JOE HOY, of Focus Forensic Telecommunications Ltd, explains the new challenges for the analyst of 3G mobile phone systems.
The second generation (2G) GSM mobile phone system was released on an unsuspecting world in the early 1990s – unsuspecting in the sense that no-one understood the profound changes to personal communications that were about to happen.
At the end of the 1980s mobile phones were the preserve of the few ‘yuppies’ who could afford them. By the end of the next decade over one billion people around the world were enjoying the ability to communicate from wherever they happened to be (even if they were on holiday abroad) and were rapidly beginning to forget what life was like before mobile phones came along.
The vast majority of mobile subscribers are content to use their phone for calls and text messages – services that GSM excels at supporting. More adventurous subscribers make use of GPRS services to browse the internet and send picture messages. However, GPRS only allows users to connect to the internet at about the same speed as an old dial up modem and, as the personal communications market began to mature, the time appeared to be ripe for an evolution.
The magic number?
Third generation (3G) networks were designed to offer all of the services found in the GSM portfolio – voice calls, text messages, international roaming, etc – plus a number of more advanced facilities.
The main ‘new’ service offered by 3G networks was the ability to make video phone calls to other 3G users. N etwork operators expected ‘video calling’ to be hugely popular and were somewhat disappointed that virtually nobody used it. Their hope that video calling would be 3G’s ‘killer application’ overlooked the fact that most people use mobile phones while doing something else – walking, working on a PC, even driving – none of which are possible if you’re stuck in front of a camera.
The real new income stream for the new networks has instead been from internet users. The faster data rates offered by 3G allow networks to offer a ‘mobile broadband’ service to compete with more established internet providers. That has proved popular with mobile workers and residential customers who can’t get ‘normal’ broadband connections.
In the UK, 3G licences were won by the four existing GSM operators plus a ‘greenfield’ newcomer – the Hutchison ‘Three’ network – and in the early part of this decade billions of pounds were spent rolling out a new set of base stations across the country.
Keeping it covered
Most operators have concentrated their 3G efforts on urban areas and business parks, where the majority of likely users are to be found, leaving large parts of the country covered only by the older technology. For that reason, shiny new 3G mobile phones also work as 2G phones and ‘fall back’ onto GSM service if no 3G cells are available.
The original four network operators – O2, Orange, Vodafone and T Mobile – still have their GSM networks in place to provide continuity of service to their 3G users. As a new operator, Three doesn’t have a GSM network and has established ‘national roaming’ agreements that allow their users access to other operators’ 2G networks when necessary.
Whatever its differences, 3G is still a ‘cellular’ technology like GSM, with each base station providing services within the limited geographical coverage area of a radio cell. In order to handle the high data rates required to carry mobile broadband services and video calls, 3G radio channels use a far more complex set of technologies than those employed by GSM. That means that, although 3G radio channels carry a much wider range of services than their 2G counterparts, their signals don’t travel as far, leading to smaller cells and a requirement to install a much larger number of base stations.
In many ways, the complexity of the 3G radio system aids the job of a cell site analyst. The smaller cells employed in 3G systems mean that phones are more likely to be close to the base stations they’re connected to when making a call, which in turn means that we can define a smaller area from which those calls are likely to have been made.
Some aspects of 3G cell site analysis are more complex, however; mainly due to the phones’ ability to move between 2G and 3G when required.
If a phone making calls on a 3G network occasionally falls back to using GSM cells, analysts are forced to undertake more comprehensive network surveys and to perform a more complex analysis.
The experts in the field
The superficial similarities between 2G and 3G cell site analysis can be deceptive for the unwary analyst. The team at Focus consists of engineers and analysts whose experience of 2G and 3G networks was gained from working within the mobile phone industry.
We provide defence solicitors with expert assessment of cell site evidence that helps them cut through the jargon and make a meaningful evaluation of the real strength of that evidence. We also provide legal professionals with training in technical topics that can be exchanged for CPD points.
Cell site analysis is an evidential tool increasingly being used by the prosecution – how many defence cases would benefit from access to the same techniques?