5G Remote Radio Head (RRH) Explained: Manufacturers & Modules

This page describes the basics of a 5G Remote Radio Head (5G RRH) and the functions of its internal modules. It also lists vendors or manufacturers of 5G RRH units.

The Remote Radio Head (RRH) architecture consists of a baseband unit (BBU) and a remote radio unit (RRU). Both the BBU and RRU are connected using fiber optic cables to transport digital data and control information.

Initially, the Common Public Radio Interface (CPRI) was developed as an interface protocol in RRH deployments, especially in 4G LTE and 5G networks. The CPRI interface carries digital baseband signals, including data, control, and synchronization information, over optic fiber cables at high data rates.

Later, enhanced CPRI (eCPRI) was developed to meet the low latency and high data rate requirements of 5G NR (New Radio) signals.

What is 5G RRH?

In a 5G New Radio network, the Remote Radio Head (RRH) plays a vital role in providing wireless coverage and capacity. RRH specifications vary depending on the equipment manufacturer, deployment scenario, and telecom network operator.

In general, common specifications or features of 5G RRHs are as follows:

• Frequency bands and Bandwidth: Including sub-6 GHz and mmWave frequencies.
• Multiple Antennas: RRH should support multiple antennas to enable MIMO transmission and reception.
• Digital Beamforming: RRH should support digital beamforming.
• TDD and FDD Modes: RRH should be capable of operating in TDD and FDD modes as per the specific deployment scenario.
• eCPRI Interface: RRH should support the eCPRI interface between baseband and radio units.
• Adequate Power Transmission: RRH should be capable of transmitting the required power to ensure adequate coverage.
• Low Latency Design: RRH should be designed to minimize processing and transmission delays so that the required latency can be achieved.
• Remote Monitoring and Control: RRH can be monitored and controlled remotely.
• Energy Efficiency: RRH should be energy efficient to maintain overall network performance.
• Compact Size and Environmental Resilience: RRH should be compact in size and should withstand all environmental conditions during outdoor usage.
• Power Supply: RRH should work with a 48V DC power supply.

Figure 1: Typical cellular base station using RRH technology.

As shown, radio units (i.e., RE) are installed close to the RF antennas, and BBUs (Baseband Units) are installed at some distance from the radio part. Both the radio front end (RFE) and BBU are connected using fiber optic cables.

5G Remote Radio Head Modules

The REC part of the RRH consists of ADC/DAC, RF up/down converter, Power Amplifier (PA), Low Noise Amplifier (LNA), and RF duplexer/switch. The RE part consists of PHY layer modules as defined in eCPRI and 5G NR specifications.

Let’s understand the functions of these modules:

PA, LNA, and RF duplexer/switch are collectively known as the RF Front end. Both the BBU and Radio end part are connected via fiber optic cables. The information fields (data, sync, control & management) are transmitted using the CPRI/eCPRI format.

Figure 2: Block diagram of RRH (Remote Radio Head).

As shown in the block diagram of RRH (Remote Radio Head), the transmit chain performs the following functions:

• Physical Layer Processing: Information to be transmitted is passed through Physical layer modules such as LDPC encoding, scrambling, modulation, etc. Read eCPRI and 3GPP specifications for layer-1 blocks of 5G NR.
• Optical Conversion: The modulated baseband signal is converted to optical form as per the eCPRI format and transmitted using fiber optic cables.
• Electrical Conversion: The optical signal is converted back to electrical form at the radio end (RE part) of the RRH.
• DAC Conversion: The digital signal is converted to analog form using a DAC (Digital to Analog Converter).
• RF Up-conversion: The analog signal is up-converted to RF (Radio Frequency) level using an RF mixer and LO (Local Oscillator).
• Power Amplification: The up-converted RF signal is amplified to the desired power level using a PA (Power Amplifier).
• Transmission: The amplified RF signal is transmitted into the air using an antenna or antenna array as per requirements.

The receiver chain performs the reverse functions of that performed by the transmit chain. It passes the RF signal through an LNA (Low Noise Amplifier), RF down converter (using mixer and LO), and ADC (Analog to Digital Converter).

The analog electrical signal is converted to optical form and transmitted via fiber optic cables to the BBU (Baseband Unit). At the baseband unit, physical layer blocks (demodulation, descrambling, LDPC decoding, etc.) retrieve the information.

An RF duplexer or switch is used to share the same antenna between transmit and receive portions. For FDD topology, an RF duplexer is used to separate transmit and receive frequency bands. For TDD topology, an RF switch is used for the separation of transmit and receive time slots.

5G RRH Manufacturers or Vendors

The following table mentions 5G RRH manufacturers or vendors.