Blind channel estimation for DS-CDMA with long codes

In this paper, blind channel estimation is considered for Code-Division Multiple-Access systems employing randomized spreading codes with periods longer than a symbol duration. The motivation for such a study is both current commercial as well as proposed military wireless systems, where such signature sequences are under consideration. This kind of spreading presents particular challenges that render impossible the use of existing techniques based on short signature waveforms. The proposed blind channel estimation method is based on the second order statistics of the received signal, in addition, the algorithm exploits knowledge of the desired spreading code and its properties. The new method uses the Toeplitz structure of the autocorrelation matrix. A theoretical analysis of the mean squared error is provided and the resulting approximations are shown to be tight via simulation.