隨著無線技術接受度的增加，把資訊很有效率地傳送給客戶端是個很重要的問題。跟客戶端相比較的話，資訊的伺服器端有較多的可用頻寬，所以我們所考慮的環境是不對稱的。於此情況下，在伺服器端，應該週期性地來廣播資訊，這樣的系統已經被提出。在行動計算的背景下，Acharya 等人已經提出一個使用週期散播的架構，稱為廣播磁碟(Broadcast Disks)。使用廣播磁碟可以建立一個階層式結構，其中最高層次含有較少項目並且以較高頻率來廣播它，之後的層次含有越來越多的項目並且以越來越少的頻率來廣播它。然而，基於Acharya等人的方法，如果在磁碟上之資料量無法很平均地被分成某些區塊，則一些廣播的槽縫位置就會沒有被使用到而導致頻寬的浪費和存取時間的增加。Yang已提出一彌補空槽的方法 （彌補法）不僅解決空槽所導致的問題，且減少了平均存取時間。然而，基於彌補法，兩相同資料頁的間距並不固定，這會導致平均存取時間的增加。在這篇論文裡，我們提出了兩個方法來改善上述的現象，並解決空槽的問題。一個是改良式的彌補空槽方法，另一個是可調適的方法。在過去大部分的研究中，大都假設客戶端一次只需要一個資料。但在現實生活中，很多時候客戶端一次需要多個資料。Ke已提出在多個廣播頻道中針對查詢資料群所設計的廣播排程方法，稱為不重疊的集合基準法（Set-based strategy – Non-overlap version）。不重疊的集合基準法儘量將一集合中的資料放在一起，還儘量不將同個集合中的資料放在同一時槽中。但是不重疊的集合基準法有兩個缺點：（1）一個擁有高存取率的資料會被排在廣播週期的末端，這會使得總期望存取時間增加；（2）某頻道的時槽會一直被延伸，而導致其他頻道頻寬的浪費。在這篇論文裡，我們提出一在多頻道中有效處理資料集合的廣播排程方法，稱為混合式的集合基準法（Hybrid Version of the Set-based strategy）。從效能分析和模擬測試中，我們顯示出我們所提的兩個方法比廣播磁碟法產生比較短的廣播週期，也比廣播磁碟法和彌補法需要較短的平均存取時間。此外，我們的混合式集合基準法比不重疊的集合基準法產生較短的廣播週期和較少的空槽並需要較短的總期望存取時間。

With the big improvement of wireless technology, people can get their desired
information at any time and any place. Due to communication asymmetry -
physical asymmetry and/or information ow asymmetry, broadcast data deliv-
ery is rapidly becoming the method of choice for disseminating information from
server to clients. The main advantage of broadcast delivery is its scalability:
it is independent of the number of users the system is serving. Acharya et al.
have proposed the use of a periodic dissemination architecture in the context of
mobile systems, called Broadcast Disks. Broadcast Disks can construct a mem-
ory hierarchy in which the highest level contains a few items and broadcasts
them with high frequency while subsequent levels contain more and more items
and broadcast them with less and less frequency. However, based on Acharya
et al.'s approach, some broadcast slots may be unused, which resulting in the
waste of bandwidth and the increase of access time. Yang has presented a com-
plementary approach to solve the empty slots problem, which also reduces the
mean access time. However, based on the complementary approach, the dis-
tances between slots containing the same page may not be a constant, resulting
in an increase of the mean access time. Therefore, in this thesis, we propose
two eÆcient broadcast programs to mitigate the above phenomenon and also
to solve the empty slots problem. The rst one is a revised version of the com-
plementary approach, and the second one is an adaptive approach. Most of the
previous approaches assume that each mobile client needs only one data page.
However, in many situations, a mobile client might need data of more than one
page. Ke has proposed the SNV strategy for query set broadcast scheduling
in multiple channels. In the SNV strategy, the data pages of the same query
set are put as together as possible and it tries to avoid scheduling two or more
pages of one query set at the same time slot of di erent channels. However,
there are two disadvantages in the SNV strategy: (1) a data page with high
access frequency may be scheduled at a time slot near the end of the broad-
cast cycle, which results in the longer access time for requiring the whole query
sets; (2) it may extend the number of slots in a certain chain, which results
in the wasteness of bandwidth of the other channels. Therefore, we propose
an eÆcient broadcast scheduling strategy, the Hybrid Version of the Set-based
strategy ( HVS ) to improve these two disadvantages. From our performance
analysis and simulation, we show that both our revised version of the com-
plementary approach and adaptive approach create smaller number of slots in
one broadcast cycle than Acharya et al.'s algorithm and require shorter mean
access time than Acharya et al.'s algorithm and the complementary approach.
Moreover,from our performance analysis and simulation, we also show that our
HVS strategy requires shorter total expected delay access time, and creates
smaller number of slots and smaller number of empty slots in one broadcast
cycle than the SNV strategy.

