Direct-Sequence Spread-Spectrum Acquisition for High Dynamic Environments via Signal Partitioning

Time-varying Doppler shifts can arise in low-earth orbit satellites and other high-dynamic environments, and are a significant impediment to the acquisition of spread-spectrum signals. In this paper we propose delay-Doppler efficient exhaustive search (DEES), an efficient algorithm that can acquire direct-sequence spread-spectrum signals with long spreading codes in the presence of both Doppler rate and Doppler frequency shifts. DEES combines the second-order keystone transform and the fractional Fourier transform to mitigate the effects of time-varying channel delays, before jointly estimating both the code phase offset and the Doppler frequency. Numerical results demonstrate that DEES can acquire spread-spectrum signals in the high-acceleration regime of the low-earth orbit satellite channel at low SNR.