User Association Strategies in 5G/6G IAB Networks With Multicast and Unicast Traffic

The increasing demand for mobile video and emerging extended/augmented reality services necessitates significant advancements in network capacity. 5G New Radio (NR) and future 6G systems address this with the introduction of high-band, above 24 GHz, spectrum (Frequency Range 2, FR2), but also resource-efficient multicast communications. Another 5G NR innovation, the Integrated Access and Backhaul (IAB) enables wireless self-backhauling and offers a promising solution for cost-efficient network densification needed for FR2. This paper examines the impact of user association in FR2 IAB deployments that concurrently support unicast and multicast traffic. We consider a multi-node IAB network implementing a practical hierarchical codebook-based beamforming and investigate two types of cell and beam selection strategies: those that aim to save backhaul resources and those that favor multicast grouping. Our extensive system-level simulation explicitly accounts for intra- and inter-cell interference, spacial multiplexing, FR2 propagation specifics such as human-body blockages, and the IAB duplexing mode. The study provides valuable insights into how various environmental and system parameters, including the share of multicast traffic, affect the IAB network capacity and the gains from multicast delivery. The results show that in half-duplex FR2 IAB with mixed traffic the most efficient user association policy combines the backhaul-saving strategy with a controlled multicast grouping and can achieve up to a 40 % increase in system capacity.