Per-Subcarrier Antenna Selection with Power Constraints in OFDM Systems

Antenna selection can be an efficient way of exploiting spatial diversity while offering low feedback rates and simple receivers. In an OFDM system, antenna selection can be performed on a per-subcarrier basis, which can exploit the frequency-selectivity of the channel. However, this will cause a power imbalance across the antennas, which may lead to problems with the power amplifiers. An increased dynamic range may require power back-off, which results in a performance loss. To avoid this problem, we devise an optimum scheme that allocates the same number of subcarriers to all antennas, while still offering substantial diversity gains. This is achieved by using integer optimization. We show that this is solvable by linear relaxation, which results in a reduced complexity. Simulation results illustrate that the proposed scheme performs better than a previously published ad hoc method and only slightly worse than the impractical conventional per-subcarrier antenna selection where no subcarrier allocation constraints are imposed.