A Robust Acquisition Technique Using CFAR Adaptive Thresholding in Hybrid Spread Spectrum Systems

Abstract

Acquisition schemes for hybrid spread spectrum (HSS) systems with a fixed threshold cannot provide satisfactory performance, due to the instantaneous changes of channel state information, environmental interferences, and mobility referred to as outliers. In these conditions, the received signal level varies rapidly. The fixed thresholding method (TM) can cause too many false alarms or the reduction of the detection probability for the selected threshold value. In this paper, we consider a robust acquisition method for the HSS systems using an adaptive constant false-alarm rate (CFAR) TM. In our proposed algorithm, the adaptive threshold is calculated based on the statistical analysis and average energy of the adjacent cells. We derive the exact closed-form solution of the acquisition time as a function of the detection probability, false-alarm probability, and the systemic parameters. Another issue is the extraction of the secure frequency-hopping pattern search period, which we examine in this paper. The theoretical analysis and simulation results show that the proposed algorithm can reduce the acquisition time by more than 45% and prevents the performance degradation in the outliers conditions without increasing hardware cost, compared to the conventional fixed TM.