What are cells in mobile communications?

Mobile networks are also called cellular networks because they consist of a large number of interconnected cells. In mobile communications, cells are the most fundamental piece of the network that enable wireless connectivity.

A cell is a geographical area that defines the cellular coverage zone created by the base station of a mobile network. The base station, also known as a cell tower, is equipped with transceivers that transmit and receive radio signals at licensed frequencies between the network and mobile phones.

Cell towers, also known as radio base stations, are part of a mobile network owned by a mobile network operator – MNO. The radio base station is responsible for communicating with the mobile phone and is part of a mobile operator’s radio network. Cells in mobile communications work together to create a cellular network.

A mobile network consists of many interconnected cells created by a large network of cell towers that mobile operators deploy throughout villages, towns and cities within a country. These cells create cellular coverage that allows SIM-enabled mobile devices to connect to the mobile network.

The concept of a cell in mobile communications

The cells in a mobile network are represented by interconnected hexagons that cover a geographical area where cellular coverage is required. In real life, the shape of a cell is determined by its range which depends on how far the radio signals from a base station can travel before fading entirely.

The hexagonal shape is just for the conceptual view for cell planning and documentation purposes. In real life, the cells have a certain level of overlap with neighbouring cells to allow for a handover when a user moves from one location to another. The radio signals are communicated between the base station and our mobile phones at certain frequencies and transmission power. When a mobile phone is in an area covered by a base station, it can transmit radio signals to the base station at frequencies allocated by the base station. So basically, a cell is just a geographical range within which the communication between a base station and a mobile phone can occur through radio waves. The base stations transmit and receive the radio signals at certain frequencies within a well-defined range, and the mobile phones within this range do the same for two-way communication.

how cell phones work
Conceptual diagram of how a cell phone connects to a mobile network

Cells are part of the radio access network (RAN)

Cells are created by the radio waves emitted by the radio base station, which is part of a mobile radio network. The radio network in mobile communications is called a radio access network or RAN. The radio network is responsible for wireless connectivity through the air interface.

Simplified diagram showing the key components of a mobile network

These base stations have transceivers (transmitter + receiver) that can receive signals from the cell phone and transmit signals from the network back to the phone to enable two-way communication. The emission of radio waves from the base stations creates network coverage that the cell phones use to connect to the mobile network.

The network coverage area created by the radiations through a particular radio unit within a base station is called a cell. The radio network that the base stations belong to is only one part of the overall mobile network. The mobile radio network connects to the mobile core network, which then connects to external networks like PSTN and the Internet. That way, a mobile service provider is able to connect you to anyone, no matter which mobile or fixed network they are on.

A group of cells is called a cluster

A cluster in mobile networks refers to a group of interconnected cells in a specific geographical area. The term cluster is used in cell planning where RF engineers ensure that the available frequency channels (e.g. ARFCN, UARFCN, EARFCN) are allocated to cells with minimal interference.

At a very basic level, if any two adjacent cells get allocated the same frequency channel, that can lead to co-channel interference. If any two adjacent cells are allocated adjacent frequency channels, e.g. ARFCN # 1 and ARFCN # 2, that can lead to another type of interference called adjacent-channel interference.

cells for cell phones and mobile phones
Example of a cluster of cells

Our mobile phones always communicate with the mobile network even in idle mode when no one is using the phone. The mobile phone keeps the network updated about its location and presence. In cases when we are moving, e.g. driving from home to work, we may come out of the range of one cell and move into the range of another cell.

When that happens during an active session, e.g. during a voice call, our session (or call) gets ‘handed over’ from one cell to another. This way, throughout a journey, our call or data session keeps hopping from cell to cell to make sure we stay connected without dropping the call or interrupting the data session.

Frequency channels used by cells: ARFCN, UARFCN and EARFCN

ARFCN stands for Absolute Radio Frequency Channel Number, and it is a range of frequency channels available in the GSM networks. UARFCN or UTRA ARFCN refers to the ARFCN in 3G UMTS networks, whereas EARFCN or Evolved-UTRA ARFCN refers to ARFCN in 4G LTE networks.

