  Satellite communications have recently entered a period of renewed interest
motivated by technological advances and nurtured through private investment and
ventures. The present survey aims at capturing the state of the art in SatComs,
while highlighting the most promising open research topics. Firstly, the main
innovation drivers are motivated, such as new constellation types, on-board
processing capabilities, nonterrestrial networks and space-based data
collection/processing. Secondly, the most promising applications are described
i.e. 5G integration, space communications, Earth observation, aeronautical and
maritime tracking and communication. Subsequently, an in-depth literature
review is provided across five axes: i) system aspects, ii) air interface, iii)
medium access, iv) networking, v) testbeds & prototyping. Finally, a number of
future challenges and the respective open research topics are described.
