1	An Adaptive MP3 Player: Reducing Power Consumption and Increasing Application Performance Thomas Kunz Systems and Computer Engineering Carleton University http://kunz-pc.sce.carleton.ca/ tkunz@sce.carleton.ca
2	Mobile Computing Challenges
3	Related Work Typically, related work focuses on bandwidth variation Other resources are also constrained (memory, power, CPU capabilities) and may vary over time Majority of solutions: introduce proxy between client (application executing on mobile device) and server, proxy compresses and filters data stream sometimes, degree of compression depends on available bandwidth user mobility often not addressed/supported Other solutions: view mobile purely as User Interface (WWW browsers, Teleporting, ....) partition client application between mobile and proxy partition directed by application (Rover, MaROS, ....) partition transparent to application (our own focus)
4	Adaptive Mobile Applications: System Overview
5	Proposed Architecture
6	Mobile Code Toolkit: Proxy Objects
7	Mobile Code Toolkit: Components Extend JVM on client and proxy server Monitor Code Storage Object References and Profiling Object Server Remote Method Invocation Protocol Dynamic Decision Communication Control Layer Extend garbage collection to deal with remote references Provide abstractions to notify runtime system about environment and changes in environment (bandwidth, power, …), based on events and event notification
8	Required Info: Application Object Graph
9	Objects
10	Inter-Object Communication
11	Experimental Results Implemented MP3 player, decoder (set of heavily communicating objects) can execute locally or remotely Various performance experiments, study impact of Available Bandwidth (19.2 kbps – 2 Mbps) Relative CPU speed (Mobile CPU: Proxy CPU) 1:4 for laptop as client device 1:116 for Windows CE palmtop as client device Results (more details in paper): for high bandwidth and slow client, offloading decoder to proxy can speed up application performance by a factor of 20 and reduce power consumption by 95% For faster client devices, independent of bandwidth, no benefit (actually worse performance) when decoding sound samples in access network
12	Conclusions and Current Status Implemented Mobile Code Toolkit with small footprint for Windows CE devices Collected experimental evidence to verify validity of our approach Built framework to study scalability Started to improve RMI performance (reduced time by up to factor of 4, so far) Port to Palm OS (KVM problems): No reflection No serialization No JNI
13	Future Work Improve toolkit: better RMI performance, automatic generation of proxy objects, port to Palm OS, build object graph “on-the-fly”, dynamic partitioning decisions Study additional applications and more dynamic scenarios, including proxy-to-proxy handoffs Conflicting objectives (power saving vs. application performance) Interaction between application-aware (MP3 player reduces sound quality, sampling rate, …. ) and application-transparent (runtime system migrates decode objects from handset to proxy) adaptation