WLC31-3: Adaptive Modulation in MIMO Eigen beamforming with Outdated Channel State Information

Channel state information(CSI) at the transmitter, even imperfect, can improve the capacity of a multiple-input multiple-output(MIMO) communication system and substantially reduce the receiver complexity. Eigenbeamforming has been proven to be the preceding scheme that not only achieves the channel capacity, but also minimizes the mean square error (MSE) at the output of the receiver in this case. This paper presents a novel adaptive modulation scheme that loads power and integer bits over the eigenmodes in a MIMO communication system according to outdated CSI at the transmitter. An un- coded narrowband system is considered in a time-varying and spatially uncorrelated fading channel. Simulations indicate that the proposed scheme provides a much higher spectral efficiency than the standard strategy which simply adds energy margin to achieve the target error performance.