Perfect communication with imperfect chips

Error-correcting codes discovered at MIT can still guarantee reliable communication, even in cellphones with failure-prone low-power chips.

Graphic: Christine Daniloff

One of the triumphs of the information age is the idea of error-correcting codes, which ensure that data carried by electromagnetic signals - travelling through the air, or through cables or optical fibers - can be reconstructed flawlessly at the receiving end, even when they've been corrupted by electrical interference or other sources of what engineers call ''noise.''

For more than 60 years, the analysis of error-correcting codes has assumed that, however corrupted a signal may be, the circuits that decode it are error-free. In the next 10 years, however, that assumption may have to change. In order to extend the battery life of portable computing devices, manufacturers may soon turn to low-power signal-processing circuits that are themselves susceptible to noise, meaning that errors sometimes creep into their computations.

Fortunately, in the July issue of IEEE Transactions on Information Theory, Lav Varshney PhD '10, a research affiliate at MIT's Research Laboratory of Electronics, demonstrates that some of the most commonly used codes in telecommunications can still ensure faithful transmission of information, even when the decoders themselves are noisy.

The same analysis, which is adapted from his MIT thesis, also demonstrates that memory chips, which present the same trade-off between energy efficiency and reliability that signal-processing chips do, can preserve data indefinitely even when their circuits sometimes fail.

According to the semiconductor industry's 15-year projections, both memory and computational circuits ''will become smaller and lower-power,'' Varshney explains. ''As you make circuits smaller and lower-power, they're subject to noise. So these effects are starting to come into play.''