Rated Output Power, Power Rated at Antenna Terminal

Description

Rated output power, PRAT (Power Rated at Antenna Terminal) is a term used in 3GPP specifications for TDD base stations to denote the mean power level per carrier that the manufacturer declares to be available at the antenna connector. It is essentially the same concept as Rated Output Power, but the acronym PRAT is used in certain specifications, particularly 3GPP TS 25.105 (UTRA TDD BS) and TS 25.142 (UTRA TDD BS conformance testing). The term ensures that TDD base station power declarations are unambiguous and testable, especially given the bursty nature of TDD transmissions.

The definition has evolved slightly over releases. In early releases (Rel-4 and Rel-5), it was simply described as "The Output Power that the manufacturer has declared to be available." This wording was less precise, potentially leading to ambiguity. In Release 11, the definition was refined to explicitly state: "Rated output power of the base station is the mean power level per carrier that the manufacturer has declared to be available at the antenna connector." This change aligned PRAT with the general Rated Output Power definition, ensuring consistency across FDD and TDD specifications.

PRAT is a critical parameter for TDD base station conformance testing. It is used to verify that the base station can deliver the declared power under specified reference conditions. The measurement is typically conducted at the antenna connector, and for TDD, it is averaged over the active timeslots. This ensures that the power declaration accounts for the duty cycle of TDD, preventing overestimation of the actual transmitted power. The parameter is also used in link budget calculations and interference analysis for TDD networks.

In the context of multi-carrier TDD base stations, PRAT is declared per carrier. This allows operators to understand the power available for each carrier, which is essential for carrier aggregation and capacity planning. The term is closely related to Rated Total Output Power, which aggregates power across all carriers within an operating band. While PRAT focuses on per-carrier power, Rated Total Output Power provides a holistic view of the base station's total transmit power capability.

The term PRAT is specific to UTRA TDD specifications and has not been widely adopted in LTE or NR specifications, where the term Rated Output Power is used uniformly. However, its introduction and subsequent refinement highlight the importance of precise power definitions in TDD systems, which are increasingly relevant with the deployment of 5G NR in TDD bands. Understanding PRAT is therefore valuable for engineers working with legacy UTRA TDD networks and for historical context.

Purpose & Motivation

The term Rated output power, PRAT was created to provide a clear and standardized definition of base station output power specifically for TDD systems in the context of UTRA. In TDD, transmission is not continuous; it occurs in bursts within assigned timeslots. This makes the definition of output power more complex than in FDD, where transmission is continuous. The term PRAT (Power Rated at Antenna Terminal) was introduced to explicitly tie the power declaration to the antenna connector, ensuring that measurements are consistent and comparable across vendors.

The motivation behind PRAT was to eliminate ambiguity in early TDD specifications. The initial definition in Rel-4 and Rel-5 was vague, stating only that it is the output power declared by the manufacturer. This could lead to different interpretations, especially regarding whether the power is averaged over active timeslots or over the entire frame. The refinement in Rel-11 clarified that it is the mean power per carrier at the antenna connector, aligning it with the FDD definition and making it testable. This solved the problem of inconsistent power declarations, which could affect network planning and interference coordination.

PRAT also serves regulatory purposes. National regulators need to ensure that TDD base stations do not exceed licensed power limits. By providing a precise definition, PRAT enables conformance tests that verify compliance. It also facilitates coexistence between TDD networks and other systems, as accurate power levels are essential for interference analysis. Although the term is now largely historical, its development reflects the ongoing effort in 3GPP to standardize and clarify technical parameters for emerging technologies.