--- DuBose Walt Civ AETC CONS/LGCA <[EMAIL PROTECTED]> wrote: > Greeings All, > > How hard is it to demodulate a 16QPSK as compaired > to a 8QPSK signal.
Demodulation...I think it is about the same. Carrier regeneration is a bit more complex. Decoding it is something else, but also doable. > And I have forgotten but does a 16QPSK signal will > allow for 6 bites per cycle? Four bits per symbol (constellation position). > Looking back at some very old hand written notes I > took at an HF conference at Scott AFB, IL where > Collins-Rockwell, Magnavox and Harris Comm Gp were > making presentations, they said that they all > agreeded that 45 baud (maybe 45.5) should be the > highest baud rate for the low end of the HF band and > even though you could go higher closer to the MUF, > if you needed a fixed buad rate, chose the one that > was the lowest. Certainly... Close to the MUF allows fewer rays, hopefully only one ray to propagate, which eliminates ISI. But there is still ionospheric doppler and noise/QRM to damage your received signal. > Thus, if you have a single tone/carrier with 16QPSK, > modulates at 45 baud, 1) what would its bandwidth be > and 2) what is the total bit rate for the signal? (I > would give you my answer; but think I might be > really wrong and you will question my math. Hi Hi.) Formulas are in "Communications Systems", by Carlson et al (4th Edition). Maybe "Digital Communications", by Bernard Sklar could help. Maybe taking a peek at Wikipedia could help. I do not remember the formulas in detail by heart... Making more complex constellations carries more price tags than you could think at first sight. First, a more complex constellation has more capacity, but beyond QPSK the distance between the constellation points gets smaller, and the BER for the same RECEIVED power gets worse (on a clean channel, say wire or microwave, leave alone a noise HF channel). Complex constellations should be meant for clean, non dispersive channels. You can get an idea by drawing circles around the canonical points of a constellation up to half the distance between them. As long as signal plus noise falls within that circle, it MIGHT be identified correctly. Beyond that, confusion reigns... BPSK and QPSK have the same distance between constellation points, beyond that, distance begins to decrease, be it nPSK or mQAM. Second, you can get a better SNR to maintain the same BER using more power. And even when dB's are dB's, a 3 dB increase in power is not a thing to take too lightly (ask NASA Deep Space...). On HF you can only beat noise by increasing power...or using a better antenna...a hard feat to accomplish at those wavelengths. Have you ever seen a video presentation of a conference given by Doug Smith, KF6DX at the Georgia Tech about digital voice? There are two versions, the highest quality video tales some 100 MB. It is interesting, and deals with many aspects of digital voice, DSP, etc. I liked it a lot. Very practical, with solid theoretical foundations. And there you can see someting that separate the pros from the rest. IMD on your transmitter becomes another source of noise, as it creates distortion products that interfere with your PSK or QAM signal. What works on PSK31 (say, -20 dB on John Doe's japanese transceiver) would not work wel enough for a more complex constellation. 73 de Jose, CO2JA __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/digitalradio/join (Yahoo! ID required) <*> To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
