I. Introduction
Health monitoring plays an important role in disease diagnosis and treatments. For instance, electrocardiogram (ECG) monitoring or fall detection systems can help to detect abnormalities and send messages to caregivers about the abnormalities in real-time. Recently, fall detection systems using wearable devices are widely used because of several advantages such as light-weight, low-cost, energy efficiency and non-intrusiveness [1]–[4]. These wearable devices often collect 3-dimensional (3-D) acceleration or 3-D angular velocity or both of them from a human body. The devices then transmit the collected data to a gateway which forwards the data to cloud. However, there are still drawbacks in these systems. For instance, they cannot function properly in many scenarios like areas with unstable or lack of a Internet connection.