Correlation matching in channel estimation for multirate DS/CDMA

Channel estimation is studied for a multicode (MC) or multiple processing gain (MPG) multirate CDMA system based on correlation matching. All users are partitioned into groups in terms of their raw data rates. Since a communication channel may span several symbol intervals especially for a high rate user, severe intersymbol interference (ISI) exists in the received data. However, signature waveforms of various symbols from a user are convolutions of spreading codes with a common channel. This structure is beneficial to channel estimation due to multiple contributions to the output correlation. By properly selecting a weighting matrix in the matching cost function, significant improvement is observed. The optimal weighting matrix and covariance of the channel estimate are further derived in closed forms.