Out-of-band information aided mmWave/THz beam search:a spatial channel similarity perspective

Abstract The transition to higher frequency bands, e.g., millimeter-wave (mmWave) and terahertz (THz), will be capitalized on the long term for future wireless communications. One of challenges relates to rapid establishment of mmWave/THz links with low beam training overhead due to highly directional transmission. A promising solution is to take advantage of the coexistence of sub-6 GHz, mmWave, and THz wireless networks and to use out-of-band spatial information for enabling fast beam search. The success depends on the spatial similarity of radio channels across different frequency bands. In this article we promote a feasibility study of low-frequency spatial channel information assisted high-frequency beam search from a radio channel point of view. We develop multi-band channel similarity measure of desired beam directions extracted from radio channels, which are obtained via filtering propagation paths by different beampatterns at different frequencies. Measurementand ray-tracing-based evaluations across multiple frequencies and environments are performed, which prove the usability of out-of-band information aided beam search strategy in line-ofsight (LOS) dominated scenario and even in non-LOS scenario. Finally, we discuss the challenges associated with exploiting spatial channel similarity

On the feasibility of out-of-band spatial channel information for millimeter-wave beam search

Abstract Prolonged beam alignment is the main source of overhead in mobile wireless communications at millimeter-wave (mm-wave) frequencies due to narrow beams following the requirement of high antenna gains. Out-of-band spatial information may be used in initial beam search when lower frequency band radios are operating in conjunction with mm-wave radios. The feasibility of using low-band channel information for coarse estimation of high-band beam directions strongly depends on the spatial congruence between the two frequency bands. In this work, we try to answer two related questions. First, how similar is the power angular spectrum (PAS) of propagation channels between two widely separated frequency bands? Then, what is the impact of practical antenna configurations on spatial channel similarity? We propose a beam directions based metric to assess the power loss and number of false directions if out-of-band spatial information is used instead of in-band information. This metric is more practical and useful than comparing the PASs directly. Point cloud ray tracing and propagation measurement results across multiple frequency bands and environments are used to show that the degree of spatial similarity of beamformed channels is related to antenna beam widths, frequency gap, and radio link conditions

Measurement-based characterization of D-band human body shadowing

Abstract The D-band among all sub-THz and THz radio frequencies is foreseen as the first one to be utilized for communications. Such high frequency communication links are particularly susceptible to shadowing events, e.g., caused by the human body. In this paper we present results of a D-band channel measurement campaign, which was conducted to characterize the impact of human blockage, with a focus on the excess attenuation and temporal evolution of human body shadowing. The attenuation caused by single-person blockers with different physical characteristics was measured with human frontal and lateral crossing the line-of-sight link. Predicting results of two knife-edge diffraction models are compared with the measurement curves, which both underestimate the attenuation levels especially for the volunteer with larger size. Meanwhile, we quantify the deep fading duration varying with the fading depth, which helps to optimize the beam alignment strategy in order to maintain the sufficient signal-to-noise ratio when the dominant path is heavily obstructed