You've probably heard of 4G, but also (probably) haven't used it yet. It's an umbrella term covering various faster mobile data connection standards, which are gradually taking off in various parts of the world.
The US is rapidly adopting it, with all manner of special-edition smartphones arriving in 4G, WiMAX and LTE branded editions to take advantage of the demand for faster mobile web connections.
As with digital and HDTV, you won't just automatically "get" 4G on your existing phone or mobile broadband connection when it's launched. You'll need a new plaything. 4G needs new hardware just like 3G did when it arrived here in 2003, plus the mobile networks need to install new equipment at their end, too.
In some countries, advanced versions of 3G, like HSPA+, are often labelled "4G" due to simply being a bit faster than 3G (and because it sounds cool to say "these are 4G.") What O2 is trialling here is the Long Term Evolution (LTE) option, which is the proper next-generation mobile network we can expect to see replace the 3G network a few years from now.
There's been quite some controversy over the use of the actual term "4G" over the years. The International Telecommunication Union, which sets the standards, originally decided that a proper 4G network should be able to download at speeds of 100Mbps when mobile, and 1Gbps through a static connection, but it's subsequently been downgraded to let the term cover next-gen networks that are near enough. Like the LTE system.
The core boasts of LTE are higher data speeds and increased throughput, allowing more people to use the system simultaneously and benefit from reliable download speeds.
On average, users can expect to see speeds around ten times faster than are currently managed through a 3G connection, with O2 saying users of the London trial may experience download speeds of up to 150 megabits per second in dreamy conditions.
As with our 3G connections which are extremely unlikely to ever hit their 7.2Mbps theoretical maximum speeds, load on the 4G network will reduce that to a realistic 10 - 15Mbps once it's live, and depending on how the backhaul copes with demand.
Backhaul is a nerdy telecoms term describing how the masts connect to the actual fun part of the network we know as the internet. Cambridge Broadband Networks is one of the partners providing technology for use in O2's London trial, taking on the job of providing the backhaul with its VectaStar Multipoint Microwave system.
It uses the point-to-multipoint system to link several simple base stations with one more powerful hub that handles the link to the actual internet backbone.
For the O2 trial, O2 positioned one hub on a high spot, which provides the general link to the web for the geographical area. Smaller local base stations link to this, wirelessly. According to Cambridge Broadband Networks, this makes the network much easier to manage and quicker to enhance, as the smaller, local base stations can be up and running within "hours".
As with the 3G network, your connection speed will be dependent on how far you are from the individual masts, the make-up of the building you're in and how many other users are online.
It's the "ping" that'll make the most difference to how 4G feels on your phone or laptop. Ping is the network latency, or the delay between your device asking for data and the network responding with your web page, and it's the critical part of the machine in making online gaming possible, and web browsing and VOIP services more responsive.
The 4G network will massively reduce this ping, taking typical overall data response times down from over a second to well under a tenth of a second, which ought to help mobile web-browsing sessions near the speeds and multi-tab madness levels of wired desktop connections.
Well, very soon if you get in on O2's London trial. But for the rest of the country, Ofcom is still messing about with plans to auction off the parts of the radio spectrum 4G will use, so it's going to be at least 2013 or even 2014 before it launches nationally.
The 4G switch-on will coincide with the analogue TV switch-off, as parts of the spectrum used by the UK's 4G network -- the 800MHz and 2.6GHz frequencies -- are currently used to beam Coronation Street into the homes of those still defiantly watching analogue television.
Tomorrow, we'll take you through the ins and outs of the UK's current 4G landscape, taking in all the gossip from the impending auction and detailing what you can expect once it launches properly.