Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request From: mitel!spock!meier@uunet.uu.net (Rolf Meier) Newsgroups: comp.dcom.telecom Subject: Re: Baud per Hertz Message-ID: <8807@accuvax.nwu.edu> Date: 8 Jun 90 14:32:09 GMT Sender: news@accuvax.nwu.edu Reply-To: Rolf Meier Organization: Mitel. Kanata (Ontario). Canada. Lines: 32 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 10, Issue 422, Message 2 of 8 In article <8731@accuvax.nwu.edu> Henry Troup writes: >In article <8683@accuvax.nwu.edu> Rob Warnock writes: >>...(Pushing a 7 baud signal through a 5 Hz pipe is >>quite good! The theoretical maximum is 2 baud/Hz: one state for each >>half-cycle of bandwidth.)... >I don't see a theoretical limit, not if you allow phase modulation. >For real phase discriminators and real lines there certainly are >limits, but in theory you could shift each half cycle by as fine an >increment as you could measure ... I guess Heisenberg limits that >somewhere, but not for a long time. Not Heisenberg, but Shannon sets the limit. The theoretical maximum is: max bit rate = bandwidth x log(2)(1 + S/N) where S/N is the signal to noise ratio log(2) is log base 2 (not 0.30103 :-)) For example, using a normal telephone line with a 3 kHz bandwidth and a 60 dB (1000:1 for the formula) S/N ratio, you can in theory transmit 30,000 bits/sec. You can use phase, frequency, or amplitude modulation. The maximum bit rate is reached when you can no longer resolve the signal variation due to noise. Rolf Meier Mitel Corporation