[e2e] Collaboration on Future Internet Architectures
David P. Reed
dpreed at reed.com
Thu May 3 07:18:47 PDT 2007
Jon Crowcroft wrote:
> 1/ some people have claimed that one can build many-to-many multihop radio
> systems that offer more capacity as the number of nodes join. If this is true,
> this can operate within quite a narrow band (e.g. ISM) and should be sufficient
> for a very long time. If we can show its true in that band, other bands can
> follow - within regions we still need to multipelx spectrum in some hard non
> liquid (dave reed) way just til some of the technology is better the identifiers
> and management of this could be done through Virtual Private Wireless Channel
> Idenfiers which might use some name space we have seen before
A linear growth in capacity as nodes join probably does not provide more
capacity per node. The simple model one might imagine achieving is:
Cap[System] = o(M*W*log(S/N)) where M is the number of nodes, W is the
bandwidth, and S is signal power per station. It is actually unknown
whether this is an upper bound, if only because the standard analysis
presumes that the noise process is independent at each receiver, an
overly non-physical and way-too-conservative-assumption by a factor
likely o(M^k) where k is >= 1.
The per-node capacity in this hypothetical conservative model is thus
Cap[node] = o(W*log(S/N)), and as you can see from that the English
language translation would be "narrow band radio sucks!" or "narrow band
radio is good for cooking!" W is a limit, unless you want to fry any
biological organisms in the field who respond not o(log(S)) but o(S).
In other words, the reason for multiplexing a wideband system is that
everyone can potentially achieve much higher burst rates without turning
the world into a microwave oven.
This is the same reason that packet systems rather than rate-limited
systems are better for many applications other than 3 kHz telephony -
around which one might believe the entire communications incumbency
rallies every time its government or god granted monopoly is threatened
by technology change.
But there are still people out there who reason that "no one will ever
need more bits per second than a human can type or a human can read",
and US Senators who babble about Internets made of clogged pipes.
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