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Re: TDMA - Reading the mail

>That's correct!  Additionally difficult is how to assign the slots.  I
>suppose the satellite would do that, but how when there are hundreds of
>stations calling at once?

See my last message. The satellite would *not* assign the timeslots,
although by periodically injecting a telemetry frame it might *define*
the timeslots.

The simplest distributed algorithm I can think of for allocating
timeslots works like this:

The station wanting to transmit picks an empty timeslot at random.  It
transmits a message on this slot to claim it. If it hears this message
come back from the satellite, it assumes everyone else did. Otherwise
it picks another slot and tries again, probably after waiting a short
random interval.

Because the amount of time a station will need a time slot will vary,
we might want to define some slots for one-shot use only, effectively
using slotted Aloha on these slots.

Propagation delay is an important factor in the performance of these
schemes. That alone is a strong argument for LEO satellites vs high

I need to do some more reading here. Multiple access schemes such as
the ones we're talking about here have been heavily studied since at
least the mid 1970s and there is a rich body of literature out there.


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