Now this has my wholehearted support. YEAH! I knew we would agree on
something sooner or later.
Ten years ago, I wrote a full FS-1045A demodulator and decoder and I
wrote the government's first general purpose computer-DSP based Mil Std.
188-110-A1 demodulator (with a guy name Greg Klassen) and began the A3
but we did not finish. I am giving up on A3 in favor of doing an OFDM
based on turbo trellis coded modulation, designed specifically for the
fading environment. Frank and I are experts in MAP (maximum a
posteriori) signal processing, having done it since the late 70's and
80's so the TTCM is right up our alley. The "EM" or "Dempster"
algorithm was developed by the place Frank and I work (worked) years
before it saw the light of day. I used these techniques at the request
of Ed Posner and Lew Allen to secretly demodulate the Venus Vega Balloon
probe signals even though we promised "them" we would not record them.
;-) The MAP I did was a fully nonlinear filtering and smoothing
model for the PLL to track the residual carrier from the balloon. Every
extra tenth dB was needed to get the Viterbi decoder to pick the right
paths (to bad we didn't do MAP for that!). Maureen Quirk wrote the
Viterbi decoder. Did you know Posner before he died or Quirk when she
worked there? She got wrapped around the SETI axle there and took
deliverance when her husband was put on the Princeton faculty and she
landed a tenure position at the Institute where we work. Ed was the
chief engineer of the DSN and an indomitable force at JPL and taught
information theory at Cal Tech. I don't know how long you have been there.
There is a group doing this SDR/modem work already and that has been
taking up some of my time. This is sponsored by the ARRL SDR working
group and the ARRL HSMM working group. We believe we can achieve 10^-5
BER with 5 dB Eb/N0 on a truly nasty channel. I will be bringing my
FS-1045A c code out of the dark, and releasing it soon. Frank and I
intend (the ARRL work I just mentioned) doing the ALE from it (the
hailing waveform and protocol) and to set up channels and initiate the
follow on. We intend communicating all sorts of stuff in the "UUF" user
unique fields which could include coordinates, etc. at the users
request. This would be extremely interesting to all sorts of folks as
you can surely imagine. The ALE does not need to be tied to the
follow-on modem of course. It can initiate CW or SSB for that matter!
I hope the JPL folks are interested in pursuing this as you could surely
help one of the principals involved in this work, KD6OZH, even though he
is 200 miles away in Fresno in particular, and all of us in general.
Bob
Jim Lux wrote:
At 08:43 PM 9/13/2005, Jim Lux wrote:
Something to throw into the requirements pot:
It sure would be nice if the SDR (software) supported MIL-STD-188 style ALE
(-141) and digital comm (-110). Not that it should be a part of the SDR,
but whatever interfaces there are should support it.
On the performance testing aspect, I haven't gone through the recent test
results Bob posted, nor, for that matter matched up the QST test results
against MIL-STD-188, but if someone else has already done that, it would be
useful.
I suspect that the run of the mill ham rig won't meet the requirements of
188 (certainly, my old FT-757 doesn't meet the frequency stability
requirement), but the SDR might.
One further note... if we wanted to actually do some verification testing
against MIL-STD-188 towards the end of providing EMCOMM with SDR, I'm sure
that the JPL amateur radio club could devote some of its considerable
technical resources to the activity. Not only do we have access to the
required test equipment, but we also have people who have the measurement
expertise.
James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875
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