Novel adaptive techniques for digital beamforming quadrature amplitude modulation (QAM) receivers

This paper presents two efficient adaptive signal processing techniques for co-cancel interference suppression in digital beamforming Quadrature Amplitude Modulation (QAM) receivers. The adaptive techniques are employed at the receiver´s baseband in the digital signal processor, and a time-varying weight update is automatically generated at each iteration during the adaptation process. The first method separately updates the real and imaginary parts of the weight vector along their respective gradient directions with distinctive optimum step sizes, while the second method directly updates the weight vector components as complex numbers, aiming at minimizing the error signal in th next iteration. Computer simulations are performed to validate the effectiveness of the proposed techniques. The simulation results confirm that, compared to the classic complex-valued Least Mn Square (LMS) algorithm, both proposed techniques exhibit satisfying interference suppression performance, with th second method performing slightly better than the first one.