Total radiated power

Description

Total radiated power (TRP) is a fundamental metric in radio frequency (RF) engineering that quantifies the total power radiated by an antenna system. Unlike conducted power, which is measured at the antenna port, TRP accounts for the actual electromagnetic energy emitted into space, including the effects of antenna gain, directivity, and efficiency. In 3GPP specifications, TRP is defined as 'the total power radiated by the antenna' and is used to characterize the radiated performance of base stations and user equipment, particularly in systems employing advanced antenna technologies such as beamforming and massive MIMO.

TRP is measured in watts (W) or dBm and is typically determined by integrating the power density over a sphere surrounding the antenna. This integration captures all radiation directions and polarizations, providing a comprehensive measure of the antenna's output. In practice, TRP is often measured in an anechoic chamber or using near-field to far-field transformation techniques, as specified in 3GPP TS 37.105 and TS 37.145 for base stations, and TS 38.108 for UE. The measurement is crucial for verifying compliance with regulatory limits on electromagnetic exposure and for ensuring that the antenna system meets performance requirements.

In the context of 5G NR, TRP has become increasingly important due to the widespread use of active antenna systems (AAS) and massive MIMO. Traditional base stations used passive antennas with fixed radiation patterns, and conducted power measurements at the antenna port were sufficient to characterize performance. However, with AAS, the antenna elements are integrated with the radio transceiver, and the radiated power cannot be easily measured at a conducted interface. Therefore, TRP and related metrics like equivalent isotropically radiated power (EIRP) are used to specify and test the radiated performance of these advanced systems.

TRP is closely related to other RF parameters such as EIRP, which is the power that would be radiated by an isotropic antenna to produce the same power density in the direction of maximum gain. While EIRP is directional, TRP is omni-directional and represents the total power radiated. In beamforming systems, the TRP remains relatively constant regardless of the beam direction, while EIRP varies with beamforming gain. This makes TRP a more stable metric for assessing overall power consumption and regulatory compliance.

The 3GPP specifications define TRP for various frequency ranges, including FR1 (sub-6 GHz) and FR2 (millimeter wave). For FR2, where beamforming is essential to overcome high path loss, TRP measurement is particularly challenging due to the need for over-the-air (OTA) testing. TS 38.104 and TS 38.141 provide detailed requirements for base station TRP, while TS 38.108 and TS 38.101 cover UE TRP. The specifications also define test methods, such as the use of a compact antenna test range (CATR) or a near-field scanner, to ensure accurate and repeatable measurements.

In summary, TRP is a critical parameter for characterizing the radiated power of modern antenna systems. It ensures that base stations and UEs comply with regulatory limits, meet performance requirements, and operate efficiently in complex propagation environments. As wireless systems continue to evolve towards higher frequencies and more advanced antenna technologies, TRP will remain a cornerstone of RF performance assessment.

Purpose & Motivation

Total radiated power exists to provide a standardized, comprehensive measure of the electromagnetic energy emitted by an antenna system. Its primary purpose is to ensure that radio transmitters comply with regulatory limits on human exposure to electromagnetic fields and with spectrum emission masks that prevent interference to adjacent bands. Unlike conducted power measurements, which only capture the power delivered to the antenna port, TRP accounts for the actual radiated energy, including antenna gains and losses, making it essential for systems where the antenna is integrated with the radio (e.g., active antenna systems).

Historically, before the advent of active antenna systems, conducted power measurements at the antenna port were sufficient because the antenna was a passive component with known characteristics. However, with the introduction of massive MIMO and beamforming in 5G NR, the antenna and radio became inseparable, and conducted measurements were no longer feasible. This necessitated the development of over-the-air (OTA) testing methodologies and metrics like TRP and EIRP. TRP was introduced in 3GPP Release 15 to address these challenges, providing a way to verify the radiated power of advanced antenna systems without physical test ports.

The concept of TRP also solves the problem of accurately assessing power consumption and thermal performance in integrated systems. By measuring the total radiated power, manufacturers can ensure that their equipment operates within safe thermal limits and meets energy efficiency targets. Furthermore, TRP is used in link budget calculations to predict coverage and capacity, especially in millimeter-wave bands where beamforming is critical. Overall, TRP enables the deployment of high-performance 5G networks while ensuring regulatory compliance and interoperability.