Quantized Precoding Under ACLR Constraints with FIR-DACs for Downlink MU-MIMO

Scaling massive multiuser multiple-input multipleoutput (MIMO) to larger antenna numbers constrains each chain in terms of power consumption and implementation. In this paper, the use of low resolution digital-to-analog converters (DACs) enabling these large scale arrays in downlink multiuser massive MIMO is studied with a focus on reaching adjacent channel leakage ratio (ACLR) targets. A quantization aware precoder with constraints on out-of-band (OOB) emissions is designed based on the multi-block alternate directions method of multipliers (ADMM) algorithm. With conventional DACs, simulation results indicate that these constraints do not provide sufficient ACLR. In response, Finite impulse response (FIR)DACs are introduced as a reconfigurable alternative to analog filters. Numerical results show that ACLR targets can be reached, even at 1 bit, at a lower hardware cost than high resolution DACs.