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Tech Head - The Technology Section
Einstein's Alcove
Pioneer missions & one last attempt to contact P10.
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<blockquote data-quote="spiney" data-source="post: 159678" data-attributes="member: 192438"><p>Anyway, whatever, the problem of sending/receiving data from distant spacecraft is the same - in principle - as digital tv !!!</p><p></p><p>Convolutional codes are used, so a limited number of "already known" data words can assessed for "reception probability". In digital tv, that's same as "outer coding". "Inner coding" isn't used for spacecraft, (I think!), because we don't want to transfer lots of numeric data using "wasteful" (!) CRC codes, just receive from as far away as possible!</p><p></p><p>As spacecraft gets further away, within a power-limited bandwidth-limited communications channel, it's possible to keep slowing down the data transmission speed, to keep "received error" probability low, until the Shannon "minimum rate" is finally reached, after which the link finally fails!</p><p></p><p>See: <a href="http://deepspace.jpl.nasa.gov/technology/95_20/95-20.pdf" target="_blank">http://deepspace.jpl.nasa.gov/technology/95_20/95-20.pdf</a> , especially fig 10.</p></blockquote><p></p>
[QUOTE="spiney, post: 159678, member: 192438"] Anyway, whatever, the problem of sending/receiving data from distant spacecraft is the same - in principle - as digital tv !!! Convolutional codes are used, so a limited number of "already known" data words can assessed for "reception probability". In digital tv, that's same as "outer coding". "Inner coding" isn't used for spacecraft, (I think!), because we don't want to transfer lots of numeric data using "wasteful" (!) CRC codes, just receive from as far away as possible! As spacecraft gets further away, within a power-limited bandwidth-limited communications channel, it's possible to keep slowing down the data transmission speed, to keep "received error" probability low, until the Shannon "minimum rate" is finally reached, after which the link finally fails! See: [url]http://deepspace.jpl.nasa.gov/technology/95_20/95-20.pdf[/url] , especially fig 10. [/QUOTE]
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Tech Head - The Technology Section
Einstein's Alcove
Pioneer missions & one last attempt to contact P10.
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