[LINK] Google's WiFi bungle

Bernard Robertson-Dunn brd at iimetro.com.au
Tue May 18 11:59:56 AEST 2010

On 18/05/2010 11:31 AM, Richard Chirgwin wrote:
> But - here's where I need a technologist to confirm my understanding -
> changing channels is one of those things WiFi does. Isn't "frequency
> hopping spread spectrum" in the definition?

In WiFi, channel is not the same as frequency.

Each channel uses spread spectrum techniques. There are two main 
mechanisms - Direct-sequence spread-spectrum, which "smears" the energy 
over a  frequency range The other, frequency-hopping spread spectrum 
</wiki/Frequency-hopping_spread_spectrum>, pseudo-randomly re-tunes the 

In both cases the channel relates to the way the signal is spread and 
de-spread. Multiple channels can (do) occupy the same frequency range.

> So what I suspect is the "changing channels five times a second" is just
> blowing smoke to create a general fog to confuse the media. Or am I
> horribly mistaken?

When Google say that their in-car WiFi changes channel five times a 
second they are implying that they do listen very long on a particular 
channel and therefore don't gather much information from each user.

It's an effort to make the case that they have not been collecting user 
"payload" data.

If you haven't seen Google's official response (as opposed to media 
reports), there is a copy here.


> RC
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Bernard Robertson-Dunn
Canberra Australia
brd at iimetro.com.au

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