臺灣博碩士論文加值系統

下一代無線通訊網路的目標是在任何時間、任何地點，向用戶提供高頻寬和新的服務。需要這種網路服務的使用者使行通訊網路的服務提供商考慮結合第三代行動系統與無線網路的優點。因此，網路選擇的方式對於在異質網路中保證服務品質扮演重要的角色。為了提高系統效能，我們提出了新的網路選擇演算法，保證轉換到其他網路是有利的，亦即保證用戶永遠有最佳連接。

在本篇論文中，我們測量無線網路的可用頻寬來確保使用者連結到最佳的網路，並利用使用者的位置、移動方向來避免頻繁的網路切換。目的是提高行動主機的總吞吐量和減少網路切換的次數以避免服務惡化。並透過系統模擬的方式來評估本文所提出方法的效能。實驗結果顯示我們的機制可以得到很好的改進並和我們的目標吻合。

The objective of next generation wireless network is to provide users with anywhere, any-
time connectivity, high bandwidth and novel data service. People demanding for this kind
of service cause cellular network provider to consider the integration of 3G cellular systems
and wireless LAN, since WLAN has the advantages of high data rates and unlicensed spec-
trum. Therefore, network selection technique plays a vital role in ensuring quality of service
in heterogeneous networks. To improve system performance, we propose a novel network
selection algorithm that guarantees making o® to the other access network is pro‾table,
which means mobile users is always-best-connected(ABC).
In our selection approach, in order to decide the optimum network for mobile users,
available bandwidths of all usable networks are estimated. User''s location, moving direction
is used to avoid frequent hando®s. This new approach is aimed at improving performances
with regard to total throughput/goodput and number of hando®s which deteriorates service
quality in mobile host''s life time. We evaluate the performance of our scheme via simulations
and the results agree with our goals.

1 Introduction 1
1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Research Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Our Contribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.4 Paper Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Related Works 4
2.1 UMTS-WLAN Internetworking Architecture . . . . . . . . . . . . . . . . . . 4
2.2 Relative Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3 ANSWER: Adaptive Network Selection in WLAN/UMTS EnviRonment 9
3.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2 Assumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3 De‾nition of Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.4 Available Bandwidth Estimation . . . . . . . . . . . . . . . . . . . . . . . . 11
3.5 Sojourn Time Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.6 Selection Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4 Performance Evaluation 15
4.1 Network Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.2 Performance Metrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.3 Mobility Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.4 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.4.1 Goodput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.4.2 Number of Vertical Handoffs . . . . . . . . . . . . . . . . . . . . . . . 22
4.4.3 Accuracy of Available Bandwidth . . . . . . . . . . . . . . . . . . . . 24
4.4.4 Dynamic sleep time . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5 Conclusions and Future Works 28
Bibliography 29

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