Detection of DS-SS Signals over Fading Channels without Prior Knowledge of Spreading Sequence by Measuring Signal Nongaussianity

Direct sequence spread spectrum transmissions (DS-SS) are now widely used for secure communications, as well as for multiple access. Since DS-SS signals use a large bandwidth, their power spectral densities can be well below the noise level. Hence, such signals are difficult to be detected. In this paper, we propose two different methods (ratio peaks greater than threshold (RPT) and mean distance between peaks greater than threshold (MDP)) for detecting the presence of DS-SS signals hidden in the noise over flat or frequency selective fading channels. These methods require no prior knowledge of the spreading sequence used by the transmitter. Both methods use the estimated autocorrelation of the received signal. We also propose a new algorithm, which is based on the kurtosis function of the received signal autocorrelation. This new proposed algorithm performs better than RPT method. Simulation results show that these methods can detect a signal far below the noise level and the exact code length of the DS-SS signal can also be determined