On subspace channel estimation for chip-level space-time block coded multi-rate CDMA

We investigate the problem of blind channel estimation for the downlink of a variable spreading gain (VSG) multi-rate DS/CDMA (MR CDMA) system which uses the orthogonal space-time block code (STBC) proposed by Alamouti. In contrast to traditional symbol-level STBC CDMA systems, we consider a chip-level ST block coding system for which we derive a simple subspace based blind channel estimation method. For this algorithm we investigate the necessary and sufficient conditions for the channel to be uniquely identifiable up to a complex multiplicative constant. Furthermore, we analyze the behavior of the channel estimation algorithm as a function of the data samples utilized, establishing its unbiasedness and providing a closed form expression for the mean-square-error (MSE) as well as the Cramer-Rao bound for the channel estimation performance