A robust PN length estimation in down link low- SNR DS-CDMA multipath channels

In this paper an efficient method is proposed for blind detection of multiuser spread spectrum signal and pseudo noise (PN) length estimation in downlink scenario. This method is based on fluctuating observation of second order statistic (SOS) estimator of received signal; estimating length of spreading code with no need to primary information based on observing second order peaks of correlation estimator is presented. In low SNR, the fading multipath phenomenon especially in length of small codes leads to problem in detecting place of correlation estimator peaks. In this paper besides expanding blind estimation to multiuser environment, by using searching method in updating the length of correlation window coordinated with length of spreading code and also choosing proper adaptive algorithmic thresholds for smoothing this difficulty is presented. In practice, like computing the number of users and estimating code of every user, knowing the length of code is required. Simulation results focus on efficiency of algorithm in detection and exact estimation of spreading code length in low SNRs and multipath environment.