This contribution describes the concept and implementation of a wearable arm gesture recognition system based on motion tracking. The system relies on an ultrasound body area network for communication and to enable distance measurements between torso and arms. The network nodes use new capacitive micromachined ultrasonic transducer technology with increased bandwidth which allows multiple nodes to communicate simultaneously and share spectral resources. The operation and performance is shown with the help of a real time demonstrator for arm gesture recognition.