A remote radio head (RRH), also called a remote radio unit (RRU) in wireless networks, is a remote radio transceiver that connects to an operator radio control panel via electrical or wireless interface. When used to describe aircraft radio cockpit radio systems, the control panel is often called the radio head.
In wireless system technologies such as GSM, CDMA, UMTS, LTE the radio equipment is remote to the BTS/NodeB/eNodeB. The equipment is used to extend the coverage of a BTS/NodeB/eNodeB in challenging environments such as rural areas or tunnels. They are generally connected to the BTS/NodeB/eNodeB via a fiber optic cable using Common Public Radio Interface protocols.
RRHs have become one of the most important subsystems of today's new distributed base stations. The RRH 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. This will be increasingly true as LTE and WiMAX 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 Gallium nitride (GaN) RF power devices and envelope tracking technology within the RRH RF power amplifier (RFPA).
When we pass a cellular tower, we often see a small structure at the tower’s base. These six-foot tall climate controlled shelters house the base transceiver station (BTS) equipment that enables wireless communication between the mobile user and cellular network. Long runs of coaxial cable connect the BTS on the ground to antennas on the top of the tower. For decades this architecture remained unchanged. However, as cost and efficiency started becoming increasingly important to wireless operators, it was time for an alternative.
An alternative solution is a distributed base station, in which the majority of the base station equipment is no longer located in the shelter, but in an enclosure at the top of the tower near the antennas. This separate but integrated radio frequency (RF) unit is called a remote radio unit or remote radio head. It is compact in size; generally no larger than two feet by one foot by six inches.
The remote radio head is connected to the main, digital portion of the base station via a fiber optic link. This helps reduce the coaxial feed line losses, increase system efficiency, and provide a high level of flexibility in cell site construction. While remote radio heads offer unique advantages, they also come with complexity due to the sheer number of components that are required to build the unit.
Given that remote radio heads are installed at the top of the tower in very harsh environmental conditions, withstanding the weather is an important challenge. Ensuring optimal performance is also critical, as access to the tower top is harder and more costly if repair or replacement work needs to be done.
RRH protection in fiber to the antenna systems
Fourth-generation (4G) and beyond infrastructure deployments will include the implementation of Fiber to the Antenna (FTTA) architecture. FTTA architecture has enabled lower power requirements, distributed antenna sites, and a reduced base station footprint than conventional tower sites. The use of FTTA will promote the separation of power and signal components from the base station and their relocation to the top of the tower mast in a Remote Radio Head (RRH).
According to the Telcordia industry standard that establishes generic requirements for Fiber to the Antenna (FTTA) protection GR-3177, the RRH shifts the entire high-frequency and power electronic segments from the base station to a location adjacent to the antenna. The RRH will be served by optical fiber and DC power for the optical-to-electronic conversion at the RRH.
RRHs located on cell towers will require Surge Protective Devices (SPDs) to protect the system from lightning strikes and induced power surges. There is also a change in electrical overstress exposure due to the relocation of the equipment from the base station to the top of the mast.