Some practical aspects of digital transmission

There are three worlds of digital transmission-digital transmission as an area of academic research, in which theoretical limitations and complicated schemes of modulation and encoding play the starring role; digital transmission in exotic space and military applications, in which it is, or may seem to be, worthwhile to search through the noise in a huge bandwidth in order to receive a few bits per second; and the digital transmission of everyday bulk communication. This article is concerned with that third area, in which apparatus must be economical and reliable; in which the FCC limits the bandwidth we may use in radio transmission; in which the increase in attenuation with frequency limits the bandwidth it is practical to use in cable transmission; in which error rates should be low enough that error correction is an expedient that need be resorted to only in special situations.