A Tutorial on Terahertz-Band Localization for 6G Communication Systems

Abstract

Terahertz (THz) communications are celebrated as key enablers for converged localization and sensing in future sixth-generation (6G) wireless communication systems and beyond. Instead of being a byproduct of the communication system, localization in 6G is indispensable for location-aware communications. Towards this end, we aim to identify the prospects, challenges, and requirements of THz localization techniques. We first review the history and trends of localization methods and discuss their objectives, constraints, and applications in contemporary communication systems. We then detail the latest advances in THz communications and introduce THzspecific channel and system models. Afterward, we formulate THz-band localization as a 3D position/orientation estimation problem, detailing geometry-based localization techniques and describing potential THz localization and sensing extensions. We further formulate the offline design and online optimization of THz localization systems, provide numerical simulation results, and conclude by providing lessons learned and future research directions. Preliminary results illustrate that under the same transmission power and array footprint, THz-based localization outperforms millimeter wave-based localization. In other words, the same level of localization performance can be achieved at THz-band with less transmission power or a smaller footprint.

Signal Processing and Machine Learning Techniques for Terahertz Sensing: An overview

“…Spectral data can reconstruct higher resolution images at arbitrary directions in the THz band due to antenna array beamforming capabilities and reduced scattering loss [7]. Compared to the fairly developed millimeter-wave (mmWave)-band technology [11], the THz band offers better sensing capabilities and spatial resolution, but at the expense of shorter propagation distances. Furthermore, it is more convenient to characterize and spectroscopically analyze concealed contents, such as metallic and explosive materials and illicit drugs at the THz band, for which comparable spectral fingerprints do not exist in the mmWave region.…”

“…In conjunction with such learning mechanisms, the manifold sensing capabilities at the THz band can provide data-driven THz networks capable of achieving operational intelligence required to recognize the stochasticity of the environment in real-time. Moreover, recent advances in probabilistic machine learning and Bayesian methods, such as Gaussian processes, are bound to ultimately provide promising interpretable modeling of complex spatio-temporal and highdimensional THz sensing problems for 6G wireless networks [11].…”

“…Moreover, the scalability challenge of the learning methods remains partially tackled. The latter is true because the collected data for model training are scenario-dependent, leading to a continuous update in the THz data in reference to the environment and system in use [11]. To overcome this issue, intermediate sensing parameters such as the angle-of-arrival can first be acquired utilizing learning-enabled methods instead of directly acquiring an end-to-end position estimate.…”

Sparse Space Shift Keying Modulation with Enhanced Constellation Mapping

“…Meanwhile, with the idea of the fifth generation (5G) becoming reality, the upcoming sixth generation (6G) [ 18 ] has focused on even enhanced transmission rate by exploring the use of high-frequency bands as terahertz [ 19 ]. Due to the expansive implementation cost on this band, more efficient transmission technologies such as space modulation have been suggested [ 20 ] to further reduce the implementation cost.…”

Radio Localization and Sensing—Part II: State-of-the-Art and Challenges

“…In contrast, mmWave communication (30-300 GHz, though 5G utilizes only lower mmWave bands around 24-53 GHz) has provided unique opportunities for localization, especially when combined with massive arrays, typically analog or hybrid arrays, [4]. In 6G, which is expected to utilize upper mmWave bands (100-300 GHz), with even larger available spectrum, cm-level accuracy is attainable [5].…”