On the Quantization of Phase Shifters for Hybrid Precoding Systems

Hybrid precoding that combines analog RF processing and digital baseband processing has been shown to be a promising technique for transceivers with limited number of RF chains. The RF processing, due to power and complexity issue, is typically done by using phase shifters. A recent study shows that hybrid precoding is no loss of generality if each coefficient of the analog precoder is implemented by using two phase shifters. In this paper, we consider two possible implementation structures that use Two pHase shIfters for each Coefficient (THIC). These two structures, having the same performance when the phases can take on continuum values, behave differently upon quantization, as the analysis shows. For a small number of quantization bits, the precoder implemented using THIC is a good approximation of the unquantized one. With 3-bit phase shifters, the performance is close to that of the unquantized system in multiuser communications, where the performance is more sensitive to quantization errors. While the analysis in this paper is done assuming high-resolution quantization, simulations show that the result is accurate even for coarse quantization.