Adaptive Modulation for MIMO Systems With Channel Prediction Errors
The performance of Multiple-Input Multiple-Output (MIMO) systems using spatial multiplexing is analyzed under channel prediction errors. The authors derive exact closed-form expressions for the conditional and average Bit Error Rate (BER) for both fixed and adaptive modulation. They apply their analysis to design a rate adaptation policy that optimally adapts antenna use between beamforming and spatial multiplexing. Their results indicate that the prediction error degrades BER in MIMO systems with spatial multiplexing much more than in MIMO systems with beamforming due to the self-interference that arises from channel coupling. In particular, if interference between eigen-channels is high, spatial multiplexing should not utilize the weakest eigen-channels.