This paper extends the self-contained theory of linear precoding to the field of covariance based spatio-temporal downlink processing for direct-sequence code-division multiple-access (CDMA) systems and shows the applicability to the release 6 of high-speed downlink packet access (HSDPA). To this end, a unifying theory is developed to formulate the three known linear filters, namely, the transmit matched filter, the transmit zero-forcing filter, and the transmit Wiener filter, as optimization problems even in systems, where only covariance knowledge is available at the transmitter. Second, the solutions of these transmit filters are given for such systems with partial channel state information (CSI). Finally, it is shown how covariance-based linear precoding can be employed in the new generation CDMA system HSDPA, i.e., how channel estimation on the secondary common pilot channel allows for optimum full rank linear precoding employing only partial CSI.

Like numerous other applications, novel cross-layer optimization schemes require the determination of the outage probability of fading channels. Relying on the assumption of frequency selective Rayleigh fading channels we develop a closed form expression for the probability density function of the sum of the square channel coefficients at the output of maximum ratio combining (MRC) receivers. This allows for the formulation of the channel outage probability directly in terms of the channel energy and thus enables the analytic derivation of the outage probability in multi-user CDMA systems. Moreover, low complexity lower and upper bounds are derived, which provide the means for a well fitting approximation of the exact result directly through the cumulative distribution of the channel energy as obtained at the MRC output