||During the past few years, there has been a proliferation of wireless technology. In next-generation personal communication networks, high transmission rates are needed in order to support a wide range of services including high-quality voice, data, Facsimile, still pictures and video. In this thesis we devise new or improved schemes for wireless communications using MIMO antenna systems. First, an exact BER expression of MIMO zero-forcing for BPSK and QPSK in flat fading channels is derived. Approximate M-PSK and M-QAM formula are also derived which show a good match with simulation results. Then two new detection algorithms called Error Sensitive Symbol Near MLD (ESS-NMLD) and Error Sensitive Vector Near MLD (ESV-NMLD) for MIMO antennas system are proposed. Both of the schemes have a performance close to optimal maximum likelihood detection (MLD) but with much less complexity than MLD. Three MLSE forms were also generalized to the situation when the channel is a time-varying MIMO channel. They show that the complexity of Ungerboeck is lowest among the three MIMO MLSE forms. On the other hand, Foney form and Partial Ungerboeck form provide the best performance. These MLSE forms are also applied to the equalization of space-time coding.