Input Back-Off Optimization in OFDM Systems Under Ideal Pre-Distorters

In this letter, we have analyzed the effects of nonlinear distortion introduced by high-power amplifiers (HPAs) on orthogonal frequency division multiplexing systems. By using established results on nonlinear processes with Gaussian inputs, we derived an optimum input back-off (IBO) level for maximum signal-to-noise-plus-distortion ratio initially in additive white Gaussian noise channels, but being the results further extended to time dispersive channels. Considering the HPA and channel characteristics as fixed, our formulation and numerical results have demonstrated that the optimum IBO level depends only on the channel noise power and the saturation power of the HPA. Thus, it is independent of the input signal peak-to-average power ratio, modulation order, and number of subcarriers.