Remote Radio Head (RRH) Systems

- Overview

A Remote Radio Head (RRH) is a device that is installed on top of an eNodeB's antenna. It is a complex node in LTE-A that performs the following functions:

• Converts optical signals to electrical signals
• Amplifies signals
• Schedules uplink and downlink
• Performs baseband processing
• Converts RF in a distributed base station
• Uses fiber optic cables to communicate with the Base Band Unit (BBU)
• Contains the base station's RF circuitry
• Contains analog-to-digital or digital-to-analog converters
• Contains up/down converters

RRHs are usually mounted near the antenna to reduce transmission line losses. An eNodeB is made up of one BBU (Base Band Unit) and up to three RRHs that can be connected. The BBU and each RRH are connected using an optical interface that is compliant with the common public radio interface (CPRI) specification.

Please refer to Wikipedia: RRH

- Base Band Unit (BBU)

A Remote Radio Head (RRH) connects to a Base Band Unit (BBU) using optical fiber or protocols like Common Public Radio Interface (CPRI) or Open Base Station Architecture Initiative (OBSAI). 

Both the RRH and BBU are transceivers that can connect to radio stations and other endpoints wirelessly or with wires. The BBU is a component of the base station that handles radio communications and radio control processing functions. 

Here's some more information about the RRH and BBU: 

• RRH: Part of D-RAN, the RRH improves network coverage and capacity. It performs RF conversion and baseband processing in a distributed base station. The RRH is usually mounted near the antenna to reduce transmission line losses.
• BBU: A component of the base station, the BBU converts data into a digital signal and sends it to the RRH, which then converts it into an analog signal. The BBU is responsible for communication through the physical interface to the core network.

- Remote Radio Head

A Remote Radio Head (RRH) or Remote radio unit (RRU) is the RF circuitry of a base station enclosed in a small outdoor module. The RRH performs all RF functionality like transmit and receive functions, filtering, and amplification. It also contains analog-to-digital or digital-to-analog converters and up/down converters. An RRH can also provide advanced monitoring and control features that allow operators to optimize performance from a remote, centralized location. 

In wireless system technologies such as GSM, CDMA, UMTS, LTE this Radio equipment is remote to the BTS/NodeB/eNodeB, and is also called Remote Radio Head. These equipment will be used to extend the coverage of a BTS/NodeB/eNodeB like rural areas or tunnels. They are generally connected to the BTS/NodeB/eNodeB via a fiber optic cable using Common Public Radio Interface protocols.

The RRH is usually mounted near the antenna to reduce transmission line losses and is connected to the main, digital portion of the base station (BBU) with an optical fiber. 

Common Public Radio Interface (CPRI) is the standardized protocol for communication between the BBU (Base Band Unit) and RRH, developed jointly by major RRH manufacturers. 

[Remote Radio Head (RRH) - Corning]

- Two 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 ...]