Is 3G wireless doomed in cities?

December 29, 2009
Phorgy says yes:

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Is AT&T’s inability to provide decent wireless broadband in tech-savvy cities like New York and San Francisco a simple matter of physics? Phorgy says yes:

At low frequencies, radio waves are kind of like molasses. They can ooze around corners and through buildings…

As frequencies increase, the waves start acting more like laser beams. They no longer ooze around corners. You start to get “shadows” or dead spots with no signal. It becomes more difficult for the signals to penetrate walls etc. These problems get worse the higher you go in frequency…

So we have two extremes: low frequency molasses waves and high frequency laser beams. As bandwidth demands increase, we begin moving the dial away from molasses (where we have good wireless signals) to laser beams (where we have dark spots, shadows, with no signal, etc).

There are many clever modulation tricks that delay the inevitable, but the basic rule is that you cannot defeat Heisenberg.

The fundamental insight here is true: smartphones operate at very high frequencies, sometimes above 2.5 GHz. And covering a city with wireless broadband at those frequencies is hard. But after a brief email exchange with Ultimi Barbarorum’s Baruch, who knows much more about this kind of thing than I do, I’m far from convinced that what we’re seeing right now with AT&T has anything to do with the hard physical limits that Phorgy is talking about.

For one thing, Phorgy’s limit of 1,000mps in total for a few city blocks is I think far higher than anything AT&T is currently able to provide. With what Baruch calls “compression, prioritisation, all that level 4-7 stuff you can do at the packet level” (don’t ask me), you can serve a lot of people with that kind of bandwidth.

But more to the point, we already have a real-world counterexample which pretty much disproves any thesis that AT&T is bumping up against Heisenbergian limits. Phorgy’s saying that the problem with New York and San Francisco is that (a) they are very high density, complete with skyscraper canyons and the like; and (b) they have lots of people all trying to use 3G cellphones at once. But there’s a city with even higher density than either of those two, with even more people using 3G cellphones, and which has no signal-quality problems at all.

Tokyo is proof positive that this can be done.

The bottleneck is money, not Heisenberg. Building a Japan-style 3G network is extremely expensive: it involves lots of high-frequency and low-frequency base stations and base station relays and femtocells and backhaul capacity and IT investment and other things I don’t pretend to understand.

And of course this kind of investment doesn’t scale. If AT&T puts enormous of money into solving the problems of New York and San Francisco, they can use similar techniques in, um, Chicago. But nowhere else in the US has that kind of density — in contrast to Japan, where density issues are endemic.

If I were an AT&T shareholder, then, I’m not sure how much money I’d want my company to spend on beefing up 3G wireless in New York and San Francisco, especially when there’s little obvious return on such an enormous investment. Sometimes you make more money with cheaper unhappy customers than with more expensive happy customers. And this could well be one of those times.

Update: Some good comments, especially from Mark. Meanwhile, Paul Krugman asks whether central Tokyo might not be such a great counterexample after all: is it maybe less dense than Manhattan? Probably depends on how you define the two areas. But there are other cities which serve just as well: Hong Kong, for example.


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