2.4Ghz: Don't Believe the Hype
By Justin Ried, Fri Dec 15 00:00:00 GMT 2000

Industry watchdogs made headlines this week by announcing that 3G speeds could be delivered to your mobile without using 3G spectrum. How is it possible? Well, it's not.


Radio-controlled car aficionados of the 80s will be familiar with the problem: You show up at the track with your new souped-up RC car, only to find out someone else is already running a car using the same radio frequency. No worry, that's why you brought another crystal set that transmits at another frequency. What's that? That one's already in use by someone else, too? Shoot. Guess you'll have to just sit on the sidelines until one of them has had enough.

Now, fast-forward to the present, and apply the same principles to the 2.4Ghz spectrum. Except in France, where small parts were allocated for military use, 2.4Ghz frequencies are unlicensed and see little regulation. That being the case, we've got everything from Bluetooth, to home security systems, to WLANs, to cordless phones, to expensive walkie-talkies using them. Virtually anyone who wants to create a device using the bandwidth may legally do so. A digital version of the old-fashioned traffic jam is in the making.

Today, people are often finding their 2.4Ghz cordless phones interfering with their X10 audio/video transmitters and other home devices. Manufacturers are complicating the matter by creating devices that are by default able to use only one small frequency spread, then programming the device to hop between the limited number of channels available in that spread. There are, of course, some devices (usually the more expensive ones) that allow you to choose between operating frequencies - such as direct-sequence WLANs, which usually have 11 options - but these are the exceptions, and not the rule.

Which is what made me so curious to find out why reporters were claiming that Finnish ISP Jippii has been able to implement a technology developed by Professor Hannu Kari from the Helsinki University of Technology that aims to reliably deliver 3G speeds to mobile phones using this free spectrum. Professor Kari's creation, Dynamics HUT mobile IP, is a piece of software is used to route data between base stations compatible with the IEEE 802.11 protocol.

The Helsinki service using it, dubbed Freedom, is basically a network of rooftop 802.11 transmitters used as a wide-area wireless network. Subscribers to the service are able to hop from base-station to base-station as they roam using a standard PCMCIA card fitted to their laptops.

The real secret is finding out how Professor Kari plans on making the bandwidth available to mobile phones. I haven't figured that out yet, and it seems like no one else has either.

Here's what seems to have happened: Someone reported that Hannu Kari claimed the money being spent on 3G auctions is a waste, and that there is a better way - use the unlicensed 2.4Ghz spectrum - as it's already being used by Finnish ISP Jippii.

The headline spread like wildfire, but no one ever bothered to check the facts behind it. Is there a service delivering 2.4Ghz spectrum to handsets that's even in testing? No. Are there any mobile handsets that are compatible with such a service? No. Considering the other devices that use it, does the 2.4Ghz spectrum offer the capacity and reliability needed to offer such a service? No.

So don't get too excited just yet. Getting a mobile phone to access a spectrum that it wasn't intended to use is impossible. Operators would need new infrastructure, and subscribers would need new handsets. There's no way around that fact.

The operators who paid big money for 1.8-2.2Ghz 3G spectrum are getting what they paid for: Clean, regulated frequency defined by industry consortiums like the 3GPP. That's where 3G services will live and that's where they'll remain.

As for 2.4Ghz, many predict that, given enough time, it'll simply become over-crowded. More and more people will use more and more devices causing an ever increasing amount of interference - and it will end up becoming a digital wasteland.

But many forward-thinking engineers have long-since recognized the traffic problems facing the 2.4Ghz spectrum. The answer? Move on up to the next unlicensed spread at 5.7Ghz and begin again.

When he's not pondering the potential of the 500W 2.45Ghz radio transmitter in his microwave oven, Justin Ried writes about mobile technology for TheFeature.