This document discusses microwave communication and digital microwave communication systems. It defines microwave frequencies as ranging from 300 MHz to 300 GHz, but focuses on 3 GHz to 30 GHz for communication. Digital microwave communication modulates a digital baseband signal onto an intermediate frequency or directly onto a microwave carrier using techniques like PSK, QAM, ASK, and FSK. It describes the development of analog and digital microwave systems over time with increasing transmission capacities. It also discusses different types of digital microwave stations and relay stations.