In this letter, we derive an approximate analytical expression for the uplink achievable rate of a massive multiinput multi-output (MIMO) antenna system when finite precision analog-digital converters (ADCs) and the common maximalratio combining technique are used at the receivers. To obtain this expression, we treat quantization noise as an additive quantization noise model. Considering the obtained expression, we show that low-resolution ADCs lead to a decrease in the achievable rate but the performance loss can be compensated by increasing the number of receiving antennas. In addition, we investigate the relation between the number of antennas and the ADC resolution, as well as the power-scaling law. These discussions support the feasibility of equipping highly economical ADCs with low resolution in practical massive MIMO systems.Index Terms-massive MIMO, quantization, AQNM, uplink rate, MRC.
Three-dimensional
(3D) printing technologies are widely applied
in various industries and research fields and are currently the subject
of intensive investigation and development. However, high-performance
materials that are suitable for 3D printing are still in short supply,
which is a major limitation for 3D printing, particularly for biomedical
applications. The physicochemical properties of single constituent
materials may not be sufficient to meet the needs of modern biotechnology
development and production. To enhance the materials’ performance
and broaden their applications, this work designed and tested a series
of titanate nanofiller (nanowire and nanotube)-enhanced polycaprolactone
(PCL) composites that were 3D-printable and provided superior mechanical
properties. By grafting two different functional groups (phenyl- and
thiol-terminated ligands), the nanofiller surface showed improved
hydrophobicity, which significantly improved their dispersion in the
PCL matrix. After characterizing the surface modification, we evaluated
the significance of the homogeneity of the ceramic nanofiller in terms
of printability, formability, and mechanical strength. Melt electrowriting
additive manufacturing was used to fabricate microfibers of PCL and
PCL/nanofiller composites. Improved nanofiller dispersion enabled
intact and uniform sample morphology, and in contrast, nanofiller
aggregation greatly varied the viscosity during the printing process,
which could result in poorly printed structures. Importantly, the
modified ceramic/PCL composite delivered enhanced and stable mechanical
properties, where its Young’s modulus was measured to be 1.67
GPa, which is more than 7 times higher compared to that of pristine
PCL (0.22 GPa). Retaining the cell safety properties (comparable to
PCL), the concept of enhancing biocompatible polymers with modified
nanofillers shows great potential in the field of customized 3D printing
for biomedicine.
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