多通道時槽阿羅哈協定在過去已經被大量的討論，並且廣泛應用於GSM, WCDMA, LTE, LTE-A等蜂巢式行動系統的隨機存取通道(random-access channel, RACH)。多通道在飽和狀態的穩態效能一直以來都備受關注，但近幾年對於機器間通訊需求的增加，使得我們需要藉由觀察多通道時槽的暫態行為去分析大量機器湧入造成的壅塞，進而達到根據不同的預估訊務量來設計最佳化的系統。
根據以往的研究，本論文提出二階多通道時槽阿羅哈系統。我們提出的模型可分析過去所提出的許多多通道時槽阿羅哈協定的變形機制，如即時傳送、延遲傳送、前置後退機制等。主要概念是將多通道資源分成兩部分，提供給兩階段的使用者。其中，使用者的傳送階段是依據使用者傳送的次數區分。
因為考慮了傳送階段區分與通道分配，二階多通道時槽阿羅哈系統提供系統設計上更大的彈性，但同時也增加運算複雜度。高運算複雜度無法像傳統藉由模擬去找到系統最佳操作點，因此我們提出了分析模型去估測在各種參數設定下的效能。我們考慮的效能指標為成功機率及平均延遲時間，並定義最佳工作點為高成功機率與低平均延遲。在模擬結果中，討論了不同參數對系統的影響及在不同負載下的工作點。並且驗證了分析模型能有效率地找到此系統的最佳工作點。

Multi-channel slotted ALOHA protocol have been devoted for years and widely applied in the random-access channel (RACH) of cellular network, e.g. GSM, WCDMA, LTE, and LTE-A. The most of researches focus on the steady-state behavior of multi-channel slotted ALOHA system. However, the requirement of machine-to-machine (M2M) communication increased the in past few years. Through observing the transient behavior of the system, we can analysis the network congestion due to bursty arrivals of M2M devices and design the optimum system according to estimating traffic.
By observing the previous studies in multi-channel slotted ALOHA systems, we proposed a unified model called two-stage multi-channel slotted ALOHA systems. Our unified model can analysis the main schemes proposed in past years, e.g. Immediately-first transmission, delay-first transmission, and pre-backoff scheme. The concept of two-stage multi-channel slotted ALOHA systems are divided the available channels into two parts for the users in different stages. The stage is determined by how many attempts user transmitted.
Two-stage multi-channel slotted ALOHA system can provide a highly flexible in system design because the stages and channels division are considered, but the computational complexity increased. The high computational complexity leads to traditional method that search optimum operating points by simulation being useless. Therefore, we proposed an analytical model to estimate the performance metrics of different parameters setting. We consider the access success probability and the average access delay as performance metrics. The point with high success probability and low average access delay is regards as the optimum operating point. The effect of the different parameters and the optimum operating points are investigated in simulation. The results showed that our analytical model can efficiently find the optimum operating points of the two-stage multi-channel slotted ALOHA systems.

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