The goal of this project is to carry out research on sensing social context, modeling human behavior and developing a new mobile architecture for social applications. It will build a new analyzing system by combining the latest navigation technology and self-contained sensors to capture the social contexts in real time and use the system to study human movement and behavior in natural environments. A handheld platform consisting of several navigation sensors and a visual sensor will be developed for sensing social contexts. The navigation sensors include an accelerometer, a digital compass, a gyroscope, a high sensitivity GPS receiver, a WLAN and a Bluetooth chip, while the visual sensor is a digital camera. In addition to the handheld sensor platform, a network consisting of pseudolites, WLAN and Bluetooth base stations will be used for composing a multi-sensor multi-network solution of positioning and motion detection. All these sensing technologies are miniature in size, meet the design constraints of mobile devices and are suitable for studying social context when moving in natural environments. The system will be tested with different groups of people on test fields that have different pre-defined attractions and relevant social contexts. Real-time modeling of human behavior in relation to the social environment will be investigated. Furthermore, architecture for mobile social applications will be developed for exploring the potential applications such as assisted living and abnormal behavior detection. The project will deliver an entire solution that includes sensing social contexts, modeling human behavior and developing a related mobile social application.