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In this thesis, after a short overview of information theoretic results, we show improvements in reliability, efficiency, and coverage in three different scenarios of satellite communications. First, we present a solution that could improve speed or reliability in broadcast and unicast satellite connections. It is based on the idea that two (or more) neighbor users could cooperate using a side-channel to exchange information about the received signals. Different possible schemes are derived and analyzed. To make it more realistic, we used the hypothesis that the side-channel has not an infinite capacity but it is constrained to a maximum fixed information rate that could pass through it. The second scenario is about Earth observation satellites. A suitable scheme for both transmitters and receivers is found, describing the improvements in spectral efficiency through the use of a signal predistorter and optimization of the transmission parameters. Moreover, we discuss the benefits of advanced low-complexity receivers. The last scenario, describes a way to extend the coverage of Internet of Things (IoT) networks in areas far from the gateway, through a Low Earth Orbit (LEO) satellite. The study is based on a proprietary IoT protocol called LoRa, designed to be used on Earth. We describe the main properties of the LoRa modulation and propose a receiver scheme that could allow the reception of LoRa signals on a LEO satellite scenario, where Doppler effects can be detrimental.