Equivalent Isotropically Radiated Power Accuracy Directions Set

Description

The EIRP Accuracy Directions Set is a concept defined in 3GPP specifications for radiated testing of beamforming antenna systems, particularly in the context of 5G NR and advanced LTE. It specifies the set of beam peak directions for which the Equivalent Isotropically Radiated Power (EIRP) accuracy requirement is intended to be met. EIRP is a measure of the power radiated by an antenna in a specific direction, and its accuracy is critical for ensuring that user equipment (UE) and base stations (BS) comply with regulatory and performance requirements. The directions set is typically defined as a contiguous range or a discrete list of beam centre directions, and the beam peak directions are related to these by beam direction pairs included in the set.

In practice, the EIRP accuracy directions set is used in test methodologies for assessing the radiated performance of multi-antenna systems. For example, in 3GPP TS 37.105, which covers active antenna system (AAS) base station radiated requirements, the EIRP accuracy directions set helps define the spatial region over which the EIRP accuracy is evaluated. This is essential because beamforming systems can steer beams in various directions, and the accuracy of the radiated power may vary across directions. By specifying a set of directions, the standard ensures that testing is both comprehensive and repeatable.

The set is characterized by beam direction pairs, which map beam peak directions to corresponding beam centre directions. This mapping allows test equipment to position the device under test (DUT) and measure EIRP at specific angles. The directions can be expressed in a spherical coordinate system, typically using azimuth and elevation angles. The set may cover a contiguous range, such as a sector, or a discrete list of directions, depending on the beamforming capabilities and the test requirements.

From a regulatory perspective, the EIRP accuracy directions set ensures that the maximum radiated power and its accuracy are verified in all relevant directions, preventing excessive interference and ensuring efficient use of spectrum. It also facilitates global harmonization of testing procedures, as different regions may have varying regulatory limits. The concept has evolved over releases, with the definition being refined and sometimes simplified. In Rel-15, the definition was shortened to focus solely on the beam peak directions, removing the explicit mention of beam direction pairs, though the underlying concept remains the same.

Overall, the EIRP Accuracy Directions Set is a fundamental element in the radiated testing of advanced antenna systems, enabling consistent and reliable verification of EIRP accuracy across the spatial domain. It bridges the gap between theoretical beamforming models and practical over-the-air (OTA) measurements, ensuring that devices meet both performance and regulatory standards.

Purpose & Motivation

The EIRP Accuracy Directions Set exists to provide a standardized framework for testing the accuracy of radiated power in beamforming systems. Before its introduction, radiated testing of multi-antenna systems lacked a clear definition of the spatial directions over which EIRP accuracy should be verified. This led to inconsistent test results and difficulties in comparing devices from different vendors. The set solves this by explicitly defining the beam peak directions that must be considered, ensuring that tests cover the intended coverage area of the beams.

Additionally, as beamforming technology became prevalent in LTE and 5G, regulatory bodies required assurance that devices do not exceed power limits in any direction. The EIRP accuracy directions set provides a common language for manufacturers, test labs, and regulators to specify and verify compliance. It also supports the development of test equipment and methodologies by providing a clear target for measurement uncertainty and repeatability.

Historically, the concept emerged with the introduction of Active Antenna Systems (AAS) in 3GPP Rel-13, where the need for over-the-air testing of integrated antennas became apparent. Since then, it has been refined to accommodate new beamforming capabilities and frequency ranges, including millimeter wave. The set continues to evolve to address emerging technologies such as massive MIMO and beam management in 5G-Advanced.