  Given the increasing number of space-related applications, research in the
emerging space industry is becoming more and more attractive. One compelling
area of current space research is the design of miniaturized satellites, known
as CubeSats, which are enticing because of their numerous applications and low
design-and-deployment cost. The new paradigm of connected space through
CubeSats makes possible a wide range of applications, such as Earth remote
sensing, space exploration, and rural connectivity. CubeSats further provide a
complementary connectivity solution to the pervasive Internet of Things (IoT)
networks, leading to a globally connected cyber-physical system. This paper
presents a holistic overview of various aspects of CubeSat missions and
provides a thorough review of the topic from both academic and industrial
perspectives. We further present recent advances in the area of CubeSat
communications, with an emphasis on constellation-and-coverage issues, channel
modeling, modulation and coding, and networking. Finally, we identify several
future research directions for CubeSat communications, including Internet of
space things, low-power long-range networks, and machine learning for CubeSat
resource allocation.
