IEEE 802.11ah 是一種用於物聯網(Internet of Thing, IoT)的無線網路通訊協議。由於 IEEE 802.11ah 允許至多 8,192 個裝置同時與一個 AP 連接，因此，IEEE 802.11ah 設計了受限存取視窗 (Restricted Access Window, RAW) 機制來解決資訊傳輸時所可能引發的衝突問題。在此機制中，與IEEE 802.11ah AP關聯的所有裝置被分成若干組以在其相應RAW所分配的時隙(slot)中進行資料傳輸。藉此避免大量的裝置同時進行資料傳輸以減少衝突的可能性。然而，碰撞仍可能發生，其關鍵原因是從裝置上傳資料給AP屬於自發性的傳輸行為。AP無法事先得知這些裝置的存在，而這些自發性傳輸可能會和原本已經安排好的資料傳輸發生碰撞。因此，我們首先採用了註冊後退時間(Registered Backoff Time, RBT)機制，以便每個裝置都可以先和AP註冊一個後退(Backoff)時間以方便於資料傳輸時使用，接著透過聲明RAW(Claiming RAW)機制，藉由裝置通知AP是否有資料需要上傳。由此，AP可以除了可以事先知道有哪些裝置有資料要上傳外，更可以利用這些已知資訊將這些裝置重新排程。由於每個時隙中要進行資料傳輸的裝置數量不同，因此會衍伸出流量負載不平衡的問題。因此我們提出的基於註冊時間的重組以達成負載平衡之網路通道使用方式(RRG-LBCA)，它根據各個裝置的流量需求和時隙容量對這些裝置重新排程，解決負載不平衡的問題可以提高 IEEE 802.11ah網路的性能。性能評估結果表明，RRG-LBCA可以消除碰撞發生，相較於傳統方法更可以增加總吞吐量。

IEEE 802.11ah is a wireless network protocol that was designed for Internet of Things (IoT). Since IEEE 802.11ah allows up to 8,192 wireless stations (STAs) to connect with an AP simultaneously, it needs to have a sophisticated control mechanism to avoid collisions for channel access. Thus, IEEE 802.11ah devised the Restrict Access Window (RAW) mechanism to tackle the collision problem. In the RAW mechanism, STAs that are associated with an IEEE 802.11ah AP are separated into several groups to access channel in their assigned slots of the corresponding RAW. As a result, STAs can avoid accessing the channel simultaneously to decrease the possibility of collision. However, the collision still may happen in the slot, for which the key reason is the spontaneous data that are uplinked from STAs to the corresponding AP. This work adopted (i) the Registered Backoff Time (RBT) mechanism such that each STA can register the backoff time for its future channel access in AP and (ii) the Claiming RAW mechanism such that STAs are allowed to notify AP that they have uplinked data to transmit. In this way, AP can (1) know which STAs have uplinked data to transmit and (2) re-schedule those STAs from the overloaded slots to the slots (i) that are underloaded or (ii) in which no allocated STAs need to access channel based on STAs’ RBTs in advance. Thus, the proposed Registration-based Regrouping for Load-balance Channel Access (RRG-LBCA), which uses the re-scheduling process to re-arrange STAs based on these STAs’ traffic demands and slots’ capacity, can tackle the load balance problem to increase the performance of an IEEE 802.11ah network. The performance evaluation results shown that the proposed RRG-LBCA method can eliminate the collision situation and increase the aggregate throughput.

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