Mobile Networks and Applications
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Multimedia-enabled mobile devices need to support multimedia quality of service (QoS) requirements under limited battery energy and also provide new opportunities due to the adaptive hardware and software components. Researchers have therefore introduced adaptation into various system layers. Previous adaptation work often adapts only some layers or only at coarse time. We believe that to fully reap the benefits of adaptation, it is necessary to take a cross-layer adaptation approach, in which all system layers adapt cooperatively in response to system changes at different time granularity. This thesis presents a novel operating system, called GRACE-OS, to support such cross-layer adaptation by coordinating the adaptation in different layers and enforcing the coordinated decisions via energy-aware real-time scheduling. This thesis makes four major contributions. First, we propose a hierarchical adaptation framework to coordinate adaptation in different layers. This framework consists of global and internal adaptation. The former coordinates all three layers in response to large system changes, while the latter adapts each individual layer in response to small system changes. Second, we extend traditional real-time scheduling to decide how fast to execute applications in addition to when to execute what applications. Third, we develop a set of algorithms for internal adaptation algorithms to handle small variations in application CPU demand. Finally, we develop a kernel-based profiling technique predict the CPU demand of multimedia applications for both global and internal adaptation.We have implemented GRACE-OS in the Linux kernel and evaluated it with adaptive Athlon processor and adaptive video codec applications. Our experimental results show that GRACE-OS efficiently trades off QoS for energy with acceptable overhead. In particular, compared to previous systems that adapt only some system layers, GRACE-OS achieves the user-desired battery lifetime and saves energy by up to 59% while providing better or the same multimedia quality. Compared to previous systems that adapt only at coarse time granularity, GRACE-OS saves energy by 2% to 8.9% without affecting multimedia quality.