Persistent homology approach for human presence detection from 60 GHz OTFS transmissions

Orthogonal Time Frequency Space (OTFS) is a new, promising modulation waveform candidate for the next generation integrated sensing and communication (ISAC) systems, providing the environment-awareness capabilities together with high speed wireless data communications. This paper presents original results of OTFS-based person monitoring measurements in the 60 GHz millimeter-wave frequency band under realistic conditions, without the assumption of an integer ratio between the actual delays and Doppler shifts of the reflected components and the corresponding resolution of the OTFS grid. As the main contribution of the paper, we propose the use of the persistent homology technique as a method for processing of gathered delay-Doppler responses. We highlight the advantages of persistence homology approach over the standard constant false alarm rate target detector for selected scenarios

Sparsity in the Delay-Doppler Domain for Measured 60 GHz Vehicle-to-Infrastructure Communication Channels

We report results from millimeter wave vehicle-to-infrastructure (V2I) channel measurements conducted on Sept. 25, 2018 in an urban street environment, down-town Vienna, Austria. Measurements of a frequency-division multiplexed multiple-input single-output channel have been acquired with a time-domain channel sounder at 60 GHz with a bandwidth of 100 MHz and a frequency resolution of 5 MHz. Two horn antennas were used on a moving transmitter vehicle: one horn emitted a beam towards the horizon and the second horn emitted an elevated beam at 15-degrees up-tilt. This configuration was chosen to assess the impact of beam elevation on V2I communication channel characteristics: propagation loss and sparsity of the local scattering function in the delay-Doppler domain. The measurement results within urban speed limits show high sparsity in the delay-Doppler domain.Comment: submitted to IEEE International Conference on Communication

On the occurrence of two-wave with diffuse power fading in millimeter wave communications

Mobilkommunikation ist heute so erfolgreich, dass herkömmliche Funktechnologien in traditionellen Frequenzbändern bis 6 GHz bald an ihre Grenzen stoßen. Um die Vision der überall verfügbaren hohen Bandbreite zu realisieren, untersucht diese Studie die Verwendung höherer Frequenzbänder, der sogenannten Millimeterwellen, in der Mobilkommunikation. Diese Frequenzbänder über 30 GHz sind meistens unbelegt und schon einzelne Bänder verfügen über weit mehr Bandbreite als alle bisher genutzen Bänder. Darüber hinaus haben Fortschritte in der Elektronik nun ermöglicht, diese Bänder kostengünstig zu nutzen. In dieser Arbeit wurde der Millimeterwellen-Funkkanal mittels folgender Experimente untersucht: (1) zweier Messkampagnen mit direktionalen Hornantennen in einer statischen Büroumgebung, (2) einer Millimeterwellen-Fahrzeugkommunikationsmesskampagne mit einer Hornantenne und einer omnidirektionalen Antenne, sowie (3) einer Eisenbahnkommunikation-Raytracing-Studie mit Richtantennen auf beiden Seiten. In allen Fällen zeigen die erhaltenen Daten, dass der Millimeterwellen-Funkkanal eine sehr begrenzte Mehrwegeausbreitung hat. Der Hauptgrund für das Fehlen von vielen Mehrwegen liegt darin, dass für Millimeterwellenkommunikation Antennen mit hohem Gewinn eingesetzt werden müssen, um den hohen Pfadverlust zu kompensieren. Diese Richtantennen wirken als räumliche Filter, wodurch die Anzahl signifikanter Mehrwegekomponenten wirksam reduziert wird. Alle in dieser Arbeit vorgestellten Fälle sind durch einen oder zwei dominante Mehrwege gekennzeichnet. Daher kann der Funkkanal mittels eines Modells namens “two-wave with diffuse power” (TWDP) angemessen modelliert werden. Dieses TWDP-Modell erfasst die Interferenz von zwei nicht fluktuierenden Funksignalen und von vielen kleineren sogenannten diffusen Signalen. Bei dieser Untersuchung wird auch eine Verzögerungs-Doppler-Analyse durchgeführt, die auf den Daten der Fahrzeugmesskampagne basiert. Die Analyse zeigt, dass sich die hohe maximale Dopplerverschiebung nicht in der Dopplerspreizung widerspiegelt. Die Auswirkungen der Dopplerverschiebung sind aufgrund der räumlichen Filterung beschränkt. In dieser Arbeit wird kurz auf die Modellierung der TWDP-Modellparameter für ein vereinfachtes Szenario der Eisenbahnkommunikation eingegangen. Ebenso werden Auswirkungen des TWDP-Schwunds durch numerische Simulationen demonstriert.Mobile communications has become so successful today that conventional radio technologies, in traditional frequency bands below 6 GHz, are soon reaching their limits. To be able to develop massively deployed, ubiquitous, data-hungry, mobile applications, this study explores the use of higher frequency bands, or so-called millimeter waves in mobile communications. These radio bands above 30 GHz are mostly unoccupied and have dozens of gigahertz of bandwidth available. Moreover, advances in electronics have now made it possible to utilize these bands cost effectively. This thesis studied the millimeter wave wireless channel through conducting the following experiments: (1) two indoor millimeter wave measurement campaigns with directive horn antennas on both link ends, (2) an outdoor vehicular millimeter wave measurement campaign employing a horn antenna and an omni directional antenna, and (3) a railway communications ray-tracing study with directive antennas on both sides. In all the cases, the data obtained show that the millimeter wave wireless channel has very limited multipath propagation. The main reason for the absence of a rich multipath propagation is because the millimeter wave wireless channel requires high-gain directive antennas that compensate for the path loss. These directive antennas act as spatial filters, thereby effectively reducing the number of significant multipath components. All the cases presented in this thesis are characterized by one or two dominant multipath components. Small-scale fading is hence adequately modeled with a model named two-wave with diffuse power (TWDP). This TWDP model captures the effect of interference of two non-fluctuating radio signals and of many smaller so-called diffuse signals. A delay-Doppler analysis is also performed in this research based on the data obtained from the vehicular measurement campaign. The analysis reveals that the high maximum Doppler shift is not reflected in the Doppler spread values. Again, the effects of the Doppler shift in this setup are suppressed due to spatial filtering. Lastly, this thesis briefly addresses the modeling of the TWDP model parameters for a simplified railway communications scenario, and demonstrates the implications of TWDP fading through numerical simulations.8

