AbstractsEngineering

Security services and mechanisms in wireless networks have long been studied and developed. However, compared to upper network layers, physical layer security did not play a significant role in the OSI security model. Thanks to the easier implementation and verification methods brought by the development of software defined radio (SDR) techniques, physical layer security mechanisms have recently drawn increasing interest from researchers. Digital watermarking is one of the popular security techniques that can fully utilize various exclusive characteristics of the physical layer. This thesis proposes a physical layer watermarking technique named Watermarked Direct Sequence Spread Spectrum (DSSS) or WDSSS technique, which embeds authentication information into pseudonoise (PN) sequences of a DSSS system. The design and implementation of the WDSSS prototype system on the GNU Radio/USRP SDR platform is discussed, as well as two watermark embedding methods, the maximized minimum distance method and the sub-sequence method. Theoretical analysis and experimental results on the WDSSS prototype system are presented to evaluate the performances of both the content signal and the watermark signal. Results show that, for the 11-chip PN sequence, increasing artificial chip errors has a quantitatively predictable impact on the content signal, requiring 2 dB higher signal-to-noise ratio (SNR) to maintain an acceptable packet error rate (PER) for one additional flipped chip. In terms of the watermark signal, the two embedding methods demonstrated individual advantages in either PER or throughput. The maximized minimum distance method outperforms the sub-sequence embedding method with a 3 dB lower SNR requirement, while the latter provides 400% more throughput than the former with adequate SNR.