Partial Radiated Power

Description

Partial Radiated Power (PRP) is a radio frequency (RF) measurement metric introduced in 3GPP Release 19 for characterizing the radiated power of a device over a limited portion of the sphere surrounding it, rather than the full sphere. In traditional over-the-air (OTA) testing, metrics such as Total Radiated Power (TRP) integrate power across the entire spherical surface enclosing the device under test (DUT). However, as NR devices increasingly operate at higher frequency bands (FR2 and beyond), full-sphere measurements become costly, time-consuming, and sometimes impractical due to chamber size, measurement distance, and equipment limitations. Partial Radiated Power addresses this by defining power integrated over a specified subset of directions on the sphere.

The concept is grounded in the observation that a device's radiation pattern is not uniform across all directions. Depending on the antenna array configuration, beamforming capabilities, and the intended use case, significant radiated energy may be concentrated in specific angular regions. By defining PRP over a partial sphere, engineers can characterize the device's radiated power in the directions that matter most for a given deployment scenario or test objective. The partial sphere can be defined by a range of azimuth and elevation angles, and the integration is performed over that subset of the full spherical coordinate system.

From a measurement methodology perspective, PRP is computed by sampling the radiated power density at discrete points within the defined partial sphere and integrating those samples. The choice of sampling grid, angular resolution, and the boundaries of the partial sphere all affect the resulting PRP value. This means that PRP integrated within different ranges of the sphere will generate different metrics — a key characteristic that distinguishes it from TRP, which has a single well-defined value for a given device configuration. This flexibility is both a strength and a challenge: it allows tailored testing but requires careful specification of the measurement conditions to ensure reproducibility and comparability across test campaigns.

In the context of 3GPP specifications, PRP is being studied and specified in TR 38.870 (Study on enhanced OTA testing for NR) and referenced in TS 38.161 (Terminal conformance specification for NR). These specifications define the measurement procedures, the coordinate systems, the angular ranges, and the reporting requirements for PRP. The work is particularly relevant for mmWave devices, where the small wavelength enables compact antenna arrays with highly directional beams, and where full-sphere OTA testing at scale is economically and logistically challenging.

PRP plays a role in device certification, type approval, and performance benchmarking. It allows manufacturers and operators to assess whether a device meets regulatory and performance requirements within the angular regions relevant to its operation. For example, a device designed for fixed wireless access with a known orientation relative to the base station may only need to radiate effectively within a limited angular sector; PRP can characterize performance in that sector without requiring full-sphere characterization. As 5G-Advanced and future 6G systems push into even higher frequency bands and more complex antenna systems, metrics like PRP will become increasingly important for efficient and meaningful OTA testing.

Purpose & Motivation

Partial Radiated Power exists to solve the practical and economic challenges of full-sphere OTA testing for modern NR devices, especially those operating at FR2 and higher frequencies. Traditional Total Radiated Power (TRP) requires integrating radiated power over the entire sphere surrounding the device, which demands large anechoic chambers, extensive measurement time, and sophisticated positioning equipment. For mmWave devices with highly directional beams, much of the sphere may contain negligible radiated energy, making full-sphere integration inefficient and sometimes misleading.

The motivation for PRP comes from the need to characterize device radiated power in a more targeted, application-relevant manner. Many deployment scenarios — such as fixed wireless access, indoor hotspots, or vehicle-mounted terminals — have well-defined angular relationships between the device and the network. In these cases, measuring radiated power over the relevant angular sector provides a more meaningful and cost-effective assessment than full-sphere TRP. Additionally, regulatory bodies and industry forums have recognized that full-sphere metrics may not adequately capture the performance of beamforming devices, where the radiation pattern is intentionally non-uniform.

Previous approaches either mandated full-sphere measurements (expensive and slow) or used simplified metrics that did not adequately account for directional radiation characteristics. PRP fills this gap by providing a flexible, standardized framework for partial-sphere radiated power measurement. It enables stakeholders to define the angular region of interest, perform consistent measurements, and compare results across devices and test labs. This is particularly important as the industry moves toward 5G-Advanced and 6G, where higher frequencies, larger antenna arrays, and more diverse device form factors will make efficient OTA testing even more critical.