说明：  Much of the initial excitement about MIMO systems was due to pioneering work by Winters [132], Foschini [29], and Telatar [113] predicting remarkable capacity growth for wireless systems with multiple antennas when the channel exhibits rich scattering and its variations can be accurately tracked. This initial promise of exceptional spectral efficiency almost “for free” resulted in an explosion of research and commercial activity to characterize the theoretical and practical issues associated with MIMO systems.