A study on the angle-of-arrival estimation problem from three complementary perspectives: challenges, particularities, and applications

Abstract

This PhD dissertation condenses the outcomes of the studies developed over the course of this doctoral program. It begins with an overview chapter that provides the theoretical background required to support the topics addressed throughout the thesis. The remaining chapters are connected through the central theme of this thesis: the angle of arrival (AoA) estimation problem in wireless systems, which is explored under three distinct yet complementary perspectives. The main motivation for writing this document is to support the argument that a clear understanding of the AoA estimation problem is a key enabler for advancing the technologies envisioned for 6th generation (6G) and beyond, by bridging the communication and radar sensing domains. Accordingly, gaining insight into the nuances of this problem is of great importance, as it provides the foundation for fully exploiting the potential of both services. First, the problem is examined from a purely communication perspective, in which a novel AoA estimation approach for analog beam refinement is proposed, exploiting the polarization domain in high-frequency multiple-input multiple-output (MIMO) communication networks. Subsequently, the joint AoA and Doppler frequency estimation problem is investigated from a sensing perspective. By considering bistatic and multistatic sensing networks, the joint estimation of these two parameters enables target localization capabilities within the system. In this context, the Cramér-Rao lower bound (CRLB) is employed to assess the performance of the individual estimators under different scenario setups. Finally, the AoA and angle of departure (AoD) estimation problem is examined in a bistatic integrated communication and sensing (ISAC) network. Assuming downlink transmission, it is argued that the quality-of-service (QoS) of both sensing and communication systems can be improved through a proper allocation of space–time resources. To this end, an optimization problem is formulated to jointly enhance the time-averaged communication sum-rate—assuming a given number of users (UEs)—and the CRLB associated with the AoA and AoD of the passive target of interest. Additionally, the main conclusions derived from these chapters, along with directions for future research, are summarized in the Conclusion chapter.