Integrated Access and Backhaul Radio Frequency Bandwidth Edge

Description

IAB RF Bandwidth edge refers to the frequency of one of the edges of the IAB RF Bandwidth, which is the RF bandwidth in which an IAB-DU and/or IAB-MT transmits and/or receives single or multiple carriers within a supported operating band. This term is defined in 3GPP specifications 38.174 and 38.176, which cover NR Integrated Access and Backhaul (IAB) radio transmission and reception. The IAB RF Bandwidth edge is a critical parameter for defining the spectral boundaries of IAB operation, ensuring that transmissions are confined within the allocated bandwidth and comply with regulatory and 3GPP requirements. It is typically expressed in Hz or MHz and can refer to either the lower edge (lowest frequency) or the upper edge (highest frequency) of the IAB RF Bandwidth.

In the context of IAB, the RF bandwidth edge is used in RF performance requirements and testing. For example, the 3GPP specifications define limits for unwanted emissions at the edges of the operating band, such as adjacent channel leakage ratio (ACLR) and spectrum emission mask (SEM). The IAB RF Bandwidth edge serves as a reference point for these measurements. It also plays a role in carrier aggregation scenarios, where multiple carriers may be aggregated, and the edges of the aggregated bandwidth define the overall spectral extent. The IAB node must ensure that its transmissions do not exceed these edges, to avoid interference with adjacent channels or bands.

The IAB RF Bandwidth edge is closely related to the concept of channel edge and operating band edge. While the operating band edge is defined by 3GPP for a specific band (e.g., n257: 26.5–29.5 GHz), the IAB RF Bandwidth edge is specific to the actual bandwidth used by the IAB node, which may be smaller than the full operating band. For instance, an IAB node might operate with a 400 MHz RF bandwidth within the n257 band, and the edges of this 400 MHz are the IAB RF Bandwidth edges. These edges are used in RF testing to verify that the transmitter meets requirements such as maximum output power and EVM at the band edges, where performance may degrade.

Key components of the IAB RF Bandwidth edge include its frequency value, its relation to the carrier center frequency, and its role in defining guard bands. In multi-carrier operation, the edges of each carrier and the overall aggregated bandwidth must be considered. The IAB node's RF front-end must be designed to handle the full range between the lower and upper edges, including any guard bands. The specifications 38.174 and 38.176 provide detailed requirements for IAB-DU and IAB-MT, including definitions of RF bandwidth edges and associated test procedures. These ensure that IAB equipment can operate reliably in diverse deployment scenarios.

In network planning, the IAB RF Bandwidth edge helps operators allocate spectrum efficiently and avoid interference. By knowing the exact edges, operators can coordinate with neighboring networks and ensure compliance with local regulations. The term is also used in link budget calculations and coverage predictions, as the edge frequencies may experience different propagation characteristics. As IAB becomes more prevalent in 5G-Advanced and 6G, precise definition of RF bandwidth edges will be essential for spectrum sharing and coexistence.

Purpose & Motivation

The IAB RF Bandwidth edge concept exists to provide a precise definition of the spectral boundaries of IAB operation, which is essential for RF compliance, interference management, and spectrum coordination. In wireless communications, the edges of a transmission bandwidth are critical because they define the transition between the intended signal and adjacent spectrum. Regulatory bodies set strict limits on out-of-band emissions, and 3GPP specifies RF requirements that must be met at these edges. For IAB nodes, which operate in both access and backhaul roles, defining the RF bandwidth edges is particularly important to ensure that transmissions do not interfere with other nodes or services.

Prior to the formal definition of IAB RF Bandwidth edge, RF requirements for IAB were less clearly specified, leading to potential ambiguities in testing and certification. The introduction of this term in Release 19 (and its continuation in Release 20) addresses the need for a standardized reference point for RF measurements. It enables manufacturers to design IAB equipment that meets global regulatory requirements and facilitates interoperability between different vendors' equipment. It also helps operators in spectrum planning, as they can accurately determine the spectral footprint of IAB deployments.

The IAB RF Bandwidth edge is a foundational parameter for many RF tests, including those for ACLR, SEM, and spurious emissions. Without a clear definition, these tests would be difficult to perform consistently. By defining the edge, 3GPP ensures that all stakeholders have a common understanding of where the IAB signal starts and ends, which is crucial for coexistence with other systems, such as satellite services or fixed links. As IAB is deployed in mmWave bands where bandwidths are large, the precise definition of edges becomes even more important for efficient spectrum utilization.