LTE (Long Term Evolution)網路中使用HARQ (Hybrid Automatic Repeat reQuest)技術以降低重傳封包的錯誤率，但是目前的HARQ 技術在分配RB (Resource Block)時無法保障real-time 封包的delay constraint，為了避免real-time封包進行重傳時可能會超過delay constraint，在本論文我們提出根據RTT (Round-Trip-Time)的HARQ 排程機制。在此機制中，我們先根據封包服務品質需求分為real-time 與non-real-time 兩種，然後再將real-time 的資料流依照封包的重傳次數分成四種不同優先權的佇列，分別為初次傳送佇列(FTQ)、重傳一次佇列(RTQ1)、重傳兩次佇列(RTQ2)、重傳三次佇列(RTQ3)等四種。然後我們分別計算各佇列封包傳送所花的RTT，再根據RTT 計算重傳封包所要滿足的delay constraint 與各佇列所需要的RB 數目。對於non-real-time 封包，我們定義一個NRTQ 佇列，在real-time 佇列分配完RB 後，我們根據non-real-time 的MBR (Minimum Bit Rate)來分配剩餘的RB 數以避免starvation 的發生。
為了分析所提出的HARQ 排程機制，我們先定義一個HARQ 封包初次傳送的錯誤機率為p，建立在不同重傳次數下封包傳送發生錯誤的機率模型，進而推導出一個HARQ 封包需要重傳多少次才能成功的機率，與一個HARQ 封包需要傳送多少次才會成功的期望值。接著我們根據RTT 分配各佇列所需的RB 數目與HARQ 封包傳送成功的期望值求得各種網路效能參數，包括real-time 的average packet delay、packet loss ratio (PLR)與non-real-time 的PLR、throughput。最後我們討論改變real-time 的delay constraint 與不同p 值之下，各種網路效能參數的變化。

In an LTE (Long-Term Evolution) network, HARQ (Hybrid Automatic Repeat reQuest) is used to reduce the error probability of retransmitted packets. However, HARQ cannot guarantee delay constraints for real-time traffic when RBs (Resource Blocks) are allocated improperly. To avoid the retransmitted real-time packets exceeding their delay constraints, we propose an HARQ scheduling scheme based on RTT (Round-Trip-Time) estimation. In this scheme, traffic are classified into real-time and non-real-time queues in which real-time queue are further classified into four sub-queues according to their retransmission times; i.e., the first transmission queue,
the first retransmission queue, the second retransmission queue, and the third retransmission queue. For the four real-time queues, we estimate RTT and compute the number of RBs required satisfying the delay constraints. To prevent from starvation of non-real-time traffic, after allocating the RBs for real-time traffic, the remaining RBs are allocated for non-real-time traffic according to their MBR
(Minimum Bit Rate). To analyze the proposed scheduling scheme, we build a mathematical model to derive the successful probability of retransmitted packets and the expected value of packet retransmission times. Finally, we compute average packet delay, average packet loss rate, and the throughput for both real-time and none-real-time traffic by varying packet error probability and the delay constraints of real-time traffic.

第一章 緒論 1
1.1 研究動機 1
1.2 研究方法 1
1.3 章節介紹 3
第二章 LTE 與排程技術 4
2.1 LTE 4
2.1.1 OFDMA/SC-FDMA 4
2.1.2 OFDMA/SC-FDMA 的frame 架構 6
2.1.3 HARQ 7
2.2 LTE 的封包運作流程 10
2.3 HARQ 封包排程的相關研究12
2.4 本論文的封包排程機制 15
第三章 OFDM 排程機制 16
3.1 系統架構 16
3.2 排程機制 18
3.2.1 RTT 與RB 20
3.2.2 排程演算法 24
第四章 數學分析與結果 27
4.1 數學分析模型 27
4.2 效能參數 29
4.3 數值分析 34
4.3.1 各佇列的RB 分配量 34
4.3.2 Real-time 佇列的分析 36
4.3.2.1 Real-time 的average packet delay 36
4.3.2.2 Real-time 的PLR 37
4.3.3 Non-real-time 佇列的分析 38
4.3.3.1 Non-real-time 的PLR 38
4.3.3.2 Non-real-time Throughput 39
第五章 結論與未來工作 41
5.1 結論 41
5.2 未來工作 42
REFERENCES 44
INDEX 50

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