The combination of MIMO - OFDM is a very attractive solution for broadband wireless services. Thus, the two prominent fourth-Generation (4G) cellular systems, WiMAX and LTE-advanced, have both adopted MIMO - OFDM transmission at the physical layer. OFDM signal however suffers from nonlinear distortions when passed through High-Power Amplifier (HPA) at the RF stage. This nonlinear distortion introduces out-of-band spectral broadening and in-band distortions on the transmitted signals. 4G cellular standards have placed strict limits on the allowable spectral broadening in their spectrum mask specifications, to insure that data transmission on a given channel is not interfering significantly with an adjacent channel user.