802.11ah是WiFi聯盟因應物聯網而發展的標準，運作於1GHz以下的頻段，有著大範圍的傳輸距離，然而，因為大範圍的傳輸距離，以及物聯網的特性，在一個802.11ah的AP底下會有數以千計的STA，儘管在RAW這個機制下，限制了上行資料參與競爭的STA個數，但大量的STA需要上行資料仍然會使得頻道壅塞。 本論文設計RAW中的RAW slot裡的STA是有機率性的參與競爭，以降低期望參與競爭的STA數量，目的在於減低因為大量STA參與競爭而導致的碰撞，而降低DCF的表現。本論文將RAW slot的競爭參與率以等差的方式去設計，STA的數量與RAW slot中最大的STA數量也以等差的方式去設計，搭配上升降級的機制，一方面期望可以不失STA參與競爭的公平性，另一方面期望STA能在一定的時間內傳送成功。 由模擬結果可知，本論文提出之方法，可以在不失公平性的狀況下，降低參與RAW的STA的延遲時間並提升系統吞吐量，這是因為有效的降低了STA的碰撞率，同時也可以看到本論文所提出之方法，在STA數量增加時，相較於原有的RAW機制的方法，改善幅度越大。因此，在物聯網STA數量眾多的情況下，透過本論文的方法可以因改善碰撞率而提升系統表現，並能維持一定的傳輸品質。 ;802.11ah is a standard developed by the WiFi Alliance to support the Internet of Things. It has a long range of transmission distances in the sub 1GHz. There will be thousands of STAs (stations) under an 802.11ah AP. Although it has the RAW (Restricted Access Window) mechanism, the number of STAs that have uplink data join the RAW for contention is limited. But a large number of STAs need to uplink data will still make the channel congestion. In order to reduce collision rate by reducing the number of STAs expected to join the contention, STAs join the RAW slot of the RAW are designed to compete on a probability in this paper. The purpose method wants to reduce the collisions caused by a large number of STAs join the contention because it will degrade the performance of DCF. This paper designs that the probability of RAW slot is an equal-difference manner. The number of STAs and the maximum number of STAs in RAW slot are also designed in an equal-difference manner. With the mechanism of the up-downgrade, it is expected that the STAs can join contention in fairness. On the other hand, it is expected that the STA can successfully transmit within a certain period of time. The method proposed in this paper can reduce the delay of STAs participating in RAW and improve the system throughput without sacrificing fairness because of reducing the collision. Therefore, we can use this method to reduce the high collision rate and maintain a transmission quality.
