说明：   we present a practical link adaptation algorithm for MIMO-OFDM systems. The proposed solution is based on sounding the channel periodically and choosing the optimal mode that will maximize the throughput or energy efficiency (EE) while satisfying the application’s quality of service (QoS) requirements. In addition, we address practical problems such as the computational complexity of the algorithm and determination of sounding period by novel closed form solutions and iterative algorithms. Realistic link level simulations confirm that the proposed solution achieves significant improvement over existing link adaptation algorithms when the aim is to maximize the throughput, and provides orders of magnitude gain in energy efficiency compared to poorly chosen fixed modes when used for energy efficiency maximization purposes. The resulting algorithms are implemented on a real time MIMOOFDM testbed, and we report on the experimental results.