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第六章、 結論與未來展望方向
大型天然災害發生時通訊系統常會癱瘓，而有效運作的通訊系統卻是災情傳遞、資 源調度以及互助協調是否順利的關鍵因素。我們提出利用無線電將功能完整但無法對外 進行正常連線的基地台連接起來，建構一個臨時性的行動通訊網路，稱為應急蜂巢式行 動通訊網路(Contingency Cellular Network，CCN)，由於各個地方受災情況不盡相同且通 訊資源有限，CCN 必須反應災區需求之輕重緩急妥適分配頻寬，因此在網路拓樸規劃 完成，基地台依排程陸續開通服務後，必須根據各地災情緊急程度及網路拓樸進行 CCN 頻寬分配規劃，以達到最大的救災效益。
本研究提出一個兼顧各基地台間通訊需求、通訊需求緊急程度以及通訊需求差異，
且適合於 CCN 樹狀結構的最佳化頻寬分配模型，以追求救災效益的最大化。這些模型 可供使用者(救災指揮單位)系統化的解決 CCN 跨基地台頻寬分配問題。頻寬分配給基地 台間通訊需求可獲得之效益由救災單位根據所收集到的各地災情、救災資源、救災需求 自行定義，本模型及頻寬分配演算法可決定 CCN 跨基地台頻寬使用之分配。
CCN 跨基地台頻寬分配問題是一個較為複雜的 0-1 Knapsack Problem，我們證明該 問題屬於 NP-Hard 問題，但因為發生突發性大型天然災害時，可容許之計算時間極為短 暫，因此我們提出一個啟發式演算法：CBBAG，以快速得到一個相近於最佳解的頻寬 分配。CBBAG 演算法透過頻寬救災效益密度找出每次頻寬分配的最佳 profit 配置，並 在確認頻寬資源後配發，直到剩餘的 CCN 跨基地台頻寬無法再配發任何一種 channel 使用為止。因此在限定時間內即可提供不錯的頻寬分配組合，並且每當網路拓樸、可用 頻寬、災情程度或基地台間通訊需求變動時，能快速的重新運算修改頻寬分配。
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我們利用電腦模擬評估 CBBAG 演算法之效能，假設網路拓樸及頻寬資源固定，
以基地台個數多寡以及有通訊需求之轉送路徑來分析其對 CBBAG 演算法的影響，實驗 一、二分別以不同之頻寬救災效益密度計算方式帶入。實驗案例由亂數隨機產生，以正 規化的誤差值來評估頻寬分配組合之優劣。結果顯示，我們提出之 CBBAG 演算法採取 Additive profit density 的計算方式可在數秒內得出與最佳解誤差範圍在 0~21.18%之近似 最佳解。
本研究提出的模型仍有改進之空間，例如以各種通訊需求的救災效益做為頻寬分配 的依據、以需求對-channel 配對為單位作為頻寬分配效益遞減範圍、網路拓樸變化對 CBBAG 演算法效能及誤差之影響與改良、反應需求對變化之動態頻寬分配、配合允入 控制的調適以及針對動態救災資源設計出一套頻寬分配方法，以避免系統太過頻繁的重 新分配頻寬。此外若 CCN 網路拓樸不再是樹狀結構時，各存在通訊需求之基地台間的 轉送路徑將不再是單一選擇，必須在需求對的數個轉送路徑中擇一轉送，如何於多重轉 送路徑考量下妥適分配頻寬亦是研究課題。在有限的資源之下，使每一分資源都發揮其 最大的效用，搶救更多的生命，是 CCN 頻寬分配所至臻的目標。
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