[Namaste-dev] FH-CDMA uplink

Howie DeFelice howie at aosusa.com
Tue Jul 1 12:39:51 PDT 2008


I couldn't agree more with Bob's assessment of the uplink. Giving the
transponder a channelized appearance will certainly make operation
easier to understand and use. Since the receivers are SDR, there is no
reason channel bandwidths couldn't be changed individually so that high
performance class ground stations had access to a larger variety of
bandwidths (channels) than lower performance earth stations. 

Along those lines, I was thinking there might be a benefit to adopt a
standard DVB-S downlink format, mapping channels into PIDs in the
downstream frame. The largest single benefit of this is that it allows
beginners to assemble a receive only earth station using very low cost
parts; i.e. PCI bus DVB receive card (under $100), C-band LNB (under
$50), small antenna (under $50). What would be needed is the magic
software that pulls the data out of the PIDs and sends them to the
appropriate codec or socket. I did a link budget based on a 2Mbps
downlink using 3/4 rate viterbi with 188/204 Reed Solomom, QPSK
modulation and the link closed into a .6 meter antenna. I used some of
the worst case parameters discussed on the message board. When I needed
to estimate parameters, I used typical Intelsat specs for global beam
edge of coverage.

OK, I know that build-it-yourself ground stations was not part of the
design criteria, but I thought it was worth putting out there for
discussion...

Howie
AB2S



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