EMR: A new metric to assess the resilience of directional mmWave channels to blockages

Millimeter-wave (mmWave) communication systems require narrow beams to compensate for high path loss and to increase the communication range. If an obstacle blocks the dominant communication direction, alternative paths (directions) should be quickly identified to maintain reliable connectivity. In this paper, we introduce a new metric to quantify the Effective Multipath Richness (EMR) of a directional communication channel in the angular domain. In particular, the proposed metric takes into account the strength and spatial diversity of the resolved Multipath Components (MPCs), while also considering the beamwidth of the communication link and the blockage characteristics. The metric is defined as a weighted sum of the number of distinct MPC clusters in the angular domain, where the clustering of the MPCs is performed based on the cosine-distance between the dominant MPCs. For a given transmitter (TX) and receiver (RX) pair, the EMR is a single scalar value that characterizes the robustness of the communication link against blockages, as it captures the number of unique communication directions that can be utilized. It is also possible to characterize the blockage robustness for the whole environment by evaluating the spatial distribution of the EMR metric considering various different TX/RX locations. Using our proposed metric, one can assess the scattering richness of different environments to achieve a particular service quality. We evaluate the proposed metric using our 28 GHz channel measurements in a library environment for Line-of-Sight (LOS) and NLOS scenarios, and compare it with some other commonly used propagation metrics. We argue that EMR is especially informative at higher frequencies, e.g., mmWave and terahertz (THz), where the propagation attenuation is high, and directional Non-Light-of-Sight (NLOS) communication is critical for the success of the network.

Anisotropic metamaterial with the ε-near-μ property in the entire angular domain enables broadband all-angle transmissions

Epsilon-near-mu metamaterials play a significant role in many fields such as radar, communication, and stealth technology, due to their ideal transmission responses. However, when electromagnetic (EM) waves illuminate such metamaterials at large angles, undesired reflectance occurs that greatly restricts the applications. Here, we propose a theoretical approach that can fundamentally eliminate the adverse effects of the incident angle on the transmission response of an anisotropic ε-near-μ material by adjusting the structural permittivity and permeability tensors. We take advantages of the nonresonance regions of electric and magnetic resonators so that the material parameters can attain the desired values in a wide frequency band. This allows us to design a nonreflective material with broadband all-angle transmissions from 0° to almost 90°, which is further verified by experiments with good performance. This work opens up a new route for the design of ultrawide-angle transmission-type metamaterials with high-efficiency and wideband properties, reaching significant applications in antenna radomes.

Borel Directions and the Uniqueness of Algebroid Functions Dealing with Multiple Values

In this paper, we investigate the uniqueness of algebroid functions in angular domain by the method of conformal mapping. We discuss the relations between the Borel directions and uniquenss with the multiple values of algebroid functions and obtain some results which extend some uniqueness results of meromorphic functions to that of algebroid functions.