Carrier aggregation configuration

Description

Carrier aggregation (CA) configuration in the context of 3GPP refers to the specification of a set of one or more operating bands across which a base station (BS) or, in later releases, an Integrated Access and Backhaul (IAB) node aggregates multiple component carriers (CCs) to increase the overall transmission bandwidth and data rates. This configuration is essential for meeting the technical requirements defined for multi-carrier operation, including aspects such as maximum output power, unwanted emissions, and adjacent channel leakage ratio (ACLR). The configuration is typically described in terms of the operating bands, the number of carriers, and the bandwidths of each carrier, as well as the aggregation of these carriers in the frequency domain.

In the context of IAB, which was introduced in Release 16, the carrier aggregation configuration applies to both the IAB-DU (Distributed Unit) and the IAB-MT (Mobile Termination). The IAB-DU is responsible for the access link to user equipment (UEs) and the backhaul link to parent IAB nodes, while the IAB-MT handles the wireless backhaul connection to the parent node. The carrier aggregation configuration ensures that the IAB node can aggregate carriers across multiple operating bands to achieve the required performance and spectral efficiency. This is particularly important for IAB nodes that need to provide high-capacity backhaul and access in dense deployments.

The technical requirements for carrier aggregation configurations are specified in 3GPP TS 38.104 (Base Station radio transmission and reception), TS 38.141 (Base Station conformance testing), and TS 38.174 (IAB radiated conformance testing). These specifications define the radio frequency (RF) requirements for different aggregation scenarios, including intra-band contiguous, intra-band non-contiguous, and inter-band carrier aggregation. The configuration impacts the design of the transmitter and receiver chains, including power amplifiers, filters, and antennas, to ensure compliance with regulatory and performance requirements.

From an architectural perspective, the carrier aggregation configuration is a key parameter in the radio access network (RAN) that determines how the available spectrum is utilized. It enables the network to flexibly allocate resources across multiple carriers, improving peak data rates, coverage, and reliability. For IAB nodes, the configuration must also consider the half-duplex constraint and the need to multiplex access and backhaul links, which adds complexity to the aggregation strategy. The configuration is typically signaled to the UE via radio resource control (RRC) messages, and the UE must support the corresponding aggregation capabilities.

In summary, the carrier aggregation configuration is a fundamental concept in 3GPP that defines the multi-carrier operation for base stations and IAB nodes. It ensures that the aggregated carriers meet the necessary technical requirements and enables high-performance wireless communication in 5G NR and beyond.

Purpose & Motivation

The carrier aggregation configuration exists to provide a standardized way to specify the multi-carrier operation of base stations and IAB nodes, ensuring that the aggregated carriers meet the necessary technical requirements. It solves the problem of fragmented spectrum by allowing operators to combine multiple carriers across different bands to increase bandwidth and data rates. This is particularly important in 5G NR, where wide bandwidths are needed to support enhanced mobile broadband (eMBB) and other services.

Historically, carrier aggregation was introduced in LTE Release 10 to enable higher peak data rates by aggregating multiple LTE carriers. In 5G NR, carrier aggregation was further enhanced to support higher bandwidths, lower latency, and more flexible deployment scenarios. The introduction of IAB in Release 16 extended the concept to wireless backhaul, where the IAB node must aggregate carriers for both access and backhaul links. The carrier aggregation configuration ensures that these nodes can operate efficiently across multiple bands while meeting regulatory and performance requirements.

Without a clear configuration, the aggregation of carriers could lead to interference, inefficient use of spectrum, and non-compliance with RF requirements. The configuration provides a framework for testing and certification, ensuring that equipment can be deployed globally. It also enables network operators to plan their spectrum usage and deploy multi-carrier networks that meet the demands of modern mobile broadband.