OPTIMUM OUTPUT POWER BACK-OFF in NON-LINEAR CHANNELS for OFDM BASED WLAN

Cyclically extended OFDM based WLAN systems have the capability to easily counteract frequency selective fading channels by one-tap equalizers in the frequency domain. Conversely, the sensitivity to nonlinear distortions, mainly introduced by power amplifiers, is one of the drawbacks of this modulation technique. Usually, the optimum Output power Back Off (OBO) is the one that minimizes the Total Degradation. Aim of this work is to show that the optimum OBO is a function of the channel behavior (e.g. AWGN, frequency selective Rician or Rayleigh fading channels). The effectiveness of amplifier predistortion and the gain introduced in the system link budget is also considered for different M-QAM constellation size. Computer simulations are shown and compared to an analytical approach.