Improving Analog Zero-Forcing Null Depth with N-bit Vector Modulators in Multi-beam Phased Array Systems

Multiantenna systems can increase the spatial reuse of the wireless spectrum by nulling the interfering directions. However, the efficiency of the spatial interference suppression is highly sensitive to errors in the progressive phase applied to the antenna elements. We examine the impact of one particular source of error resulting from the quantization of the analog beamforming weights. In particular, we focus on vector-modulator based RF beamforming system. To improve the quantization error, we propose a sliding reference approach for using a floating phase reference minimizing the quantization error of the RF beamformer. Monte-Carlo simulations are performed to analyze the performance of the zeroforcing with quantized coefficients. With small arrays, the simulation results showed almost 10 dB of improvement in the average null depth compared to the conventional round-off method.