Advances in Communication Systems: Theory and Applications, Volume 1 focuses on the innovations in the methodologies, technologies, processes, and applications in communication systems. The selection first offers information on signal selection theory for space communication channels, theories of pattern recognition, and digilock orthogonal modulation system. Discussions focus on digilock mechanization of an orthogonal modulation system, restrictions placed on practical system waveforms, minimum of distance recognition, synthesis of threshold function, and regular simplex coding. The text then ponders on telemetry and command techniques for planetary spacecraft and communication from weather satellite, including planetary missions, telemetry and command system philosophy, Tiros operation and performance, and the Nimbus spacecraft system. The book examines the information theory of quantum-mechanical channels, as well as the capacity of an ideal quantum-mechanical channel, amplifiers in spatial representation, quantum theory of parametric amplifiers, photon correlation, and moment formula for phase-locking amplifiers. The selection is a dependable reference for researchers in communications interested in the advancements in communication systems.