The world's first test public LTE networks have been deployed by the Scandinavians in Oslo and Stockholm (by TeliaSonera) offering up to 80Mbps download speeds (http://www.theregister.co.uk/2009/12/14/lte_deployment/) which gives rise to the question: what on Earth is LTE?

LTE stands for Long Term Evolution and is the technology behind the next generation of cellular communications, or 4G. LTE promises to outstrip the data rates offered by 'fixed-line' broadband services, delivering a theoretical maximum of up to 200Mbps download speeds in its first iteration. As always, a theoretical maximum implies a certain coding scheme is being used, no one else is sat next to you, and it isn't raining (water in the atmosphere affects radio reception) - but the reality is still hugely impressive compared with current capabilities.

At the time of writing, in the UK at any rate, the mobile landscape is a mix of 2G, 2.5G and 3G services, all operating within very narrow, tightly-controlled, frequency bands. The frequencies used for these different services in Europe do not necessarily match those used for their counterparts in Asia-Pacific or the US. To fully understand the current architecture I recommend you read my introduction to mobile data here - http://blog.brightpointuk.co.uk/introduction-mobile-data-technologies

As with all cellular technologies, it is important to appreciate that the terms 2G, 2.5G, 3G and 4G refer to a type of service, NOT a specific technology. 3G services offer such features as media streaming, but encompass such technologies as EDGE and WCDMA. Therefore to say to a geek like myself that you are "connected via 3G", is akin to telling me you are watching television "through an aerial" and not whether it is an HD signal delivered via satellite, for example.
The same applies to the term 4G: it could equally apply to LTE as it might to WiMAX, but the two are different.

To understand how the faster data rates are achieved by LTE, it is necessary to understand how cellular data communications function.
In a nutshell, mobile devices are able to send and receive data over the air by adjusting the physical properties of a radio wave to denote either a binary 1 or a 0 (all data is made up of 1s and 0s). Provided that both the mobile device and the cell tower it is registered with are configured to 'look' for the same changes to the carrier signal, data can be sent and received.
This is essentially the same principle used by all communication mediums: fibre optics use light pulses; Ethernet uses copper cables; cellular devices use radio waves.
It is beyond the scope of this overview to go into high-level physics, but essentially it breaks down like this.
The properties of a radio wave can only be altered so far - you can adjust its amplitude, its frequency or its phase - or a combination of all of them. The key to achieving ever-faster data rates is to refine the extent to which a variation in a wave's properties constitutes a data value.
This is a massive simplification but essentially what this means is that whereas 2.5G systems might adjust a wave's amplitude by 1 measurement unit to denote a binary 1, 3G systems might refine the detection mechanism to mean that the wave can be altered by up to 1/4, 1/2, 3/4 and 1 measurement units. Therefore, whereas the 2.5G system can present a binary 1 or a binary 0 by changing the wave once, 3G can change the wave up to 4 times and therefore present 4 binary values between 00, 01, 10, and 11. This is achieved without needing to change the properties of the wave itself, just the processors at the sending and receiving units at each end of the wave. This also means that by changing the wave once to denote a value of 01, this is twice as fast as having to change the wave twice to denote both a 0 followed by a 1 - hence it's twice as fast. Make sense?
The ability to assign 4 values to a single carrier wave is known as Quadrature Amplitude Modification, or QAM.

LTE takes this approach much further. The same laws of physics apply - the radio wave itself is the same and can only have its physical properties adjusted in the same way. What differs is the distinct degrees to which a change in the wave's properties can be interpreted by the sending and receiving equipment as a binary data value - LTE can detect up to 16 different values (16 QAM) per wave cycle: 0000, 0001, 0010, etc et etc and is hence 4 times as fast: 0000 in one go rather than 0,0,0,0 in 4 goes. 64 QAM is also on the roadmap.
This takes increased complexity in the processors in the sending and receiving equipment - most notably in timing, and also in power (which is why early generation 3G handsets only lasted a few hours and got incredibly hot) - we are bound to see the same thing with early generation LTE kit.

Are you with me so far? Well it gets a bit involved from here on I'm afraid.

It gets much more complicated when you realise that the values being broadcast are not even 0000, 0010, 0100 or 1000, but are symbol values to represent more commonly occurring, larger bit sequences. Essentially communications between the device and the cell tower are compressed, in a manner similar to how ZIP applications can compress large files into smaller archive files.

So far we have looked at adjusting the properties of a wave's amplitude. It is also possible to adjust a wave's frequency at the same time as adjusting its amplitude.
"Carriers" are typically 20KHz each - meaning that any phone can transmit on any frequency within a 20,000Hz range to be identified as being on a specific carrier - this gives quite a lot of leeway for the wide variety of different phones available on the marekt to all work work properly on the network, and also provides for 'spacing' between carriers to identify them as being distinct from each other.
This is the approach taken by 2G and 2.5G systems - phones are assigned 'carrier' signals.
This involves a lot of frequency wasteage: if a phone is on a 20,000Hz range, it's only broadcasting on 1 of those Hz at any given time, meaning that 19,999Hz is being wasted. Again this is a huge simplification, but you get the idea.

What UMTS (3G) and now LTE (4G) do, is to assign all frequencies to all phones, at the same time. Each phone is assigned its own radio identifier and allowed to send and receive data across a wide range of frequencies using what is called Orthogonal Frequency Division Multiplexing (OFDM). In the same way that you can all use your company Internet feed at the same time and not get each other's traffic, the same is accomplished by OFDM. This means a hugely more efficient use of the radio network, and more concurrent users, and more speed. This is also why 4G services are referred to as "MIMO" (Multiple In, Multiple Out): they can operate across a range of frequencies rather than just one and often involve devices using multiple aerials.

How come more speed? Because each cell tower has x amount of radio to play with, if only 3 people are using that tower, they will get all of that x divided by 3. As more people join, their share of x will decrease. The important thing is that with LTE your radio allocation is now DYNAMIC. With 2.5G systems radio allocation was static: you'd get your share of x regardless of who was sharing your tower with you.

So what does that all mean for the user?

Apart from the higher data rates, not a huge amount. It is important to remember that these massive technological leaps extend between your phone and the nearest cell tower. As soon as your data hits the tower it goes down a cable into the ground and joins the landline network like everyone else. It is purely the efficiency of the radio link that is being tweaked. In terms of the setup and configuration process to be able to connect to the Internet from your LTE device, it will be the same as configuring a UMTS connection: you will need to enter the Access Point Name (APN) for your operator. Most devices can now determine the correct connection settings to use automatically based on the SIM card inserted.

Key to the development of LTE has been the ability to "hand off" from LTE networks to UMTS networks, meaning that your one device will be able to use LTE services where they are available, but will fall back to 3G service automatically when you roam outside of LTE coverage.

The future is now!