Quantization error reduction scheme for hybrid beamforming

In a multiple-input multiple-output (MIMO) system of a large number of antennas, the requirement of an analog to digital converter (ADC) in each antenna string causes high implementation cost and excessive signal processing. Hence, a hybrid beamforming has been proposed in the literature as a solution. However, still quantization errors introduced at the analog beamformer part can lead to performance degradation. This paper is to present a quantization error reduction scheme for a hybrid beamformer in a 2 by 2 MIMO system. The key idea is to sacrifice the data rate from a full rate to a half rate, estimate all user data in a digital baseband, and then restore the received signal at each antenna string. By using the restored received signal and the residual (which is calculated in the estimator), quantization error can be reduced. Simulation results verify that the proposed scheme can improve the bit error rate performance with a resolution of smaller number of bits.