無線感測網路(wireless sensor network; WSN)是由複數個感測節點彼此經由無線傳輸的方式來溝通，所形成的網路系統，由於是無線傳輸，所以比起有線網路來說，不需要額外考量佈線的成本。無線感測網路，具有低速率、低成本、低功耗的特性需求，IEEE 802.15.4 標準定義了無線感測網路實體層與媒體存取控制層的運作，正好符合上述之特性。
在IEEE 802.15.4 標準中，可為較高的服務品質要求(quality of service; QoS)之裝置提供特定的傳輸區間，當裝置已經確定可在這個區間傳輸，便不需要再透過競爭的方式與其他裝置競爭傳輸通道，這個區間稱為免競爭週期(contention-free period; CFP)，免競爭週期是由超碼框架構中之時槽作為傳輸單位，任一裝置被配置後的傳輸時間稱為保證時槽(guaranteed time slots; GTSs)，一個保證時槽可能包含了一個或多個時槽以進行資料之傳輸；以上的傳輸方式，容易出現部分的時槽空間沒有使用的情況，而導致時槽空間的浪費，進而導致傳輸效率的降低，此種情形於超碼框級數(superframe order; SO)越大時越為明顯。
為了解決上述時槽空間未使用而導致浪費的問題，本論文提出了增強型保證時槽配置機制(enhanced GTS allocation scheme; EGAS)，本機制可以提升免競爭週期內時槽的使用率。而透過程式來模擬的結果，可以發現本論文所提出的機制，與IEEE 802.15.4 標準及過去被提出的方法的比較下，在免競爭週期頻寬之使用率、免競爭週期的有效產能、免競爭週期之佔用比率、免競爭週期之封包丟棄率均有顯著的改善。

Wireless sensor network (WSN) is a network system formed by many sensors. The sensors communicate with each other by wireless transmission. In contrast with wire transmission, wiring is needless. WSN has some special requirements such as low rate, low cost, and low power. IEEE 802.15.4 standard defines WSN operating at physical and MAC layer, so the standard is just fit for the properties.
In the IEEE 802.15.4, system can provide special time period for device with high quality of service (QoS) requirement. When a device is already decided to transmit data in this period, it will not have to content channel with others. The period is called contention-free period (CFP). CFP use the slot in superframe structure as transmission unit. These slots are called guaranteed time slots (GTSs). A GTSs can contain one or more slots to transmit data. The above transmission method brings that a portion of slot is unused, so it wastes space of slot and lowers transmission efficiency. When the value of superframe order (SO) increases, the situation becomes clearer.
To solve the above-mentioned problem about waste of unused slot, we propose Enhanced GTS Allocation Scheme(EGAS) to promote utilization of GTSs in CFP. Through simulating by program, we compare our proposed scheme, IEEE 802.15.4 standard, and some previous schemes. Our proposed scheme has improvement on the others about average bandwidth utilization of CFP, CFP goodput, ratio of CFP, and drop ratio of CFP.

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