Analysis of the Local Quasi-Stationarity of Measured Dual-Polarized MIMO Channels

It is common practice in wireless communications to assume strict or wide-sense stationarity of the wireless channel in time and frequency. While this approximation has some physical justification, it is only valid inside certain time-frequency regions. This paper presents an elaborate characterization of the non-stationarity of wireless dual-polarized channels in time. The evaluation is based on urban macrocell measurements performed at 2.53 GHz. In order to define local quasi-stationarity (LQS) regions, i.e., regions in which the change of certain channel statistics is deemed insignificant, we resort to the performance degradation of selected algorithms specific to channel estimation and beamforming. Additionally, we compare our results to commonly used measures in the literature. We find that the polarization, the antenna spacing, and the opening angle of the antennas into the propagation channel can strongly influence the non-stationarity of the observed channel. The obtained LQS regions can be of significant size, i.e., several meters, and thus the reuse of channel statistics over large distances is meaningful (in an average sense) for certain algorithms. Furthermore, we conclude that, from a system perspective, a proper non-stationarity analysis should be based on the considered algorithm

Germany in Search of a Mythology

Thomas Mann, in an essay on Freud, defined myth as the foundation of life because it is timeless and provides insight into the higher truth. The verbal power of the mythologically oriented artist bends the phenomena around him to fit his ironic and superior gaze. His tools are words. He molds them into symbols, metaphors, and images with which he connects apparent irreconcilables in a striking new image or impression, thereby creating his mythical world. Ernst Cassirer established the indissoluble union of language and myth in the unconscious grammar of experience. Language and myth are two diverse shoots from the same parent stem, the same impulse of symbolic formulation, springing from the same basic mental activity … the same inner process …; they are both resolutions of an inner tension, the representation of subjective impulses and excitations in definite objective forms and figures

Dual-Polarized Ricean MIMO Channels: Modeling and Performance Assessment

In wireless communication systems, dual-polarized (DP) instead of single-polarized (SP) multiple-input multiple-output (MIMO) transmission is used to improve the spectral efficiency under certain conditions on the channel and the signal-to-noise ratio (SNR). In order to identify these conditions, we first propose a novel channel model for DP mobile Ricean MIMO channels for which statistical channel parameters are readily obtained from a moment-based channel decomposition. Second, we derive an approximation of the mutual information (MI), which can be expressed as a function of those statistical channel parameters. Based on this approximation, we characterize the required SNR for a DP MIMO system to outperform an SP MIMO system in terms of the MI. Finally, we apply our results to channel measurements at 2.53 GHz. We find that, using the proposed channel decomposition and the approximation of the MI, we are able to reproduce the (practically relevant) SNR values above which DP MIMO systems outperform SP MIMO systems.Comment: submitted to the IEEE Transactions on Communication

3D ultrastructural organization of whole Chlamydomonas reinhardtii cells studied by nanoscale soft x-ray tomography

The complex architecture of their structural elements and compartments is a hallmark of eukaryotic cells. The creation of high resolution models of whole cells has been limited by the relatively low resolution of conventional light microscopes and the requirement for ultrathin sections in transmission electron microscopy. We used soft x-ray tomography to study the 3D ultrastructural organization of whole cells of the unicellular green alga Chlamydomonas reinhardtii at unprecedented spatial resolution. Intact frozen hydrated cells were imaged using the natural x-ray absorption contrast of the sample without any staining. We applied different fiducial-based and fiducial-less alignment procedures for the 3D reconstructions. The reconstructed 3D volumes of the cells show features down to 30 nm in size. The whole cell tomograms reveal ultrastructural details such as nuclear envelope membranes, thylakoids, basal apparatus, and flagellar microtubule doublets. In addition, the x-ray tomograms provide quantitative data from the cell architecture. Therefore, nanoscale soft x-ray tomography is a new valuable tool for numerous qualitative and quantitative applications in plant cell biology

Структурно-динамические режимы образования золото-сульфидно-кварцевой минерализации в Сюльбанской золоторудной зоне (бассейн среднего течения реки Витим)

Приведено описание важнейших разломно-трещинных структур Уряхского рудного поля, определяющих размещение золотосульфидно-кварцевой минерализации, и диаграмм трещиноватости горных пород. Реконструированы планы силового поля на предрудном и рудном этапах формирования структуры рудного поля. Показаны различия масштабов рудовмещающих структур, образованных в Каралонском и Уряхском рудных полях. В сравнительном аспекте обсуждаются результаты изучения структурно-динамических режимов образования золотого оруденения на северном фланге Сюльбанской золоторудной зоны и формулируются выводы