MIMO technology, is to have more than one antenna at both the transmitter and receiver, MIMO can be used with any modulation technique or access, and is currently the most commonly used technique called multiplexing for Orthogonal Frequency Division (OFDM), which can divide the frequency selective channel into several flat fading channels and then apply MIMO technology to each one of these sub-channels. Research on MIMO channels for both single and multi-user; have focused on 2 main problems of optimization, which are: maximizing performance (capacity) and power control. In MIMO-MU (multiple input - multiple output, Multi-user), one of the major topics to be discussed is the elimination of co-channel interference which use the block diagonalization technique which is a method based on orthogonal projection. This algorithm is a linear pre-encoding alternative that transmitting multiple data frames each user while removing inter user interference at the same time, which is an extension of Zero-forcing algorithm for multi-user MIMO downlink; that is a generalization of the investment channel.