FTTA is a broadband network architecture in which optical fiber is used to connect the remote radio head (RRH) to the base station in new antennas, or retrofitted in existing ones, to replace all or part of the coax local loop. One advantage of fiber-optic cable is that it is easier to install because it is lighter than coax cable.
Signal integrity and increased energy efficiency are also driving FTTA deployment. Coaxial cables add noise and degrade signal quality, thus requiring tower amplifiers. By placing the RRH at the top of the antenna and generating signals from there, short coaxial jumpers can be used, thus eliminating tower amplifiers. As for power consumption, unlike traditional base stations where power amplifiers must be cooled using air conditioning, RRHs located at the top of a tower can simply take advantage of ambient cooling.
Another advantage of optical fiber is that baseband units (BBU) no longer have to be stuck to the RRH. The BBUs can be moved to wherever it is most convenient.
Most importantly, FTTA is required to support low-latency, high-speed backhaul and increase traffic bandwidth.
Remote Radio Head
The RRH houses RF component circuitry including analog-to-digital/digital-to-analog and up/down converters. It connects to the base station via an optical interface, provides operation and management processing capabilities and supports multiple inputs and multiple outputs (MIMO).
The cell site is where the antenna and electronic communications equipment are located, namely the base station, remote radio head, transmitter/receiver transceivers, digital signal processors, control electronics, a GPS receiver for timing as well as primary and backup electrical power sources.
Distributed Antenna Systems
An outdoor distributed antenna system (DAS) is a network of spatially separated antenna nodes connected to a central office via a transport medium that provides wireless service within a geographic area. By splitting the transmitted power among several antennas, the coverage remains the same, but it requires less power and is more reliable. Essentially, penetration and shadowing losses can be overcome with less power, and a line-of-sight channel is present more frequently, thus reducing fade depths and delay spread.
An indoor DAS requires a cellular signal source that is connected to either a base station or a bidirectional amplifier (a.k.a. a repeater). In the case of a repeater, a donor antenna is required to pull the signal from the nearest macrocell site. When the RF signal is sent to the headend equipment or DAS interface, it is converted to light. Fiber-optic cables distribute the signal to remote units on each floor of the building that then convert it back to an RF signal, amplify it and distribute it to indoor antennas (directional or omnidirectional) via coaxial cables.