A Robust Semi-Blind Approach for Scramble Code Estimation in Non-Cooperative Interception of a Scrambled DSSS Signal

Communication intelligence (COMINT) refers to the interception of communication signals to extract intelligence from the information enclosed in the transmission. The intercept receiver incorporates robust blind signal detection and estimation techniques to detect a certain type of signal, from which intelligence may be extracted. Direct sequence spread spectrum (DSSS) communication signals are characteristically weak and hidden in background noise, which impose a challenge for blind interception. Scrambling disrupts the cyclostationary feature of DSSS signals, which makes blind interception an extremely demanding contest. If some a-priori parameter information is known, semi-blind techniques may be leveraged to facilitate non-cooperative interception. A semi-blind method based upon data matrix correlation is proposed in this paper to estimate the scrambling code. This is done to descramble the received DSSS signal before estimation of spread spectrum parameters. The proposed methodology requires code length to precisely estimate the scrambling code. It is quite noteworthy that although the proposed methodology is formulated for DSSS signals, it can be flexibly used for other signals as well. Analytical and numerical results clearly highlight that the proposed method can estimate scrambling code at low SNRs with substantial estimation accuracy and reduced computational cost.