On Tue, 24 Aug 1999, James Cameron wrote:

> Assuming I'm going to be generating between two to eight words of twelve
> bits each in a data stream over a remote control UHF link, what sort of
> checksum or CRC is appropriate?
>
> I get the impression that calculating a checksum or a CRC on such small
> data streams might be ineffective, because of the probabilities
> involved.
>
> For example; sending 24 bits of data followed by a 12 bit arithmetic
> checksum ... the chances of corruption affecting one of the 24 bits and
> then also one of the 12 bits of checksum to mask the corruption seem to
> be higher.
>
> I'm not exactly sure how to express this ... but is there a concern?

James,

Read up on ECC's (error correction codes). ECC's are used to identify
and/or fix errors in one or more bits much in the same way a parity bit is
used as a simple integrity check. For 2^n bits, you need n extra bits to
identify and fix single bit errors. So in your case, 5 extra bits are
needed. The downside is that they're computationally more difficult than
CRC's. The upside (for this amount of data) is that they're more efficient
from a bandwidth point of view.

Scott