[pskmail] Fwd: RE: [digitalradio] 16QPSK Modulation and Baud

  • From: Vojtěch Bubník <bubnikv@xxxxxxxxx>
  • To: pskmail@xxxxxxxxxxxxx
  • Date: Wed, 20 Sep 2006 17:07:57 +0200 (CEST)

Hi guys.

I hope this message may be of interest to all of you, especially to Rein. The 
description of choosing number of non acknowledged frames is quite detailed 
IMHO.

73, Vojtech OK1IAK

# ------------ Původní zpráva ------------
# Od: DuBose Walt Civ AETC CONS/LGCA <walt.dubose@xxxxxxxxxxxxxxx>
# Předmět: RE: [digitalradio] 16QPSK Modulation and Baud
# Datum: 20.9.2006 17:01:24
# ----------------------------------------
# I have talked to some scientist at a large research independent facility who 
are
# doing HF modem research for the government.  Here is some of what they
# believe...
#
# For a broadcast mode, use heavy FEC.  If the receiving stations have transmit
# capability, let them NAK missed data periodically.
#
# For individual or group connections, use a small to moderate amount of FEC 
with
# CRC and ARQ based on NAKs rather than ACKs.
#
# Start off with moderate FEC and send 3-7 frames depending on the length/size 
of
# your frame.  Short frames send 7, long frames send 3.  If no station sends a
# NAK, send 6-14 frames.  If no NAKS, send 12-28 frames, etc.  If at any time 
only
# one NAK from one station, resend the frame and continue on.  If you are for
# example sending 6-14 frames and receive two NAKs, back off to 3-7 frames.  If
# sending 12-28 frames and receive two or more NAKs, back off to 6-12 frames OR
# just drop back to 3-7 frames.
#
# They also recommend manually setting a real-time propagation index for the
# frequency used and base your baud rate on that or use a fixed baud rate for
# various MUFs or bands.
#
# There was much discussion among the group concerning using varying baud rates 
or
# a single baud rate.  About half felt that a 45.5 baud rate (or perhaps 31 baud
# rate) should be used on HF.  The other half thought that 31, 45, 90 and 180 
baud
# rates could be used.
#
# For their testing using a channel simulator close to a Watson channel 
simulator
# (they tested to a poor CCIR channel with varying fading, noise, etc. with a 
goal
# of 0 to -10 dB SNR).
#
# Their modem manually switched baud rates depending on the frequency (band) 
used
# and of course the band chosen was based on the projected path distance and 
MUF.
#
# Their transmission length were from 10-30 seconds.  I don't know how many 
frames
# they sent but I do know that a 10 second transmission took 15 seconds to 
decode
# with moderate to heavy FEC in the broadcast mode.  Their 30 second 
transmission
# produced a little over two pages (72-76 characters per line and 60 lines per
# page) of ASCII characters.
#
# They were getting 3 bits of information per tone and were using multi-tone.
# They said that  their "mode" use much like OFDM and I am almost sure they were
# using somewhere between 50-80 tones.
#
# Their ultimate goal was a full page of ASCII characters being "decoded" in 
less
# than 15 seconds in a broadcast mode.  The did mention the error rate but don't
# know what it was...but I am almost sure that had to be less than 1 character 
per
# page considering the type of information the system was to send.
#
# I wish I could tell you more, but the entire project is considered 
intellectual
# property by the research organization.
#
# Walt/K5YFW
#
# -----Original Message-----
# From: digitalradio@xxxxxxxxxxxxxxx [mailto:digitalradio@xxxxxxxxxxxxxxx]
# Sent: Tuesday, September 19, 2006 3:04 PM
# To: digitalradio@xxxxxxxxxxxxxxx
# Subject: Re: [digitalradio] 16QPSK Modulation and Baud
#
#
# Jose Amador wrote:
# > Taking adventage of SCS experience, they chose PSK
# > (cannot tell by heart if differential or not, a peek
# > to the manual is needed) as a modem, and depending on
# > the retry rate (closely related to BER) it tries more
# > complex constellations and more carriers. One of the
# > "secrets" is the switchover criteria...when retries
# > rise, then jump to the next "lower speed", whatever it
# > means.
#
# I think that FEC could be used wisely...
#
# For instance: Initially, use ARQ, with the modulation "A", working at
# "A" bauds. When retries rise, enable FEC dinamically. If it fails again,
# jump to the lower speed, or even to another stronger modulation (versus
# noise, I mean).
#
# When the retries diminish, it may try with more carriers, or more
# complex constellations, or more speed.
#
# The key is to do it automatically, or adaptatively. The switchover
# criteria is the most complex problem... but it could be reached even 
# with the trial and error mode.
#
# 73 de Nestor, CM3NA
#
# __________________________________________
#
# XIII Convención Científica de Ingeniería y Arquitectura
# 28/noviembre al 1/diciembre de 2006
# Cujae, Ciudad de la Habana, Cuba
# http://www.cujae.edu.cu/eventos/convencion
#
#
# 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)
#
#
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