Constrained Clipping for Crest Factor Reduction in OFDM

In this paper, we propose a constrained clipping method for reducing the peak to average power ratio (PAR) or crest factor of an orthogonal frequency division multiplexing (OFDM) signal. This is a transmitter-side processing technique that does not impose any modification at the receiver. Specifically, constrained clipping achieves PAR reduction while simultaneously satisfying spectral mask and error vector magnitude (EVM) constraints which are specified by most modern communications standards. Our proposed constrained clipping method consists of two independent processing units, one to satisfy the in-band EVM constraint and the other to satisfy the out-of-band spectral constraint. Achievable PAR reduction results vary depending on the particular standards´ requirements, but we show that by using constrained clipping on a QPSK WiMax signal with 256 subcarriers, a 4.5 dB PAR reduction at the 10^-2 complementary cumulative distribution function (CCDF) level can be obtained