Rated beam Equivalent Isotropically Radiated Power

Description

Rated beam EIRP is a fundamental radio frequency (RF) performance parameter defined in 3GPP specifications for base stations (BS) and Integrated Access and Backhaul (IAB) nodes that employ beamforming. It represents the maximum power that a transmitter is declared to radiate in the peak direction of a specific beam during the transmitter ON period. This parameter is critical for ensuring that the radiated power remains within regulatory limits and for verifying the beamforming capabilities of advanced antenna systems (AAS) and multi-antenna arrays used in 5G NR and LTE.

The concept is closely tied to the beam-based operation of modern cellular networks. In systems using beamforming, the base station or IAB node can generate multiple beams, each pointing in a different direction. For each declared beam and its associated beam direction pair, the rated beam EIRP specifies the maximum power level that the equipment is allowed to radiate. This is measured at the beam peak direction, which is the direction of maximum radiation for that beam. The parameter is used in conformance testing to ensure that the equipment does not exceed declared power levels, which could cause interference to other systems or violate regulatory constraints.

Technically, rated beam EIRP is determined by the combination of the conducted power fed to the antenna array and the antenna gain in the beam peak direction. It is typically expressed in dBm or dBW. The measurement is performed during the transmitter ON period, which is the time when the transmitter is actively transmitting. This ensures that the power is measured under normal operating conditions. The parameter is applicable to both FR1 (sub-6 GHz) and FR2 (millimeter wave) frequency ranges, although the specific measurement methodologies and limits may differ.

In the context of IAB, which is a key feature of 5G NR, the rated beam EIRP applies to both the IAB-DU (Distributed Unit) and IAB-MT (Mobile Termination). The IAB-DU is responsible for providing access to user equipment (UE), while the IAB-MT handles the backhaul link to the parent node. Both entities can use beamforming, and their rated beam EIRP must be declared and tested to ensure proper operation and coexistence with other nodes. The parameter is specified in various 3GPP technical specifications, including 38.104 (BS radio transmission and reception), 38.141 (BS conformance testing), and 37.145 (active antenna system base station conformance testing).

Overall, rated beam EIRP is a crucial parameter for the design, testing, and deployment of beamforming base stations and IAB nodes. It ensures that the radiated power is within declared limits, facilitates coexistence, and enables efficient use of the spectrum. As beamforming technology evolves towards more advanced antenna systems with higher order MIMO and beam management, the accurate declaration and verification of rated beam EIRP will remain essential.

Purpose & Motivation

The rated beam EIRP parameter was introduced to address the need for a standardized metric to declare and verify the maximum radiated power of beamforming base stations and IAB nodes. Traditional conducted power measurements at the antenna connector are insufficient for active antenna systems where the antenna is integrated with the radio, and the beamforming gain cannot be easily separated. Rated beam EIRP provides a way to specify the radiated power in the beam peak direction, which is what ultimately determines the coverage and interference potential of the transmitter.

Before the introduction of this parameter, there was no consistent way to declare the radiated power for beamforming systems, leading to potential ambiguities in testing and regulatory compliance. The rated beam EIRP solves this by providing a clear, measurable quantity that can be used in conformance tests. It also supports the deployment of advanced antenna systems by allowing manufacturers to declare the performance of each beam, which is essential for network planning and optimization.

Furthermore, with the advent of IAB in 5G, the need for a unified parameter that applies to both access and backhaul nodes became evident. The rated beam EIRP was extended to cover IAB-DU and IAB-MT, ensuring that both types of nodes meet the same regulatory and performance requirements. This facilitates the integration of IAB into cellular networks and enables flexible deployment of small cells without wired backhaul.