The mathematical model of MIMO MAC is provided. In a MIMO MAC system with receiver antennas at AP and a transmit antenna for each user where , the channel of MIMO MAC can be described as where is the transmitted symbol for user , and are the vector of received symbols and noise respectively, is the vector of channel coefficients. Also, is the concatenation matrix of the channel vectors for all users and is the concatenation vector of the transmit symbols for all users.