Efficient and Secure Spectrum Utilization for Communication & Sensing in UDN by Beamspace Processing

Motivated by a few potential use cases, this paper concerns how to further improve the utilization of the already-crowded electromagnetic spectrum for joint communication and sensing. Although tremendous efforts have been made in the last few decades towards spectrum efficiency, there is still room for improving spectrum utilization by exploiting multiple domains of the radio resources and considering synergy of multiple functions, such as communication and sensing. Detectability or sensitivity is a concerning issue especially for radio pollution monitoring and passive radar based on communication signals of opportunity. We try to improve the sensitivity without sacrificing coverage by exploiting beamspace processing. Specifically, a concept of joint transmitter-receiver (Tx-Rx) multi-beam sweeping (or hopping) based Integrated Sensing and Communication (ISAC) is proposed, taking advantage of densely deployed base stations (BSs) with beamforming capability. The Ultra-Dense Network (UDN) infrastructure with Cloud Radio Access Network (CRAN) configuration favors centralized coordination and data processing (e.g., multi-receiver-based localization). We propose a resource partition technique to work with beam sweeping, and examine it using simulation. A passive multi-target localization framework suitable for the joint Tx-Rx multi-beam sweeping in UDN is studied, where the traditional Range-Difference (RD)-based locating technique is extended from single target to multiple targets by using a grouping algorithm. Furthermore, security issues related to narrow beam sweeping are considered from a non-cryptography perspective. We propose a space-time decoupling method and a challenge-response verification scheme against spoofing attacks in the UDN that supports beam sweeping.