Re: WiMax whats up?

[David Farber <dave () farber net>]

Begin forwarded message:

From: Christian Huitema <huitema () windows microsoft com>
Date: September 1, 2008 12:18:35 PM EDT
To: "dave () farber net" <dave () farber net>
Subject: RE: [IP] Re:     WiMax whats up?

> To feed the {I'd guess} several hundred WiMAX towers in say the DC/ 
> Balt
> market, you'd need 100MB/s backhaul from each to the Big Kuhuna. Is  
> that
> going to come from the Bandwidth Fairy, nightly leaving a bucket of
> packets under the site's pillow?

That may explain the interest in wireless backhaul, which I understand  
is what Clearwire uses (http://www.unstrung.com/document.asp?doc_id=154063&f_src=unstrung_FinancialContent 
).

We heard a lot about wireless limitations, but we can also look at  
wireless successes. The progress of the Wi-Fi technology has been  
impressive. First, we saw the transition from direct sequence  
(802.11b) to OFDM (802.11a, 802.11g), getting about 5 times more bit  
per Hertz in the same condition. With 802.11n, we are getting MIMO,  
which uses multiple simultaneous radios and antennas in the same  
frequency to further increase the bandwidth. The interesting part  
about MIMO is that with multiple antennas we can obtain multiple  
independent channels between two points, and effectively bypass the  
single channel limit predicted by Shannon's theorem. The visible  
result is that, for short range networks, Wi-Fi bandwidth is likely to  
follow Moore's law.

The same technologies are being used in 3G, 4G and WiMax systems.  
Indeed, the competition with WiMax has significantly accelerated the  
technology adoption curve by 3G and 4G providers. We are not at Wi-Fi  
speed there, and probably never be, since long range transmission  
always will be more difficult than short range. Spectrum sharing is  
also an issue, since contention based access like Wi-Fi is highly  
sensitive to transmission latency. In practice, that means that  
cellular system need to operate on licensed spectrum, on relatively  
narrow channels. But Moore's law is at work there as well, and we can  
expect the cellular bandwidth to easily match copper based DSL, and  
eventually bypass it.

The good old point-to-point microwave transmissions are evolving as  
well, and can be used between tall buildings, or between towers. There  
are multiple systems available today, some operating on licensed  
frequencies and some operating on unlicensed spectrum, e.g. 60GHz.  
Again, these technologies improve with Moore's law. You can buy  
systems today that provide Gigabit transmission, and I expect to see  
more in the future. Cellular and WiMax are clearly creating a market  
for these products.

So, I can see that in quite a few places, people are going to drop the  
DSL and use wireless instead, just like they are dropping landlines  
for cell phones. We might get some competition after all.

-- Christian Huitema





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