Integrated Access and Backhaul for 5G, 6G and Beyond

Doctoral thesis, 2025

Enabling network densification to support coverage-limited millimeter-wave (mmWave) frequencies is a fundamental requirement for 5G, 6G and beyond. However, connecting a high density of base stations (BSs) to the core network remains a significant challenge. While fiber-based backhaul provides high-capacity, reliable links, its deployment may involve substantial costs and long installation times. Wireless backhaul offers a more flexible and rapidly deployable alternative but is often constrained by lower data rates and environmental vulnerabilities. To address these challenges, integrated access and backhaul (IAB) has emerged as a promising solution that repurposes part of the available spectrum for both access and backhaul, enhancing deployment flexibility and reducing time-to-market. Here, the same node/hardware is used to provide both backhaul and cellular services in a multi-hop architecture.
This thesis investigates IAB as a scalable transport solution by analyzing and optimizing its performance under realistic conditions. Using analytical models and simulations, we study the effects of blockage, foliage, and rain attenuation on service coverage and compare IAB deployments with fully fibered and hybrid architectures. We develop methods for optimizing IAB topology design under practical constraints such as inter-node distance and geographical limitations, and evaluate routing strategies to mitigate temporary blockages. We also explore how complementary technologies including reconfigurable intelligent surfaces (RIS), network-controlled repeaters, and free-space optical (FSO) links can enhance IAB-based networks. Our results show that well-planned hybrid deployments can improve coverage and energy efficiency while reducing infrastructure costs.

Overall, the thesis offers an integrated assessment of IAB-based architectures and shows how careful planning and technology integration can enable cost-efficient and robust network densification. The findings suggest that, with appropriate design and optimization, IAB can serve as an effective and scalable backhaul solution for future wireless systems.