Getting up to speed

The 3G bandwidth of up to 2Mb/sec is easily enough for multimedia in the sky. But Missouri-based Angel Technology has produced this prototype of a suitable plane. It can beam 10Gb/sec over a 75-mile footprint. One suggestion is for robot planes to stay aloft for as long as six months. like videophones or high-quality audio. Mobiles will also in effect be always on, charged only for data transmitted.

Imagine instant access to your intranet and immediate email delivery without tedious dialups, all while avoiding time-based call charges.

The key to these services is packet switching. An ISDN line and 2G mobile networks like current GSM are circuit switched: a fixed line size is opened and used exclusively by you until hanging up.

This is fine for constant downloads but uneconomical for web browsing where a link is idle for 95 percent of the time. In such bursty traffic, sending data in individually addressed packets allows many more users to share a network, saving bandwidth.

In the new year, a packet-switched layer will be added to many European GSM networks. Called the General Packet Radio Service (GPRS) it will in itself boost data rates to 'only' 21Kb /sec, but will lead to bigger things. Expected by the end of this year is High Speed Circuit Switched Data (HSCSD) which boosts the air interface to push 14.4Kb/sec through a single time slot and allows aggregation of adjacent slots, giving 28.8Kb/sec on two, and so on. GPRS on aggregated slots could achieve up to 100Kb/sec, without hogging precious resources.

An enhancement known as EDGE (Enhanced Data rates for GSM Evolution) will arrive within two years. This boosts single time-slot rates for HSCSD and GPRS to 38.4Kb/sec and 60Kb/sec respectively, by improving modulation; it can achieve up to 400Kb/sec using multiple GPRS time slots.

It is expected that HSCSD, GPRS and EDGE, together known as 2.5G systems, will indicate regional demand for 3G and may be sufficient for some areas.

3G may be deployed only in areas like city centres where the highest data rates and largest user capacities are required. Many experts predict 'islands' of 3G in a sea of 2G and 2.5G systems; future phones will be able to roam seamlessly between them.

2.5G may be all that a mobile operator can afford, or even be granted. In the UK, five UMTS licences have been granted, for which our existing four 2G networks are expected to bid. Other bidders are thought to be Deutsche Telekom, Virgin and maybe even BT (which may wish to run a service independently of Cellnet).

There's another reason we may get 'islands' of 3G performance: 3G macro, micro and pico-cells suffer from lower coverage than their GSM counterparts, with ranges of only 1000, 400 and 75 metres from their respective base stations.

Data rates of 2Mb/sec will be available only to people standing still or wandering slowly around pico- or quiet micro-cells. But people driving through large macro-cells should still enjoy up to 400Kb/sec.

This also suggests applications for privately owned pico-cells providing the infrastructure for a corporate wireless network. Shopping centres might fit pico-cells, attracting 3G users with cheaper rates and bombarding them with multimedia advertising and services. Why not incorporate smart-cards into 3G mobiles for e-commerce applications? Enhancements to pico-cells could even see them delivering up to 155Mb/sec in the future.

Beyond macro-cells, satellites will take over your call, although most operators are hazy about how this may work and the troubles of operator iridium have raised questions about at least some satellite operations.

Some visionaries have suggested that a network of high-altitude aircraft (see picture, above) could be a far more economical proposition. One criticised global satellite coverage as 'broadband for penguins'.

Nearer the ground, packet-based 3G networks are the future. AT&T, BT, Ericsson, Lucent, Nokia, Nortel and others recently formed a 3G.IP focus group to develop an entirely IP-based 3G architecture. Could voice over IP herald the end of circuit-switched networks? Will the ITU agree on the OHG's unified WCDMA standard? Could WAP users be charged by units of data and not time?

All these questions remain unresolved, but the future is closer than you may think. Check out Nokia's soon-to-be-released 7110, supporting HSCSD and WAP) and Ericsson's R380, which flips open to boast a much bigger display.

WAP forum: www.wapforum.org

Phone.com (formerly Unwired Planet): www.phone.com

www.ericsson.com

www.umts-forum.org

www.itu.int

www.nokia.com.

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