Andreas F. Molisch

Multipath channel simulations at millimeter-wave frequencies require more accurate knowledge of the geometry of physical environments than at below-6 GHz frequencies because of the shorter wavelength. The accurate geometry can be obtained as a point cloud through LIDAR (light detection and ranging) scanning of environments. While the use of point clouds for ray-optics simulations of multipath channels has become a popular approach recently, optimized point cloud parameters - for example its density - that allow accurate reproduction of multipath channels are not yet known. Motivated by a conjecture that a same-sized physical object contributes differently to multipath channels when they are near vs far from communicating antennas, we propose to use a point cloud that is denser for environments near antennas and is sparser when further from antennas. Compared to using a uniform-density point cloud …

A redirecting rotating mirror arrangement includes a directional antenna subcomponent having a direction of maximum received or transmitted beam intensity. The redirecting rotating mirror arrangement also includes a rotatable mirror that reflects an electromagnetic beam to or from the directional antenna subcomponent. The rotatable mirror is inclined at an inclination angle with respect to a horizontal plane. The arrangement also includes a motor that rotates the rotatable mirror about the direction of maximum received or transmitted beam intensity such that the electromagnetic beam is either received from or transmitted to a range of angles as the rotatable mirror rotates.

Sub-THz communication systems are anticipated to play a major part in 6G. To develop those systems further, it is important to both analyze the possible coverage, and investigate the propagation channel properties that impact the design of equalizers, guard intervals, and other measures for combatting dispersion. This article describes the key effects based on extensive measurements with both a channel sounder and a real-time testbed. Transmission over more than 120m with data rates in excess of 2.3 Gb/s is demonstrated with the testbed. Then the requirements for equalization are discussed, and explanations provided for the seeming difference of recent results by different groups; it is shown that equalization requirements strongly depend on the modulation and coding scheme used in the system.

Backhaul traffic congestion caused by the video traffic of a few popular files can be alleviated by storing the to-be-requested content at various levels in wireless video caching networks. Typically, content service providers (CSPs) own the content, and the users request their preferred content from the CSPs using their (wireless) internet service providers (ISPs). As these parties do not reveal their private information and business secrets, traditional techniques may not be readily used to predict the dynamic changes in users' future demands. Motivated by this, we propose a novel resource-aware hierarchical federated learning (RawHFL) solution for predicting user's future content requests. A practical data acquisition technique is used that allows the user to update its local training dataset based on its requested content. Besides, since networking and other computational resources are limited, considering that only a subset of the users participate in the model training, we derive the convergence bound of the proposed algorithm. Based on this bound, we minimize a weighted utility function for jointly configuring the controllable parameters to train the RawHFL energy efficiently under practical resource constraints. Our extensive simulation results validate the proposed algorithm's superiority, in terms of test accuracy and energy cost, over existing baselines.

Path-Loss is one of the essential characteristics of wireless propagation channels. It is usually captured from channel measurements with (quasi-) isotropic antennas. To characterize the wireless channels at high frequencies, beamforming or directional antennas are commonly used, in which case a method for estimating the isotropic path-loss is needed. The method should account for the possible spatial overlap of the different directional measurements while including the received signal from all the multipath components (MPCs) in the channel. In this letter, we propose an efficient method that uses a weighted sum of the powers received from the directional measurements. The weights can be calculated using matrix inversion. We verify the solution using synthetic data and demonstrate the usage with measurements at sub-THz frequencies.

Methods, devices, and systems for communication techniques that use the quasi-static properties of wireless channels are described. One example method to improve communication performance includes receiving a set of pilots over a transmission channel between the wireless communication apparatus and a far-end communication apparatus, the transmission channel comprising a first portion that is time-invariant and a second portion that is time-variant, processing the received set of pilots to generate an estimate of the first portion, processing the received set of pilots to generate an estimate of the second portion, and performing a communication based on a channel state information that is a weighted combination of a first term based on the estimate of the first portion and a second term based on the estimate of the second portion.

We present the design of a dual-mode metallic antenna coupler that can simultaneously couple two separate signals into orthogonal polarizations of a dual-polarization metal-coated dielectric waveguide. The coupler sits on the top surface of the waveguide and features two side-by-side excitation ports, which excite the E x polarization of the waveguide when driven differentially and the E y polarization when driven in common mode. Design is done using random coordinate ascent (RCA). Simulation results show that both modes can be operated simultaneously in the 88.6 – 94 GHz range, achieving 6% fractional bandwidth and a coupler-to-coupler channel insertion loss of 3dB per channel. Due to the symmetric design of the coupler, the interconnect has theoretically zero cross-coupling between the two polarization channels. The design is also amenable to fabrication via standard microfabrication techniques …

This paper considers a full-duplex (FD) multi-user massive multiple-input multiple-output system where the base station (BS) and user equipment (UE) bi-directionally transmit and receive multiple independent data streams over the same frequency band. The BS and UEs are equipped with a large-scale antenna array. Accounting for imperfect channel state information, we derive the closed-form expressions for the achievable sum-rate and sum spectral efficiency (SE) for the proposed model using maximum-ratio combining and zero-forcing detection. The analytical solutions are verified with simulations. In addition, our analytical results highlight the benefits of multi-stream transmission and show an improved SE for fewer UEs. Moreover, the results show that increasing the antenna array size helps combat self-interference.