MIMO-OFDM Downlink with Memoryful Hardware Non-Linearities

The frequency and spatial characteristics of nonlin-ear distortion from a MIMO-OFDM (multiple-input multiple-output orthogonal frequency-division multiplexing) basestation with memoryful nonlinear amplifiers (modeled by a generalized memory polynomial) is studied herein. We prove a theorem about a linear representation of the amplified signal from which the nonlinear distortion is obtained. Our measurement results demonstrate that the generalized memory polynomial can provide better accuracy of the nonlinear distortion than the memoryless and memory polynomial models. Furthermore, it is shown that in contrast to the memoryless amplifier, the amplifier with memory can distort the useful linear signal and introduce interference in a wider range of sub carriers. The derived theory is useful to predict how the nonlinear distortion will behave, to analyze the in-band and out-of-band radiation, and to schedule users in the frequency plane to minimize the effect of nonlinear distortion.