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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. M9129022 郭文漢. Outline. Introduction Preliminaries
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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 M9129022 郭文漢
Outline • Introduction • Preliminaries • Index Allocation for Skewed Data Access • Optimal Order for Sequential Data Broadcasting
Introduction 背景 問題 舊方法問題 解決方法 效益 Optimal order for sequential data broadcasting 建立index tree 有限電力 節省電力 不使用 Data Access Skew Algorithm CF Algorithm VF Algorithm ORD
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 theindex 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 Indexed broadcasting Index tree a3 a1 a2 R1 R2 R3 R4 R5 R6 R7 R8 R9 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 Client Tuning time I Probe wait Bcastwait a3 a1 a2 R1 R2 R3 R4 R5 R6 R7 R8 R9
Index Allocation For Skewed Data Access • Imbalanced Index Tree Construction for Fixed Fanouts • Employing Variant Index Fanouts to Minimize Index Probes • 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 R4 0.05 R1 0.4 R2 0.4 R3 0.05 R4 0.05 R5 0.02 R6 0.02 R7 0.02 R8 0.02 R9 0.02 R2 0.4 a3 0.06 R3 0.05 R5 0.02 R6 0.02 R7 0.02 R8 0.02 R9 0.02 R1 0.4 R2 0.4 a2 0.09 a3 0.06 R3 0.05 R1 0.4 R2 0.4 a1 0.2 R4 0.05 R5 0.02 R6 0.02 R7 0.02 R8 0.02 R9 0.02 R3 0.05 a2 0.09 a3 0.06 R4 0.05 R5 0.02 R6 0.02 R7 0.02 R8 0.02 R9 0.02
Algorithm CF I R1 0.4 R2 0.4 a1 0.2 a2 0.09 a3 0.06 R3 0.05 R4 0.05 R5 0.02 R6 0.02 R7 0.02 R8 0.02 R9 0.02 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
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.
Optimal Order for Sequence Data Broadcasting • Ordering Broadcasting Data to Minimize Data Access Time • Experimental Results on Order of Broadcasting • Remarks
