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<title>RE: [hfsig] What can you do with an OFDM signal in a 3.5 KHz bandpass?</title>
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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Here are some first thoughts on estimating
OFDM throughput over a voice bandwidth channel.</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Here are some assumptions:</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>12 audio channels (carriers), spaced at
multiples of 100 Hz over the audio band.</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Each carrier is DPSK modulated,
differential phase shift keying, 4 different phase angles, therefore encoding
two bits per symbol period (2 bits per baud).</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Baud rate is 100 per second.</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>So the net raw throughput is 12 carriers x
2 bits/symbol/channel x 100 symbols/second or 2400 bits per second.</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>However this is the raw data rate. This
gets reduced by several factors—</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Protocol overhead within each packet, that
is, need for headers, send sequence numbers, checksums, etc.</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Coding overhead, that is, need to send
extra bits, implementing some form of FEC, forward error correction.</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Ack/nak time, that is, need to stop
sending periodically to allow the receiving unit to acknowledge packets.</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Poor transmission conditions, which often
cause one more more of the 12 carrier channels not to be useful in transmitting
data.</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>50% net throughput might be a goal in good
HF conditions—that is, equivalent of 1200 bps.</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Many of the above details could be changed
or optimized but my guess is that the above is not off by a large amount.</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Comments from those with experience in
this area would of course be welcome.</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<div>
<p class=MsoAutoSig><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Kerry Berland</span></font><font size=2
color=navy face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:navy'> @ home</span></font></p>
<p class=MsoAutoSig><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>kberland@ix.netcom.com</span></font></p>
<p class=MsoAutoSig><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>773-267-1563</span></font></p>
</div>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal style='margin-left:.5in'><font size=2 face=Tahoma><span
style='font-size:10.0pt;font-family:Tahoma'>-----Original Message-----<br>
<b><span style='font-weight:bold'>From:</span></b> hfsig-bounces@lists.tapr.org
[mailto:hfsig-bounces@lists.tapr.org] <b><span style='font-weight:bold'>On
Behalf Of </span></b>tattje<br>
<b><span style='font-weight:bold'>Sent:</span></b> Saturday, August 20, 2005
3:14 PM<br>
<b><span style='font-weight:bold'>To:</span></b> TAPR HF Modes SIG Mailing List<br>
<b><span style='font-weight:bold'>Subject:</span></b> RE: [hfsig] What can you
do with an OFDM signal in a 3.5 KHzband pass?</span></font></p>
<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'> </span></font></p>
<div>
<p class=MsoNormal style='margin-left:.5in'><font size=2 color=blue face=Arial><span
style='font-size:10.0pt;font-family:Arial;color:blue'>The POTS will give you 56
kbit/sec in the same bandwidth.</span></font></p>
</div>
<div>
<p class=MsoNormal style='margin-left:.5in'><font size=2 color=blue face=Arial><span
style='font-size:10.0pt;font-family:Arial;color:blue'>Using OFDM some channels
will not be available, fec is not enough, so one has to spread the info over
all the channels.</span></font></p>
</div>
<div>
<p class=MsoNormal style='margin-left:.5in'><font size=2 color=blue face=Arial><span
style='font-size:10.0pt;font-family:Arial;color:blue'>Reread the fs-1052, why
do you think are so many different throughput speeds defined?</span></font></p>
</div>
<div>
<p class=MsoNormal style='margin-left:.5in'><font size=2 color=blue face=Arial><span
style='font-size:10.0pt;font-family:Arial;color:blue'>10 kbits in 3 kHz? Forget
it, may be sometimes, but not always.</span></font></p>
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<div>
<p class=MsoNormal style='margin-left:.5in'><font size=2 color=blue face=Arial><span
style='font-size:10.0pt;font-family:Arial;color:blue'>HF is a naughty channel,</span></font></p>
</div>
<div>
<p class=MsoNormal style='margin-left:.5in'><font size=2 color=blue face=Arial><span
style='font-size:10.0pt;font-family:Arial;color:blue'>Regards</span></font></p>
</div>
<div>
<p class=MsoNormal style='margin-left:.5in'><font size=2 color=blue face=Arial><span
style='font-size:10.0pt;font-family:Arial;color:blue'>Henk</span></font></p>
</div>
<blockquote style='margin-top:5.0pt;margin-right:0in;margin-bottom:5.0pt'>
<p class=MsoNormal style='margin-right:0in;margin-bottom:12.0pt;margin-left:
.5in'><font size=2 face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>-----Oorspronkelijk
bericht-----<br>
<b><span style='font-weight:bold'>Van:</span></b> hfsig-bounces@lists.tapr.org
[mailto:hfsig-bounces@lists.tapr.org]<b><span style='font-weight:bold'>Namens </span></b>DuBose
Walt Civ AETC CONS/LGCA<br>
<b><span style='font-weight:bold'>Verzonden:</span></b> vrijdag 19 augustus
2005 22:25<br>
<b><span style='font-weight:bold'>Aan:</span></b> 'TAPR HF Modes SIG Mailing
List'<br>
<b><span style='font-weight:bold'>Onderwerp:</span></b> RE: [hfsig] What can
you do with an OFDM signal in a 3.5 KHz band pass?</span></font></p>
<p style='margin-left:.5in'><font size=2 face="Times New Roman"><span
style='font-size:10.0pt'>When talking to EOC, disaster relief and military
contingency personnel about HF data modes, they no longer ask how many words
per minute is it, now they are asking how many pages per minute is your
capability.</span></font></p>
<p style='margin-left:.5in'><font size=2 face="Times New Roman"><span
style='font-size:10.0pt'>We can no longer think in WPM capability; but rather,
pages per minute (ppm).</span></font> </p>
<p style='margin-left:.5in'><font size=2 face="Times New Roman"><span
style='font-size:10.0pt'>73,</span></font> </p>
<p style='margin-left:.5in'><font size=2 face="Times New Roman"><span
style='font-size:10.0pt'>Walt/K5YFW</span></font> </p>
<p style='margin-left:.5in'><font size=2 face="Times New Roman"><span
style='font-size:10.0pt'>-----Original Message-----</span></font> <br>
<font size=2><span style='font-size:10.0pt'>From: hfsig-bounces@lists.tapr.org
[<a href="mailto:hfsig-bounces@lists.tapr.org">mailto:hfsig-bounces@lists.tapr.org</a>]On
Behalf Of DuBose Walt Civ AETC CONS/LGCA</span></font> <br>
<font size=2><span style='font-size:10.0pt'>Sent: Friday, August 19, 2005 2:41
PM</span></font> <br>
<font size=2><span style='font-size:10.0pt'>To: 'hfsig@lists.tapr.org'</span></font>
<br>
<font size=2><span style='font-size:10.0pt'>Subject: [hfsig] What can you do
with an OFDM signal in a 3.5 KHz bandpass?</span></font> </p>
<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'> </span></font></p>
<p style='margin-left:.5in'><font size=2 face="Times New Roman"><span
style='font-size:10.0pt'>What can you do (what RAW throughput) can you get in a
3.5 Khz bandwidth using an OFDM mode? </span></font><br>
<font size=2><span style='font-size:10.0pt'>Here's what I found using some
figures based on the FS-1052, Appendix A modem. </span></font><br>
<font size=2><span style='font-size:10.0pt'>Your User Throughput will be
determined on how much RAW througput you use for FEC. </span></font><br>
<font size=2><span style='font-size:10.0pt'>Walt/K5YFW </span></font><br>
<font size=2><span style='font-size:10.0pt'> </span></font><br>
<font size=2><span style='font-size:10.0pt'> </span></font> </p>
</blockquote>
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