Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request From: Peter Desnoyers Newsgroups: comp.dcom.telecom Subject: Re: Baud per Hertz Message-ID: <8772@accuvax.nwu.edu> Date: 7 Jun 90 16:36:00 GMT Sender: news@accuvax.nwu.edu Organization: Codex Corp., Canton MA 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 419, Message 8 of 11 bnrgate!.bnr.ca!hwt@uunet.uu.net (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. You can encode multiple bits per baud with amplitude and phase shift keying, and in fact every modem above 300 bits per second does so. The only limit here is Shannon's limit - bits/sec < 2*f*log2(S/N) where S is the signal power, N is the noise power, and f is the bandwidth. However, a baud is not a bit. By the Nyquist theorem, you can only get 2f bauds per second. In practice high-speed modems such as V.32 run at about 2500-3000 bauds/sec over lines with a 3000Hz bandwidth. >Still, in the real world 7 baud on 5 Hz is very good! 9600bps over 3000 Hz is a good deal better, and is quite common. Peter Desnoyers