Over-The-Air Requirements Set

Description

The OTA requirements set is a comprehensive term that refers to the entire suite of over-the-air (OTA) requirements applied to an OTA-capable Active Antenna System (AAS) base station. Unlike a single requirement, the set includes all transmitter (TX) and receiver (RX) performance criteria that must be verified through OTA testing. This includes, but is not limited to, maximum output power (EIRP), power spectral density, unwanted emissions (ACLR, spurious), modulation quality (EVM), reference sensitivity (REFSENS), blocking characteristics, and dynamic range. The OTA requirements set is essentially the union of all individual requirements that are evaluated in a radiated manner for a base station that cannot be tested via conducted ports. The definition is intentionally broad to cover the complete compliance framework for OTA testing, ensuring that no requirement is overlooked. It is used in specifications such as 37.105 (AAS BS transmission and reception), 37.114 (AAS BS conformance testing), 37.145 (AAS BS radiated testing), 37.843 (multi-band AAS BS), and 38.817 (NR AAS BS). These specifications collectively define the OTA requirements set for different aspects of base station performance.

The concept of an OTA requirements set became necessary with the introduction of AAS base stations, which integrate the antenna array with the radio unit and do not have conventional antenna connectors. For such base stations, all RF requirements must be verified OTA, meaning the measurements are performed by radiating and receiving signals through the antenna array. This is a significant departure from traditional base station testing, where conducted measurements at the antenna port were the norm. The OTA requirements set therefore provides a single term to refer to the complete set of OTA requirements, simplifying communication and documentation. It allows manufacturers and test labs to refer to the entire suite when discussing test plans, certification, and compliance. The set is not a single test but rather a collection; each requirement within the set may have its own test method, limits, and conditions, as detailed in the relevant specifications.

Technically, the OTA requirements set is defined per base station type and per frequency band. For example, an AAS base station operating in band n257 (28 GHz) will have an OTA requirements set that includes specific limits for EIRP, TRP, and other parameters as defined in 38.104. The set is applied during conformance testing, where the base station must demonstrate compliance with each requirement in the set. The test procedures for these requirements are specified in 37.145 and 38.141-2, among others. The set is comprehensive: it covers both transmitter and receiver characteristics, and it accounts for the beamforming capabilities by defining test directions and conditions. For instance, TX requirements may be evaluated over the OTA peak directions set, while RX requirements may be evaluated over the OTA REFSENS RoAoA. The OTA requirements set thus ties together various other OTA-specific parameters into a unified compliance framework. It is important for regulatory approval, as many regions require that base stations meet certain radiated limits, and the OTA requirements set ensures that all such limits are tested.

The evolution of the definition of OTA requirements set has been minimal; it was introduced in Release 15 and has remained unchanged through Release 19, with only minor formatting differences. This stability indicates that the term is well-established and that the underlying concept has not required revision. The set itself, however, may evolve as new requirements are added or modified in different releases. For example, Release 17 introduced requirements for multi-band operation and new frequency ranges, which would be incorporated into the OTA requirements set for those base stations. But the definition of the term remains a constant reference. The OTA requirements set is also used in the context of NR-U (unlicensed spectrum) and other new features, where additional requirements may apply. Nevertheless, the term itself continues to serve as a shorthand for the complete OTA compliance suite.

In summary, the OTA requirements set is the full collection of OTA performance requirements for an AAS base station, covering both TX and RX. It is a foundational term in 3GPP specifications for OTA testing, ensuring that all necessary radiated measurements are considered. Its definition has been stable since Release 15, reflecting its fundamental role in the OTA testing framework.

Purpose & Motivation

The OTA requirements set exists to provide a single, comprehensive term for referring to all over-the-air requirements applicable to an AAS base station. Before its introduction, with traditional base stations, requirements were defined per conducted port, and there was no need for a collective term because each requirement was tested at the antenna connector. With AAS, testing moved to the radiated domain, and the number and complexity of requirements increased. Stakeholders needed a way to refer to the entire suite of OTA requirements collectively, especially in test specifications and certification processes. The term solves this by encapsulating the complete set, making it easier to discuss compliance and to ensure that no requirement is missed. It also helps in distinguishing between conducted and OTA requirements, as some base stations may support both, and the OTA requirements set specifically refers to those that must be tested OTA.

Historically, the introduction of the OTA requirements set in Release 15 coincided with the first 5G NR specifications for AAS base stations. The 3GPP recognized that AAS base stations would be tested entirely OTA, and thus a term was needed to denote the full set of requirements. This was particularly important for mmWave bands, where conducted testing is impractical. The OTA requirements set addresses the limitations of previous approaches by providing a holistic view: it ensures that all aspects of radiated performance—from power to sensitivity—are considered together. It also facilitates regulatory compliance, as regulators often reference the OTA requirements set when defining test requirements for base station certification. The term has been adopted in multiple specifications (37.105, 37.114, 37.145, 37.843, 38.817) and has remained unchanged, demonstrating its utility and clarity.