Multi-user decision-feedback space-time processing with partial cross-feedback connectivity

This paper investigates space-time receiver architectures in multi-user wireless systems where optimal idealized (infinite-length) space-time filtering is applied to minimize the mean-square error. Both feedforward, decision-feedback and cross-decision feedback filters are employed; it follows that not only does the system eliminate the post-cursor ISI (intersymbol interference) but also some portion of the post-cursor CCI (co-channel interference). Such a receiver is most useful in the context of an SDMA (space division multiple access) system since the base station then has readily available knowledge on the decisions of the in-cell co-channel interfering signals. However, significant CCI is also received from outside the cell for which there is normally no decision information available. Therefore, in-cell and out-of-cell co-channel interferers will be treated differently by the receiver since no cross-feedback filter can be implemented for the out-of-cell signals. Our analysis leads to a closed-form expression for the minimum achievable MSE (mean-square error) for both fully- and partially-connected cross-decision feedback systems (XDF). Numerical results compare the performance of XDF systems with standard space-time DF and linear processing as well as the matched-filter bound.