Decoupled delay and Doppler acquisition in DS-CDMA systems at low signal to noise ratios

This paper presents several novel acquisition algorithms for time-variant multipath channels. To acquire several closely-spaced multipath channel delays and multipath Doppler frequencies, our novel acquisition methods resort to low complexity high resolution subspace estimators. The low complexity high resolution subspace estimators perform a coherent estimation of the sample covariance matrix, which prevents the squaring loss (SL) and a reduced acquisition probability due to rapidly alternating modulation symbols. We use the multiple signal classification (MUSIC) and the unitary estimation of signal parameters via rotational invariant techniques (ESPRIT) method for the two-dimensional delay and Doppler multipath acquisition. Contrary to MUSIC, unitary ESPRIT enables the first decoupled acquisition of multipath channel delays and Doppler frequencies, which yields a high acquisition probability at low signal to noise ratios (SNRs) with a low acquisition complexity.