You've probably heard of it, but what is 4G? In short, it's the name given to the fourth generation of mobile networks, just as the previous generation is called 3G.

Another piece of jargon, which you will see tagged onto the end of 4G is 'LTE'. This stands for Long Term Evolution and is a type of 4G technology. It's arriving in the UK for the first time at the end of October and will be available to around a third of the population by Christmas 2012. See also: iPhone 5 review

4G LTE aims to offer users faster, more reliable mobile broadband internet for devices like smartphones, tablets and laptops.

Loosely speaking, 4G is around five times faster than existing 3G services. Theoretically it can provide download speeds of up to 100Mbps but you won't achieve this in real-world use.

Unless you've just bought an iPhone 5, a Samsung Galaxy S3 LTE (not a regular S3) or one of the other brand new 4G-capable smartphones, your existing handset won't work on a 4G network.

4G networks use different frequencies to transmit data than 3G so you need a handset which has a modem that supports these new frequencies.

Here, we'll explain everything you need to know about 4G. We'll be taking an in-depth look at how the technology works, where and when you can get it as well as telling you which devices support it.

We've been able to test out the first 4G network, run by EE, formally Everything Everywhere,  so we can also reveal how fast it is and how it will benefit you in practice.

Although 4G is new to the UK and we Brits like to think we have the latest technology, it has actually been around for many years. Two forms of 4G been developed and are in use: WiMAX and LTE.

In fact, you may recognise the first technology, as WiMAX was trialled in the UK in 2009. However, the first WiMAX network was launched by South Korean firm KT in 2006.

The first LTE network was deployed in Scandinavia in 2009. However, it was debatable whether the speeds on offer back then were really 4G or not.

Across the Atlantic in the US, Sprint has been using WiMAX since 2008 and MetroPCS was the first operator to offer an LTE service in 2010. Verizon and AT&T also offer LTE 4G.

In the UK, 4G networks will use LTE technology, which is why devices such as smartphones are already popping up with LTE suffixes to their names to show they are 4G capable.

3G has, of course, been around for a lot longer than 4G. In the UK the first 3G network was launched by Hutchinson Telecommunications, branded as Three or '3'. Wideband Code Division Multiple Access (WCDMA) was the first technical standard used for 3G.

It's now more commonly known as Universal Mobile Telecommunications System (UMTS). More modern forms of 3G are High Speed Packet Access (HSPA) and HSPA+. The latter allows for faster speeds up to 42Mbps, twice that of HSPA. Common spectrum used for 3G connective include: 850MHz, 900MHz, 1900MHz and 2100MHz.

4G's headline download speed is 100Mbps and a blistering 50Mbps for upload. This makes 4G is more than twice as fast as the latest 3G technology and many more times faster than previous versions.

Of course, these speeds are theoretical, and such speeds won't be reached in real-world use. However, that doesn't mean 4G isn't twice as quick. In our tests, which we'll get to later, we saw speeds around three times faster on 4G compared to 3G, and an even larger improvement with uploads.

What does this mean in practice? The faster speeds mean websites load quicker, and that you'll be able to stream videos and podcasts without first waiting for them to buffer.

Plus, you'll be able to download large email attachments or other content from the web faster. Apps which need to download data, such as maps, will work more smoothly, especially when zooming in or out as this generally requires a lot of data. The speed differential should be akin to switching from 3G to Wi-Fi.

Taking a more demanding task like video streaming, the BBC recommends a connection speed of 3.5Mbps for HD content. Although 3G can offer speeds in excess of this, the average speed across all forms of 3G in the UK is around 3Mbps.

For video streaming and similar tasks, where you would typically require Wi-Fi for smooth performance, 4G should allow you to have a 'home broadband' experience on the move. EE expects the average speed to be between 8- and 12Mbps, potentially faster than the 5.9Mbps average for ADSL home broadband.

Faster upload speeds will also be a boon. If you hate waiting for pictures to be posted to Facebook or Twitter, for example, then this should be a much faster process over 4G.

The main reason 4G is faster than 3G is because of Orthogonal Frequency-Division Multiplexing (OFDM). It sounds complicated, but it's the same technology used in Wi-Fi, ADSL broadband, digital TV and radio.

OFDM is a technique for squeezing more data onto the same amount of radio frequency. It also reduces latency and interference. Data is split up and sent via small chunks of frequency in parallel, therefore increasing the capacity of the network.

Multiple-input and multiple-output, or MIMO, is another reason 4G is able to provide faster speeds. It is simply the use of multiple antenna arrays at both the transmitter and receiver to improve communication performance.

This allows more data to be transferred without requiring additional bandwidth or drawing more power. The most common configuration currently is a 2x2 MIMO, found in many smartphones and some tablets. A 4x4 setup is also possible and promises even faster speeds but is still a little way off making its way onto devices. Since different setups are possible, one phone could provide faster 4G speeds than another.

With 3G handsets, most of us take roaming for granted. We take our phones travelling around the world, and expect to be able to pick up emails and browse websites as soon as we land. Things are different with 4G.

Although there are 4G networks in many countries around the world, your UK 4G smartphone won't necessarily work wherever you go. The reason is that 4G doesn't operated on the same frequencies in every country.

If your phone's 4G modem doesn't work on the same frequencies as those used in the country you're visiting, then you'll have to live with 3G instead. Even if the numbers do match, there needs to be a 4G roaming agreement between operators. Currently, there is no such agreement in place and even when there is, expect data prices to be high.

EE says it will provide 4G coverage in a total of 10 UK cities at launch, with 16 switched on by Christmas. The firm says it means 20 million users will be able to get the faster speeds before the year is over. The lucky cities to get 4G before the rest of the country are:

Birmingham, Bristol, Cardiff, Edinburgh, Glasgow, Leeds, Liverpool, London, Manchester and Sheffield.

Belfast, Derby, Hull, Nottingham, Newcastle and Southampton should be 4G'd up before 2013.

12 cities will have wide-ranging coverage. London 4G's signal will stretch beyond the M25, for example. The remaining four (which four haven't been announced) will have city-centre coverage only to start with.

Don't assume that if you have good 3G coverage now you will also get good 4G coverage when the new network launches in your area.

Ofcom - the independent regulator - has set a requirement that 98 percent of the UK must have 4G coverage by the end of 2017. However, EE has promised the fastest ever roll-out of a mobile network in the UK claiming it will reach 70 percent of the UK by the end of 2013. It says 98 percent of the UK will have 4G available by the end of 2014, three years ahead of Ofcom's goal.

You can check 4G coverage in your area on EE's website.