19 research outputs found
On the Maximal Diversity Order of Spatial Multiplexing with Transmit Antenna Selection
Zhang et. al. recently derived upper and lower bounds on the achievable
diversity of an N_R x N_T i.i.d. Rayleigh fading multiple antenna system using
transmit antenna selection, spatial multiplexing and a linear receiver
structure. For the case of L = 2 transmitting (out of N_T available) antennas
the bounds are tight and therefore specify the maximal diversity order. For the
general case with L <= min(N_R,N_T) transmitting antennas it was conjectured
that the maximal diversity is (N_T-L+1)(N_R-L+1) which coincides with the lower
bound. Herein, we prove this conjecture for the zero forcing and zero forcing
decision feedback (with optimal detection ordering) receiver structures.Comment: 10 pages. Submitted to the IEEE Transactions on Information Theor
Alternative EM algorithms for nonlinear state-space models
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordThe expectation-maximization algorithm is a commonly employed tool for system identification. However, for a
large set of state-space models, the maximization step cannot
be solved analytically. In these situations, a natural remedy
is to make use of the expectation-maximization gradient algorithm, i.e., to replace the maximization step by a single iteration of Newtonâs method. We propose alternative expectationmaximization algorithms that replace the maximization step with
a single iteration of some other well-known optimization method.
These algorithms parallel the expectation-maximization gradient
algorithm while relaxing the assumption of a concave objective
function. The benefit of the proposed expectation-maximization
algorithms is demonstrated with examples based on standard
observation models in tracking and localization
PCA-based lung motion model
Organ motion induced by respiration may cause clinically significant
targeting errors and greatly degrade the effectiveness of conformal
radiotherapy. It is therefore crucial to be able to model respiratory motion
accurately. A recently proposed lung motion model based on principal component
analysis (PCA) has been shown to be promising on a few patients. However, there
is still a need to understand the underlying reason why it works. In this
paper, we present a much deeper and detailed analysis of the PCA-based lung
motion model. We provide the theoretical justification of the effectiveness of
PCA in modeling lung motion. We also prove that under certain conditions, the
PCA motion model is equivalent to 5D motion model, which is based on physiology
and anatomy of the lung. The modeling power of PCA model was tested on clinical
data and the average 3D error was found to be below 1 mm.Comment: 4 pages, 1 figure. submitted to International Conference on the use
of Computers in Radiation Therapy 201
An objective comparison of cell-tracking algorithms
We present a combined report on the results of three editions of the Cell Tracking Challenge, an ongoing initiative aimed at promoting the development and objective evaluation of cell segmentation and tracking algorithms. With 21 participating algorithms and a data repository consisting of 13 data sets from various microscopy modalities, the challenge displays today's state-of-the-art methodology in the field. We analyzed the challenge results using performance measures for segmentation and tracking that rank all participating methods. We also analyzed the performance of all of the algorithms in terms of biological measures and practical usability. Although some methods scored high in all technical aspects, none obtained fully correct solutions. We found that methods that either take prior information into account using learning strategies or analyze cells in a global spatiotemporal video context performed better than other methods under the segmentation and tracking scenarios included in the challenge
Linear Prediction of Discrete-Time 1/f Processes
In this letter, the linear predictability of discrete-time stationary stochastic processes with 1/vertical bar f vertical bar(alpha)-shaped power spectral density (PSD) is considered. In particular, the spectral flatness measure (SFM)-which yields a lower bound for the normalized mean-squared-error (NMSE) of any linear one-step-ahead (OSA) predictor-is obtained analytically as a function of alpha is an element of [0, 1]. By comparing the SFM bound to the NMSE of the p-tap linear minimum-mean-square error (LMMSE) predictor, it is shown that close to optimal NMSE performance may be achieved for relatively moderate values of. The performance of the LMMSE predictor for the discrete-time fractional Gaussian noise (DFGN), which may be viewed as the conventional discrete-time counterpart of continuous-time processes with 1/vertical bar f vertical bar(alpha)-shaped PSD, shows that the DFGN is more easily predicted than the discrete-time processes considered herein