Principle of Communications is the first course to communication systems for undergraduate students, and it aims to uncover how 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 wireless communications, wireless networks, Internet of Things, 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 world and explain how to convert from digital to analog and vice versa. Next, we introduce a first statistical model, the additive noise channel, that captures the unreliable feature of physical medium, and develop the principle for optimal reconstruction based on statistical decision theory. Then, we introduce the key concept of coding in order to achieve reliable communication, together with a concrete example: convolutional code. These principles are extended to further channel models, namely, wireline (telephone) channel and wireless channel, where additional challenges such as inter-symbol interference (ISI) and fading need to be tackled. OFDM is introduced to alleviate ISI while diversity techniques are developed to mitigate fading.