Optimal technique with distortion for cubic metric reduction in OFDM systems

A main disadvantage of orthogonal frequency division multiplexing (OFDM) signals is large envelope fluctuations. Peak-to-average power ratio (PAPR) and cubic metric (CM) are well-known metrics for the envelope fluctuations, where the latter is attracting increasing attention since it can predict the power de-rating of power amplifier more accurately. CM-reduction methods with distortion can efficiently limit CM while causing in-band distortion and out-of-band radiation. In this paper, the tradeoff among CM-reduction, in-band distortion and out-of-band radiation is formulated as an optimization problem, where the error vector magnitude (EVM) is minimized subject to the allowed CM and out-of-band radiation constraints. Although this optimization problem is nonconvex, our analysis shows that after modifications it can be transformed into a convex problem, which can be solved effectively. The proposed method is an optimal CM-reduction technique and exhibits better performance than other techniques with distortion, which is verified by simulation results.