  Radio Frequency fingerprints (RFF) authentication is one of the methods for
the physical-layer information security, which uses the hardware
characteristics of the transmitter to identify its real identity. In order to
improve the performance of RFF based on preamble with fixed duration, a
nonlinear RFF authentication method based on payload symbols is proposed for
the wireless OFDM devices with the bit mapping scheme of QPSK. The
communication system is modeled as a Hammerstein system containing the
nonlinear transmitter and wireless multipath fading channel. A parameter
separation technique based on orthogonal polynomial is presented for the
estimation of the parameters of the Hammerstein system. The Hammerstein system
parameter separation technique is firstly used to estimate the linear parameter
with the training signal, which is used to compensate the adverse effect of the
linear channel for the demodulation of the successive payload symbols. The
demodulated payload symbols are further used to estimate the nonlinear
coefficients of the transmitter with the Hammerstein system parameter
separation technique again, which is used as the novel RFF for the
authentication of the QPSK-OFDM devices. Numerical experiments demonstrate that
the proposed method is feasible. The novel method can also be extended to the
OFDM signals with other bit mapping schemes.
