Power-Controlled Data Prefetching/Caching in Wireless Packet Networks

Savvas Gitzenis, Nicholas Bambos

Abstract: We investigate efficient schemes for data communication from a server to a mobile terminal over a wireless channel of fluctuating quality. A user requests to access various data items on the terminal. If a requested item is found in the local terminal buffer or cache, no access delay is incurred. If not, it is downloaded from the server and the user incurs a delay cost until it becomes locally available. Moreover, a power cost is incurred to transmit the data item at a selected power level over the wireless link. To lower both the average delay and power costs, the system may prefetch data items and predictively cache them on the terminal - especially during link quality 'highs' - in anticipation of future user requests. The goal is to minimize the overall delay and power cost, by judiciously choosing which data item to fetch and what power level to use, given the current user, buffer, and channel states. We develop a modeling framework - based on controlled Markov chains and dynamic programming - capturing the essential performance tradeoffs in the system and allowing computation of optimal decisions on items to (pre)fetch and power levels to use. To cope with emerging complexities, we then design efficient heuristics, whose simulation analysis demonstrates substantial performance gains over standard approaches.