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Proposed coded telemetry format for AO40



Over the past few months I have been developing a proposed new PSK
telemetry format for AO-40.

My format uses strong error correction coding and interleaving to
provide substantially better performance on noisy, fading channels
like those encountered with AO-40 when squint angles are bad and spin
fading is severe. The specific error coding techniques are taken
directly from established deep space practice and trace their lineage
to the Voyager spacecraft launched in 1977.

To these standards I added an additional level of interleaving to
combat the spin fading we experience on our spacecraft. Even the sync
vector is interleaved and spread across a frame to keep a short fade
from taking it out.

I have set up a web page to document this format. Besides a detailed
description of and rationale for the format, there is also a C
reference implementation and two sample sound files.  One contains a
frame directly from the transmitter, the other contains the same frame
with rapid deep fading and noise added by a channel simulator. The
frame is so noisy it can be barely heard by ear, but it is still
easily decoded without errors.

If this proposal is accepted, much work would remain before it could
become operational. The encoder would have to be implemented in IPS
and integrated into the spacecraft IHU software, and
demodulator/decoder software would have to be integrated into the
various telemetry reception programs such as AO40RCV. But I wanted to
put out this announcement to let people know what I've been up to, and
to give people a feel for the potential benefits of this new mode.

In addition to its potential use on the beacon, this mode is entirely
suitable for direct use by user stations through the transponder.

The URL is http://people.qualcomm.com/karn/ao40/ I will update this
page with software components as I release them.

73, Phil
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