Condensed Matter Theory

Abstract:

The use of multi-antenna arrays has been predicted to provide substantial throughput gains for wireless communication systems. However, these predictions have to be assessed in realistic situations, such as correlated channels and in the presence of interference. In this review, we show results obtained using methods borrowed from statistical physics of random media for the average and the variance of the distribution of the mutual information of multi-antenna systems with arbitrary correlations and interferers. Even though the methods are asymptotic in the sense they are valid in the limit of large antenna numbers, the results are accurate even for small arrays. We also optimize over the input signal covariance with channel covariance feedback and calculate closed-loop capacities. This method provides a simple tool to analyze the statistics of throughput for arrays of any size.

Abstract:

Cholesteric blue phases are a spectacular example of disclination line networks. Here we numerically investigate their response to an imposed Poiseuille flow. We show that shear forces bend and twist and can unzip the disclination lines. Under gentle forcing the network opposes the flow and the apparent viscosity is large. With increased forcing we find strong shear thinning corresponding to the disruption of the network. As the viscosity starts to drop, the imposed flow sets the network into motion. Disclinations break up and re-form with their neighbors along the flow.