機器型態通訊會產生巨量的連線要求並且帶來短時間爆炸性的負載，由於過多的裝置同時競爭有限的共享隨機存取通道，導致提高存取失敗率和產生嚴重的存取延遲問題。因此，我們提出two-phase random access (TPRA)來舒緩隨機存取通道的負載，TPRA靠著將大量的裝置分群來降低失敗機率並且允許基地台能夠根據當下得負載更有彈性的分配存取通道。我們也提出了分析模型來評估效能並用模擬結果來驗證正確性。

Machine-type communication (MTC) can generate numerous connection requests and bring explosive load within small time interval. A massive amount of simultaneous random access attempts results in a high collision probability and intolerable access delay because more devices contend in shared random access channels (RACH) with limited capacity. Thus, this thesis addressed a novel mechanism, denoted as two-phase random access (TPRA) procedure, for MTC in mobile networks to relieve the load of RACH. The proposed TPRA reduces probability of collision among the MTC devices when accessing radio resources by separation of the massive number of devices into small groups. The proposed concept allows a base station to adjust the number of additional access channels according to their current load. Furthermore, we propose an analytical model to evaluate the performance of the proposed TPRA by estimating the access success probability and average access delay. The simulations results validate the accuracy of the performance metrics derived analytically.

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