  Scientific writing builds upon already published papers. Manual
identification of publications to read, cite or consider as related papers
relies on a researcher's ability to identify fitting keywords or initial papers
from which a literature search can be started. The rapidly increasing amount of
papers has called for automatic measures to find the desired relevant
publications, so-called paper recommendation systems.
  As the number of publications increases so does the amount of paper
recommendation systems. Former literature reviews focused on discussing the
general landscape of approaches throughout the years and highlight the main
directions. We refrain from this perspective, instead we only consider a
comparatively small time frame but analyse it fully.
  In this literature review we discuss used methods, datasets, evaluations and
open challenges encountered in all works first released between January 2019
and October 2021. The goal of this survey is to provide a comprehensive and
complete overview of current paper recommendation systems.
