  The wireless physical-layer identification (WPLI) techniques utilize the
unique features of the physical waveforms of wireless signals to identify and
classify authorized devices. As the inherent physical layer features are
difficult to forge, WPLI is deemed as a promising technique for wireless
security solutions. However, as of today it still remains unclear whether
existing WPLI techniques can be applied under real-world requirements and
constraints. In this paper, through both theoretical modeling and experiment
validation, the reliability and differentiability of WPLI techniques are
rigorously evaluated, especially under the constraints of state-of-art wireless
devices, real operation environments, as well as wireless protocols and
regulations. Specifically, a theoretical model is first established to
systematically describe the complete procedure of WPLI. More importantly, the
proposed model is then implemented to thoroughly characterize various WPLI
techniques that utilize the spectrum features coming from the non-linear
RF-front-end, under the influences from different transmitters, receivers, and
wireless channels. Subsequently, the limitations of existing WPLI techniques
are revealed and evaluated in details using both the developed theoretical
model and in-lab experiments. The real-world requirements and constraints are
characterized along each step in WPLI, including i) the signal processing at
the transmitter (device to be identified), ii) the various physical layer
features that originate from circuits, antenna, and environments, iii) the
signal propagation in various wireless channels, iv) the signal reception and
processing at the receiver (the identifier), and v) the fingerprint extraction
and classification at the receiver.
