4.3.1 Existing Recommendation Techniques -- 4.3.1.1 Content-Based Filtering Algorithms -- 4.3.1.2 Collaborative Filtering Recommendation Algorithm -- 4.3.1.3 Improvement to Recommendation Systems -- 4.3.2 Location Recommendation Systems in Location-Based Social Networks -- 4.4 Conclusion -- References -- CHAPTER 5: PROXIMITY-SERVICE APPLICATION DEVELOPMENT FRAMEWORK -- 5.1 Introduction -- 5.2 Overview of Proximity Service (Basic Concept and Development View Point) -- 5.2.1 Over-the-Top and Device-to-Device Development Pattern -- 5.2.2 Typical Scenarios of Proximity Services -- 5.2.2.1 Public Safety Communication -- 5.2.2.2 Discovery Mode -- 5.2.3 Two Different Viewpoints for ProSe Development -- 5.3 From ProSe Application Designers' View: Components, Requirements, and Existing Works -- 5.3.1 Requirements in Developing ProSe Applications -- 5.3.1.1 Physical Layer -- 5.3.1.2 Context Layer -- 5.3.1.3 Application Layer -- 5.3.1.4 Crosslayer -- 5.3.2 Comparison of Existing ProSe Applications and Solutions -- 5.4 From ProSe Development Framework Builder View: Benefits and Challenges -- 5.4.1 Benefits of Introducing Development Framework -- 5.4.2 Challenges in Building ProSe Application Development Framework -- 5.5 Summary of Existing ProSe Application Development Frameworks -- 5.5.1 Commotion Wireless Project -- 5.5.2 Serval Project -- 5.5.3 AllJoyn -- 5.5.4 Proxima -- 5.5.5 Crossroads -- 5.5.6 USABle -- 5.5.7 CAMEO -- 5.6 Conclusion -- References -- PART II: FUNDAMENTAL ISSUES -- CHAPTER 6: SMARTPHONE-BASED HUMAN ACTIVITY RECOGNITION -- 6.1 Introduction -- 6.2 Background -- 6.2.1 Common Sensors Embedded in Smartphones -- 6.2.1.1 Accelerometer -- 6.2.1.2 Compass Sensor -- 6.2.1.3 Gyroscope -- 6.2.2 Activities -- 6.3 Core Techniques -- 6.3.1 Raw Data Collection and Preprocessing -- 6.3.1.1 Types of Errors