An open-loop precoder for a multiple-input multiple-output (MIMO) spatial multiplexing system having a transmitter that is provided with at least two transmit antennas and is configured to transmit spatially multiplexed signals and a receiver that is provided with at least two receive antennas and is configured to receive the spatially multiplexed signals from the transmitter, the open-loop precoder comprising: a signal decomposition and modulation unit configured to decompose a transmit signal to match a number of the at least two transmit antennas and to modulate the decomposed signals; a search unit storing a precoding matrix for the number of the at least two transmit antennas, wherein the precoding matrix includes a rotational matrix and a phase rotation matrix and wherein the precoding matrix can be expressed as F = cos θ − sin θ sin θ cos θ 1 0 0 e jφ, wherein a first term is the rotational matrix depending on a phase θ of the rotational matrix, and a second term is the phase rotation matrix depending on a phase φ of the phase rotation matrix; a determination unit configured to determine an optimum of the parameters (θ), (φ) for the precoding matrix such that a system error is minimized by assuming a worst channel state; a precoding application unit configured to apply a precoding matrix having the optimum θ and φ to modulated signals output from the signal decomposition and modulation unit; and a transmit unit configured to transmit each of precoded signals via the at least two transmit antennas, wherein determining the optimum θ and φ comprises θ opt, φ opt = arg min P e θ, φ, wherein P e is an average pairwise error probability defined as P e θ, φ = E ∑ i = 1 M N T ∑ j = 1, i ≠ j M N T PE P i, j where " M " denotes a modulation order, " N T " denotes the number of the at least two transmit antennas and the pairwise error probability i,j (PEP i,j) is a PEP between two codewords x i and x j and is defined as PE P i, j ≤ 1 SNR 4 N T ‖ R T 1 2 F x i − x j ‖ 2 N R wherein " R T " denotes a channel correlation matrix, " N R " denotes a number of the at least two receive antennas and " (x i -x j) " denotes a difference of codewords depending on the modulation order, and wherein the channel correlation matrix is defined as R T = 1 α e jβ α e − jβ 1, 0 ≤ α ≤ 1, 0 ≤ β ≤ 2 π wherein α is a transmit correlation coefficient for the phases of each component of the precoding matrix, wherein α is set to 0 under a best channel state and to 1 under a worst channel state, wherein an optimum β capable of minimizing the average PEP is obtained by setting α to 1 in the channel correlation matrix, and wherein the optimum phase θ is obtained such that the average PEP is minimized by setting the phase φ and setting α to 1 assuming a worst channel state. a signal decomposition and modulation unit configured to decompose a transmit signal to match a number of the at least two transmit antennas and to modulate the decomposed signals; a search unit storing a precoding matrix for the number of the at least two transmit antennas, wherein the precoding matrix includes a rotational matrix and a phase rotation matrix and wherein the precoding matrix can be expressed as F = cos θ − sin θ sin θ cos θ 1 0 0 e jφ, wherein a first term is the rotational matrix depending on a phase θ of the rotational matrix, and a second term is the phase rotation matrix depending on a phase φ of the phase rotation matrix; a determination unit configured to determine an optimum of the parameters (θ), (φ) for the precoding matrix such that a system error is minimized by assuming a worst channel state; a precoding application unit configured to apply a precoding matrix having the optimum θ and φ to modulated signals output from the signal decomposition and modulation unit; and a transmit unit configured to transmit each of precoded signals via the at least two transmit antennas,