Cooperative Terahertz and Sub-6 GHz Integrated Sensing and Communication for Beam Management

The Terahertz (THz) band offers high capacity and high-precision sensing, enabling data-demanding and perceptive services. However, THz communications suffer from high path loss, line-of-sight (LoS) blockage, and beam misalignment challenges. Although integrated sensing and communication (ISAC) has been introduced for assistance, stand-alone THz network still faces challenges such as coverage and high signaling overhead for beam management. Thanks to the 5G protocol that allows dual-connectivity (DC), users can connect to two different frequency bands simultaneously. Following the existing 5G beam management protocol and frame structure, we propose a cooperative THz and sub-6 GHz ISAC scheme for efficient beam management, where THz-band ISAC enables precise predictive beam switches while sub-6 GHz provides low-cost wide-angle coarse localization and always-on communication alternatives. An analyzable framework for beam misalignment and beam switch overhead is subsequently provided. It indicates the maximum supported user speed and data payload efficiency, offering guidelines for configuring signaling periods and network densities to support diverse use cases. Numerical results confirm the effectiveness of this cooperative THz and sub-6 GHz ISAC scheme, showing an average reduction in beam misalignment by 40% and switch overhead by 45% across urban and highway scenarios.