On the effect of amplifier non-linearity on the capacity of MIMO systems

This paper investigates the effect of nonlinearity on the capacity of MIMO systems and develops a capacity-enhancing MIMO transmission technique suitable for deployments over nonlinear channels. Nonlinearity arises in communication systems in several ways. In this work, we focus on the nonlinearity introduced at the transmitter side by the High Power Amplifier (HPA), the last stage in the communication chain at the transmitter. Water-filling and Eigen beamforming solutions, which are well-known capacity-enhancing techniques in linear MIMO channel are re-examined for the case of nonlinear channels. We show that these algorithms degrade significantly when used over MIMO channels exhibiting nonlinearities, except when the amplifier nonlinear distortions effects are factored into the algorithms. Factoring the HPA effects into the algorithms, the capacity of the resulting nonlinear channel approaches the linear channel case.