RRUs

RRU stands for Remote Radio Unit, a modular component used in modern cellular networks. In split radio access network architectures, radio frequency processing is moved closer to the antenna while baseband processing is centralized in a baseband unit (BBU) or a virtualized pool. The RRU handles the RF transmission and reception tasks that interface directly with the antenna, while the BBU or central unit provides baseband processing, scheduling, and control signaling.

A typical RRU houses RF transceivers, up/down converters, a power amplifier, a low-noise amplifier, local oscillators, and other RF front-end elements. It connects to the antenna via RF cables and to the baseband unit via a fronthaul link, which carries converted I/Q data and control information. This arrangement reduces RF loss between the antenna and the radio unit and enables modular, scalable deployments.

Connectivity and protocols have evolved over time. Earlier deployments commonly used CPRI or OBSAI as fronthaul protocols. More recent and future networks have adopted eCPRI and other standardized interfaces to increase flexibility, reduce fronthaul bandwidth requirements, and support higher data rates required by 5G and dense MIMO configurations. Fronthaul often uses fiber, though some environments use high-speed copper where feasible.

Variants and deployment considerations include multi-band support, co-location with antennas, and integration with antenna systems (often called Remote Radio Head or RRH in some vendors). In 5G, RRUs may be part of complex, multi-radio, ultra-dense deployments with advanced front-end features, coordinated by centralized units and complemented by open interface ecosystems.

Standards and ecosystems involve 3GPP specifications and industry efforts like the O-RAN Alliance, which aim to improve interoperability and openness in fronthaul interfaces and radio access architectures.