Shared Radio Access Network

Description

A Shared Radio Access Network (S-RAN) refers to a deployment scenario where the Radio Access Network (RAN) infrastructure—including base stations (gNBs in 5G, eNBs in 4G), antennas, and sometimes backhaul—is used by multiple Mobile Network Operators (MNOs) or Mobile Virtual Network Operators (MVNOs). This is a form of network sharing that goes beyond core network sharing. In an S-RAN setup, the participating operators share the physical RAN elements while maintaining independent core networks, subscriber databases, and service platforms. This allows each operator to provide its own services and maintain control over its subscribers while drastically reducing capital and operational expenditures on the radio layer.

The technical implementation of S-RAN can follow different models as defined by 3GPP, primarily Multi-Operator Core Network (MOCN) and Gateway Core Network (GWCN). In the MOCN model, the shared RAN node broadcasts the Public Land Mobile Network (PLMN) IDs of all sharing operators. A User Equipment (UE) camping on the cell can select its home PLMN, and the RAN routes the signaling and user data to the respective operator's core network based on the selected PLMN. The RAN must support separate configuration contexts for each operator, including distinct cell identities, tracking areas, and potentially radio resource management policies. The GWCN model is a variant where operators also share certain core network elements like the Mobility Management Entity (MME) in 4G.

Key architectural components enabling S-RAN include the shared base station hardware, shared or partitioned radio spectrum, and the transport network that connects the RAN to each operator's core. The RAN must implement robust isolation mechanisms to ensure that traffic and signaling for one operator do not interfere with another, and to prevent unauthorized access between operators. This involves logical separation at the data plane and careful management of operational support systems (OSS). S-RAN is particularly valuable for covering high-cost areas (e.g., rural), indoor venues (airports, stadiums), or for new market entrants who wish to launch services without the prohibitive cost of building a full RAN footprint from scratch.

Purpose & Motivation

S-RAN was developed to address the economic and practical challenges of deploying dense radio access networks, especially as mobile data demand skyrocketed and network upgrades to 4G and later 5G required significant investment. Building duplicate RAN infrastructure by multiple operators in the same geographical area is often economically inefficient, leads to visual pollution, and can face regulatory hurdles regarding site acquisition. S-RAN provides a solution by allowing operators to share the most expensive part of the network—the radio infrastructure—thereby reducing capital expenditure (CAPEX) and operational expenditure (OPEX) while still competing on services and core network features.

The concept gained formal specification in 3GPP around Release 12, evolving from earlier, more limited sharing concepts. It was motivated by the need to improve coverage, especially in rural and underserved areas where the business case for a single operator is weak. Sharing makes deployment viable. Furthermore, for 5G deployments, which require a denser network of cells, S-RAN is seen as a key enabler for rapid and cost-effective rollout. It also supports the neutral host model, where a third party builds and operates a RAN that is leased to multiple MNOs, commonly used in large indoor venues or private networks. S-RAN thus balances competition and collaboration in the telecommunications industry, promoting infrastructure efficiency without sacrificing service differentiation.