Physical layer built-in security analysis and enhancement of CDMA systems

Historically developed for secure communication and military use, CDMA is now serving as one of the most widely used wireless airlink interface and has been identified as a major technique for 3G wireless communications. In addition to the wide bandwidth and low power spectrum density which make CDMA signals robust to narrow band jamming and easy to be concealed within the noise floor, the physical layer built-in information privacy of CDMA system is provided by pseudo-random scrambling. In this paper, first, the physical layer security weakness of the operational IS-95 CDMA airlink interface is analyzed. Secondly, based on the advanced encryption standard (AES), we propose to enhance the physical layer built-in security of CDMA systems through secure scrambling. Performance analysis demonstrates that while providing significantly improved information privacy, CDMA system with secure scrambling has comparable computational complexity and system performance with that of the IS-95 system. Moreover, it is shown that by scrambling the training sequence and the message sequence separately with two independent scrambling sequences, both information privacy and system performance can be further improved. The proposed scheme can readily be applied to 3G systems and IEEE 802.11b WLAN systems.