Definition
RRU (Remote Radio Unit) is a remote module in distributed base station architectures that separates and deploys the RF front-end components, such as RF transceivers, power amplifiers (PA), and filters, from baseband processing. The RRU connects to the BBU (Baseband Unit) via optical fiber, transmitting baseband IQ data using the CPRI (Common Public Radio Interface) or eCPRI protocol. Installed close to the antenna, the RRU replaces the traditional long feeder line solution, significantly reducing feeder loss (coaxial feeder loss can reach several dB per 100 meters), improving downlink power efficiency and uplink reception sensitivity, making it a core network element in 4G/5G macro sites, indoor distributed systems, and DAS scenarios.
Architecture and interfaces
The RRU and BBU are connected via a fronthaul fiber link, and the CPRI interface transmits the sampled baseband IQ stream at a fixed bitrate. A typical single-channel rate can reach 9.8Gbps (20MHz LTE) or higher. eCPRI was introduced in the 5G era, supporting functional splits and compressed transmission to reduce fronthaul bandwidth requirements. The RRU integrates DAC/ADC, up/down converters, power amplifier (PA), low-noise amplifier (LNA), duplexers, and other RF chain components, supporting multi-band, multi-standard (2G/3G/4G/5G NR) co-site deployment.
Technical advantages
- Minimization of feeder loss: The RF unit is positioned close to the antenna, eliminating insertion loss and standing wave ratio deterioration caused by long feeders.
- Flexible deployment: Supports various installation forms such as tower-top, rooftop, and pole stations, facilitating dense network deployment and coverage enhancement.
- Modular expansion: RRU can be independently added per carrier or sector, without replacing the entire site.
- Multi-antenna support: Integrates MIMO channels, supporting 2T2R, 4T4R, 8T8R, and beamforming
Typical Use Cases
RRU is widely used in outdoor macrocell coverage, indoor distribution systems (in conjunction with leaky cables or antennas), high-speed rail/subway tunnel coverage, stadiums, and other high-capacity scenarios, as well as in the RF front-end implementation of 5G Massive MIMO AAU (Active Antenna Units). When IoT devices access via cellular networks, their uplink signals are received by the RRU and then forwarded to the BBU for processing. The coverage quality of the RRU directly affects the access success rate and speed of terminals such as NB-IoT and Cat.1.
SimtoLink's IoT SIM cards rely on operator cellular network access, with network-side wireless coverage provided by distributed base stations composed of macro RRUs and BBUs. The deployment density and multi-band support capability of the RRU determine the access quality of IoT devices in industrial zones, buildings, underground, and other scenarios. When selecting and deploying IoT solutions, SimtoLink takes into account the local operator RRU coverage and recommends suitable bands and standards (such as B3/B8 LTE, B5 NB-IoT) to ensure that devices stay stably online and data is reliably returned.