Remote Radio Head (RRH) or Remote Radio Unit (RRU)

 A Remote Radio Head (RRH), also called a Remote Radio Unit (RRU), is a small outdoor transceiver used with wireless base stations. They connect wireless devices with cellular wireless networks. They are used to extend coverage into rural locations, improve urban services, and address dead spaces found in tunnels and similar blind spots for existing cellular coverage. 

The Remote Radio Head is typically mounted near the antenna to reduce transmission line losses. It connects with a Base Band Unit (BBU) with optical fiber using a Common Public Radio Interface (CPRI) or the Open Base Station Architecture Initiative (OBSAI) protocols. The BBU provides the interface to and from the cellular network.

A Remote Radio Head transceiver has two major parts: transmit and receive. The transmit section consists of a digital-to-analog converter (DAC), mixer, RF power amplifier, filters, and duplexer. It takes the data signal provided by the BBU through optical fiber, converts it to analog, upconverts it to the required radio frequency, amplifies it, and sends it out via the antenna.

The receive section consists of a filter, Low Noise Amplifier (LNA), mixer, and analog-to-digital converter. It receives the signal from the antenna via the duplexer, filters and amplifies it, converts it to a digital signal, and sends it via the fiber to the BBU and into the cellular network.