gNodeB

Description

gNB (gNodeB) is the base station in 5G New Radio (NR) that serves as the radio access node for User Equipment (UE). It is responsible for radio resource management, scheduling, and providing connectivity to the 5G Core Network (NGC). The gNB is the NR counterpart to the eNB in LTE and supports a wide range of deployment scenarios, including standalone (SA) and non-standalone (NSA) architectures. In SA, the gNB connects directly to the 5G Core via the NG interface; in NSA, it may operate as a secondary node (en-gNB) under an LTE Master Node. The gNB interfaces with other gNBs via the Xn interface for handover and dual connectivity, and with the AMF/UPF via NG-C and NG-U respectively.

Architecturally, a gNB can be implemented in a centralized unit (CU) and distributed unit (DU) split, as defined in 3GPP TS 38.401. The CU handles higher-layer protocols (e.g., RRC, SDAP, PDCP) while the DU handles lower layers (RLC, MAC, PHY). This functional split allows flexible deployment, with the CU located in a central office and DUs at cell sites, connected via F1 interface. The gNB also supports network slicing, enabling multiple logical networks on the same physical infrastructure, and advanced features like beamforming, massive MIMO, and dynamic spectrum sharing. Key specifications include TS 38.401 (NG-RAN architecture), TS 38.413 (NGAP), and TS 38.473 (F1AP).

The gNB performs several critical functions: radio resource management (scheduling, handover, power control), connection management (establishment, maintenance, release), and data forwarding. It also participates in mobility procedures such as handovers and dual connectivity, and supports QoS flows through the SDAP layer. The gNB communicates with the UE via the Uu interface, using OFDM-based waveforms and flexible numerology. In multi-connectivity, the gNB can act as a Master Node (MN) or Secondary Node (SN), coordinating with other nodes (e.g., eNB or other gNBs) for dual connectivity.

gNB is essential for delivering 5G services with high data rates, low latency, and massive connectivity. It enables use cases like eMBB, URLLC, and mMTC by providing the necessary radio capabilities and core network integration. The gNB also plays a key role in network sharing, allowing multiple operators to share the same infrastructure. Its design is highly scalable, supporting dense deployments and diverse spectrum bands (sub-6 GHz and mmWave).

The term gNB was introduced in Release 14 as part of initial 5G study, and its definition was later simplified to reference TS 38.300. This reflects the maturation of 5G specifications, where the gNB is now fully defined in the RAN architecture specs. The gNB continues to evolve with 5G Advanced, incorporating features like AI/ML-based optimization, energy efficiency, and integrated access and backhaul (IAB).

Purpose & Motivation

The gNB was created to provide the radio access for 5G NR, addressing the limitations of LTE eNB in supporting new spectrum, higher bandwidths, and advanced antenna technologies. While LTE eNB could be upgraded to support some 5G features via EN-DC, the true potential of 5G required a new base station designed from the ground up to handle mmWave frequencies, beamforming, and network slicing. The gNB exists to deliver the enhanced mobile broadband (eMBB), ultra-reliable low-latency communication (URLLC), and massive machine-type communication (mMTC) services that define 5G.

Previous generations of base stations (e.g., eNB) were not designed for the flexibility and scalability demanded by 5G. They lacked the ability to dynamically allocate resources across diverse services, support massive MIMO with beam management, or integrate with a service-based core network. The gNB solves these problems by adopting a modular architecture with CU/DU split, enabling centralized coordination and distributed processing for low latency. It also supports network slicing, which allows operators to create multiple virtual networks on a single physical infrastructure, each tailored to specific service requirements.

The gNB was motivated by the need to handle the extreme variability of 5G use cases, from high-throughput video streaming to ultra-reliable industrial automation. Its design allows for flexible numerology, wide bandwidth operation, and advanced antenna systems, which were not feasible with LTE. Additionally, the gNB's integration with the 5G Core (NGC) via NG interfaces ensures end-to-end QoS and policy control, enabling new business models and revenue streams for operators. Overall, the gNB is the cornerstone of 5G radio access, enabling the full realization of 5G's potential.