Several existing signal processing problems in wireless communication systems with multiple transmit and/or receive antennas are modeled by means of matrix decompositions that represent the transformations on the transmitted signal from the transmitter to the receiver. At the receiver, signal processing is generally used to combat multipath fading effects, inter-symbol interference, and multiuser (co-channel) interference by means of multiple receive antennas. The usually considered signal processing dimensions are
dimensions . This area has progressed over the past 20 years and has resulted in several powerful solutions. In order to allow for a higher spectral efficiency, numerous works have proposed blind signal processing techniques, which aim at avoiding the loss of bandwidth due to the use of training sequences.