Coding Theory: No more to do

Erica Klarreich from Science News reports on how coding has almost reached the Shannon limit.

The Shannon limit (for Claude Shannon who discovered it) tells how efficient a code can be so that the original message can be recovered from a digitized version of the message. Take the message, put it into bits, and transmit it. When you receive the message some of the bits may have (likely will have!) errors. Coding theory has devised many clever ways to send the data bits with extra bits to correct the errors, at some efficiency. Not long ago, that efficiency was much less than what was theoretically possible.

Now, two engineers have discovered Turbo Codes that get close to the Shannon limit. What's more, an older discovery called low-density parity-check (LDPC) coding could get even closer.

So, much of what engineers spent careers trying to do can be done. But, most of that previous work is obsolete.

" 'The ideas behind turbo codes and LDPC codes have rendered much of the preceding 50 years of coding theory obsolete', says David MacKay of Cambridge University in England, one of the coding theorists who rediscovered LDPC codes. 'Future generations won't have to learn any of the stuff that has been the standard in textbooks,' he says."