Radio Access Technology Power

Description

RAT power (Radio Access Technology power) is a metric defined in 3GPP specifications that represents the aggregate transmit power across all carriers belonging to the same radio access technology (RAT) type. It is used primarily in the context of multi-standard radio (MSR) base stations, where a single base station may simultaneously operate carriers of different RATs such as GSM, WCDMA, LTE, and NR. The concept is specified in TS 37.141 (MSR conformance testing), TS 37.802 (MSR architecture), and TS 37.900 (MSR performance requirements).

In a multi-RAT base station, each RAT may have one or more carriers. For example, an MSR base station might support two LTE carriers, one WCDMA carrier, and one GSM carrier. The RAT power for LTE would be the sum of the transmit powers of the two LTE carriers; the RAT power for WCDMA would be the power of the single WCDMA carrier; and so on. This aggregation is important because regulatory and conformance requirements often specify limits on total power per RAT, and because interference analysis between RATs must account for the combined power emitted in each technology's frequency band.

The definition is deliberately simple: 'the sum of all carrier powers for all carriers of the same type.' However, its application is nuanced. Carrier power itself is typically defined as the mean power over a carrier's bandwidth, and the sum must account for the fact that carriers of the same RAT may be non-contiguous or in different bands. In MSR base stations, the total power across all RATs is also constrained by the base station's overall power rating, so RAT power is one of several power metrics used to characterise the transmitter.

RAT power is used in conformance testing to verify that a base station does not exceed declared power levels for each RAT, and in network planning to estimate coverage and interference. For example, when deploying LTE and NR carriers in the same base station, engineers use RAT power to ensure that the LTE carrier power plus the NR carrier power does not exceed the total available power, and to calculate the coverage of each RAT independently. It also helps in spectrum sharing scenarios where multiple RATs share a band.

Although the term is most closely associated with MSR base stations, the underlying concept applies to any multi-carrier, multi-RAT environment. In 5G, where a gNB may support multiple NR carriers and potentially LTE-NR dual connectivity, RAT power remains a useful abstraction for power budgeting and regulatory compliance. The term is defined consistently across releases, reflecting its stable and fundamental nature in radio network engineering.

Purpose & Motivation

RAT power was defined to provide a clear and standardised way to characterise the transmit power of a base station when multiple radio access technologies share the same hardware and spectrum. Before MSR base stations became common, each RAT was typically deployed on separate hardware with its own power budget. As operators sought to reduce cost and site footprint by co-locating multiple RATs in a single base station, it became necessary to define power metrics that could distinguish between the total power of the base station and the power allocated to each RAT.

The problem RAT power solves is twofold. First, it enables conformance testing: regulatory bodies and 3GPP specifications set limits on the maximum power that can be emitted in each technology's band, and RAT power provides the measurable quantity to verify compliance. Second, it supports network planning and interference coordination: by knowing the aggregate power per RAT, engineers can predict coverage and interference between technologies, and can allocate power budgets dynamically as traffic patterns change.

The concept also facilitates spectrum sharing and refarming. When an operator refarms spectrum from one RAT to another, RAT power helps quantify the change in emitted power and its impact on neighbouring cells and technologies. In modern multi-RAT deployments, including those with LTE and NR, RAT power remains a foundational metric for ensuring that the base station operates within its declared power envelope while meeting the performance requirements of each RAT.