Principle of Communications is the first course on communication systems for undergraduate students, aiming to uncover how a communication system works and the underlying beautiful theoretical principles. It builds the foundations for students to explore more advanced topics related to communications, ranging from theoretical development to practical implementation, such as 5G communications, wireless networks, Internet of Things (IoT), etc. Lectures are developed to answer the following key question: how to reliably deliver information over an unreliable physical medium?
Towards answering this question, we begin with the interface between the cyber and the physical (electromagnetic) world and explain how to convert from digital data to analog signals and vice versa. Next, we introduce the simplest statistical model, the additive noise channel, which captures the unreliable feature of physical medium, and discuss how to perform optimal guessing for the data at the receiver. Then, we introduce the key concept of coding in order to achieve reliable communication, together with an example linear code. Finally, these principles are extended to other channel models, namely, wireline and wireless (4G, WiFi) channels, where new challenges such as inter-symbol interference (ISI) and fading need to be tackled. OFDM is introduced to cancel ISI while diversity techniques are developed to combat deep fading.