Radio equipment

Description

In 3GPP terminology, 'Radio equipment' refers to a functional entity that comprises both a Radio digital unit and a Radio unit. This term is defined in specifications such as TS 21.905, TS 25.113, TS 36.113, TS 37.113, and TS 51.021. The Radio digital unit is responsible for digital signal processing, including modulation, demodulation, channel coding, and baseband processing. The Radio unit, on the other hand, handles the analog RF processing, such as up-conversion, down-conversion, filtering, amplification, and coupling to the antenna. Together, they form a complete radio transceiver chain that enables wireless communication between user equipment and the core network.

The concept of Radio equipment is foundational to the architecture of base stations (e.g., NodeB, eNodeB, gNB). In a typical base station, multiple Radio equipment entities may be deployed to support multiple sectors or carriers. The split between the Radio digital unit and the Radio unit allows for flexibility in deployment; for example, the digital unit can be located at a centralized baseband pool, while the radio unit can be placed remotely near the antenna, connected via a fronthaul link (e.g., CPRI). This architecture is known as a distributed base station or Cloud RAN (C-RAN).

3GPP specifications define the requirements and test methods for Radio equipment to ensure compliance with regulatory and operational standards. For instance, TS 25.113 and TS 36.113 specify the base station conformance testing for UTRA and E-UTRA, respectively, covering aspects like transmit power, frequency error, and spurious emissions. TS 37.113 provides similar requirements for multi-standard radio (MSR) equipment. These specifications ensure that Radio equipment from different vendors can interoperate and meet performance criteria.

The Radio equipment term is also used in the context of radio equipment directive (RED) and other regulatory frameworks, where it denotes any equipment that intentionally emits or receives radio waves for communication. In 3GPP, the definition is more specific, focusing on the internal composition of the base station radio chain. This precise definition helps in standardizing interfaces and testing procedures.

Over the releases, the definition of Radio equipment has remained remarkably stable, indicating that the fundamental concept has not changed. However, the implementation of Radio equipment has evolved significantly with advances in technology, such as the introduction of massive MIMO, where the number of transceiver chains increases, and the integration of radio units and antenna arrays into Active Antenna Systems. Despite these technological shifts, the basic definition of Radio equipment as containing a digital unit and a radio unit continues to apply.

Purpose & Motivation

The term 'Radio equipment' exists to provide a clear and standardized definition of the hardware entity that performs radio transmission and reception in a cellular network. It solves the need for a common understanding among vendors, operators, and regulators about what constitutes the radio portion of a base station. By defining it as containing both a Radio digital unit and a Radio unit, 3GPP ensures that all aspects of the radio chain—from digital baseband to analog RF—are considered as a single functional entity for the purposes of specification, testing, and certification.

Historically, before the widespread adoption of distributed base station architectures, the radio equipment was typically integrated into a single cabinet along with the baseband processing. However, as networks evolved towards higher capacity and flexibility, the split between digital and radio units became more pronounced, leading to remote radio heads (RRHs) and centralized baseband units (BBUs). The 3GPP definition accommodates this split by explicitly including both units within the scope of Radio equipment, regardless of their physical location.

The definition also facilitates regulatory compliance. Regulatory bodies often require type approval of radio equipment to ensure it meets spectrum emission masks and other radio requirements. By having a standardized definition, manufacturers can design and test their equipment against 3GPP specifications, which are recognized worldwide. This reduces barriers to entry and ensures a level playing field. Furthermore, the definition supports the development of multi-standard radio equipment that can operate across different technologies (e.g., GSM, UMTS, LTE, NR) by providing a consistent framework for describing the radio components.