Licensed Shared Access Exclusive Access Cell

Description

The LSA exclusive access cell is a concept introduced in 3GPP Release 4 as part of the Licensed Shared Access (LSA) framework. LSA is a regulatory approach that allows for the shared use of spectrum between an incumbent user (e.g., a government or military entity) and one or more licensed shared access users (e.g., mobile network operators). The LSA exclusive access cell is a cell that is deployed under an LSA license and is intended for use only by UEs that have a subscription to the LSA service. The cell broadcasts information indicating that it is an LSA exclusive access cell, and UEs that do not have the appropriate subscription are not allowed to camp on it, except for emergency calls.

The LSA exclusive access cell is defined in 3GPP TS 21.905 (Vocabulary for 3GPP Specifications) and TS 25.304 (UE procedures in idle mode and procedures for cell reselection in connected mode). The cell may be part of a Public Land Mobile Network (PLMN) that is dedicated to LSA users, or it may be a cell within a regular PLMN that is designated as LSA exclusive. The UE determines whether it can camp on the cell based on its subscription information, which includes the LSA identities (LSA IDs) that the user is authorized to access. The LSA IDs are typically stored in the UE's SIM/USIM.

When a UE is in idle mode, it performs cell selection and reselection according to the procedures in TS 25.304. If the UE encounters an LSA exclusive access cell, it checks whether the cell's LSA ID is in its list of subscribed LSA IDs. If it is, the UE may camp on the cell. If not, the UE must not camp on the cell, except for the purpose of originating an emergency call if no other cells are available. This ensures that non-LSA users can still make emergency calls even when only LSA exclusive cells are present, which is a regulatory requirement in many regions.

The LSA exclusive access cell concept is part of the broader LSA architecture, which includes the LSA controller, the LSA repository, and the LSA spectrum resource. The LSA controller manages the spectrum sharing between the incumbent and the LSA licensee, ensuring that the incumbent's usage is protected. The LSA repository stores information about the LSA spectrum resources and the associated conditions. The LSA exclusive access cell is a radio access network element that operates under the LSA license and enforces the access restrictions.

In terms of mobility, the LSA exclusive access cell may be used to provide coverage in specific areas, such as a stadium, a campus, or a factory, where the LSA licensee has exclusive rights to use the spectrum. The cell may also be part of a network slice that is dedicated to LSA users. The UE's ability to camp on the cell depends on its subscription and the network's configuration. The LSA exclusive access cell concept has been maintained across releases from Rel-4 to Rel-19, with the definition remaining unchanged, indicating its stability and continued relevance in the context of spectrum sharing.

Purpose & Motivation

The LSA exclusive access cell exists to enable the shared use of spectrum between an incumbent user and a mobile network operator while ensuring that only authorized users can access the shared spectrum. Licensed Shared Access (LSA) was developed to address the growing demand for spectrum by allowing mobile operators to use spectrum that is primarily allocated to other services (e.g., government, military) on a shared basis. The LSA exclusive access cell is a key element of this framework, as it allows the operator to deploy cells that are exclusively for LSA subscribers, thereby protecting the incumbent's usage and ensuring that the shared spectrum is used efficiently.

Before LSA, spectrum sharing was often limited to cognitive radio techniques or unlicensed bands, which lacked the quality-of-service guarantees and interference protection required for commercial mobile services. LSA provides a regulatory framework that allows for predictable and controlled sharing, with the incumbent having priority access. The LSA exclusive access cell ensures that only UEs with the appropriate subscription can camp on the cell, which is necessary to prevent unauthorized access and to manage the shared spectrum resource. It also allows the operator to offer differentiated services to LSA subscribers, such as higher data rates or guaranteed quality.

The emergency call exception is a critical feature that ensures regulatory requirements for emergency services are met. Even if a UE does not have an LSA subscription, it can still originate an emergency call from an LSA exclusive access cell if no other cells are available. This is important because emergency calls must be possible from any network, regardless of subscription. The LSA exclusive access cell concept has been stable since Rel-4, demonstrating its effectiveness and the lack of need for fundamental changes. It continues to be relevant in the context of 5G and beyond, where spectrum sharing is expected to play an even greater role.