在進階長程演進系統 (LTE-Advanced) 網路中，機器類型通訊 (MTC) 提供了基於隨機存取的自動化應用。機器類型通訊中最關鍵的議題之一，是大量出現的 MTC 裝置可能同時傳送請求至基地台，導致嚴重的碰撞。當 MTC 裝置需要傳送資料時，MTC 裝置必須進行隨機存取程序以取得資源塊。若發生碰撞，該次資料傳送即視為失敗，並造成訊息延遲的積累。
在本論文中，我們提出一個兩階段無線電存取方案，以降低碰撞並且減少訊息延遲。所有的 MTC 裝置被分成數個群組，第一階段的隨機存取由群組內的某個 MTC 裝置 (稱為 MTC 閘道器) 主導，可有效減緩第二階段 (在基地台端) 的隨機存取碰撞。為了觀察群組數量及群組內 MTC 裝置數量對效能的影響，我們提出理論分析模型及模擬模型來探討隨機存取時槽的利用率、存取成功率以及平均訊息延遲。模擬結果顯示，當群組數量約為 64 時，整體的效能有較好的表現。

In Long Term Evolution-Advanced (LTE-A) network, Machine type communication (MTC) provides random access-based communication for automation applications. In MTC, one of the most critical issues is the emergence of large number of MTC devices which may send requests to the base station at the same time, such that severe collision occurs. Whenever MTC devices have data to send, the MTC devices perform random access procedure to obtain resource blocks. When collision occurs, the message delay accumulates, and the data delivery fails. In this case, limiting the number of MTC devices' access to eNB at the same time can alleviate the collision.
In this thesis, we propose a two-stage radio access scheme to alleviate collision and reduce message delay for MTC. MTC devices are divided into several groups, where random access in each group (as the first step) is controlled by a device called MTC gateway. Collision of random access to the base station (as the second stage) is then effectively alleviated. To observe the effect of numbers and sizes of groups, we propose analytical model and simulation model to investigate the performance in terms of utilization of random access slots, access success probability and average message delay. Simulation results show that better performance is observed when the number of groups is around 64.

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