ARFCNs have numbers allocated to them, and each ARFCN represents a pair of frequencies, one for transmission and one for the reception when different frequency bands are used for uplink and downlink (Frequency Divison Duplex – FDD). Have a look at our dedicated post on GSM frequencies to understand how ARFCNs are allocated. To learn more about FDD and how it is used in 4G LTE networks, check out this dedicated post on Duplex schemes for LTE networks.

What is a handover between two cells?

A handover, also known as a handoff, is when a voice call or data session is transferred from one serving cell to another. A handoff happens when you start a call or a data session in a certain location, and then during the session, you move out of the area such that the cell that was serving you cannot reach you any longer.

In that case, the serving cell will hand over the responsibilities of handling your session to another nearby cell better situated to serve you. For example, if you sit on a train from London Heathrow airport to central London and start watching a YouTube video (assuming you are using mobile data and not WiFi), your data session will keep getting handed over from one cell to another as you move from one location to another.

Why mobile phones are referred to as cell phones?

A mobile phone is also called a cell phone because it works on cellular technologies like GSM, UMTS, IS-95, CDMA2000, UMTS, LTE and NR. While the term cell phone is often used in the US and the term mobile phone mostly in Europe, the term cell refers to cellular technologies.

A mobile phone is often referred to as a cell phone because it employs cellular technologies such as GSM, UMTS, cdmaOne, CDMA2000, LTE and NR to communicate with other phones. From a terminologies viewpoint, the term cell phone is mostly used in the US and countries that follow the US terminologies.

However, in the UK and many parts of Europe, the term mobile phone is used for referring to cellular phones. Cell phones connect to a network of interlinked cells that allows them to communicate with other phones and devices that are on the same or other networks. Mobile cellular networks use advanced technologies to establish a connection between the cell phone and the strongest available base station used by the mobile service provider.

Mobile operators constantly keep introducing new cellular technologies and enhancements to keep up with the network traffic demand. For a user, that means having to upgrade phones from time to time. For example, you may be someone who once bought a GSM phone and then had to upgrade to a 3G phone and then to a 4G phone.

With enhancements like High-Speed Packet Access, LTE-Advanced and Advanced Pro, and now 5G NR, it can be confusing for a mobile user to know if they need to buy a new phone. As a rule of thumb, all cellular technologies are backwards compatible. It means if you have a 3G phone for a particular 3G technology (e.g. UMTS), the phone will also work on the 2G technology (e.g. GSM) relevant for that 3G technology.

However, cellular technologies will keep on evolving, and the older technologies will at some point be phased out. Have a look at this GSM vs CDMA post if you live in the US and are on CDMA technology (e.g. CDMA2000/cdmaOne). If you have a 4G phone and wonder whether it should work on 5G or not, check out this dedicated post on 4G phones on 5G networks.

Types of cells used by a mobile network

A mobile network consists of various types of cells, including macrocells, microcells, picocells and femtocells. The microcells, picocells and femtocells are collectively called small cells. Macrocells have the longest range (tens of km), whereas femtocells have the shortest range (up to 10m).

There are various types of cells used in mobile communication, including macrocells, microcells, femtocells and picocells. The cells are differentiated in this way based on the range they cover and the capacity they have. Macrocells are the largest cells and can cover tens of kilometres, whereas femtocells are the smallest of the cells that cover a range of up to 10 metres. Microcells are the largest of the small cells with a range of up to 2 kilometres. Picocells are slightly larger than femtocells, with a range of up to 200 metres.

Cell TypeCell range
MacrocellsTens of kilometres
MicrocellsUp to 2 kilometres
PicocellsUp to 200 metres
FemtocellsUp to 10 metres

—Table showing the types of cells and the range for macrocells, microcells, pico and femtocells—

Macrocells are the large or regular cells that provide the main mobile network coverage in your area. These cells usually have their antennas mounted at the top of tall masts on the ground, rooftops of high-rise buildings and other similar locations.

