[amsat-bb] Re: BBsat Call for ideas
Timothy J. Salo
salo at saloits.com
Sun Nov 30 14:32:12 PST 2008
Greg D. wrote:
> Ah, but how does one know that a time slot is not being used?
> With many stations on the ground, there is a good chance that
> multiple stations will pick the same "empty" slot to be theirs,
> and we're back to collisions.
For good performance, some sort of media-access control (MAC)
protocol is required. Time-slotted protocols have a lot to
be said for them, although some have suggested using a CDMA
protocol. You could create a system that assigns time slots
to active ground stations. But, if these stations are generating
very bursty traffic, like voice, a lot of the uplink bandwidth
may be wasted. In general, I think this is what I call a "hard
problem" (i.e., we don't know how to solve it [yet], and
perhaps nobody else does either).
> So, this is what I was talking about when I suggested, as
> essentially you do, to work on a prototype of the ACP messaging
> system that is being proposed for Eagle.
I think this is a great idea.
Unfortunately, as far as I can tell, all development work on
the Eagle and the ACP ceased several months ago. The
Microwave Engineering Project (MEP) is or might become, in
some vague sense, a terrestrial variant of the ACP.
I am hopeful that at least some of the work on the MEP
will be applicable to the ACP.
> There are two significant technical challenges that I see,
Actually. I think there are a quite a few technical challenges
> and the protocol used to facilitate fair and resilient access
> to the satellite by all the ground stations it overflies is one.
> ... I haven't checked, but has the Eagle team published their
> protocol for doing this? ...
The team developing the ACP ground station made pretty much
everything they wrote freely available online. [What a
concept!} Unfortunately, they didn't get all that far before
work ceased. See the ACP ground station Web site:
> The other challenge is the modulation system ...
You might look at these two documents:
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