Mobile Integrated Access and Backhaul Mobile Termination

Description

Mobile IAB-MT (Integrated Access and Backhaul Mobile Termination) is a functional entity within the 3GPP 5G-Advanced architecture that enables mobile relay nodes to connect wirelessly to the network. Unlike traditional fixed IAB nodes, mobile IAB nodes are mounted on moving platforms such as vehicles, trains, or drones, providing temporary or dynamic coverage extension. The IAB-MT function acts as the user equipment (UE)-like interface of the IAB node, terminating the radio interface towards the parent node (donor or another IAB node) and managing the backhaul link. This allows the mobile IAB node to relay traffic between user devices and the core network without requiring a fixed fiber or cable backhaul connection.

The Mobile IAB-MT operates in Frequency Range 1 (FR1), which covers the sub-6 GHz spectrum, and is specified in 3GPP Technical Specifications 38.174, 38.175, and 38.455. These specifications define the radio transmission and reception requirements for the mobile IAB node, including both conducted requirements measured at individual TAB connectors and Over-The-Air (OTA) requirements measured at the Radiated Interface Boundary (RIB). The conducted requirements ensure that the hardware meets performance criteria under controlled test conditions, while OTA requirements validate the overall radiated performance in a real-world environment. This dual approach ensures that mobile IAB nodes can be tested reliably and consistently.

Architecturally, the Mobile IAB-MT communicates with a parent node (which could be a donor gNB or another IAB node) using the same air interface as regular UEs, but with enhancements for backhauling. It supports beam management, power control, and mobility procedures to maintain the backhaul link as the node moves. The IAB node also contains an IAB-DU (Distributed Unit) function that serves UEs and child IAB nodes, effectively acting as a base station for its coverage area. The Mobile IAB-MT and IAB-DU can operate on the same or different frequencies, enabling flexible deployment scenarios.

Key technical challenges addressed by Mobile IAB-MT include maintaining robust backhaul connectivity under mobility, managing interference between access and backhaul links, and ensuring seamless handover between parent nodes. The 3GPP specifications define requirements for frequency stability, output power, error vector magnitude (EVM), and adjacent channel leakage ratio (ACLR) to ensure reliable operation. The OTA requirements are particularly important for mobile IAB because the antenna system is integrated into the moving platform, and radiated performance directly impacts link budget and coverage.

In the broader 5G ecosystem, Mobile IAB-MT enables new use cases such as temporary event coverage, disaster recovery, and mobile hotspots for public transportation. It reduces deployment costs by eliminating the need for fixed backhaul infrastructure and allows rapid network expansion in areas where fiber is unavailable. As part of 3GPP Release 19, Mobile IAB-MT represents an evolution of the IAB framework introduced in Release 16, specifically tailored for mobile scenarios with enhanced mobility and performance requirements.

Purpose & Motivation

Mobile IAB-MT exists to provide wireless backhaul connectivity for mobile relay nodes, solving the problem of extending network coverage in scenarios where fixed backhaul is impractical or unavailable. Traditional IAB nodes are stationary and rely on fixed backhaul links, which limits their deployment flexibility. Mobile IAB-MT enables IAB nodes to be mounted on moving vehicles, trains, or drones, allowing the network to follow the movement of users or provide coverage in dynamic environments.

The motivation for Mobile IAB-MT stems from the growing demand for ubiquitous connectivity in high-mobility scenarios, such as high-speed trains, buses, and emergency response vehicles. In these cases, maintaining a reliable backhaul link is challenging due to rapid changes in channel conditions and the need for frequent handovers. Mobile IAB-MT addresses these challenges by defining specific radio requirements and procedures that ensure robust backhaul performance under mobility.

Furthermore, Mobile IAB-MT reduces the cost and complexity of deploying temporary or ad-hoc networks. Instead of laying fiber or setting up microwave links, operators can deploy mobile IAB nodes that automatically connect to the network and provide coverage. This is particularly valuable for disaster relief, large public events, and rural coverage extension. The Release 19 specifications for Mobile IAB-MT build on the foundation of Release 16 IAB, adding mobility enhancements and FR1-specific requirements to make mobile backhaul a reality.