Abstract

Due to the limited power supply of mobile devices, much research has been done on reducing the power consumption of mobile devices in mobile computing environments. Since supporting indices on the broadcast data items can effectively reduce the power consumption of the mobile clients, most of the existing research on data broadcasting has focused on designing efficient indexing schemes. In this paper, we propose to cache indices on the mobile clients and to use cached indices to facilitate the access of the broadcast data items. To manage the cache usage of the mobile clients, we propose two cache management policies. The lower-level-index-first policy caches the index nodes that are at the lower level of the index tree, while the cut-plane-first policy caches the index nodes that belong to a cut-plane of the index tree. Through experiments, we compare the performance of the two proposed policies with some existing policies in terms of tuning time and access time. The experiments show that index caching significantly reduces the tuning time of a mobile client without increasing its access time. In terms of tuning time, the experiments show that, when the access pattern of a mobile client is not skew, the cut-plane-first policy outperforms the lower-level-index first policy, LRU and LRFU. On the contrary, when the mobile client has a small cache and its access pattern is skew, the lower-level-index-first policy outperforms the cut-plane-first policy, LRU and LRFU. In terms of access time, the lower-level-index first policy outperforms the cut-plane-first policy, LRU and LRFU.

Keywords: Index caching; Energy efficiency; Data broadcast; Power consumption

Article Outline

1. Introduction

2. Preliminaries

2.1. The broadcast structure

2.2. Index organization

3. Index caching

3.1. Using a cached index

3.2. Tuning time reduction and the location of an index node

4. Cache management

4.1. Cache management policies

4.2. The lower-level-index-first management policy

4.3. The cut-plane-first management policy

4.3.1. Phase 1: Cut-plane initialization

4.3.2. Phase 2: Cut-plane adjustment

4.3.3. The computational complexity of the CPF algorithm

5. Experimental results

5.1. Experiment 1: Effect of cache size on tuning time

5.2. Experiment 2: Effect of cache size on access time

5.3. Experiment 3: Effect of data access skew on tuning time

5.4. Experiment 4: Effect of data access skew on access time

5.5. Summary of the Effects of cache size and data access skew

5.6. Experiment 5: Effect of height of index tree

5.7. Experiment 6: Effect of degree of index tree

6. Conclusions and future work

References