On channel adaptive wireless cache invalidation and game theoretic power a ware wireless data access
Abstract of thesis entitled
On Channel Adaptive Wireless Cache Invalidation and Game Theoretic Power Aware Wireless Data Access
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 broadcasting 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 performance 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 adaptation 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 invalidation 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 information. 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
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:cache memory mobile computing energy consumption telecommunication traffic
Date of Publication:01/01/2004