This book features selected papers presented at the 5th International Conference on Wireless Communications and Applications (ICWCA 2021), held at Hainan University, China. The book will focus on the presentation of the newest trends and achievements in the development of intelligent algorithms and network technologies in smart communications, with application in underwater communications, IoT-based marine surface communications as well as state-of-the-art real-time precise location technologies, WiFi/Bluetooth locationing, array signal processing and many others.