Remote Radio Head (RRH) Systems

- Overview

A Remote Radio Head (RRH) is a, tower-mounted transceiver in 4G/5G networks that converts optical signals to RF, amplifies signals, and handles analog/digital conversion. By connecting to a baseband unit (BBU) via fiber optic cables (CPRI/eCPRI), RRHs reduce transmission losses, optimize power, and enable flexible, high-capacity cell site architectures.

RRHs are critical components in modern, distributed radio access networks (D-RAN) and Cloud RAN (C-RAN) architectures.

Key Aspects of RRH Systems:

• Location: Mounted near the antenna to minimize coaxial cable losses between the radio and antenna.
• Core Functions: The RRH contains RF circuitry, including amplifiers, filters, and digital-to-analog/analog-to-digital converters.
• Connectivity: Connects to the BBU via CPRI (Common Public Radio Interface) or fiber optic, typically with one BBU supporting up to three RRHs.
• 5G & Beyond: Essential for enabling technologies like Massive MIMO, beamforming, and small cell deployments.
• Benefits: Reduced power loss, smaller equipment footprint, lower operating costs, and enhanced network coverage.

Please refer to Wikipedia: RRH

- Baseband Units 

A Baseband Unit (BBU) is a critical, modular network component in telecommunication base stations that processes, modulates, and demodulates digital baseband signals. Acting as the system's "brain," 

A BBU  converts data for transmission between user equipment and the core network, typically interfacing with Remote Radio Units (RRU) via fiber optic cables to facilitate high-speed, reliable wireless communication. 

The BBU serves as the central processing point, ensuring that raw data is translated into signals suitable for radio frequency transmission.

Key Functions and Characteristics:

• Signal Processing: Handles modulation, demodulation, encoding, decoding, and channel coding for wireless traffic.
• Interface Hub: Connects to RRUs/RRHs (Remote Radio Heads) to bridge baseband processing with RF signal transmission.
• Deployment: Often located in equipment rooms, known for modular design, small size, and low power consumption.
• 5G Terminology: In 5G networks, the BBU is often referred to as a gNodeB (gNB).
• Versatility: Used in modern cellular networks (4G/5G) and for applications like smart city infrastructure.

- Remote Radio Heads

A Remote Radio Head (RRH) or Unit (RRU) is a compact, outdoor-mounted, and weather-hardened RF module in 5G and earlier networks that houses radio transceiver circuitry, including amplifiers, filters, and digital-to-analog converters. Mounted near the antenna, it reduces signal loss and connects to a centralized Baseband Unit (BBU) via fiber optic cables using the Common Public Radio Interface (CPRI). 

1. Key Aspects of 5G RRH/RRU:

• Functionality: Performs RF modulation, power amplification, filtering, and up/down conversion, enabling superior signal quality.
• Infrastructure: Connects to the BBU (or gNodeB in 5G) via fiber, reducing transmission line losses compared to traditional coax.
• Benefits: Enables flexible, distributed antenna sites, lower power requirements, increased efficiency, and reduced base station footprint.
• Technology & Standards: Supports advanced MIMO, beamforming (e.g., 64T64R), and multi-band operations. It typically uses CPRI or eCPRI (enhanced CPRI) for high-speed, low-latency interfacing with the baseband unit.
• Placement: Usually installed at the top of towers or on street poles for improved coverage in rural areas, tunnels, and urban environments.

2. Components of a 5G RRH:

• Transceiver (TRX): Handles transmit and receive functions.
• Power Amplifier (PA): Amplifies signals for transmission.
• Low Noise Amplifier (LNA): Boosts weak signals received from the antenna.
• Filter/Duplexer: Separates transmit and receive signals.
• CPRI/eCPRI Interface: Converts digital data between optical fiber and RF components.

- RRH and BBU Networking

Remote Radio Heads (RRH) and Base Band Units (BBU) are connected via fiber optic cables using CPRI or OBSAI protocols, enabling a flexible, high-bandwidth "fronthaul" link. 

