Adaptive physical layer security using code bank of sequences for CDMA

Wireless security is an important concern in todays technological world. Wireless devices are used to access data and private applications. From broadband to Wi-Fi, 3G to LTE Advanced, WiMAX to satellite communication every network demands on-the-air security from attacks. Tapping or Jamming attacks leak the secret data, while Service Disruption Attacks affecting QoS (Quality of Service) are relatively easy to perform. In CDMA, the channel and antenna dependent attacks are quite critical to avoid because of its wide bandwidth usage. The critical exchange of time and frequency parameters makes the physical layer elements vulnerable to security related attacks. In order to enable data security and secrecy, there is need of signal protection at the physical layer of CDMA system. Gold codes, M-sequences, OVSF and De-Bruijn sequences were used individually in wireless systems for scrambling purposes in previous proposals. These codes have their own advantages and disadvantages, when channel bandwidth and noise conditions change. This paper proposes a system which would select scrambling codes from a bank of all these mentioned codes depending upon the Signal to Noise Ratio (SNR) or Channel State Information (CSI). This code bank technique is shown as a highly practical solution in selection of proper code for mitigation of attacks and hence, to provide security at the physical layer of CDMA

De Bruijn sequences for DS/CDMA transmission: Efficient generation, statistical analysis and performance evaluation

Nowadays, Direct Sequence Code Division Multiple Access (DS/CDMA) still represents the core technology for the physical layer of several commercially-remunerative applications and standards, ranging from cellular networking, radiolocalization, satellite communications, automotive radar, etc. A very critical issue of Spread Spectrum and CDMA is still represented by the necessity of keeping the probability of intercept as lowest as possible, therefore, a secure information hiding must be guaranteed at the physical layer. The use of De Bruijn binary sequences may represent a valuable solution to the aforesaid issue. De Bruijn sequences are nonlinear shift register sequences, whose sets are characterized by a cardinality much larger than the sequence length. This paper aims at considering some significant aspects about the usage of De Bruijn sequences in DS/CDMA, not yet addressed by prior works: the performance of De Bruijn sequences in asynchronous DS/CDMA transmission is assessed by means of explicit computations of multi-user interference statistics (variance and kurtosis), and closed form Bit-Error-Probability (BEP) analytic expressions. Numerical results on the obtained BEP after Reed-Solomon coding evidence that, when randomly selected, De Bruijn sequences perform very close to Gold sequences having the same length. The performance provided by De Bruijn sequences get remarkably better than the Gold ones when a proper selection procedure, aimed at minimizing the pairwise aperiodic cross-correlation, is adopted. The selection procedure and the corresponding results are discussed in details within the paper