Base Station Type 1-O (OTA-Only FR1 Base Station)

Description

BS type 1-O is a 3GPP-defined base station category introduced in Release 15 for NR. It designates an NR base station operating in Frequency Range 1 (FR1, 410 MHz – 7125 MHz) whose entire radio requirement set consists of Over-The-Air (OTA) requirements defined at the RIB (Radiated Interface Boundary). The 'O' suffix indicates that all requirements are OTA, with no conducted requirements at TAB connectors.

This base station type is characteristic of fully integrated active antenna systems where the radio and antenna array are combined into a single unit with no accessible per-element RF connectors. Because there are no TAB connectors at which conducted measurements could be made, all conformance testing must be performed in a radiated (OTA) manner. The RIB is the conceptual boundary at which these OTA requirements are defined and measured, typically in an anechoic chamber or a specified test environment.

The architecture of BS type 1-O implies a high degree of integration. The base station may contain a large antenna array (e.g., massive MIMO), integrated transceivers, and beamforming circuitry. Since requirements are defined only at the RIB, the internal implementation is largely transparent to the conformance framework — what matters is the radiated performance at the boundary. This aligns with the principle of 'black-box' testing for integrated antennas.

In the 3GPP base station taxonomy, BS type 1-O is the FR1 counterpart to BS type 2-O (which is FR2 OTA-only). It contrasts with BS type 1-H, which has a hybrid requirement set. The classification determines the applicable test methods in TS 38.141, the emission requirements in TS 38.113, and the radio requirements in TS 38.104. OTA testing for BS type 1-O involves measuring parameters such as EIRP, TRP, EVM, and unwanted emissions in a radiated setup, which is more complex and costly than conducted testing but necessary for integrated designs.

BS type 1-O is particularly relevant for 5G deployments using massive MIMO in sub-6 GHz bands, where integrated AAS base stations are common. It reflects the industry's shift toward OTA-centric conformance testing as antenna integration becomes the norm. The specifications covering it include TS 38.104, 38.113, 38.141, 38.174, 38.817, 38.820, and 38.908.

Purpose & Motivation

BS type 1-O was created to provide a clear regulatory and conformance framework for fully integrated FR1 base stations that cannot be tested via conducted methods. As 5G pushed toward massive MIMO and active antenna systems, many base stations eliminated external RF connectors entirely, making traditional conducted testing at antenna ports impossible. A new category was needed to define requirements purely at the radiated boundary.

The term solves the problem of how to specify and verify radio performance when the only accessible interface is the radiated one. By defining all requirements at the RIB, 3GPP ensured that integrated base stations could still be subject to rigorous, standardized conformance testing, even without conducted access. This was essential for global type approval and spectrum regulation.

Historically, the concept builds on earlier work on Active Antenna Systems (AAS) in 3GPP, which introduced OTA requirements and the RIB. NR Release 15 formalized the BS type taxonomy, with BS type 1-O as the OTA-only FR1 category. It addresses the limitations of conducted-only frameworks that could not accommodate integrated antennas, and provides a consistent basis for OTA test methods that were being developed in parallel.