non-Active Antenna System Base Station

Description

A non-AAS BS (non-Active Antenna System Base Station) is a term defined in 3GPP specifications to distinguish base stations that do not employ Active Antenna System (AAS) technology from those that do. The definition, found in TS 37.105 and TS 37.145, states that a non-AAS BS is a BS conforming to one of the specifications in 3GPP TS 25.104 (UTRA FDD), TS 25.105 (UTRA TDD), TS 36.104 (E-UTRA), or TS 37.104 (Multi-standard radio). These specifications cover the radio transmission and reception requirements for base stations using traditional passive antenna systems, where the antenna is a separate passive component connected to the radio unit via a feeder cable.

In a non-AAS BS, the radio frequency (RF) signal is generated by a radio unit (RU) and transmitted to a passive antenna through a feeder. The antenna does not contain active electronic components; it simply radiates the signal. This architecture has been the standard for cellular networks for decades and is characterized by its simplicity, reliability, and cost-effectiveness. However, it has limitations in terms of beamforming capabilities, as the antenna pattern is fixed and cannot be dynamically adjusted. The non-AAS BS typically supports basic MIMO (Multiple-Input Multiple-Output) configurations, such as 2x2 or 4x4, but not the advanced massive MIMO or beamforming features enabled by AAS.

The term was introduced in Rel-13, coinciding with the development of AAS specifications. As networks evolved towards 5G, AAS became crucial for achieving higher capacity and spectral efficiency through 3D beamforming and massive MIMO. The non-AAS BS term provides a clear distinction, ensuring that regulatory and conformance requirements are applied appropriately. For example, the maximum output power and unwanted emission limits may differ between AAS and non-AAS BS, and the term helps in classifying equipment for testing and certification.

Non-AAS BSs are still widely deployed in existing networks, particularly in legacy 2G, 3G, and early 4G deployments. They continue to play a vital role in providing coverage and capacity, especially in areas where advanced features are not needed or where cost is a primary concern. The specifications TS 37.105 and TS 37.145 define the conformance testing for AAS BS, and by exclusion, non-AAS BS are tested according to the legacy specifications. This ensures that all base stations, regardless of antenna technology, meet the necessary performance and interference criteria.

In summary, the non-AAS BS term is a classification that helps differentiate traditional base station architectures from modern AAS-based ones. It is essential for regulatory compliance, network planning, and equipment procurement, ensuring that the right specifications are applied. As networks continue to evolve, non-AAS BSs will coexist with AAS BSs, serving different roles in the heterogeneous network landscape.

Purpose & Motivation

The non-AAS BS term was created to provide a clear regulatory and technical distinction between base stations using traditional passive antenna systems and those using Active Antenna Systems (AAS). With the introduction of AAS in Rel-13, which integrates active electronics into the antenna array to enable advanced beamforming and massive MIMO, it became necessary to differentiate the two architectures. This distinction is crucial because AAS BS have different RF characteristics, such as higher integration, different power consumption, and unique conformance requirements. The non-AAS BS term ensures that legacy base stations, which conform to older specifications like TS 25.104 and TS 36.104, are not subjected to the new AAS-specific requirements, which could be inappropriate or overly burdensome.

Historically, before AAS, all base stations were non-AAS by default. The specifications for these base stations were well-established and focused on passive antenna systems. As AAS technology emerged, it promised significant performance improvements but also introduced new challenges in terms of testing, installation, and network planning. The non-AAS BS term allowed regulators and operators to continue deploying and certifying traditional base stations without confusion, while also paving the way for AAS adoption. It also facilitated the coexistence of both technologies in the same network, as operators could gradually upgrade to AAS where beneficial.

The term also serves an important role in international standards and regulatory frameworks. Many countries have specific regulations for base station emissions that are based on the type of antenna system. By defining non-AAS BS, 3GPP provides a common language for manufacturers, operators, and regulators to discuss and regulate these devices. This helps in streamlining type approval processes and ensuring that equipment meets the necessary legal requirements. Overall, the non-AAS BS term is a practical classification that supports the smooth evolution of cellular networks from legacy to advanced antenna technologies.