Phase-Modulated Local Oscillator Effects on RF-DNA Fingerprints in IEEE 802.11a Wi-Fi Signals*

With the increasing dependence on the internet in more and more consumer products, there is an urgent need to enhance existing digital security systems. RF-DNA fingerprints are one such approach to utilize discriminating waveform characteristics to augment the detection (rejection) of approved (unapproved) Wi-Fi devices. This work investigates a time-dependent approach to manipulate the RF-DNA fingerprints of a transmitting device through local oscillator phase modulation of the clocking system in Wi-Fi transmitters. Experimental results are used to investigate the ability for an unaffected receiver to detect a corresponding clock-modulated transmitter, as well as the changes of 802.11a Wi-Fi preambles of clock phase modulated transmissions. Changes in the waveforms are further analyzed using the Discrete Gabor Transform in the time-frequency domain. Analysis shows a predictable pattern of change over time, proportional in frequency to the phase-modulation frequency, and the ability for preamble structures to remain intact up to 30 kHz of phase modulation.