[e2e] Overly Overlay; Peer to peer is commonplace

[David P. Reed]

At 04:10 PM 1/2/2002 -0600, Nitin H Vaidya wrote:
>Yes, you are right that channel capacity can grow with N
>Does that necessarily mean that bit rates of different "links"
>are independent? I did not think so, but I could be
>mistaken, particularly, considering that I did not know that the
>capacity can grow *linearly* with N without imposing some constraints.
>Does this result require some assumptions about the channel, or receivers?


This is really not understood completely.  One set of approaches involves 
taking advantage of diffusive media (multipath is your friend!) to make the 
transmission matrix full-rank.  I am not aware that this is the only case 
that applies.  There are folks actively working on more general theories.

An interesting pair of articles in Science led me to this area, which has 
(as far as I know) been pioneered mostly by folks at AT&T Bell Labs 
(Foschini & Gans).  Three online references (the first two may require you 
to register/have a membership in AAAS):

Moustakas, et al. Communication Through a Diffusive Medium: Coherence and 
Capacity (http://www.sciencemag.org/cgi/content/abstract/287/5451/287)

Stuart, Dispersive Multiplexing in Multimode Optical Fiber 
(http://www.sciencemag.org/cgi/content/full/289/5477/281)

Foschini & Gans, On the Limits of Wireless Communications in a Fading 
Environment when Using Multiple Antennas 
(http://www.bell-labs.com/project/blast/wpc-v6n3.pdf)

Gupta and Kumar have combined some of these ideas with their models of 
multihop repeater network capacity models, to derive a class of networks 
that scale faster than the sqrt(N) scaling that they proved was the maximum 
for networks that treat wireless connections as wires - I can't find their 
workshop paper from this fall at the moment.








- David
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