IEEE 802.15.4低速率無線個人區域網路是一套近距離的通訊標準，其特點有低成本、低功耗、彈性的傳輸率，因此非常適合無線感測網路(wireless sensor network ; WSN)之應用。為了滿足特定頻寬需求或時間急迫性的應用，IEEE 802.15.4標準可適時的選用免競爭週期(contention-free period ; CFP)來傳送資料，藉此以降低負載提高時，傳輸所造成的碰撞機率，進而提升無線感測網路的有效產能。
IEEE 802.15.4標準定義的免競爭週期中，每個保證時槽(guaranteed time slots ; GTSs)由一個以上的時槽所組成，並且只能提供單一裝置使用，由於是以單位時槽為配置單位，因此會發生配置的頻寬大於所需的頻寬之情形，進而造成頻寬浪費的問題，尤其是隨著超碼框級數(superframe order ; SO)的上升，保證時槽中的單位時槽也隨之變大，此一問題將更加明顯。
為了解決上述的問題，本論文提出了動態保證時槽配置機制(dynamic GTS allocation scheme ; DGAS)，透過本機制可有效的提升免競爭週期的使用率，藉此降低頻寬浪費。由模擬結果可以發現，本論文所提出的機制，無論是在免競爭週期的使用率、有效產能、能量消耗均比IEEE 802.15.4標準及先前被提出的機制有較好的表現。

IEEE 802.15.4 low-rate wireless personal area networks is a set of near field communication standard, it is characteristic of low cost, low power, and flexible transfer rate, therefore it can apply in WSN. In order to meet the need of fixed bandwidth and time sensitive application, IEEE 802.15.4 standard can optionally use contention-free period (CFP) to transmit data. To reduce the probability of collision from transmission and promote wireless sensor network goodput when the load increase.
By IEEE 802.15.4 standard definition, in contention-free period, each guaranteed time slots (GTSs) is composed by more than one time slots, and provide use of single device, because CFP allocate guaranteed time slots based on unit time slot, so bandwidth allocation greater than bandwidth required, and then CFP shall have the waste problem, when the value of superframe order (SO) increases , to the unit slot larger, so waste problem will become worse.
In order to solve the above-mentioned problems, we propose dynamic GTS allocation scheme (DGAS). by this mechanism can promote utilization of CFP, and reduce the bandwidth waste. We compare our proposed scheme, IEEE 802.15.4 standard, and some previous schemes by simulations, the simulation results of CFP utilization, goodput and power consumption shows the improvement of our scheme.

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