Autoregressive modelling for Sub‐THz spatio‐temporal wideband scattered reflection coefficient measurement of complex structures

Abstract

The authors present spatio‐temporally resolved wideband measurements of Sub‐Terahertz (Sub‐THz) reflection coefficients in the frequency range of 92–110 GHz. A stochastic model for single reflection fixed links that is capable of modelling random scattering from small‐scale discontinuities such as those encountered in complex structures in walls and partitions of buildings is presented. The model auto‐regressively produces filter coefficients that are fed into an Infinite‐Impulse‐Response (IIR) filter which convolves them with the spatio‐temporal series in order to generate the next output sample based on previous observations. The IIR filter allows for flexible stochastic generation of samples, and its parameters can be adjusted as needed to suit different channel conditions. A total of 20 suitable start‐up filter coefficients are generated from 21.7 % of the sample size for each complex delay tap distribution, which corresponds to 50 complex instances of the channel. These coefficients are then utilised to validate the remaining measured sample set. The model is in quantitative agreement with measurement statistics and can be used to construct relatively simple modified reflection coefficients that can be used in micro‐cellular ray‐optical network planning tools.

Angular scattering measurements and modelling from building surfaces at sub‐THz frequencies between 92‐110 GHz

“…Figure 5c demonstrates the case were angular frequency scans were taken over a plastered wall with a metallic stud found behind it. The presence of the stud can be verified by the component arriving at τ 0 + 0.165, which is expected to have a similar magnitude to the specular component [9]. All distributions follow a similar shape, showing consistency in scattering up to about 30 • , after which it mainly flattens out, despite the incoherence in scattering seen around those angles, which is due to a deep multipath fade from the edge of the stud at 28 • , causing the polynomial fit to slightly increase in magnitude at the later angles.…”

“…Following WRC-23 [3], the ITU highlighted multiple bands for investigation within the sub-THz range (102-109.5, 151.5-164, 167-174.8, 209-226, and 252-275 GHz), complementing those specified in the IEEE 802.15.3d-2017 standard [4], that will facilitate the development of sixth-generation (6G) wireless networks. Some of the deployment scenarios envisioned within the sub-THz band include kiosk downloads [5], data centre communications [6], backhaul [7], intra-device communications [8] and indoor/outdoor hotspots [9]. The high path loss and highly directive beams formed at sub-THz give value to non-line-of-sight (NLoS) fixed link propagation, such as a path around a corner with a single reflection, to combat blockages and challenges in extending fiber optic deployment.…”

“…The work in reference [17] presents reflection coefficient measurements of 50 different building materials that were modelled based on the Fresnel-Rayleigh equations and Kirchhoff scattering theory with limitations to resolve the scattering coefficients of materials with a complex structure. The authors' recent work in reference [9] demonstrated that seemingly "smooth" surfaces with a complex internal structure are prone to random scattering effects that cause frequency selectivity, with the potential to be exploited for fixed NLoS communications. Hence, such structures cannot be regarded as "homogenized", nor can they be described as "rough" in the sense that they consist of surface height variations comparable to the wavelength.…”