This book concerns digital communication. Specifically, it addresses the transport of bit streams from one geographical location to another over various physical media, such as wire pairs, coaxial cable, optical fiber, and radio. It also discusses multiple-access channels, where there are potentially multiple transmitters and receivers sharing a common medium. Ten years have elapsed since the second edition, and there have been remarkable advances in wireless communication, including cellular telephony and wireless local-area networks. This third edition expands the treatment of communication theories underlying wireless technology, especially advanced techniques involving multiple antennas, which transform the traditional single-input single-output channel into a multiple-input multiple-output (MIMO) channel. This is more than a trivial advance, as it stimulates many advanced techniques such as adaptive antenna.