Blind chip rate estimation in multirate CDMA transmissions using multirate sampling at slow flat fading channels

This paper considers blind chip rate estimation of direct sequence spread spectrum (DS-SS) signals in multirate and multiuser direct-sequence code division multiple accesses (DS-CDMA) in channels having slow flat Rayleigh fading plus additive white Gaussian noise. Channel impulse response is estimated by a subspace method, and then the chip rate of each signal is obtained using number of zero crossing of differential of estimated channel impulse response. For chip rate estimation of each user, weighted zero-crossing ratio is proposed. Maximum value of the weighted zero crossing ratio takes place in the sampling frequency, which is equal to the Nyquist rate, and it is same chip rate. Furthermore bit time of each user is estimated using fluctuations of autocorrelation estimators. Since code Length of each user can be obtained using bit time and chip time.