-user and the
three-user cases. The performance improvement of our SNC scheme mainly comes
from efficient utilization of the signal subspaces for conveying independent
linear equations of messages to the central processor.Comment: 12 pages, 4 figures, submitted to the IEEE Transactions on Vehicular
Technolog
Landmark-Matching Transformation with Large Deformation Via n-dimensional Quasi-conformal Maps
We propose a new method to obtain landmark-matching transformations between n-dimensional Euclidean spaces with large deformations. Given a set of feature correspondences, our algorithm searches for an optimal folding-free mapping that satisfies the prescribed landmark constraints. The standard conformality distortion defined for mappings between 2-dimensional spaces is first generalized to the n-dimensional conformality distortion K(f) for a mapping f between n-dimensional Euclidean spaces (n ≥ 3). We then propose a variational model involving K(f) to tackle the landmark-matching problem in higher dimensional spaces. The generalized conformality term K(f) enforces the bijectivity of the optimized mapping and minimizes its local geometric distortions even with large deformations. Another challenge is the high computational cost of the proposed model. To tackle this, we have also proposed a numerical method to solve the optimization problem more efficiently. Alternating direction method with multiplier is applied to split the optimization problem into two subproblems. Preconditioned conjugate gradient method with multi-grid preconditioner is applied to solve one of the sub-problems, while a fixed-point iteration is proposed to solve another subproblem. Experiments have been carried out on both synthetic examples and lung CT images to compute the diffeomorphic landmark-matching transformation with different landmark constraints. Results show the efficacy of our proposed model to obtain a folding-free landmark-matching transformation between n-dimensional spaces with large deformations
Protective effects and potential mechanisms of Pien Tze Huang on cerebral chronic ischemia and hypertensive stroke
<p>Abstract</p> <p>Background</p> <p>Stroke caused by brain ischemia is the third leading cause of adult disability. Active prevention and early treatment of stroke targeting the causes and risk factors may decrease its incidence, mortality and subsequent disability. Pien Tze Huang (PZH), a Chinese medicine formula, was found to have anti-edema, anti-inflammatory and anti-thrombotic effects that can prevent brain damage. This study aims to investigate the potential mechanisms of the preventive effects of Pien Tze Huang on brain damage caused by chronic ischemia and hypertensive stroke in rats.</p> <p>Methods</p> <p>The effects of Pien Tze Huang on brain protein expression in spontaneously hypertensive rat (SHR) and stroke prone SHR (SHRsp) were studied with 2-D gel electrophoresis and mass spectrometric analysis with a matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF)/TOF tandem mass spectrometer and on brain cell death with enzyme link immunosorbent assay (ELISA) and immunostaining.</p> <p>Results</p> <p>Pien Tze Huang decreased cell death in hippocampus and cerebellum caused by chronic ischemia and hypertensive stroke. Immunostaining of caspase-3 results indicated that Pien Tze Huang prevents brain cells from apoptosis caused by ischemia. Brain protein expression results suggested that Pien Tze Huang downregulated QCR<sub>2 </sub>in the electron transfer chain of mitochondria preventing reactive oxygen species (ROS) damage and possibly subsequent cell death (caspase 3 assay) as caused by chronic ischemia or hypertensive stroke to hippocampus and cerebellum.</p> <p>Conclusion</p> <p>Pien Tze Huang showed preventive effects on limiting the damage or injury caused by chronic ischemia and hypertensive stroke in rats. The effect of Pien Tze Huang was possibly related to prevention of cell death from apoptosis or ROS/oxidative damage in mitochondria.</p
Modulation and coding in DS/SSMA communication systems
In this work, we consider several different issues concerning the design and the analysis of direct-sequence spread-spectrum multiple-access (DS/SSMA) communication systems. The performance of DS/SSMA systems can be improved with coding. We have proposed a new system that employs trellis coding and continuous phase modulation (CPM). The trellis code provides coding gain while CPM provides desirable spectral properties. An analysis of this system with deterministic sequences shows that significant improvement can be achieved over the standard binary DS/SSMA system. Besides the design of a new system, we also consider the analysis of different DS/SSMA systems under the random sequence model. A generalized quadrature DS/SSMA system is examined. An algorithm that determines tight upper and lower bounds on the average probabilities of error is derived. An approximation algorithm, called the Conditional Gaussian Approximation, and further approximations are also provided. Systems with random polyphase signature sequences are also considered. An asymptotic analysis is provided and an approximation algorithm, again called the Conditional Gaussian Approximation is derived to estimate the probabilities of error. Finally, through an asymptotic analysis, the Standard Gaussian Approximation is rigorously derived and the Conditional Gaussian Approximation is extended to cover most systems with linear modulation. The results of the asymptotic analysis also provide directions on the design of DS/SSMA systems