The miniaturization of all components and their operation in close quarters are a huge challenge, particularly with
respect to power consumption. As length shrinks, volume drops cubically, thus leading to a dramatic reduction of battery
capacity [7]. On top of that, the reliance on batteries is a serious drawback for systems that are supposed to operate without
human supervision. Aside from energy harvesting, which has been the subject of a significant number of studies and was
recently surveyed in [26], a promising effort in battery-free communication is ambient backscatter communication [6].
With traditional backscatter communication (used, for instance, in RFID), a device modulates its reflected radio waves
as opposed to generating new ones. While traditional backscatter communication requires the use of a dedicated power
infrastructure, such as an RFID reader that energizes an RFID tag, ambient backscatter uses energy that is already in the
air and enables device-to-device communication. Ambient backscatter may become a key communication technology for
small-scale human-free pervasive sensing over the next decade.