OUT-OF-BAND POWER REDUCTION IN MIMO OFDM

One of the main disadvantages of orthogonal frequency-division multiplexing (OFDM) is its large peak-to-average power ratio (PAR). In case of nonlinear power amplification this fact causes undesired out-of-band radiation. In this paper PAR reduction schemes for multiple-antenna OFDM, in particular variants of selected mapping (SLM), are considered. Directed SLM (dSLM), where a joint PAR reduction over the antennas is performed, is reviewed and compared to the obvious application of SLM to each single antenna (oSLM). Due to the avoidance of the signal peaks, less out-of-band radiation is caused. It is shown that both, oSLM and dSLM, provide significant gains in the reduction of the out-of-band radiation compared to conventional OFDM. However, using the same complexity, dSLM provides significant extra gain over oSLM. The gain, which is clearly dependent on the type of nonlinearity and the chosen power backoff, is assessed by means of numerical simulations.

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