The BBU processes digital baseband signals, while the RRH, located near the antenna, handles RF conversion (analog-to-digital/digital-to-analog), amplification, and filtering to minimize signal loss. 

1. Key Aspects of RRH and BBU Networking:

• Fronthaul Connection: The fiber link connecting the RRH to the BBU is known as the "fronthaul," which separates the radio equipment from the baseband processing, a key feature of Distributed-RAN (D-RAN) and Cloud-RAN (C-RAN).
• Protocols: The most common communication standard is CPRI (Common Public Radio Interface), with OBSAI (Open Base Station Architecture Initiative) and increasingly Ethernet-based solutions also used.

2. Signal Flow:

• Downlink: The BBU converts data into a digital signal and sends it to the RRH, which converts it to an analog signal for transmission.
• Uplink: The RRH receives analog signals from the antenna, converts them to digital, and sends them to the BBU for processing.

3. Advantages:

• Low Loss: Mounting the RRH near the antenna reduces transmission line losses, as the coaxial cable length is significantly reduced.
• Flexibility & Cost: Allows for centralized BBU locations, reducing operational costs and enabling efficient resource sharing.
• Performance: High-speed optical fiber ensures low-latency, reliable, and high-capacity communication.

[Remote Radio Head (RRH) - Corning]

- RRH Parts: Transmit Part and Receive Part

The Remote Radio Head (RRH) has two parts, a transmit part and a receive part. The transmit part usually consists of a DAC, Mixer, Power Amplifier and Filters. A digital signal is received via a CPRI interface, converted to analog, upconverted to an RF Frequency, amplified, filtered and then sent out via an antenna. 

The Receive part consists of a filter, Low Noise Amplifier, Mixer and an ADC. It receives a signal from the antenna, filters it, amplifies it, down-converts it to an IF Frequency and then converts it to a digital signal, before sending it out via the CPRI to a fiber for further processing.

Remote radio heads (RRHs) have become one of the most important subsystems of today’s new distributed base stations. The remote radio head contains the base station’s RF circuitry plus analog-to-digital/digital-to-analog converters and up/down converters. RRHs also have operation and management processing capabilities and a standardized optical interface to connect to the rest of the base station. Modern interfaces standards for RRH interconnect are CPRI and OBSAI which enable interoperability between hardware items and faster time-to-market for complete solutions. 

This will be increasingly true as LTE networks are deployed. Remote radio heads make MIMO operation easier; they increase a base station’s efficiency and facilitate easier physical location for gap coverage problems. RRHs will use the latest RF component technology including GaN RF power devices and envelope tracking technology within the RRH RFPA.

- Functions of eNodeB

The base stations in 4G LTE networks are called evolved Node B or eNodeB. In network architecture diagrams, eNodeB is often also abbreviated as eNB. eNodeB is an essential part of the 4G LTE radio network and is capable of performing network control functions in addition to creating mobile network coverage.

Here are some functions of an eNodeB (eNB) in LTE:

• Radio access point: eNBs connect users to the LTE network through an air interface.
• Radio resource management: eNBs manage radio resources, including radio bearer control, radio admission control, and scheduling of uplink and downlink radio resources.
• Mobility management: eNBs manage the mobility of user devices, such as smartphones, within the LTE network.
• Control plane functions: eNBs terminate the ciphering of user plane data over the radio interface, and also terminate the ciphering and integrity protection of RRC signaling.
• Network access control: eNBs manage authentication and authorization for the UE, and facilitate UE access to the network to gain IP connectivity.

Other functions of an eNB include: 

• Radio bearer control
• Connection mobility control
• Dynamic allocation of resources to UEs in both uplink and downlink (scheduling)
• IP header compression and encryption of user data stream
• Selection of an MME at UE attachment
• Measurement configuration
• Scheduling and transmission of paging messages, Broadcast Info

[More to come ...]