Tuesday, April 08, 2008

The Old “Peak Speeds” Game Again

I'll have more to say on this in Communications Day next week – I need a little time for research – but it may as well be blogged as well.

Part of the ongoing muddying of the waters in Australia's WiMAX-versus-mobile debate comes from confusion about the intended applications of technologies (for example, fixed WiMAX is older than mobile and therefore it's obsolete).

But the misuse of speed specifications also plays a role here.
Hence we're told by breathless journalists that the next generation of LTE-based mobile cellular technologies will deliver speeds of 40 Mbps.

So if anyone's listening – it has to happen eventually – here's a three-second primer.

1) Peak speed is meaningless

The peak speed game is played over and over again: years ago, someone discovered that 802.11g (peak speed 54 Mbps) didn't deliver those speeds to end users. But the press still gets very excited at peak speeds. Whatever the 40 Mbps represents in LTE, it doesn't represent the user data download speed from a base station to a device.

2) Users share channels

This is not unique to cellular environments. In Ethernet, users eventually share the total available bandwidth (even if it's the backplane of the switch). In WiFi, users share the base station bandwidth. In DSL, users share the capacity of the DSLAM. In LTE, as in all cellular environments, users will share the data capacity of the cell. I'm still doing the research to put a number to this, but I can state categorically that a user will only get the base station's top speed if that user is the only one running data through the base station at any given moment.

3) Remember Shannon's Law

The 40 Mbps now carelessly cited all over the place for LTE is a best-case test result. Any white paper from the industry makes it clear that in LTE as in every communciations technology, Shannon's Law still holds true. In the case of cellular data, the practical upshot of this is that as you move away from the base station, your speeds drop.

4) Carriers provision services

The service speeds carriers eventually offer over LTE won't just depend on what the cells can do. They'll be constructed according to the different plans the carrier wants to offer. I'll bet a dollar, here and now, that carriers won't be rushing to sell users $29 mobile broadband plans with 40 Mbps download speeds.

So the next time someone says "the next generation of cellular wireless will give us download speeds of 40 Mbps", the correct answer is "bulldust".

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