Cellular repeater

A cellular repeater (also known as cell phone signal booster or amplifier), in the cell phone industry, is a type of bi-directional amplifier used for boosting the cell phone reception to the local area by the usage of a reception antenna, a signal amplifier, and an internal rebroadcast antenna. These are similar to the cellular broadcast towers used for broadcasting by the network providers, but are much smaller, usually intended for use in one building. Modern cellular repeater amplifiers can rebroadcast cellular signals inside a building. The systems usually use an external, directional antenna to collect the best cellular signal, which is then transmitted using coaxial cable to a signal amplifier unit, and then transmitted using more coaxial cable to an interior antenna which retransmits it to the users, thus providing significantly improved signal strength. The more advanced models often also allow multiple cell phones to use the same repeater at the same time, so are suitable for commercial as well as home use. Some political jurisdictions require these systems in all new large buildings to support emergency use (i.e. police, fire and paramedic).

1. Analog Signal Boosters
Most common type of amplifiers. These signal boosters are usually analog repeaters that use traditional technology to amplify (usually) all frequencies from cell phone carriers. They are almost always wide band (or broadband) repeaters. Such boosters are usually sold with a kit of outdoor antenna and cable and require an installation. These are sometime called BDA units, short for Bi-Directional Amplifier.

2. Smart Signal Booster
This is a new category of Signal Boosters. This new category of modern boosters utilizes powerful all-digital baseband processors to clean the signal before it is rebroadcast (hence the "Smart" in the name Smart Signal Booster). Most of the Smart Signal Boosters have gains of 100 dB (compared to analog booster's gain of 63 to 70 dB) and are carrier-specific (hence they can have higher gain in the US according to new FCC regulations). Some of these new boosters, while more expensive than traditional analog booster, are plug and play: they usually don't need the installation of outdoor antennas (usually the donor antenna is inside the booster box). Most of the time, Smart Signal Boosters are carrier-specific and are under consideration by the FCC's new rules starting in 3/2014.

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Wikipedia