Vector Modulator-Based Analog Beamforming Using the Least Euclidean Distance Criterion

Abstract

In traditional multiple-input multiple-output (MIMO) receivers, radio frequency (RF) front-ends are exposed to interference as no analog spatial filtering is employed before the digital beamforming stage. Therefore the RF front-end is power-hungry, and analog to digital converters require a high dynamic range. In this paper, we consider an analog beamforming system in case of narrowband signals to cancel interference early in the analog domain, thus reducing the required ADC resolution. In contrast to existing analog beamformers with only phase shifts, our proposed design employs vector modulators where the coefficients can be selected from a set of weights with variable phases and amplitudes. We also propose an efficient and fast Euclidean distance algorithm to determine the analog beamformer coefficients while being suitable for realistic scenarios. Finally, an expression is introduced to estimate the interference rejection achieved by employing the proposed algorithm and a vector modulator in the RF domain. The introduced algorithm leads to considerable improvement in computational complexity by slightly sacrificing interference rejection.