Uplink multiuser MIMO-OFDM in widely spaced antenna arrays

The ability of the base station to separate several users spatially depends on the pair-wise cross-correlations between the channel vectors of the users. In this paper we propose an improved uplink multi-user MIMO-OFDM system that reduces the intra-user correlations resulting in significant enhancement in the SDMA system performance. In this system, several base station multi-antenna arrays are distributed in a given area. Each array is communicating with the base station via optical fiber links. All signal processing is performed at the base station. Users are spatially separated such that in each tone of the OFDM symbol only a certain number of users (out of the total number of users) are selected. The selection is based on an algorithm that reduces the pair-wise intra-user correlations. Such a reduction in channel matrix correlations decreases the convergence time of iterative adaptive algorithms such as the LMS algorithm. The channel vector of each user is assumed correlated and Ricean distributed