For the first half of the last century, multipath phenomena were harmful. In radio frequency transmission they caused signal fading as different paths became variously additive or destructive. In wire-line transmission there were similar effects due to the nonuniform delay of signal frequency components, resulting in intersymbol interference and degraded speeds.
These multipath impairments were eventually alleviated through diversity and adaptive signal processing. Still, I think of these adaptive systems as robust, rather than truly antifragile. Perhaps, though, we crossed the line to antifragile with the advent of multiple-input/multiple-output MIMO systems, in which we deliberately send multiple copies of the signal from different antennas, hoping there will be multipath phenomena that with processing can be used to enhance system performance. MIMO [PDF] is now commonly used in IEEE 802.11n (Wi-Fi), and elsewhere.

via Antifragile Systems – IEEE Spectrum.