On Channel Adaptive Wireless Cache Invalidation and Game Theoretic Power a Ware Wireless Data Access

This dissertation, "On Channel Adaptive Wireless Cache Invalidation and Game Theoretic Power a Ware Wireless Data Access" by Kai-ho, Mark, Yeung, 楊啟豪, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled On Channel Adaptive Wireless Cache Invalidation and Game Theoretic Power Aware Wireless Data Access submitted by Mark Kai Ho YEUNG for the degree of Master of Philosophy at The University of Hong Kong October 5, 2004 The availability of on-demand information access in client-server wireless networks would provide valuable support to many interesting mobile computing applications. Researchers have proposed two promising techniques to mitigate the existing bandwidth and energy constraints: data broad- casting and client caching. Data broadcasting exploits the sharing nature of the wireless medium, while client caching leverages the skewed access pattern. The major challenge of client caching is to maintain cache consistency. Clients should ensure that the cache is valid before using it to answer any query. Several cache invalidation schemes have been proposed, most of which also take advantage of data broadcasting. The basic scheme is to broadcast periodic invalidation reports (IR). Recently, the addition of updated invalidation reports (UIR) has been proposed. The IR+UIR scheme achieves a much shorter query delay than the basic IR scheme. However, existing invalidation schemes are based on two impractical simplifying assumptions: (1) the broadcast channel is error-free; and (2) no other downlink traffic exists. We studied the per- formance of IR and IR+UIR under a more realistic system model: (1) the quality of the wireless channel is time-varying; and (2) there are other downlink traffic sources in the system. Link adap- tation allows more efficient use of bandwidth via dynamically adjusting the transmission rate with channel quality. In the light of these observations, we propose three cache invalidation schemes to meet the challenges inherent in these two assumptions. Our results indicate that the proposed schemes outperform both IR and IR+UIR under a wide range of system parameters. Inevitably, every cache consistency scheme involves communication overheads between server and clients. Each mobile client expends additional battery energy in: (1) processing of cache in- validation information; and (2) replacing obsolete entries with updated ones. However, the extra energy cost incurred may not always justify the amount of energy conserved from caching. This motivates us to study the detailed energy consumption characteristics of the on-demand data access process. Apparently, without caching, each client should always request the server for informa- tion. Using game theory, we show that a without-cache scheme can achieve similar effects as with-cache schemes. We also compare the performance of without-cache and with-cache schemes, and demonstrate that caching does not always conserve energy for every client. In particular, caching benefits clients with high query rates, but reduces the lifetime of other clients. (Total words: 383) Mark Kai Ho YEUNG DOI: 10.5353/th_b2979797 Subjects: Cache memory Mobile computing - Energy consumption Telecommunication - Traffic