Wireless physical-layer security performance of UWB systems

Traditionally, spread-spectrum systems have been employed to provide low probability-of-intercept (LPI), low probability-of-detection (LPD) performance at the physical layer, but the messages transmitted over such a system are still encrypted with a powerful cipher to protect their secrecy. However, it has recently been suggested that the cryptographic security of the system can be enhanced by exploiting physical properties of ultra-wideband (UWB) signals. With an eavesdropper observing the communications over multipath channels between two legitimate partners sharing a secret key of a limited length, we consider both coherent and reference-based UWB schemes to enhance security. The security of the legitimate nodes is achieved by signal attributes based on the secret key, giving them an advantage over the adversary. In particular, we propose transmission schemes and investigate the physical layer security performance of UWB systems intended for coherent reception and UWB transmitted-reference (TR) systems in IEEE 802.15.4a multipath environments. Critical to the TR scheme is employing true randomness to keep a sophisticated adversary from decoding the signal coherently. Numerical results for IEEE 802.15.4a channel models reveal not only that the proposed schemes provide promising support for higher-layer cryptographic protocols, but also, perhaps surprisingly, that the baseline UWB TR system can demonstrate better security tradeoffs than the baseline UWB system intended for coherent reception under the IEEE 802.15.4a channel model.