Polarimetric properties of indoor MIMO channels for different floor levels in a residential house

This paper analyzes polarimetric characteristics of power delay profiles (PDPs), cross polarization discrimination (XPD), and received power of specular and diffuse multipath components of indoor MIMO radio channels at 2.45 GHz. Measurements were done in a residential house at two floors levels: "same floor" and "cross floor". Variations of 5 to 15 dB in PDPs between co-and cross-polar links were found in the same floor level; however these changes decrease as radio links move from line-of-sight to non-line-of-sight propagations. XPDs of radio waves were found to be higher for cross floor configuration, about 5 dB in horizontally and 7 dB in vertically polarized waves. Also, diffuse components of channels were less affected compared to that of specular components in same floor setups for cross-polar links. Our results demonstrate that the contribution of diffuse components to total channel power is higher than previously presented studies for large industrial indoor environments

Robustness of high-resolution channel parameter estimators in presence of dense multipath components

The estimation accuracy of specular multipath components in radio channels that include dense multipath is investigated. Classical multipath estimation algorithms such as ESPRIT and SAGE do not include dense multipath in their signal model whereas recent ones, such as RiMAX, do. These estimation algorithms are applied to a priori known synthetic channels which include both specular components (SCs) and dense multipath components (DMCs). The estimation errors of the SCs are computed as a function of the DMC power to evaluate the estimator's robustness. The results of this work clearly indicate large estimation errors for the SC parameters when the estimator does not include DMCs in its data model

Accuracy of specular path estimates with ESPRIT and RiMAX in the presence of measurement-based diffuse multipath components

This paper presents performance results of three high-resolution parameters estimation algorithms: ESPRIT, SAGE and RiMAX. MIMO indoor radio channels which include measurement-based time-delay diffuse multipath scattering (DMC) were emulated to evaluate the estimation performance of both algorithms. The impact of the DMC on the parameter estimation accuracy is studied by adjusting its power with respect to the specular component. For all discussed scenarios, it is clearly demonstrated that RiMAX outperforms ESPRIT and SAGE which do not include DMC estimation into their data model. The preliminary results clearly highlight the importance of DMC and the necessity to account for its presence in data models to accurately estimate the channel parameters. Otherwise, very poor estimates of the coherent component parameters are expected which would in turn result in wronged propagation prediction models

Mimicking the colourful wing scale structure of the Papilio blumei butterfly

The brightest and most vivid colours in nature arise from the interaction of light with surfaces that exhibit periodic structure on the micro- and nanoscale. In the wings of butterflies, for example, a combination of multilayer interference, optical gratings, photonic crystals and other optical structures gives rise to complex colour mixing. Although the physics of structural colours is well understood, it remains a challenge to create artificial replicas of natural photonic structures(1-3). Here we use a combination of layer deposition techniques, including colloidal self-assembly, sputtering and atomic layer deposition, to fabricate photonic structures that mimic the colour mixing effect found on the wings of the Indonesian butterfly Papilio blumei. We also show that a conceptual variation to the natural structure leads to enhanced optical properties. Our approach offers improved efficiency, versatility and scalability compared with previous approaches(4-6).</p

A biological quarter-wave retarder with excellent achromaticity in the visible wavelength region

Animals make use of a wealth of optical physics to control and manipulate light, for example, in creating reflective animal colouration1, 2, 3 and polarized light signals4. Their precise optics often surpass equivalent man-made optical devices in both sophistication and efficiency5. Here, we report a biophysical mechanism that creates a natural full-visible-range achromatic quarter-wave retarder in the eye of a stomatopod crustacean. Analogous, man-made retardation devices are important optical components, used in both scientific research and commercial applications for controlling polarized light. Typical synthetic retarders are not achromatic, and more elaborate designs, such as, multilayer subwavelength gratings or bicrystalline constructions, only achieve partial wavelength independence6. In this work, we use both experimental measurements and theoretical modelling of the photoreceptor structure to illustrate how a novel interplay of intrinsic and form birefringence results in a natural achromatic optic that significantly outperforms current man-made optical devices