The raised structure typically supports antenna[clarification needed] and one or more sets of transmitter/receivers transceivers, digital signal processors, control electronics, a GPS receiver for timing (for CDMA2000/IS-95 or GSM systems), primary and backup electrical power sources, and sheltering.

Cell sites are sometimes required to be inconspicuous;[2] they may be blended with the surrounding area[3] or mounted on buildings[4] or advertising towers.

This background handoff process is imperceptible to the user and can occur in the middle of a phone call without any service interruption.

Each cell phone has an automated full duplex digital transceiver and communicates with the cell antenna over two digital radio channels in the UHF or microwave band, one for each direction of the bidirectional conversation, plus a control channel which handles registering the phone with the network, dialing, and the handoff process.

In any case the limiting factor is the ability of a low-powered personal cell phone to transmit back to the mast.

When the terrain is hilly, the maximum distance can vary from as little as 6 to 8 km (3.7 to 5.0 mi) due to encroachment of intermediate objects into the wide center Fresnel zone of the signal.

[8] Depending on terrain and other circumstances, a GSM Tower can replace between 3 and 80 km (2 and 50 mi) of cabling for fixed wireless networks.

To do this, the signal of a cell mast is intentionally kept at low power and in many cases tilted downward to limit its reach.

The signals do not need a clear line of sight but greater radio interference will degrade or eliminate reception.

When many people try to use the cell mast at the same time, e.g. during a traffic jam or a sports event, then there will be a signal on the phone display but it is blocked from starting a new connection.

An advanced forward link is where a device is within range of at least three cell sites and where the carrier has implemented timing system use.

Another method is using angle of arrival (AoA) and it occurs when the device is in range of at least two cell sites, produces intermediate precision.

[12] According to the U.S. Federal Communications Commission: "Measurement data obtained from various sources have consistently indicated that 'worst-case' ground-level power densities near typical cellular towers are on the order of 1 μW/cm2 (or 10 mW/m2) or less (usually significantly less).

COWs are also used at permanent cell sites—as temporary replacements for damaged equipment, during planned outages, and to augment capacity such as during conventions.

Marshals utilizes spy devices, known as "dirtboxes", to mimic powerful cell tower signals.

The devices are placed on airplanes to effectively create a "dragnet", gathering data about phones as the planes travel above populated areas.

Traditionally, sites have used internal-combustion-engine-driven generator sets,[20][21] however, being less efficient than public power, they increase operating expense and are a source of pollution (atmospheric, acoustic, etc.)

They can be backed up by a fuel generator system which allows the cell site to work when the renewable sources are not enough.

Researchers at Alcatel-Lucent have developed a cell site called lightRadio that fits in the palm of hand.