下一世代行動通訊系統將整合多個異質無線網路,因此,
如何為異質無線網路環境設計出有效的網路選擇機制 (Network Selection Scheme, NSS),
以符合行動終端 (Mobile Terminal, MT)的需求,這將是一項重要議題。
在本論文中,我們將提出一評分式網路選擇機制 (Score-Based NSS, SBNSS),
SBNSS考慮頻寬 (Bandwidth)、接收訊號強度 (Received Signal Strength, RSS)、
連線成本 (Connection Cost)
、3G費率 (Price)以及行動終端速度 (Velocity)
來設計網路評分函數(Network Score Function)。
在接收訊號強度的部分,其將設定最佳門檻值,而僅當接收訊號強度低於此門檻值時,
才會發生換手,以減少不必要的換手;在使用3G網路時,其會根據費率不同,讓使用者享受到不同的網路服務;而在頻寬的部分,
其可以有效地將頻寬的使用均分在各網路內,並且完善地使用網路頻寬,以降低阻斷和中斷的機率;至於速度部分,
其將依據行動終端的速度選擇適合的網路。透過模擬,
我們將呈現SBNSS較文獻上之相關機制於阻/中斷機率與水平/垂直換手率之優越性。

The next-generation mobile comunication system targets to integrate heterogeneous wireless
networks, how to design an efficient network selection scheme (NSS) to suit the requirements of
a mobile terminal (MT) becomes an important issue. In this thesis, we will propose a score-based
NSS (SBNSS) utilizing design a network score function with consideration of bandwidth,
received signal strength,
connection cost, price, and velocity of the MT.
For the received signal strength, an optimal threshold that the handoff will execute when
the received signal strength below the threshold is determined to avoid unnecessary handoff.
When using the 3G network, we allow users to enjoy different network services according to
different prices.
SBNSS balances the requests on bandwidth among networks
to decrease the blocking and dropping probabilities.
As for the velocity, SBNSS chooses a suitable network based on the velocity of the MT.
Via simulations, we will show the superiority of SBNSS over the related work in terms of
blocking/dropping probability and horizontal/vertical handoff rate.

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