Code and Frequency Synchronization for DS-CDMA Systems

Joint estimation of code timing and carrier frequency offset for (DS) direct sequence CDMA systems is investigated. The goal is to provide an algebraic solution to the joint estimation problem, in a near-far time-varying frequency-selective fading channel. First, the multiuser estimation is decoupled into a series of single-user estimation problems; then, analytical tools of polynomial matrices are invoked for joint carrier and code timing estimation of the desired user. The performance of the proposed study is examined analytically, where expressions for the variance of propagation delay and frequency offset estimation errors are derived. A subspace code-timing estimator for CDMA systems that utilize bandlimited chip waveforms is also presented. The proposed estimator relies on converting the received signal to the frequency domain, then, the code-timing estimates are obtained by exploiting the unique structure of the spectra of the spreading waveform. The proposed method can be implemented both blindly and in a training-assisted fashion.