What is a cell site?

Do you sometimes wonder why the word “cell” is often used in mobile communications? For example, people, especially in the US, often refer to mobile networks as ‘cellular networks’. A mobile site is also often referred to as a ‘cell site’. So what is this “cell” in mobile communications that people talk about? Mobile networks consist of a very large number of “cells” that provide mobile network coverage in any geographical area. A cell in mobile communications is a coverage area created by the transmission and reception of signals from a mobile base station.

A cell site or a site in mobile communications is a location where radio base stations and associated network equipment are installed in order to transmit and receive mobile signals. The most visible part of a cell site is the base station (cellular tower) which looks like the picture below.

Why mobile operators have cell sites?

Mobile operators in any country use a large number of sites or cell sites to provide nationwide coverage to their customers. These cells are formed by the antennas installed in these cell sites that propagate radio waves in any given area which in turn creates the network coverage. These antennas are powered up (through electricity) and the range of each cell is determined by how far the signals can travel from mobile phone to the network and back. As we move from one location to another, our calls and data sessions can be handed over from one cell to another. This way, the mobile network makes sure that we stay connected when we are on the move and the calls or data sessions can continue without any interruptions.

Just to summarise the cell site; a cell site is basically a location where cellular antennas are mounted on the cellular towers also known as the mobile base stations. There are different terminologies used for these base stations depending on which technology we are talking about. The base station is known as Base Transceiver Station (BTS) in GSM networks, Node B in UMTS networks, and eNodeB in LTE networks. In 5G networks, the base stations are called gNB and they support the New Radio technology (NR) used by 5G. The base stations can be seen as the tall masts where the cellular antennas are mounted which are responsible for managing all the radio communication between a mobile handset and the mobile network.

2G base station

In GSM networks, BTS or Base Transceiver Station is a fundamental part of the radio part of the network. GSM stands for Global System for Mobile and is the technology that enables the second generation (2G) of mobile communications. BTS is responsible for managing all the radio communication that takes place between a mobile phone and the network over the air interface. If you are on 2G (GSM or EDGE), the signal bar on your phone shows how close or far you are from the base station. When people say “I can’t get the signal here”, this is what they are talking about. BTS is controlled by another network entity called Base Station Controller (BSC), which controls a number of BTSs. Both BTS and BSC are part of the Base Station Subsystem (BSS) in the GSM network which then connects them to the mobile Core Network.

3G base station

In 3G UMTS networks, the equivalent of BTS is called Node B which connects the mobile phone to the mobile network. UMTS stands for Universal Mobile Telecommunications System) and is one of the key technologies that enable 3G. So when people talk about 3G coverage, this Node B is the entity that enables that coverage. Node B is an essential part of the UMTS radio network and manages all the communication between the mobile phone and the network over the air interface. Node B is controlled by another network entity known as Radio Network Controller (RNC) which controls a number of Node Bs. Both Node B and RNC are part of the UMTS Radio Access Network (UTRAN). As part of the UTRAN, RNC then connects the Node Bs to the mobile core network.

4G base station

In 4G LTE networks, the base stations are called eNodeB. eNodeB stands for evolved Node B. Just like BTS and Node B in the earlier networks, eNodeB connects the 4G enabled phones to the mobile network. However, eNodeB does a lot more in 4G networks than what BTS and Node B do in GSM and UMTS respectively. So, in contrast to BTS and Node B, eNodeB has an additional role as the radio network controller in 4G LTE networks. As we discussed earlier, in GSM and UMTS networks, the radio control function is handled by separate entities i.e. Base Station Controller or BSC in GSM and Radio Network Controller or RNC in UMTS.

Similar to the approach used in 2G, 3G and 4G, 5G networks also use specialised base stations that support 5G technology. 5G base stations are called gNB and they support the New Radio (NR) technology used by 5G. 5G also has other base stations that support LTE radio access.

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