博士论文答辩：太赫兹静态与动态信道建模
日期：2025/05/21 - 2025/05/21
博士论文答辩：太赫兹静态与动态信道建模
主讲人：Yuanbo Li, Ph.D. candidate at UM-SJTU Joint Institute
时间：2025年5月21日（周三）下午4:00-6:00
地点：密西根学院龙宾楼503会议室
讲座摘要
Terahertz (THz) communications, spanning the frequency range from 0.1 THz to 10 THz, are envisioned as a key technology for the next-generation wireless communication networks. Applications of the THz band in wireless communications include both static scenarios like indoor WiFi, data center, outdoor backhaul, etc., and mobile scenarios like space-to-ground links, air-to-ground links, as well as vehicular communications. Therefore, the study of underlying THz wireless propagation channels in both static and mobile scenarios provides the foundations for the development of reliable THz communication systems and their applications. However, existing channel studies in the THz band exhibits several limitations, including but not limited to, inaccurate channel parameter estimation, limited channel measurements in terms of frequency bands and scenarios, and lack of accurate modeling of temporal non-stationarity and time-varying channel models, etc.
In this dissertation, to accurately estimate the channel parameters of multipath components (MPCs) in THz direction-scan sounding (DSS), the author firstly proposes the DSS-oriented space-alternating generalized expectation-maximization (DSS-o-SAGE) algorithm. To begin with, an accurate signal model involving scanning-direction-dependent phase terms is proposed to include the phase instability in THz DSS, which is further validated with real measurements. In addition, the maximum likelihood estimator in DSS-o-SAGE algorithm is derived, where low computational complexity is achieved by exploring the narrow antenna beam in THz DSS and using a coarse-to-fine search process with partial data. Furthermore, to demonstrate the efficacy of the proposed algorithm, its performance is compared with existing space-alternating generalized expectation-maximization (SAGE) algorithms through simulations as well as realistic measurements. The results show that with special considerations for THz DSS, the DSS-o-SAGE algorithm has higher estimation accuracy and lower computational complexity compared to existing methods. Extensive simulations are performed to model the scatter distance boundary, beyond which the far-field simplification can be used in DSS-o-SAGE. By using the proposed DSS-o-SAGE algorithm, the channel characterization in THz bands is more accurate and reasonable.
Furthermore, to fully characterize and model THz channels in static scenarios, the author conducts extensive channel measurement campaigns in typical indoor and outdoor scenarios. Specifically, two measurement systems are built, including a vector network analyzer (VNA)-based channel sounder and a correlation-based channel sounder, to fulfill different needs when conducting experiments in different environments. Moreover, extensive channel measurements are conducted in various scenarios, including corridor, atrium, laboratory, street, and urban microcell (UMi), across various frequency bands from 140 GHz to 315 GHz. More than 18000 of channel impulse responses are measured. Based on the measurement results, the propagation phenomena of THz waves in typical indoor and outdoor environments are analyzed, such as the scattering of objects in indoor scenarios and blockage of foliage in outdoor scenarios. Moreover, the statistical channel properties are modeled and analyzed. The differences and generality in the THz channels across different scenarios and frequency bands are revealed. Besides, the digital twin enabled hybrid channel model (DTeHCM) is proposed for the outdoor UMi scenario, which combines the ray-tracing technique, digital twin of foliage, and stochastic approaches. The comparison with measurement results and existing statistical channel models validates the effectiveness of the proposed DTeHCM.
Last but not least, to investigate the time-varying properties of mobile THz channels, the author implements ray-tracing techniques to obtain numerous channel data in both the vehicle-to-infrastructure (V2I) and air-to-ground (A2G) scenarios. The ray-tracing simulator is firstly calibrated and validated by using realistic channel measurement data. Furthermore, extensive ray-tracing simulations are conducted, based on which the channel characteristics, including path loss, shadow fading, K-factor, delay and angular spreads, cross-polarization ratio (XPR), coherence time and bandwidth, etc., are calculated and analyzed in both the V2I and A2G scenarios. Moreover, the temporal non-stationarity is modeled considering the birth and death processes in the time-varying channels. With the accurate modeling of the birth and death processes, hybrid time-varying channel models are proposed, which generates higher accuracy compared to the existing channel models. To summarize, this dissertation deeply studies the channel characterization and modeling in both static and mobile scenarios in the THz band. A channel parameter estimation algorithm is proposed, which lays a foundation for accurate analysis of the THz propagation mechanisms. Moreover, channel measurement campaigns are conducted in various frequency bands and scenarios to fully capture the propagation phenomena in static scenarios, based on which the interaction between THz waves and typical environments are analyzed and thorough channel characterization is conducted. Furthermore, the time-varying properties and temporal non-stationarity are studied and modeled in the THz band in mobile environments, such as V2I and A2G channels. Hybrid channel models are proposed and validated, which possesses both high accuracy and low complexity. The observations and results in this dissertation will pave the way for effective usage and implementation of future THz wireless communication networks.
主讲人介绍
Yuanbo Li received the B.E. degree in Communication Engineering from Harbin Institute of Technology, Harbin, China, in 2020. Since 2020, he has been working toward the Ph.D. degree with Terahertz Wireless Communication Laboratory, Shanghai Jiao Tong University, China. His research interests include Terahertz band channel modeling and time-varying channel modeling.