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We present a link adaptation strategy for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) based wireless communications. Our objective is to choose the optimal mode that will maximize energy efficiency or data throughput subject to a given quality of service (QoS) constraint. We formulate the link adaptation problem as a convex optimization problem and expand the set of parameters under the control of the link adaptation protocol to include: number of spatial streams, number of transmit/receive antennas, use of spatial multiplexing or space time block coding (STBC), constellation size, bandwidth, transmit power and choice of maximum likelihood (ML) or zero-forcing (ZF) for MIMO decoding. Additionally, we increase the fidelity of the energy consumption modeling relative to the prior art. The resulting solution allows us to easily and quickly search the space of possible system parameters to deliver on the QoS with minimal energy consumption. Moreover, it provides us insight into where crossovers occur in the choice of the radio parameters. Application of the results to a generic MIMO-OFDM radio shows that the proposed strategy can provide an order of magnitude improvement in energy efficiency or data throughput relative to a static strategy.
Date of Publication: September 2010