Adaptive modulation for SVD-based MIMO systems with outdated CSI

The performance of singular value decomposition (SVD)-based multiple-input multiple-output (MIMO) with adaptive modulation (AM) is dependent on the accuracy of the channel state information (CSI) at the transmitter and the receiver. However, for a time-varying channel, the CSI obtained at the transmitter or the receiver is incorrect owing to an inherent delay or error. A typical system employing SVD suffers degradation in capacity when outdated CSI is used to transmit data. This article first addresses the adaptive modulation MIMO system designed under perfect CSI assumption. Based on that, two scenarios of outdated CSI are investigated and analyzed. The effect of imperfect CSI on the system performance is focused on and a simple post processing SNR (pSNR) adjustment design is proposed on AM system in the two scenarios for reducing degradation in average spectral efficiency (ASE). Simulation results show that these designs provide good performance in an adaptive way, and enable the adaptive MIMO system considerably more to be robust against CSI imperfection.