On Fri, Aug 10, 2012 at 10:48 AM, bill <[email protected]> wrote: > How long does it take from the time Curiosity takes a pictures/processes > it for transmission to reception by NASA? > > Is the picture sent in segments and does NASA use a 'checksum' type system > to make sure of proper reception. > > Today's pics were better than I took of my dogs yesterday, and they were > just a few feet away from me lying in my lawn! >
I presume you want a serious answer. No, they do not use a "checksum" system because it takes too long to send back a NAK to say, "sent that one again." (It is a 20+ minute round trip for the radio signal.) They actually use forward error correction with enough redundancy so that, when the bits arrive back on earth, even if some of them are wrong, the receiver can correct the errors so an error-free data block (or part of a picture) is recreated in the receiver. In ham radio we have a couple of systems that work this way, e.g. Olivia, MFSK16, Contestia, DominoEX/FEC, Thor, MT63, JT65, WSPR, etc. That is why they get good copy on a poor signal without having to retransmit the data. -- Brian Lloyd, WB6RQN/J79BPL 3191 Western Dr. Cameron Park, CA 95682 [email protected] +1.767.617.1365 (Dominica) +1.916.877.5067 (USA) _______________________________________________ Flexedge mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz This is the FlexRadio Systems e-mail Reflector called FlexEdge. It is used for posting topics related to SDR software development and experimentalist who are using beta versions of the software.
