How a 3G mobile network works.

Switching on your new mobile

A mobile phone is like a two way radio, it works off signals between it and a transmitter/aerial, so allowing you to be mobile whilst talking to others.

Today, technology also allows you to perform a range of Internet applications, social networking and video streaming activities.

To bridge the gap between simply talking on your mobile and full Internet access a standard called 3G was introduced and adopted for use in the UK.

So when your hear the term 3G, it relates to the service that the mobile operators provide to address your Internet needs, whilst still allowing you to talk to each other…on the move.

2G refers to simple voice services and SMS text only.

Building blocks – Your home broadband                          

The Internet is built around cables, be they copper (as would run the Broadband service into your home), or optical fibre that links our towns and cities together.

In your home, the broadband service runs over the same copper cables that run your phone. The cables will typically run from the Broadband hub/router in your home to the local telephone exchange and then out to the Internet.

Based on the distance between you and that exchange, the Internet Service Provider(ISP) allocates the speeds at which your broadband will operate at.

So as long as the link between your home and the local exchange is active, the maximum speed of Internet Access remains constant.

Building Blocks – Voice and text services

Your mobile phone is a small portable two way radio

Unlike your home broadband there are no cables just air based signals(frequencies).

Each mobile operator(Vodafone, T-Mobile etc.) has a unique set of frequencies for the UK, which come from the Masts(Cell Towers) that you see in fields or on the side of buildings.

These frequencies are active for a set distance or geographical range around each Mast, hence creating a Service footprint or Cell; hence the term Cellular Network.




The Service footprints from the Masts overlap, so your signal remains active as you move.


Each Mast is linked back to a telephone exchange and onto the national voice network. That network tracks your movement an always the call to be switched seamlessly as you move.

Building Blocks – starting a call. 

In a mobile phone you have a SIM(Service Identification Module) card which identifies which mobile operator you are with and your specific account details.

Each time you power on a mobile phone it searches for :

  • Masts with a frequency that matches you selected operator.
  • The strongest signal.
  • Other Masts(Cells) in range of your phone.
  • Once identified it registers your SIM information, with the network to start the billing process.
  • The Mast the allocates a unique send and receive frequency for your phone.
  • The Mast monitors signal strength. If you are moving the system will pass your call/connection on to the Mast with the strongest signal.

But certain rules apply:

            Rule 1. 

            The quality of voice call from a mobile phone is partially determined by  where you are in relation to a Mast or Masts.

            Rule 2. 

            As you move, the quality of the call can vary.

            Rule 3.

            If you move outside of the Service footprint, the signal and hence the call is lost.


To see the Mast locations and coverage for each operator near you go to Coverage Section.

3G Internet Access – Phone to Mast.

Now you want to access the Internet.

The first thing to realise is that Internet communications uses up significantly more data than a simple voice call.

In mobile terms that meant new technology to get data to and from your mobile phone wirelessly.

The Governments of each country typically own Radio Frequencies. Some are used for military work, for TV and Radio, whilst others are auctioned off to the mobile operators. You may remember in 2000 the UK Government making millions of pounds from the 5 spectrums bought by companies like Vodafone and Orange.

Spectrums are frequency ranges. Just as you can move through the FM and AM bands on an analogue radio, so different frequencies within the spectrum can be used to transfer data goes to your mobile.

The current UK spectrum ranges are:

2G services operating in the 900Mhz and1800Mhz bands.

3G services operate in the 2100Mhz band.

More spectrums will be auction off by the UK Government to accommodate the future 4G mobile services.

So part of the 3G standards defines how these frequencies are used to deliver data  to your mobile phone.

Today, based on the 2100MHz frequency band, UK mobile operators offer downlink speeds in the sequence 1.8Mbps, 3.6Mbps with a move to 7.2Mbps.

As technology improves, folks will work out how to send more data down the same frequency.

When you power up your 3G mobile phone, in addition to finding the local Masts and registering your details, the mobile operator must also establish how much data it can actually send down to your phone.

The amount of data sent, is typically based on how close you are to the Mast and the size and repetition of your data requests.

Rule 4

The maximum speed of your mobile Internet connection (just like voice quality) can vary dramatically.

3G Internet Access – Mast to the Internet

If, like me, you live in the countryside, my broadband service is slow. It is basic physics. Electrical signals loose strength as they travel over more and more copper. The further you are away from the local telephone exchange, the more copper cable exists and hence the less data can be exchanged per second.

Now think of all those mobile Masts, in fields or on buildings. The same rules apply. They also have to link back to the specific locations(like our local telephone exchange) where they can access the Internet and handle your voice calls. Just like your broadband service, the further away from the exchange they are, the less data can be sent per second.

So, not only is your Internet connection speed determined by your location relative to a Mast, but also the available bandwidth from the Mast to the Internet

The 3G standards accommodate all these variables, and in addition provide: 

  • a gateway function, that in effect translates the 3G signals into normal Internet traffic.
  • a voice gateway to hand off voice calls to the national voice network.

A final thought

Many countries have limited copper or fibre connectivity. They view the 3G smart phone as the primary route to improved Internet access for all. Their resources are focused not on broadband to the home, but to ensure 3G Masts have the correct connectivity.

For those communities in the UK with no Internet Access improved 3G mobile services could be a more efficient option that laying cable everywhere.

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