Base Station Type 1-H (Hybrid FR1 Base Station)

Description

BS type 1-H is a 3GPP-defined base station category introduced in Release 15 as part of the NR (New Radio) radio transmission and reception specifications. It designates an NR base station that operates in Frequency Range 1 (FR1, 410 MHz – 7125 MHz) and whose radio requirements are defined using a hybrid approach: some requirements are 'conducted' and measured at individual TAB connectors (the antenna ports on the base station), while others are 'over-the-air' (OTA) and measured at the RIB (Radiated Interface Boundary). This dual nature is what the 'H' (hybrid) denotes.

The architecture behind BS type 1-H reflects the evolution of base station design. Traditional base stations exposed physical RF connectors where conducted measurements could be made directly. Modern massive MIMO and AAS (Active Antenna System) base stations integrate the antenna array with the radio, making conducted measurements at every element impractical or impossible. BS type 1-H accommodates this transition by allowing a mix: conducted requirements at TAB connectors where they remain accessible, and OTA requirements at the RIB for the integrated antenna portions.

Key components include the TAB connectors (Test Access Boundary connectors), which are the points where conducted test signals are injected or measured, and the RIB (Radiated Interface Boundary), which is the conceptual surface enclosing the radiating structure where OTA measurements are performed. The RIB is typically defined in the far field or in a specified radiated test environment. The requirement set for BS type 1-H is therefore split between these two domains, and conformance testing (covered in TS 38.141) must address both.

In the network, BS type 1-H is one of several base station types defined by 3GPP, alongside BS type 1-O (OTA-only at FR1) and BS type 2-O (OTA-only at FR2). The classification determines which test methods, test environments, and requirement definitions apply. For operators and vendors, correctly classifying a base station as type 1-H has direct implications for type approval, conformity assessment, and regulatory compliance. It is particularly relevant for early 5G deployments where hybrid antenna architectures were common.

The specifications governing BS type 1-H include TS 38.104 (NR base station radio transmission and reception), TS 38.141 (conformance testing), TS 38.113 (emission requirements), TS 37.114 (active antenna system requirements), and various study and analysis reports (38.817, 38.820, 38.908). These collectively define the conducted and OTA requirements, test procedures, and the boundaries at which they apply.

Purpose & Motivation

BS type 1-H exists to solve a practical problem in 5G base station standardization: how to define and test radio requirements for base stations that are neither fully conducted nor fully integrated. Before 5G, base station requirements were predominantly conducted, measured at antenna connectors. With the advent of massive MIMO and active antenna systems, many base stations no longer expose per-element connectors, making purely conducted testing impossible. Conversely, purely OTA testing was immature and costly in early 5G.

The hybrid approach of BS type 1-H provided a pragmatic bridge. It allowed vendors to declare conducted requirements at the TAB connectors that remained accessible, while defining OTA requirements at the RIB for the integrated radiating parts. This preserved continuity with existing conducted test infrastructure while enabling the industry to develop OTA methodologies.

Historically, the concept emerged from 3GPP's work on Active Antenna Systems (AAS) in TS 37.105 and related studies, which first introduced the RIB and TAB concepts. NR Release 15 extended these to 5G, creating the BS type taxonomy. BS type 1-H thus addresses the limitations of a purely conducted framework that could not handle integrated antennas, and of a purely OTA framework that was not yet mature enough for all requirements.