Treffer: Inband and Out-of-Band Performance Evaluation of Downlink CF-mMIMO-OFDM Under Low-Resolution DACs

Cell-free massive MIMO (CF-mMIMO) technologyhas proved to offer significant gains in terms of spectral efficiency (SE). However, it can be economically attractive onlywhen adopting low cost and energy-efficient hardware. Thishardware includes components such as low-resolution digitalto-analog converters (DACs), and causes signal distortions calledhardware impairments (HWI). In this paper, first, we proposean analytical characterization for low-resolution DAC where theexact behavior can be described, allowing to shine a new lighton DAC-induced distortions. Based on the well-known Bussgangdecomposition, we derive for a known signal distribution throughclosed-form expressions based on the integer and fractionalresolution separately for downlink SE performance of orthogonalfrequency multiplexing (OFDM) based CF-mMIMO. Moreover,we propose a new CF-mMIMO-specific framework to observethe out-of-band (OOB) radiations on potential victim users. Wepoint out that OOB radiations is less of a problem in multi-userCF-mMIMO, where the total OOB radiated power is sufficientlylow to respect any standard mask. Meanwhile, inband distortionsrepresent a serious problem that have to be tackled.