Digital signal transmission over a wireless channel has become an important field due to the high flexibility and comfort of wireless connections for many users with the motto “telecommunications anytime and anywhere.” Therefore, in the following chapters, we describe the principles of such systems and their design in some detail. A significant part is devoted to the wireless channel. The parameters of electrical cables or optical fibers are approximately constant over time. Consequently, they have been characterized as time-invariant and described by an impulse response \(g_{c}(t)\) in Fig. 1.1 of Sect. 1.2.