Steve Simon

Abstract:

A promising new method from the field of representations of Lie groups is applied to calculate integrals over unitary groups, which are important for multiantenna communications. To demonstrate the power and simplicity of this technique, a number of recent results are rederived, using only a few simple steps. In particular, we derive the joint probability distribution of eigenvalues of the matrix GG† with G a nonzero mean or a semicor-related Gaussian random matrix. These joint probability distribution functions can then be used to calculate the moment generating function of the mutual information for Gaussian multiple-input multiple-output (MIMO) channels with these probability distribution of their channel matrices G. We then turn to the previously unsolved problem of calculating the moment generating function of the mutual information of MIMO channels, which are correlated at both the receiver and the transmitter. From this moment generating function we obtain the ergodic average of the mutual information and study the outage probability. These methods can be applied to a number of other problems. As a particular example, we examine unitary encoded space-time transmission of MIMO systems and we derive the received signal distribution when the channel matrix is correlated at the transmitter end. © 2006 IEEE.

Abstract:

The dynamics of quantum degenerate two-dimensional dipolar excitons confined in electrostatic traps is analyzed and compared to recent experiments. The model results stress the importance of artificial trapping for achieving and sustaining a quantum degenerate exciton fluid in such systems and suggest that a long-lived, spatially uniform, and highly degenerate exciton system was experimentally produced in those electrostatic traps. © 2006 American Institute of Physics.

Abstract:

We have studied the effect of optically-induced random, anisotropic disorder on the magnetoresistance of a Al0.3Ga0.7As/ GaAs two-dimensional electron system by exposing the heterojunction to an asymmetric laser speckle pattern. Changes in the amplitude of the Shubnikov-de Haas oscillations can be explained in terms of easy and hard conductivity paths parallel and perpendicular to the long axis of the oval speckle grains. We also observe corresponding changes in the electron scattering rates. © 2006 Elsevier Ltd. All rights reserved.