TABLE OF CONTENTS
LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Mobile Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Data Broadcasting . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Motivations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.4 Organization of the Thesis . . . . . . . . . . . . . . . . . . . . . . . . 13
2. Related Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.1 Acharya et al.'s Broadcast Disks . . . . . . . . . . . . . . . . . . . . . 14
2.1.1 Broadcast Disks . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1.2 An Example of the Empty-Slot Problem . . . . . . . . . . . . 16
2.2 The Complementary Approach . . . . . . . . . . . . . . . . . . . . . 18
2.3 Query Sets-based Broadcast Programs . . . . . . . . . . . . . . . . . 19
2.4 Broadcast Scheduling for Multiple Channels . . . . . . . . . . . . . . 21
2.4.1 The Environment of Multiple Channels . . . . . . . . . . . . . 21
2.4.2 The Paged-based Scheduling . . . . . . . . . . . . . . . . . . . 22
2.4.3 The Set-based Scheduling . . . . . . . . . . . . . . . . . . . . 25
3. An Improvement of the Complementary Approach . . . . . . . . . 29
3.1 A Bad Case of the Complementary Approach . . . . . . . . . . . . . 30
3.2 Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.3 The Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.4 The Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.5 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4. An Adaptive Approach . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.1 The Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
5. The Hybrid Version of the Set-based Strategy . . . . . . . . . . . . 59
5.1 Two Bad Examples of the SNV Strategy . . . . . . . . . . . . . . . . 60
5.2 Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
5.3 Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5.4 Basic Ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
5.5 The HVS Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
5.6 Problems and Errors in the SNV Strategy . . . . . . . . . . . . . . . 85
6. Performance Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
6.1 The Performance Model of the Improvement of the Complementary
Approach and the Adaptive Approach . . . . . . . . . . . . . . . . . 97
6.2 Performance Analysis of the Improvement of the Complementary Ap-
proach and the Adaptive Approach . . . . . . . . . . . . . . . . . . . 100
6.2.1 Total Number of Slots in One Broadcast Cycle . . . . . . . . . 100
6.2.2 Mean Access Time . . . . . . . . . . . . . . . . . . . . . . . . 101
6.3 Simulation Results of the Improvement of the Complementary Ap-
proach and the Adaptive Approach . . . . . . . . . . . . . . . . . . . 107
6.3.1 The Performance of the Improvement of the Complementary
Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
6.3.2 The Performance of the Adaptive Approach . . . . . . . . . . 111
6.3.3 Improvement of the Complementary vs. Adaptive . . . . . . . 114
6.4 The Performance Model of the HVS Strategy . . . . . . . . . . . . . 117
6.5 Performance Analysis of the HVS Strategy . . . . . . . . . . . . . . 118
6.6 Simulation Results of the HVS Strategy . . . . . . . . . . . . . . . . 120
7. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
7.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
7.2 Future Research Directions . . . . . . . . . . . . . . . . . . . . . . . . 129
BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
A. The Details of Procedure FindChunk and Function FindEmpty . . 134
B. The Flowchart of Procedure Broadcast in the Improvement of the
Complementary Approach . . . . . . . . . . . . . . . . . . . . . . . . . 138
C. The Flowchart of Procedure ArrangePosition in the HVS Strategy 139
D. The Set-based Strategy - Non-overlap Version . . . . . . . . . . . . 140

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