Spatio-Temporal Delta-Sigma Modulation for Massive MIMO with Low-Resolution DACs

Going toward extreme multiple input multiple output (MIMO) antenna systems, each individual radio frequency (RF) chain will require cost and energy efficient implementations. While low resolution digital-to-analog converters (DACs) present a straightforward path toward achieving this goal, the introduced quantization error will lead to degraded performance. In this paper, we propose the use a spatio-temporal delta sigma modulation (DSM) placed upstream of the converter in a downlink massive MIMO-orthogonal frequency division multiplexing (OFDM) scenario. Its role is to shape quantization noise in frequency and in space, casting it toward unused directions and frequency resources. At the heart lies an optimization based design of the modulator’s noise transfer function (NTF) using available channel state information (CSI). A constraint to shape quantization noise away from adjacent frequency bands is studied as well. Numerical results show that the additional temporal dimension enables better error vector magnitude (EVM) performance than the recently thriving spatial DSM. Additional filtering is however still required to reach spectral masks set by current communication standards.