Adaptive Step Size for OFDM CFR with Cognitive Clipping

In this paper, an adaptive step size algorithm is proposed to reduce peak-to-average power ratio (PAR) of OFDM signals. The error vector magnitude (EVM) and spectral mask constraints are considered. Unlike the existing cognitive clipping method, the proposed scheme adjusts the EVM threshold with adaptive step size, which is proportionate to the ratio between PAR of each OFDM symbol and that required by system. Compared with the original method, the new algorithm offers more than 0.2 dB PAR reduction at 10^-4 complementary cumulative distribution function (CCDF) level and 20% iteration reduction for 256 subcarriers QPSK WiMAX signal.