Adaptive subspace modulation in spatially correlated MIMO systems

We propose an adaptive modulation scheme for wireless MIMO systems. The main goal of this scheme is to maximize the bit rate for a fixed target BER. The MIMO channel is split up into several independent channels (subspaces) by a singular value decomposition. On each of these independent channels the modulation format is adapted to the subchannel SNR. The proposed algorithm allocates appropriate modulation schemes from 2PSK to 256QAM to each subchannel. The channel is assumed to be quasi static flat Rayleigh fading, perfectly known at both ends of the link. Mean data rates that can be obtained are presented as a function of the mean SNR, keeping BER below a target value of e.g. 10−3 for spatially uncorrelated and partially correlated channels without using any error correcting code. Keywords—MIMO, spatially correlated channels, adaptive modulation