Blind channel identification and projection receiver determination for multicode and multirate situations in DS-CDMA systems

We consider multicode and multirate transmission scenarios in a DS-CDMA system operating in an asynchronous fashion in a multipath environment. Oversampling w.r.t. the chip rate is applied to the cyclostationary received signal and multisensor reception is considered, leading to a linear multichannel model. Channels for different users are considered to be finite-impulse response (FIR) and of possibly different lengths, depending upon their processing gains. We consider an individualized linear MMSE-ZF or projection receiver for a given user, exploiting its spreading sequence and timing information. In the multicode case, a certain user is considered to use several spreading codes in order to transmit at a higher rate. Considering different code sequences to be issuing from different virtual users, the propagation channel impulse responses of all these users are the same. However, the total channel impulse response which includes spreading sequences is different for all users. On the other hand, in the multirate case, a periodically varying set of periodic spreading codes spread successive symbols of a certain user. Symbols spread by different codes can therefore by considered to be issuing from different virtual users. The problem therefore boils down to classical multiuser detection with time-invariant interference canceling filters for each virtual user. A blind channel estimate is also obtainable through Capon’s method (first used by Tsatsanis) as a by-product of the MMSE-ZF receiver algorithm.