An acquisition scheme, based on the least mean-squared error (LMSE), for the symbol timing, carrier phases, and multipath gains for multicarrier code-division multiple-access (MC-CDMA) systems is proposed. A new coefficient called the quasi-mean-squared accuracy coefficient (QMSAC) is introduced. This allows the search for multiple optimal parameters to be split into simpler single-parameter estimates. The symbol timing is acquired with a comparison of the QMSACs followed by a linear interpolation scheme or a search of a minimizing variable. Carrier phases and multipath gain coefficients are then estimated via some algebraic computations based only on the estimated symbol timing and the QMSACs. The spreading sequence of the desired user is the only prior knowledge required for the proposed approach. Simulation results demonstrate the near-far resistance of the approach and show that the error performance of minimum mean-squared error (MMSE) detection with acquired parameters is only a few decibels worse for the considered channel than the performance obtained with perfect knowledge about the channel impulse response.

The windows for achieving good multiple-access performance of multicarrier code-division multiple-access (MCCDMA) systems employing minimum mean-squared error receivers are studied. The mean-squared error (MSE) is used as the performance metric for the optimization. In a simplified two-user system, the rectangular window is found to be optimum while regarded as an inferior window in orthogonal frequency-division multiplexing systems because of its spectral inefficiency. Necessary conditions are given for improving the performances of spectrally efficient windows by exploiting the cyclic prefix and oversampling in the frequency domain.