Verallgemeinerter LASSO für Sensorgruppensignalverarbeitung

Abweichender Titel nach Übersetzung der Verfasserin/des VerfassersZusammenfassung in deutscher SpracheRadar, seismic and and wireless communication systems observe waves (hidden in noise) by sensor arrays. Those systems infer the originating (spatially-sparse) set of sources, within a minimum prescribed resolution and with as few sensors as feasible. These requirements lead to under-determined systems of equations. Compressed sensing is an active research field which treats the recovery of a set of sources from an under-determined system of equations exploiting sparsity. Naturally two main questions arise in this context. Firstly, what is the minimum number of equations/sensors for which reconstruction can be guaranteed and secondly, how to achieve efficient reconstruction regarding the sensors 'observations' Solutions to the first question provide insights into the design of linear measurements and use quantities like the restricted isometry property or coherence to describe well-behaved matrices, such as equiangular tight frames. Algorithms as answers to the second question mostly rely on the assumption, that the measurements were made in accordance to the reconstruction guarantees. Suppose that one has to work with existing data acquisition systems, the measurement matrix is given a priori and algorithms studied under too idealistic assumptions are prone to failure. This thesis shows that well known greedy algorithms like orthogonal matching pursuit are not suited for array processing problems. We devise an algorithm based on the generalized Least Absolute Shrinkage and Selection Operator (LASSO), which is a penalized least squares problem. The heuristically chosen l1 penalty term ensures strict convexity and that strong duality holds. The corresponding dual problem is interpretable as a weighted conventional beamformer acting on the residuals of the LASSO. Based on physical insights provided by the dual problem¿s solution, three procedures for single snapshot reconstruction and one for sequential online reconstruction are proposed and analysed. The sequential procedure assumes a weighted Laplace-like prior for the sources such that the maximum a posteriori source estimate at the current time step is the solution to a generalized LASSO problem. For the sequential implementation, the posterior distribution is fitted to the Laplace-like density by use of the dual solution

Millimeter Wave Vehicular Channel Emulation: A Framework for Balancing Complexity and Accuracy

We propose a general framework for the specification of a sparse representation of millimeter wave vehicular propagation channels and apply this to both synthetic data and real-world observations from channel sounding experiments. The proposed framework is based on the c-LASSO (complex Least Absolute Shrinkage and Selection Operator) which minimizes the mean squared error of the sparse representation for a given number of degrees of freedom. By choosing the number of degrees of freedom, we balance the numerical complexity of the representation in the channel emulation against its accuracy in terms of the mean squared error. A key ingredient is the choice of basis of the representation and we discuss two options: the Fourier basis and its projection onto a given subband. The results indicate that the subband-projected Fourier basis is a low-complexity choice with high fidelity for representing clustered channel impulse responses. Finally, a sequential estimator is formulated which enforces a consistent temporal evolution of the geometry of the interacting objects in the propagation environment. We demonstrate the performance of our approach using both synthetic data and measured 60 GHz vehicular channel traces