Home Brew StarTrek Communicator

Dean Collins Dean at cognation.net
Tue Jun 12 14:59:50 CEST 2007

Hi Ian,
Thanks for your input.

As discussed in the article the concept of the "freespace" is to
allocate bandwidth to devices that meet 'requirements' but is otherwise

Maybe it didn't come across in the blog but the idea is that in this
space you can build alternative devices no longer controlled by a single
entity like the carriers.

But yes your comments about people stepping outside the rules are valid
- hopefully you'll be able to join the conference call with your
thoughts next week.



Dean Collins
Cognation Pty Ltd
dean at cognation.net
+1-212-203-4357 Ph
+61-2-9016-5642 (Sydney in-dial).


> -----Original Message-----
> From: Ian Stirling [mailto:OpenMoko at mauve.plus.com]
> Sent: Tuesday, 12 June 2007 8:55 AM
> To: Dean Collins
> Cc: OpenMoko
> Subject: Re: Home Brew StarTrek Communicator
> Dean Collins wrote:
> > With the FCC 700 mhz spectrum coming up soon I thought some of you
> > like to join us for the Yi-Tan call next week?
> >
> > http://deancollinsblog.blogspot.com/2007/06/home-brew-startrek-
> communicator.html
> >
> Unfortunately.
> Part of the reason mobile phones work reasonably well - 2W will get
> some 15Km or so in good conditions - is that they have relatively low
> and controlled noise levels.
> The towers can have beam shaping and are closely planned, so they
> interfere overly with each other.
> The transmissions are closely scheduled, so that interference is
> reduced.
> With no regulation, people will want applications like - for example -
> streaming music from their home server.
> Collision avoidance technologies help a little.
> But the problem is that you can't do collision avoidance of signals
> can't recieve. But those signals still interfere.
> Consider an infinite plane of trancievers, evenly distributed.
> As you go away from the source, the contribution of an individual
> transmitter to your noise level falls off as the distance squared.
> But, the number of sources increases as the distance squared too.
> The noise sums to infinity.
> In practice, it won't be quite that bad - 700Mhz doesn't have infinite
> range, but it can reach hundreds of kilometers especially in some
> atmospheric conditions.
> I don't know how wide the band that is proposed is - say 20Mhz.
> Using really good coding, in good channel conditions, you may get 20
> megabytes a second.
> Neglecting distant interference, and assuming collision avoidance
> - you get possibly 10 megabytes/sec shared amongst the users.
> With a 2Km range (say) - if you've got phones scattered every 100m,
> there are 300 or so phones in range.
> It doesn't take more than a few percent of these users to be doing
> like streaming MP3 radio before it basically stops working.
> And then you get people who when their connection stops working, they
> ramp up the power, or ignore collision avoidance.
> It also gets worse as as the noise level rises, the bitrate drops
> Mobile phones don't really have these problems, as they are closely
> controlled by the operator.

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