Inband and out-of-band performance evaluation of downlink CF-mMIMO-OFDM under low-resolution DACs
Résumé
Cell-free massive MIMO (CF-mMIMO) technology
has proved to offer significant gains in terms of spectral efficiency (SE). However, it can be economically attractive only
when adopting low cost and energy-efficient hardware. This
hardware includes components such as low-resolution digitalto-analog converters (DACs), and causes signal distortions called
hardware impairments (HWI). In this paper, first, we propose
an analytical characterization for low-resolution DAC where the
exact behavior can be described, allowing to shine a new light
on DAC-induced distortions. Based on the well-known Bussgang
decomposition, we derive for a known signal distribution through
closed-form expressions based on the integer and fractional
resolution separately for downlink SE performance of orthogonal
frequency multiplexing (OFDM) based CF-mMIMO. Moreover,
we propose a new CF-mMIMO-specific framework to observe
the out-of-band (OOB) radiations on potential victim users. We
point out that OOB radiations is less of a problem in multi-user
CF-mMIMO, where the total OOB radiated power is sufficiently
low to respect any standard mask. Meanwhile, inband distortions
represent a serious problem that have to be tackled.
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