What is a Remote Radio Head (RRH)?

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.

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

Open Base Station Architecture Initiative, or OBSAI is another standard developed by Hyundai, Nokia, Samsung, and ZTE in 2002 to create an open market for standardized base station functional blocks like the Remote Radio Head.

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.