This book covers concepts and technologies that are most relevant to today's communication systems and presents them in a concise and intuitive manner. The book covers advanced topics such as OFDM and MIMO, which are enabling technologies for modern communication systems such as WiFi (including the latest enhancements) and LTE-Advanced. These two systems are described in some detail as examples of MIMO application. The book also describes other emerging technologies massive MIMO and mm-wave communications, which will likely be used in 5G cellular systems.