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.

Terahertz Communications and Sensing for 6G and Beyond: A Comprehensive Review

“…This involves acquiring the CSI of THz channels using the channel estimation at lower frequencies, leveraging the spatial correlation. To assess the feasibility of this approach, the authors of [479] and [480] studied the spatial similarity among THz, mmWave, and sub-6 GHz bands based on point cloud ray-tracing simulation and field measurement. Their results support the use of out-ofband beam search strategy, not only in LoS scenarios but also even in NLoS ones, when using well-designed antenna patterns in specific frequency bands.…”

“…Second, the correlation matrix is difficult to estimate, considering its large size and the small dimension of antenna arrays measuring at lower frequencies [60]. Third, despite the feasibility of out-of-band estimation on static THz channels, the dynamics such as user mobility, scatter mobility, and blockages, are lifting the difficulty of this task to the next level [479].…”

Analysis of Uplink and Downlink Spatial Channel Reciprocity When Using Asymmetric Transceiver

“…For example, if the power observable through the BS Rx array and RF chains P UL approximates to the power observable by the BS Tx array and RF chains P DL in angle of ϕ, i.e., P UL (ϕ) ≈ P DL (ϕ), the uplink and downlink channels are roughly reciprocal. In [20], we proposed two multi-band spatial channel similarity measures by comparing normalized PASs and beam directions, respectively, which could be further extended to characterize PAS and angle reciprocity. For example, uplink and downlink radio channels can be formed by filtering the same propagation channel with Tx and Rx beam patterns of different HPBWs.…”

Path Clustering for Radio Propagation Prediction With Moving Object in Indoor Environment

“…We conducted research on radio-propagation models of a new wireless emulation system [3]. The ray tracing method is a widely used technique for predicting indoor and outdoor propagation environments and various frequency bands [4,5,6,7,8,9]. However, because of the long computation time required for ray-tracing calculations, more efficient computation is required to predict propagation environments considering moving objects, as repeated simulations are necessary [10,11,12,13].…”