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School of Engineering
and Information Sciences
Research
Seminars
(Autumn Term 2010-11)
Abstract
Physical Layer Encryption for OFDM Communication Systems
Dr Arsenia Chorti
Middlesex University
Abstract
Shannon described encryption as a set of reversible (nonsingular) transformations from one space to another, so that a potential cryptanalyst would not be able to decipher the message unless they had access to the encryption key. Encryption has since been developed along two distinct routes. The prominent approach is based on the generation of coding schemes that are practically unbreakable because of their computational complexity, thus combining encryption with complexity theory. Along the second path lie information theoretic approaches, allowing for theoretic perfect secrecy. Analyses for the wireless fading channel and MIMO systems have established non-zero secrecy capacities for such systems, although on average the eavesdropper’s channel can be better than the legitimate user’s channel. Furthermore, information theoretic helping interferer or jamming approaches have recently been proposed. In this talk, we present a structured helping interferer encryption scheme, specifically for OFDM signals. We call the scheme Masked-OFDM, as OFDM signals are masked through faster than Nyquist signalling. A positive secrecy capacity is attained even for non-degraded wiretap channels due to the ill-conditioning of the overall system linear statistical model. The proposed scheme compromises neither the bandwidth efficiency nor the error performance of the underlying OFDM in AWGN and slow fading channels, at the cost of increased transmission power. The main motivation behind the proposed approach stems from the fact that problems modeled by ill-posed operators prevent the extraction of accurate estimates as a result of their instability. The mutual information between the transmitter and any potential unlicensed receiver decreases with increasing signal dimensionality, so that almost perfect secrecy can be attained.
Short Bio
Arsenia Chorti received the M. Eng. degree in EEE from the University of Patras in 1998, the D.E.A. degree in electronics from the University Pierre et Marie Curie - Paris VI, France, in 2000 and the Ph.D. degree in Signal Processing from Imperial College London in 2005. Following her Ph.D., she has worked as a Research Fellow at the University of Southampton in 2006, as a Research and Teaching Fellow at the Technical University of Crete in 2007 and as a Research Fellow at University College London in 2008. She is currently a Senior Lecturer at Middlesex University at the Department of Computer Communications. She is interested in multiple areas of telecommunications and stochastic signal processing including multicarrier communication systems, OFDM, FDM, physical layer encryption, system/device modelling, novelty detection and density estimators. .
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