This book covers basic communications theory and practical implementation of transmitters and receivers. In so doing, the focus of this book is on digital modulation, demodulation methods, probabilities, detection of digital signals, spread-spectrum system design and analysis, radar and radar communications, volume search, acquisition, track and cognitive system processes. This book was written for those who want a good understanding of these basic principles. It also provides an intuitive and practical approach to digital communications with a hands-on approach including several examples for the reader to really understand these wireless techniques. Therefore, it is a valuable resource for anyone involved in wireless communications, networks, radar and cognitive systems. The reader will gain a broad understanding of these topics with examples of many types of commercial and military data link systems.