Macrocells have a range of tens of kilometres, and they need to be mounted at a height from where they have a (mostly) clear view of the area they are serving. These cells require dedicated sites with adequate power supply, and usually, the operator pays rental fees for these sites. Macrocells form the main layer of cellular coverage within a geographical area.

Microcells are a type of small cell that are low-powered cellular base stations. They are the biggest of the small cells with a range of up to 2 kilometres. Microcells can add capacity and coverage to the existing mobile network alongside macrocells, picocells and femtocells. Due to the area they can cover, microcells can be a good solution for areas like large train stations and address temporary capacity needs for any sporting events, concerts, etc.

Macrocell is the cell that provides primary cellular coverage

Macrocells are the cells responsible for providing the primary cellular coverage and are used in geographical areas where the main challenge is network coverage as opposed to capacity. When a mobile operator serves an area with a low population density, they need fewer cells per square kilometre.

Macrocells are ideal for rural and sparsely populated areas such as remote villages and towns, which may have a large land area, but the population size is small. Macrocells have high transmission and reception power, giving them a large range to provide primary network coverage to vast geographical areas.

Macrocells are more suitable to serve rural areas where the traffic load on the mobile network is not as high as that in heavily populated cities. Macrocells are installed, operated, controlled and managed by the mobile operator and use a licensed frequency spectrum. Multiple macrocells can originate from the same base station of a cell site.

Which cells are used for densely populated areas?

Mobile operators use smaller, more targeted cells to improve network capacity and coverage in densely populated areas with more people per square kilometre trying to access the network. Small cells, including microcells, picocells, and femtocells, are an extension of the primary cellular network.

In densely populated areas such as central London, with thousands of people per square kilometre, there is a massive demand for a mobile network to ensure that everyone can access the network, get enough bandwidth/bit rates, and have no coverage gaps. In urban areas, many users try to access the network simultaneously for voice calls, web browsing, video streaming etc., which increases the demand for network capacity.

Urban areas also have coverage challenges with too many obstacles such as large buildings, brick walls, elevators, underground train stations, interference from WiFi/WLAN signals, and reflective surfaces to name a few. In these densely populated areas, a mobile operator can use smaller, more targeted cells, e.g. microcells and picocells, to fill the coverage and capacity gaps.

Microcells are an extension of the primary cellular network, which consists of macrocells. Microcells are controlled and managed by the mobile operators themselves. The key considerations for deploying microcells include the connectivity to the mobile core network, the frequency spectrum and the power supply.

Here are some helpful downloads

Thank you for reading this post. I hope it helped you in developing a better understanding of cellular networks. Sometimes, we need extra support, especially when preparing for a new job, studying a new topic, or buying a new phone. Whatever you are trying to do, here are some downloads that can help you:

Students & fresh graduates: If you are just starting, the complexity of the cellular industry can be a bit overwhelming. But don’t worry, I have created this FREE ebook so you can familiarise yourself with the basics like 3G, 4G etc. As a next step, check out the latest edition of the same ebook with more details on 4G & 5G networks with diagrams. You can then read Mobile Networks Made Easy, which explains the network nodes, e.g., BTS, MSC, GGSN etc.

Professionals: If you are an experienced professional but new to mobile communications, it may seem hard to compete with someone who has a decade of experience in the cellular industry. But not everyone who works in this industry is always up to date on the bigger picture and the challenges considering how quickly the industry evolves. The bigger picture comes from experience, which is why I’ve carefully put together a few slides to get you started in no time. So if you work in sales, marketing, product, project or any other area of business where you need a high-level view, Introduction to Mobile Communications can give you a quick start. Also, here are some templates to help you prepare your own slides on the product overview and product roadmap.

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