Physical layer authentication in OFDM systems based on hypothesis testing of CFO estimates

Information security is becoming a critical challenge in wireless communications due to the open nature of wireless channels and the transparency of standardized transmission schemes. Among the various wireless security techniques, user authentication is one essential measure to identify legitimate users and protect the integrity of transmissions. In this paper, a novel physical layer authentication scheme is proposed to enhance the communication security by exploiting the unique characteristics of oscillator in each communication device. In realistic scenarios, radio frequency (RF) oscillators in each transmitter and receiver pair always present some bias to the nominal carrier frequency due to manufacturing limitations and operating conditions. This bias is characterized by a device-dependent carrier frequency offset (CFO), which can be used to identify a specific wireless transmitter. In the proposed authentication scheme, the CFO at different time of the received signal is first estimated. It is then examined by a hypothesis testing to determine whether the signal has the consistent CFO for authentication purpose. Adaptive thresholds of CFO variation are derived for user discrimination based on the received signal-to-noise ratio (SNR). Simulation results further confirm the effectiveness of the proposed scheme in multipath fading environments.