“…Furthermore, various joint approaches combining channel estimation with data symbol detection at the receiver were also proposed for CDMA [289], [291], SISO OFDM [292] and MIMO OFDM [184], [293] systems. However, in the context of BLAST or SDMA type multiuser MIMO OFDM systems, all channel estimation techniques found in the literature were developed under the assumption of either the underloaded [143], [168], [227], [238], [285], [288], [294] or the fully loaded [144], [184], [190], [209], [261], [293], [295] scenario mentioned above. Unsurprisingly, in rank-deficient MIMO OFDM systems the task of channel estimation becomes extremely challenging, since the associated significant degradation of the rank-deficient MUD's performance will inevitably result in a further degraded performance of the associated channel estimators, especially in decisiondirected type receivers, which are quite sensitive to error propagation [1].…”