Re: War causes in F&SF

On Tue, 11 Dec 2007 20:31:45 +0000 (UTC), Aaron Denney <wnoise@xxxxxxx>
wrote:
On 2007-12-11, Jasper Janssen <jasper@xxxxxxxxxxxx> wrote:
On Tue, 11 Dec 2007 05:08:42 GMT, fairwater@xxxxxxxxx (Derek Lyons) wrote:
"Keith F. Lynch" <kfl@xxxxxxxxxxxxxx> wrote:

Derek Lyons <fairwater@xxxxxxxxx> wrote:
"Keith F. Lynch" <kfl@xxxxxxxxxxxxxx> wrote:
The fact that Mission Control sometimes got "ratty data" and had to
figure out whether it was distorted in transmission or accurately
represented real problems in the capsule implies that it was analog.

That depends on the natures of ones digital link.

They knew about CRC and parity bits in the '60s,

They also knew, as you seemingly do not, that such things consume
volume, computer cycles, and power. None of these three things were
available in any great supply inboard an Apollo CM.

Not to mention the relatively low power of the transmitter.

Parity bits tell you when *one* bit flips. It doesn't detect *two* bits
flipping. And CRC is computationally very intensive, by that standard.

One parity bit tells you when one bit flips. More parity bits can do
more, including correcting errors. E.g.
http://en.wikipedia.org/wiki/Low-density_parity-check_code

Yes, but 8+2 is already losing a lot of speed to accuracy.

Jasper
.

Relevant Pages

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