Path: utzoo!utgpu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!ists!sparrms!sparatd!mb From: mb@sparrms.ists.ca (Mike Bell) Newsgroups: comp.dcom.modems Subject: Re: Capacity of a Channel Summary: Answer to analog telephone channel capacity still sought... Message-ID: <1990Dec13.145323.22223@sparrms.ists.ca> Date: 13 Dec 90 14:53:23 GMT References: <1990Dec10.162413.13959@sparrms.ists.ca> <4986@optilink.UUCP> <1990Dec12.154139.20496@sparrms.ists.ca> <1990Dec13.061040.6753@ims.alaska.edu> Organization: Spar Aerospace Ltd, Toronto, Canada Lines: 36 [This thread is getting complicated and it is no longer clear who is quoting what about whom... I find myself getting quoted as making the replies to my own posting... We hope we're not schizophrenic, but...] To summarise: Shannon gives: (note 0 noise = infinite capacity for >0 Bandwidth) ++++ Channel Capacity = Bandwidth * log2( 1 + SignalPower/NoisePower ) on telephone links involving digital transmission, we know that the maximum channel capacity is <=56Kbps (since this is the information flow rate of the digitized signal). On an analog link, a realistic Signal/Noise ratio (and thus the capacity limit imposed by the analog part of the link) is still open to bidders, since the dBrn figures turned out to be noise power figures, not S/N ratios. Any offers here? Nyquist still seems to be misunderstood/misquoted: my understanding is that the theorem states that: a signal whose highest frequency is F can be reconstructed non-ambiguously from samples taken at a sampling rate of 2F. (The samples, of course, will each require an infinite number of bits (I) to represent them exactly - giving rise to an information flow rate of 2FI. :-) [Please correct me: should that be a bandwidth limited signal?] Hopefully (once the analog S/N figures are known), we can lose all the discussion which says that "you can't do that because Nyquist and Shannon and ... say you can't", when that isn't what was said they said. [If there is a comp.dcom.telecom.standard.answers, a summary of all this should be in it...] -- Mike --