 A closed-loop MIMO system utilizes Channel State Information (CSI) at the transmitter.In most cases, only partial CSI is available at the transmitter because of the limitations of the feedback channel.In a closed-loop MIMO system the input-output relationship with a closed-loop approach can be described as
where formula_16 is the formula_17 vector of transmitted symbols, formula_11 are the formula_19 vectors of received symbols and noise respectively, formula_13 is the formula_21 matrix of channel coefficients and formula_22 is the formula_23 linear precoding matrix.