Exclusive Access

Description

Exclusive Access is a concept within the Licensed Shared Access (LSA) framework, which allows for the shared use of spectrum between an incumbent user (e.g., government or military) and mobile network operators. In exclusive access mode, specific cells are designated as exclusive access cells, and access to these cells is restricted to a defined set of LSA subscribers. This means that only users who have a subscription that includes the LSA service and are authorized by the LSA controller can camp on or connect to these cells. The concept is defined in 3GPP TS 22.043 (Service aspects) and TS 42.043 (UTRAN aspects), originally introduced in Release 4.

The architecture for exclusive access involves several key components: the LSA controller, which manages spectrum availability and authorizes the mobile network operator to use the spectrum; the LSA repository, which stores information about incumbent usage; and the network elements such as the base station (eNodeB or gNodeB) that can be configured to operate in exclusive access mode. When a cell is configured for exclusive access, the network broadcasts an indication (e.g., via system information) that the cell is restricted to LSA subscribers. User Equipment (UE) that are not authorized will not attempt to access the cell, and the network will reject any unauthorized access attempts.

The primary use case for exclusive access is to provide guaranteed quality of service and capacity for specific user groups, such as public safety, enterprises, or critical communications. By restricting access to a defined set of subscribers, the network can ensure that the shared spectrum is used only by those who have priority and are authorized, thereby avoiding congestion and interference from other users. This is particularly important in scenarios where the incumbent user requires protection from interference, and the LSA spectrum is made available on a shared basis.

Exclusive access is closely related to the concept of Closed Subscriber Group (CSG) in 3GPP, but it is specific to LSA. While CSG allows a limited set of users to access a femtocell or small cell, exclusive access applies to LSA cells that operate in shared spectrum. The LSA framework was later enhanced with Licensed Shared Access (LSA) in Europe and Citizens Broadband Radio Service (CBRS) in the US, which introduced similar concepts like Priority Access Licenses (PAL) and General Authorized Access (GAA).

In terms of implementation, exclusive access requires coordination between the LSA controller and the mobile network operator's core network. The LSA controller provides a list of authorized subscribers or groups, which is then used by the network to enforce access control. This information can be stored in the Home Subscriber Server (HSS) or a dedicated LSA subscriber database. The network also needs to support the necessary signaling to indicate exclusive access status and to handle access attempts.

Overall, exclusive access is a key enabler for spectrum sharing, allowing operators to offer differentiated services and ensure that shared spectrum is used efficiently and fairly. Its definition has remained stable across releases, reflecting its foundational role in LSA.

Purpose & Motivation

Exclusive Access was created to address the need for controlled spectrum sharing in scenarios where an incumbent user (such as a government agency) owns spectrum but does not use it all the time. The LSA framework allows mobile operators to access this spectrum when the incumbent is not using it, but to ensure that the incumbent's rights are protected, access must be restricted to authorized users. Exclusive access provides a mechanism to limit access to specific cells, preventing unauthorized users from causing interference or congestion. This is particularly important for critical communications, where guaranteed access and quality of service are essential. Before exclusive access, shared spectrum was either unregulated or required complex coordination, leading to inefficiencies and potential interference. Exclusive access, along with other LSA features, provides a standardized way to manage shared spectrum, enabling new business models and more efficient use of scarce spectrum resources.