Optimizing Index Allocation for Sequential Data Broadcasting in Wireless Mobile Computing Ming-Syan Chen, Senior Member, IEEE, Kun-Lung Wu, Member, IEEE Computer Society, and Philip S. Yu, Fellow, IEEE M 郭文漢

Outline 1. Introduction 2. Preliminaries 3. Index Allocation for Skewed Data Access 4. Optimal Order for Sequential Data Broadcasting

Introduction 背景 建立 index tree Algorithm CFAlgorithm VF Optimal order for sequential data broadcasting 解決方法效益 節省電力 Algorithm ORD 舊方法問題 問題 不使用 Data Access Skew 有限電力

Introduction A mobile client to be able to operate in two different modes: doze mode and active mode. The structure of an index tree determines the index probing scenario to switch between the doze and the active modes for data access under such an indexed broadcasting. Data Access Skew ： The access frequencies of different data records are usually different from one another.

Introduction I a1a2 a3 R1R2R3R4R5R6R7R8R9 Ia1R1R2R3a2R4R5R6a3R7R8R9 Indexed broadcasting Index tree Index probing scenario to data record R5

Preliminaries A mobile client is assumed to use selective tuning to listen to indexed sequential data broadcasting. Tuning time ： The amount of time spent by a client to listen to the channel. Access time ： The time elapsed from the time a client wants an identified record to the time that record is downloaded by the client.

Preliminaries Probe wait ： The time from the point a client tunes in to the point when the first index is reached. Bcast wait ： Time duration from the point the first index is reached to the point the required record is obtained.

Preliminaries Tuning time Client I a1a2 a3 R1R2R3R4R5R6R7R8R9 Probe wait Bcast wait

Index Allocation For Skewed Data Access 1. Imbalanced Index Tree Construction for Fixed Fanouts 2. Employing Variant Index Fanouts to Minimize Index Probes 3. Experimental Results on Index Allocation

Imbalanced Index Tree Construction for Fixed Fanouts Algorithm CF will reduce the number of index probes for hot data while allowing more probes for cold data. Algorithm CF ： Use access frequencies to build an index tree with a fixed fanout d.

Algorithm CF (bottom up manner) Step 1 ： Every single node labeled with the corresponding access frequency. Step 2 ： Attach the d subtrees with the smallest labels to a new node. Label the resulting subtree with the sum of all labels from its d child subtrees. Step 3 ： n=n-d+1. If n=1 stop else goto Step2

Algorithm CF R1 0.4 R2 0.4 R R R R R R R a R1 0.4 R2 0.4 R R R R R R R a R1 0.4 R2 0.4 R R R R R R R a a R1 0.4 R2 0.4 R R R R R R R a a1 0.2

Algorithm CF a R1 0.4 R2 0.4 R R R R R R R a a1 0.2 I IR1R2a1R3a2R4R5R6a3R7R8R9 Corresponding data broadcasting sequence

Cost Model Theorem 1 ： Given a fixed index fanouts, the average number of index probes is minimized by using the index tree constructed by algorithm CF. Cost model

Cost Model

Employing Variant Index Fanouts to Minimize Index Probes An efficient heuristic algorithm VF to build an index tree with variant fanouts. We want data records to stay as close to the root as possible. Algorithm VF strikes a compromise between these conflicting factors( larger fanouts) and minimizes the average cost of index probes.

Employing Variant Index Fanouts to Minimize Index Probes

Algorithm VF (top down manner)

Algorithm VF

R1R2R3R4R5R6R7R8R9R10R

Experimental Results on Index Allocation

Optimal Order for Sequence Data Broadcasting 1. Ordering Broadcasting Data to Minimize Data Access Time 2. Experimental Results on Order of Broadcasting 3. Remarks

Ordering Broadcasting Data to Minimize Data Access Time

Algorithm ORD

Experimental Results on Order of Broadcasting

Remarks AlgorithmComplexityOperation CFsorting VFrecursive ORDsorting

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