John,
I think the memory arq which takes information from previous repeated corrupted
frames will avoid to have 6 tries but only one (at least I hope so).
An average of 2 bad frames is equivalent to a gain of 3 dB on the S/N of the
averaged frame.
Speaking of S/N and errors. The minimum S/Ns that I give for modes are obtained
with only gaussian noise and about 2 % errors. Giving a S/N for no error would
give very pessimistic results as under some noise there is rarely no error at
all (except for ARQ modes). So I have consider few errors (about 2 % but it's
only a goal). Moreover, in general when there is 2% of errors, the point when
the decoding becomes rapidly bad is very close. It is not linear at all, it's a
quick transition on 1 or 2 dB.
73
Patrick
----- Original Message -----
From: John Bradley
To: digitalradio@yahoogroups.com
Sent: Thursday, February 22, 2007 9:11 PM
Subject: Re: [digitalradio] ARQ FAE
the multiple repetitions of each packet worked in our favour last night,
since some took 6 tries to get thru
since conditions were so bad.
JOhn
----- Original Message -----
From: Patrick Lindecker
To: digitalradio@yahoogroups.com
Sent: Thursday, February 22, 2007 1:41 PM
Subject: Re: [digitalradio] ARQ FAE
Hello John,
TKS for info.
>managed to connect briefly on noisy conditions with N9DSJ, and using long
frames. would have worked better with short frames
Yes in long frames it works better where conditions are stable (as in 28,
50 or 144 MHz). In SW, it's better to have short waves.
I've just finished to implement a "Soft decision Memory Arq" (as in Pactor
but on carriers level not on bit level), which will limit mostly to one
repetition at worst. It will be interesting to see what happens with long
messages.
>would it be possbile , in future versions, to have the frame size switch
automatically, depending on signal strength?
>long frames worked well last night on 80, despite some considerable noise.
If the noise is constant, it is closed to a gaussian noise and it is
favorable. The problem is QRM and quick QSB, which is difficult to estimate.
73
Patrick
----- Original Message -----
From: John Bradley
To: digitalradio@yahoogroups.com
Sent: Thursday, February 22, 2007 5:17 AM
Subject: [digitalradio] ARQ FAE
patrick ...
managed to connect briefly on noisy conditions with N9DSJ, and using long
frames. would have worked better with short frames
but is great working under very marginal condx...
looking forward to more experiments hi hi are you going to try 20m this
weekend ?
John
VE5MU
----------------------------------------------------------------------------
No virus found in this incoming message.
Checked by AVG Free Edition.
Version: 7.5.441 / Virus Database: 268.18.3/697 - Release Date: 2/22/2007
11:55 AM
