Blind code-timing estimation for CDMA systems with bandlimited chip waveforms in time-varying multipath channels

In this paper, we present a blind code-timing estimator for asynchronous DS (direct-sequence) CDMA (code-division multiple-access) systems. that utilize bandlimited chip waveforms. The received signal is first Fourier-transformed to the frequency domain, followed by a frequency deconvolution to remove the effect of the chip waveform. The code-timing is next derived from the output of a narrowband filter with a sweeping center frequency, which is designed to suppress interference of various sources, including, e.g., MUI (multiuser interference), ISI (inter-symbol interference), CCI (co-channel interference), and narrowband interference. The proposed estimator requires only the spreading code of the desired user. It can be used in frequency-flat or frequency-selective, time-invariant or time-varying fading channels. Moreover, the proposed estimator can be readily implemented using standard adaptive schemes, making it appealing not only for acquisition but also for tracking. Numerical results are presented to illustrate the performance of the proposed scheme.