Rapid acquisition scheme for spread-spectrum radio in a fading environment

A modified two-level scheme for coarse code acquisition of spread-spectrum signals in a fading environment is considered. The scheme uses a bank of passive correlators followed by a bank of active correlators. The passive correlators are matched to short sync prefixes, which areinterspersed in the incoming signal. The passive devices correlate over sliding windows (in time), providing a rapid search capability. Threshold exceedances of the passive correlators areused to initiate active correlation over longer time intervals so that high reliability of decision is obtained. The multiple sync prefixes reduce the probability of missing the signal in a fading environment. An analytical model based on queueing and detection theory results is developed, and optimisation of the scheme is treated. A Gilbert model is used to characterise the signal fading on the channel. The performance in the presence of background noise with noisejamming is analysed. Theoretical performance curves and a discussion of the results are also presented.