Compensation of nonlinear distortion in hybrid beamforming MIMO transmitters
Compensation of nonlinear distortion in hybrid beamforming MIMO transmitters is an open and challenging field of research. The goal of the study is to find an efficient method for linearization of power amplifiers in fully connected hybrid beamforming MIMO transmitters, which would not additionally increase the complexity of the system too much. In this paper, the polynomial-based compensation method of nonlinear distortion in hybrid beamforming MIMO transmitters is presented. The method is verified through comprehensive Matlab simulations. A 64x64 fully connected hybrid beamforming MIMO system with 2 RF branches on the transmitting side and 2 RF branches on the receiving side was considered. The proposed memory polynomial digital predistortion model is based on direct transmit-end feedback. Simulations were performed for different parameters of the memory polynomial model and analyzed. The obtained results are presented in graphical form, using Power Spectrum Density, and in numerical form, using metrics in time and frequency domain, such as Normalized Mean-Squared Error and Error Vector Magnitude. It is shown that the proposed memory polynomial digital predistortion model can very well compensate nonlinear distortion in fully connected hybrid beamforming MIMO transmitter. It has been also demonstrated that with increasing model complexity, ie with increasing memory depth and nonlinearity order of memory polynomial model, better compensation of nonlinear distortion in hybrid beamforming MIMO transmitters can be achieved.