Search

A distributed scheduling approach to multi-user beamforming at a base-station (BS) is proposed. The scheme assumes the BS is equipped with multiple antennas and uses zero-forcing beamforming to schedule multiple users on the same time-frequency uplink/downlink channels. The optimal user set that the BS can schedule is the one that maximizes the sum-rate for the communication channel. The computational complexity of finding the optimal user set becomes intractable as the number of users exceeds 20-30. Sub-optimal schemes for maximizing the sum-rate generally require large control overhead. We propose an effective sum-rate performance metric that accounts for the control overhead required by the scheduling method. We also propose a user scheduling method that has both low complexity and low overhead. The complexity and overhead are reduced by adding one user at a time and distributing the computation of the scheduling problem across the users. Each user calculates the sum-rate that would result if they were added to the existing user set using their own channel and knowledge of the channels of existing users that is broadcast by the BS. The user with greatest sum-rate increase is scheduled. We use simulations to show that this approach can achieve significantly higher effective sum rates than previously proposed sub-optimal schemes. We also derive an approximate expression for the expected sum-rate with our distributed scheduling method and demonstrate its accuracy with simulations. [ABSTRACT FROM PUBLISHER]

Microwave imaging has been suggested as a promising modality for early-stage breast cancer detection. In this paper, we propose a statistical microwave imaging technique wherein a set of generalized likelihood ratio tests (GLRT) is applied to microwave backscatter data to determine the presence and location of strong scatterers such as malignant tumors in the breast. The GLRT is formulated assuming that the backscatter data is Gaussian distributed with known covariance matrix. We describe the method for estimating this covariance matrix offline and formulating a GLRT for several heterogeneous two-dimensional (2-D) numerical breast phantoms, several three-dimensional (3-D) experimental breast phantoms, and a 3-D numerical breast phantom with a realistic half-ellipsoid shape. Using the GLRT with the estimated covariance matrix and a threshold chosen to constrain the false discovery rate (FDR) of the image, we show the capability to detect and localize small (<0.6 cm) tumors in our numerical and experimental breast phantoms even when the dielectric contrast of the malignant-to-normal tissue is below 2:1. [ABSTRACT FROM AUTHOR]

This paper describes the internal structure of tablets compressed from binary mixtures of sodium chloride and pregelatinised starch. The minimum particle diameter of pregelatinised starch inside tablets compressed from mixtures was calculated from the difference between the initial pore size distribution and the pore size distribution after removal of the starch particles by burning. Subsequently, the tablets were carefully crushed. These powders, consisting of almost only sodium chloride particles, were measured by laser diffraction. It was found that the diameter of the sodium chloride particles hardly changed, whereas the minimum diameter of starch particles strongly decreased during the compaction process. As an effect of the difference in yield pressure, the harder sodium chloride particles cause deformation of the softer starch particles, resulting in a change in particle shape. The pore size distribution of tablets compressed from mixtures of sodium chloride and starch is typically that of viscoelastic materials; the larger pores (>5 μm) change, while the small pores stay constant in number and size. The median pore diameter in tablets compressed from the mixtures is higher than the median pore diameter in tablets compressed from the pure materials. This paper shows that the formation of large pores was the result of the extra porosity expansion of tablets compressed from binary mixtures of sodium chloride and pregelatinised starch. [Copyright &y& Elsevier]