Prohibited Area

Description

The Prohibited area is a concept in 3GPP specifications that defines a geographic region where a mobile station (UE) is not allowed to transmit. This is a fundamental mobility management and regulatory feature that ensures mobile devices comply with local restrictions, such as those in sensitive areas (e.g., hospitals, aircraft, or government facilities) or to prevent interference with other systems. The Prohibited area can be a predefined area (e.g., a set of geographic coordinates or a named zone) or related to specific radio cells. When a UE enters a Prohibited area, it must refrain from initiating any transmissions, including calls, data sessions, or signaling messages, unless explicitly authorized (e.g., for emergency calls).

The concept was introduced in Release 99 (R99) as part of the Location Services (LCS) specifications, specifically in TS 23.171 (Functional stage 2 description of location services in UMTS) and TS 23.271 (Functional stage 2 description of Location Services in the Evolved Packet System). These specifications define how the network can provide location information and enforce area restrictions. The Prohibited area is typically configured by the network operator and communicated to the UE via broadcast messages (e.g., System Information Blocks) or dedicated signaling. The UE stores this information and continuously monitors its location (using GPS, cell ID, or other positioning methods) to determine if it is within a Prohibited area.

In practice, the Prohibited area is used in conjunction with other location-based services. For example, in a hospital, the network may define a Prohibited area to prevent UEs from transmitting on certain frequencies that could interfere with medical equipment. Similarly, in an aircraft, the Prohibited area may cover the entire cabin to ensure compliance with aviation regulations. The UE may also use the Prohibited area to automatically switch to airplane mode or disable its transmitter when entering such zones. The network can update the Prohibited area definitions dynamically, allowing operators to adapt to changing conditions.

The implementation of Prohibited area involves several network elements. The Location Services (LCS) client or the network operator defines the area and provisions it to the UE via the Access and Mobility Management Function (AMF) or the Mobility Management Entity (MME) in 4G. The UE's positioning capabilities (e.g., Assisted GPS, OTDOA) are used to determine its location relative to the Prohibited area. If the UE is within the area, it must not transmit; if it needs to communicate (e.g., emergency call), it may request an exception from the network. The network can also enforce the restriction by denying service requests from UEs in Prohibited areas.

Over the releases, the definition of Prohibited area has remained largely unchanged, reflecting its stable role in the standards. The term has been carried forward from R99 through Rel-19 without significant modifications to its core meaning. This consistency underscores the importance of the feature and its well-understood semantics. However, the underlying technologies for location determination and area management have evolved, with 5G introducing more precise positioning methods (e.g., NR positioning) that enhance the accuracy of Prohibited area enforcement. The Prohibited area concept is also relevant for regulatory requirements in different countries, where authorities may mandate specific restrictions.

Purpose & Motivation

The Prohibited area exists to address regulatory, safety, and interference concerns by preventing mobile devices from transmitting in sensitive locations. Governments and regulatory bodies often impose restrictions on radio transmissions in certain areas, such as near hospitals, airports, or military installations, to protect critical equipment or ensure security. Without a standardized mechanism like the Prohibited area, mobile devices could inadvertently cause harmful interference or violate laws. The Prohibited area provides a standardized way for networks to communicate these restrictions to UEs and for UEs to comply automatically.

Historically, before the introduction of Prohibited area in R99, there was no standardized way to enforce location-based transmission restrictions. Users were relied upon to manually turn off their devices or switch to airplane mode, which was error-prone and not enforceable. The Prohibited area concept, developed within the Location Services (LCS) framework, allowed operators to define restricted zones and have UEs automatically adhere to them. This was particularly important for emergency services and public safety, where reliable communication must be maintained without interference.

The Prohibited area also supports lawful interception and security operations by preventing unauthorized transmissions in certain areas. It is a key enabler for compliance with national regulations and international agreements. As mobile networks evolve, the Prohibited area remains a relevant and necessary feature, adaptable to new technologies and use cases such as drone restrictions or temporary event control.