Basic limit

Description

The Basic limit is a concept in 3GPP specifications that defines an emissions limit for a single transceiver unit of a non-Advanced Antenna System (non-AAS) base station. It serves as a reference for formulating unwanted emissions and output power requirements for different types of NR base stations, particularly those with advanced antenna systems (AAS). The basic limit is specified in a number of 3GPP documents, including 36.108, 37.105, 37.145, 37.843, 38.104, 38.108, 38.141, 38.174, 38.194, and 38.817. These specifications cover the radio transmission and reception requirements for various base station types, including those operating in FR1 and FR2 frequency ranges.

The basic limit is used in conjunction with a process called emissions scaling. Emissions scaling allows the derivation of per-antenna-element or per-transceiver-unit limits for AAS base stations from the basic limit defined for non-AAS base stations. This is necessary because AAS base stations have multiple transceiver units and antenna elements, and the emissions from each element must be controlled to ensure that the total emissions from the base station meet regulatory requirements. The basic limit provides a starting point that is then scaled according to the number of transceiver units, the antenna gain, and other factors.

In the context of NR base station types, the basic limit is used for different base station classes: 1-C, 1-H, and 1-O. Type 1-C is a base station with a single transceiver unit per antenna element, while 1-H and 1-O are hybrid and over-the-air AAS base stations, respectively. For 1-C, the basic limit is used directly to formulate unwanted emissions and output power requirements. For 1-H and 1-O, the basic limit is used to derive minimum requirements for unwanted emissions by applying emissions scaling. This ensures that all base station types meet a common level of emissions performance, regardless of their antenna architecture.

The basic limit is typically expressed in terms of power spectral density (e.g., dBm/MHz) or as an absolute power level (e.g., dBm) within a specified measurement bandwidth. It is defined at the transceiver unit level, which is the point where the base station's transmitter output is measured before the antenna. This allows the limit to be applied consistently across different base station configurations. The basic limit is also used in conformance testing, where the base station must demonstrate compliance with the derived limits.

The definition of basic limit has evolved over releases. In Rel-13 and Rel-14, it was defined as an emissions limit taken from non-AAS BS specifications that is converted into a per TAB connector TX or RX min cell group AAS BS emissions limit by scaling. In Rel-15, the wording changed to emphasize that it is an emissions limit from a single transceiver unit of the non-AAS BS type, used for formulating requirements for 1-C, 1-H, and 1-O types. In Rel-16, the wording reverted to the earlier definition, and this has been maintained through Rel-19. This evolution reflects the ongoing development of AAS base station requirements and the need to provide clear definitions for different base station types.

Purpose & Motivation

The basic limit concept exists to provide a common reference for emissions requirements across different base station architectures. Before the introduction of AAS base stations, emissions limits were defined for non-AAS base stations with a single transceiver unit. However, AAS base stations have multiple transceiver units and antenna elements, and applying the same limits directly would be inappropriate because the emissions from each element combine to form the total emissions. The basic limit solves this problem by defining a per-transceiver-unit limit that can be scaled to derive the total emissions limit for AAS base stations.

The term also enables regulatory compliance. Regulatory bodies set limits on the total emissions from a base station, but these limits must be translated into equipment requirements. The basic limit provides a way to derive equipment-level requirements that, when aggregated, meet the regulatory limits. This is particularly important for AAS base stations, where the number of transceiver units can be large and the emissions from each unit must be controlled to avoid exceeding the total limit.

Historically, the basic limit was introduced in Release 13 as part of the work on AAS base station requirements. The definition has been refined over releases to clarify its application to different base station types and to ensure consistency with the evolving specifications. The stability of the definition in recent releases indicates that the concept has matured and is well understood by industry.