1. RRU stands for Radio Remote Unit and is the distributed frequency unit that connects to an operator's network and user equipment like cell phones. It is installed below antennas on towers.
2. RRU functions include transmitting and receiving signals, providing connectivity between user equipment, and interfacing between optical and electromagnetic links using ports.
3. BBU or Base Band Unit is the "heart" of communication and processes signals between analog and digital formats. It works with RRUs to form BTS and communicates with RRUs via CPRI fiber cable.
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The cellular network infrastructure consists of various components that work together to provide wireless communication. Here's the sequence of how signals travel from an antenna to the Baseband Unit (BBU), including key information about each step and associated hardware.
RRU Antenna
Antenna
- Role and Function: The antenna transmits and receives radio frequency (RF) signals from and to mobile devices like cell phones. Its design and orientation dictate the coverage area, affecting signal strength and quality.
- Remote Electrical Tilt (RET): Antennas often have RET capabilities, allowing network engineers to remotely adjust the tilt angle for better signal optimization. This feature is controlled by a Remote Control Unit (RCU), which communicates with the Remote Radio Unit (RRU).
Feeders
- Purpose and Design: Feeders are coaxial cables that carry RF signals from the RRU to the antenna. They play a critical role in maintaining signal quality by minimizing loss and interference.
- Characteristics: Feeders are designed with insulation and shielding to protect against environmental factors and electromagnetic interference (EMI). Proper installation and grounding are essential for optimal performance.
- Installation and Grounding: Feeders must be carefully routed to avoid damage and signal loss. Proper grounding is crucial for safety and to prevent static electricity buildup.
Remote Radio Unit (RRU)
Remote Radio Unit (RRU)
- Connection to Antenna: The RRU connects to the antenna via jumper cables (coaxial cables), which are responsible for transmitting RF signals. These jumper cables often have separate connections for transmitting (Tx) and receiving (Rx).
- Signal Processing and Conversion: The RRU converts RF signals into digital data for transmission to the BBU, and vice versa. This process involves amplification and filtering to ensure signal integrity.
- Location and Installation: RRUs are typically installed near the antenna, often on the tower itself. This proximity reduces signal loss and improves efficiency.
- Connectivity to BBU: The RRU connects to the BBU through a bi-directional fiber optic link, usually using the Common Public Radio Interface (CPRI). This high-speed link ensures low latency and reliable communication.
RRU Connectivity
Remote Electrical Tilt (RET)
Remote Electrical Tilt (RET) is a feature used in cellular networks to control the tilt angle of antennas remotely. This functionality allows network engineers to adjust the coverage and capacity of cell towers without having to physically visit the site. RET enables operators to manage the tilt of antennas to optimize signal strength, coverage, and minimize interference.
Remote Control Unit (RCU)
The Remote Control Unit (RCU) is the device responsible for controlling the RET system. It is typically connected to the base station's Remote Radio Unit (RRU) via a RET cable and to the antenna. The RCU sends commands to adjust the tilt angle of the antenna's radiating elements, enabling remote configuration. It can adjust the antenna tilt based on real-time network requirements or predefined configurations.
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Why RET is Important
RET is critical for optimizing network performance, especially in dynamic environments. It allows operators to:
- Optimize coverage in areas with high traffic.
- Reduce interference with other cell sites.
- Increase capacity in specific areas by adjusting the tilt of the antennas.
- Improve energy efficiency by focusing the signal where it's needed.
AISG Connecting Cables for RRU RET Port
RET Cable
The RET cable is a key component that connects the RRU to the RCU. It is typically a multi-conductor cable that carries control signals from the RRU to the RCU, allowing remote tilt adjustments. In Huawei systems, this cable often has a DB9 connector, but other manufacturers might use different connectors.
Base Band Unit (BBU)
Baseband Unit (BBU)
- Role and Function: The BBU manages the base station, handling signal processing, control plane functions, and system maintenance. It communicates with the RRU through CPRI and connects to the core network.
- Signal Processing: The BBU performs modulation, demodulation, encoding, and decoding of digital signals. It handles the control plane functions such as handovers, paging, and resource allocation.
- Connectivity and Maintenance: The BBU connects to other base stations and the core network, serving as a bridge between the radio interface and the broader telecommunications network. It also provides monitoring and maintenance functions for the entire base station.
Power Supply and Ground Ports
- Powering the RRU: The power supply port provides electricity to the RRU, typically operating at -48V. Proper wiring and grounding ensure safety and reliable operation.
- Grounding for Safety: The ground ports ensure the entire system is grounded, providing protection against surges and high voltage. Proper grounding is crucial to prevent damage from environmental factors and maintain the safety of the network infrastructure.
Summary
The flow from the antenna to the BBU involves several interconnected components, each with specific roles and responsibilities. The antenna captures and transmits RF signals, the RRU processes and converts them into digital data, feeders ensure signal integrity, and the BBU manages overall base station operations. Understanding this sequence is critical for anyone interested in cellular network infrastructure, as each component contributes to the reliability and performance of the entire system.