Exploiting noncircularity in backscattering communications

In backscatter radio systems, a passive (i.e., battery-free) device (so-called tag) is able to transmit information by harvesting energy from a carrier transmitted by an access point or base station (so-called reader), thus enabling significant power savings compared to traditional wireless communication schemes. In this paper, the physical layer of a backscatter system is revisited to develop a design framework encompassing the use of multiple antennas at both the reader and the tag, as well as the exploitation of symbol noncircularity through the employment of a widely-linear equalizer at the reader. It is also outlined how the choice of noncircular multilevel modulation formats can be coupled with optimized power harvesting at the tag.